Plum in Zone 9 -- plant

Bloom timing & cross-pollination

One tree is usually enough

Most plums are self-fruitful: a single tree sets a full crop with its own pollen, so you don’t need a second variety to get fruit. Bees still move the pollen from blossom to blossom, so strong pollinator activity through bloom is what drives a heavy set.

Green Gage (Reine Claude) blooms mid season and is self-fruitful, setting a full crop on its own.Blooms alongside: Stanley.

Bar length shows how long each variety blooms, roughly 8 to 14 days. Bars that overlap bloom at the same time.

▲ Tap a variety to see its bloom timing

Very early Early Mid Late Very late

Methley✓ same time

Santa Rosa✓ same time

Burbank✓ same time

Green Gage (Reine Claude)✓ same time

Stanley✓ same time

Italian Prune (Fellenberg)✓ same time

Damson✓ same time

The pollination rule

The most important choice with plums is pollination, and it depends on the type. European plums (Stanley, Italian prune, damson) are mostly self-fruitful, so one tree makes fruit on its own, though it often crops a little better with a second European nearby. Japanese plums (Santa Rosa, Burbank, Methley) usually need a second, different Japanese plum blooming at the same time; Methley and Santa Rosa can partly fruit alone and make good partners. Important: European and Japanese plums bloom at different times and cannot pollinate each other, so the partner has to be the same type. Bees do the pollinating, so plant the partner within about 100 feet and help bees be active at bloom.Pollination is the headline decision for plum, and it splits by type. European plums (Prunus domestica) such as Stanley, Italian prune, and damson are largely self-fruitful, so a single tree bears, though most crop somewhat more heavily with a second European variety nearby. Japanese plums (Prunus salicina) such as Santa Rosa, Burbank, and Methley are usually self-unfruitful and need a second compatible Japanese cultivar blooming at the same time; Methley and Santa Rosa are partial exceptions and also serve as good pollenizers. Crucially, European and Japanese plums bloom weeks apart and will not pollinate each other, so a pollenizer must match type. Plums are insect-pollinated, mainly by bees, so bloom-time pollinator activity matters; place a pollenizer within about 100 feet.

Steady hand on the hose

Watering

When & how much

Frequency

Water deeply now and then instead of a little every day. Plan on about once or twice a week while a young tree is getting established, easing to about once a week for a fruiting tree in summer heat, adjusting for rain and your soil. Sandy soil dries out faster and needs watering more often; heavier soil stays wet longer. In winter, when the tree is resting, it needs very little and rain usually covers it.Water on a deep-and-infrequent rhythm rather than a little every day: about once or twice a week while a young tree establishes, easing to roughly weekly for a bearing tree in the heat of summer, always adjusted for rain and soil type. A sandy soil dries faster and needs more frequent soaks; a heavier soil holds longer. Through winter dormancy, water need drops sharply and rainfall usually suffices.

Amount

Each time you water, give the tree a deep soak that reaches all the way down to the roots, not just a quick splash on top. A young tree wants about 5 gallons per soak. An older, fruiting tree wants roughly an inch of water a week through the growing season, and more when it is hot. Deep soaks help the tree grow deep roots that handle dry spells.Water deeply each time so the moisture reaches the full depth of the root zone, rather than wetting only the surface. For an establishing tree, that is on the order of 5 gallons per soak; for a bearing tree, aim for roughly the equivalent of an inch of water per week through the growing season, more in heat. Deep, thorough soaks drive the deep rooting that carries the tree through dry spells.

Method

Water at the ground around the roots using a drip line or a soaker hose, and keep the leaves and fruit dry. Spraying water over the top wets the leaves and fruit and helps diseases like brown rot take hold, so put the water on the soil, not on the tree. Spread it across the root area out to the edge of the branches, not just right at the trunk.Water at the root zone with drip or a soaker hose, and keep the canopy and fruit dry. Overhead watering that wets the leaves and fruit prolongs leaf wetness and feeds brown rot and bacterial spot, so deliver water to the soil, not the tree. Apply it across the root area out toward the drip line rather than only at the trunk.

Signs of trouble

Too much water

Too much water, or soil that drains poorly, shows up as yellowing leaves, wilting that does not go away even when the soil is wet, and a tree that slowly goes downhill. That is because waterlogged roots cannot breathe and start to rot. In plum, soil that stays wet can also bring on crown and root rot, which often kills the tree. Soil that never dries out between waterings is your warning to back off.Overwatering and poor drainage show as yellowing leaves, wilting that persists even in wet soil, and a generally declining tree, since waterlogged roots suffocate and rot. In stone fruit, chronically wet soil also invites crown and root rot, which is often fatal and rarely reversible once advanced. Soggy soil that never dries between waterings is the warning sign to act on.

Too little water

Too little water shows as wilting and dull, curling leaves, slower growth, and leaves dropping early in a long dry spell. The clearest sign is in the fruit: a tree that runs short of water while the plums are sizing up makes small, shriveled fruit, even though the tree itself lives through it. Try to catch the dry stress before the fruit suffers for it.Underwatering shows as wilting and dull, curling leaves, slowed shoot growth, and early leaf drop in a prolonged dry spell. The most telling symptom is on the fruit: a tree short of water during the final swell sizes its plums poorly, leaving them small and prone to shriveling even though the tree itself survives. Catch the dry stress before the fruit pays for it.

Feeding rhythm

Feeding

Frequency

1-2x per year

Type

balanced granular (e.g. 10-10-10)

When to start

spring at bloom to petal fall; optional light postharvest

Scatter the fertilizer evenly on the soil around the tree out to where the branches reach, keep it off the trunk, and water it in. On sandy soil it helps to split it, most in spring and a little after harvest. Do not overdo the nitrogen (the first number on the bag), because too much pushes soft, leafy growth that draws aphids and disease. Never feed late in the year, because late feeding keeps the tree growing when it should be going dormant and makes winter damage more likely.Broadcast the fertilizer evenly around the root zone out to the drip line, keeping it off the trunk, and water it in. Split timing (the bulk in spring, a lighter touch after harvest) suits sandy soils. Go easy on nitrogen: plums push vigorous shoots readily, and lush, succulent growth is more prone to aphids, bacterial canker, and black knot, and never feed late in the season, since late nitrogen delays dormancy and invites winter injury.

N · P · K = 10-10-10

A balanced fertilizer like 10-10-10 (the three numbers are nitrogen, phosphorus, and potassium) works well for backyard plums. Do not overdo nitrogen, the first number, because too much pushes leafy growth and more disease instead of fruit.A balanced ratio such as 10-10-10 suits backyard plums; a young tree that is not making about a foot of new growth a year can take a spring nitrogen boost, but a vigorous tree needs little. Avoid high-nitrogen feeding, which pushes soft, disease-prone growth at the expense of fruit.

Try 10-10-10 balanced fertilizer

Who grows well together

Companion planting

Whether a plum needs a companion tree is really a pollination question, and it depends on the type. European plums (like Stanley, Italian prune, and damson) are mostly self-fruitful, so one tree makes fruit on its own. Japanese plums (like Santa Rosa and Methley) usually need a second, different Japanese variety blooming nearby to set a good crop. Beyond that, the things that matter for a tree are not the usual vegetable-garden pairings but what grows around the roots: keep grass and weeds pulled back from under the branches, because lawn competes hard with a young tree, and a mulched, weed-free area helps the tree settle in. One thing to avoid is planting a plum near other wild or neglected plums and cherries, because those spread black knot, the black warty branch disease, to your tree. For a plum, the key interaction is pollination, and it splits by type: European plums (Stanley, Italian prune, damson) are largely self-fruitful and fruit alone, while Japanese plums (Santa Rosa, Methley, and most others) are self-unfruitful and need a second compatible Japanese cultivar blooming at the same time. The other interactions that matter are about the root zone, not classic vegetable companions: keep turf and weeds cleared back from under the canopy, since a young tree competes poorly with grass for water and nitrogen. The site rule to respect is inoculum: do not plant near wild, ornamental, or neglected Prunus (chokecherry, wild plum, purple-leaf plum), which are reservoirs of black knot and brown rot.

Other

A second compatible plum for cross-pollination

For Japanese plums, and for the many European cultivars that set more heavily with a partner, the single most useful companion is a second compatible plum. Match type to type: a Japanese cultivar needs another Japanese (or an American-Japanese hybrid) blooming at the same time, since European and Japanese plums bloom weeks apart and will not pollinate each other. Santa Rosa and Methley are widely used pollenizers for other Japanese plums; a self-fruitful European such as Stanley or Damson can stand alone but still crops more reliably with a second European nearby. Plant the pollenizer within about 100 feet so bees move freely between the trees. Research-backed

Keep apart from

Wild, ornamental, or neglected plums and cherries nearby A plum's worst neighbors are other Prunus you do not manage. Wild plum, chokecherry, ornamental purple-leaf plum, and abandoned plum or cherry trees are reservoirs of black knot and brown rot: the black-knot fungus overwinters in galls on those hosts and releases spores that infect your tree every wet spring, so an unmanaged thicket downwind undoes your own pruning. Where practical, remove or prune the black knot out of nearby wild hosts, or at least scout them, and site a new plum away from them. Research-backed

Provenance tagged inline · see methodology for the labeling system Key

Harvest signals

When to pick

A plum is ripe when it shows full color, has a natural dusty coating on the skin (that is normal, not a problem), gives a little when you press gently, and comes off the branch with an easy pull. European prune plums are ready when soft and sweet through to the pit; juicy Japanese plums are picked when full-colored and just starting to soften. If you need to carry or store them, pick when fully colored but still firm and let them soften on the counter. For eating right away, pick when they give to a gentle squeeze.A plum is ready when it reaches full variety color, develops the natural dusty bloom on the skin, gives slightly to gentle pressure, and separates from the spur with an easy pull or light twist. European prune types are ripe when soft and sweet all the way to the pit, ideal for drying and canning; Japanese types are picked when full-colored and just softening for fresh eating. If you need to handle or store the fruit, pick when fully colored but still firm and let it finish on the counter; pick at full give for eating that day.

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Yield

What to expect

A grown plum tree (about year 5 onward) usually gives roughly 2 to 3 bushels a year, which is 60 to 150 pounds of fruit. The exact amount depends on the type and variety, how you prune and thin, whether it is well pollinated, and the weather. Japanese plums often set the heaviest, but only if you thin them so the fruit sizes up.A mature standard plum (roughly years 5 and up) commonly yields about 2 to 3 bushels per tree, on the order of 60 to 150 pounds, depending on type, variety, pruning, thinning, pollination, and season. Japanese plums tend to overset and can out-yield European types when well thinned; crop is limited far more by thinning, frost, and pollination than by feeding.

A plum tree hits its full production around years 5 to 6 and keeps producing for years after, as long as you prune, thin, cut out black knot, and manage disease each year. Thinning every year also helps keep the tree from swinging between a huge crop one year and almost none the next.Trees reach full bearing around years 5 to 6 and stay productive for many years after, given annual pruning, thinning, black knot removal, and disease control. Thinning each year also evens out the alternate-year (biennial) bearing plums are prone to. Do not expect plums the first year, or really the second. If a few fruit form early, pick them off so the young tree can build roots and strong branches. Your first real harvest usually comes in years 3 to 5, with full crops by years 5 to 6.Expect no crop in the planting year and little to none in year 2. Remove any fruit that sets early so the tree puts its energy into roots and framework; the first meaningful harvest typically comes in years 3 to 5, with full bearing by years 5 to 6.

What changes yield

type and varietypollination (European self-fruitful vs Japanese cross-pollination)fruit thinningannual pruning and black knot removalwinter chill accumulationlate-frost damage at bloomdisease and insect controltree age and establishment

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Off the vine

Storing your harvest

Room temp

Leave firm plums on the counter, out of direct sun, to ripen the rest of the way, usually 2 to 4 days, until they give to a gentle squeeze and smell sweet. Plums you picked already soft will only keep a day or two out, so eat or refrigerate them soon.Hold firm-picked plums at room temperature out of direct sun to finish ripening, typically 2 to 4 days, until they yield to gentle pressure and smell fragrant. Tree-ripe fruit picked soft lasts only a day or two on the counter, so plan to eat or refrigerate it promptly.

Fridge

Put plums in the fridge once they are ripe or almost ripe, and eat them within about a week. Plums keep in the fridge better than peaches do, so it is a good spot for ripe fruit. For the best taste, let cold plums warm back to room temperature before you eat them.Refrigerate plums once they are ripe or nearly so, then eat within about a week. Unlike peaches, plums tolerate refrigeration well and are less prone to mealy chilling injury, so the fridge is a good holding place for ripe fruit. Bring them back to room temperature before eating for the fullest flavor.

Freezer

Plums freeze nicely if you halve and pit them first. Cut ripe plums in half, take out the pits, spread them on a tray to freeze, then pack them into freezer bags. Freestone types (where the pit pulls free) are easiest. They keep for several months and are best for cooking, baking, and sauces instead of eating fresh.Plums freeze well halved and pitted. Cut ripe fruit in half, remove the pits, and freeze on a tray in a single layer, then transfer to freezer bags; freestone European prune-plums are easiest since the pit pulls free. Frozen plums keep their quality for several months and are best used for cooking, baking, and sauces rather than fresh eating.

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When something goes wrong

Common problems

The tree flowered but I got almost no plumsTree bloomed well but set little or no fruit

01 of 04

What happened The tree bloomed but barely fruited. On plums the first thing to check is pollination, and it depends on the type. A Japanese plum (like Santa Rosa or Methley) usually needs a second, different Japanese plum flowering at the same time, so a single Japanese tree sets almost nothing on its own. European plums (like Stanley and damson) usually fruit by themselves. The other common causes are a late frost on the early flowers and, in mild-winter areas, too little winter cold. The fixes are a matching partner tree, a spot less prone to frost, and a variety whose chill fits your winters.The tree flowered heavily but few or no plums formed. On plum the first thing to check is pollination, because it splits by type: a Japanese plum (Santa Rosa, Methley, Burbank) is usually self-unfruitful and needs a second compatible Japanese cultivar blooming at the same time, so a lone Japanese tree, or one whose partner bloomed at a different time, sets almost nothing. European plums (Stanley, Italian prune, damson) are mostly self-fruitful and should set alone. The other common cause is a late frost on the early bloom (Japanese plums are especially exposed), and in mild-winter areas too few chill hours give a weak, uneven bloom. The fixes are a matched pollenizer, a frost-aware site, and a variety whose chill suits your winters. Next season If it is a Japanese plum, plant a second Japanese variety that blooms at the same time (Santa Rosa or Methley work well); make sure both flower together, keep a cover handy for frost, and check the variety suits your winters.If it is a Japanese plum, add a compatible Japanese pollenizer that blooms at the same time (Santa Rosa and Methley are reliable); confirm bloom overlap, keep a frost cover ready, and check the variety's chill requirement fits your region.

Black lumpy growths on the branchesHard black warty galls on the branches

02 of 04

What happened Hard, black, warty lumps have grown along the branches, and the branch beyond them is dying. This is black knot, the classic plum disease, caused by a fungus. Spraying will not fix the lumps that are already there; the fix is to cut them out. Prune each one 3 to 4 inches below the black lump while the tree is bare in winter, carry the pieces away and destroy them, and clean up or remove any wild plums and cherries nearby that keep re-infecting your tree.Hard, black, elongated warty galls have appeared along twigs and branches, girdling and killing the wood beyond them. This is black knot, the signature disease of plum, caused by the fungus Apiosporina morbosa. Growers often reach for a spray, but the galls are already established; the effective action is to cut them out. Prune each gall 3 to 4 inches below the visible swelling into clean wood during the dormant season before the fungus sporulates, remove and destroy the prunings, and deal with any wild or neglected Prunus nearby that re-infect the tree each spring. Next season Check the bare branches every winter and cut out every knot before spring, cutting well below the lump; clean up nearby wild plums and cherries, and choose a more resistant variety next time.Scout the bare branches every dormant season and remove every knot 3 to 4 inches into clean wood before growth resumes; clean up nearby wild Prunus and consider a less-susceptible cultivar when you replant.

Lots of tiny plums, or a big crop only every other yearMany small, poor-quality plums (and alternate-year bearing)

03 of 04

What happened The tree had lots of small plums, or it gives a big crop one year and almost nothing the next. Plums, especially Japanese ones, set far more fruit than they can size, and a tree that is not thinned splits its energy among too many and falls into bearing only every other year. More food will not fix it; the problem is too many plums. The fix is thinning: remove the small fruit early to about one every 4 to 6 inches so the rest grow large and the crop evens out.The tree carried a heavy crop of small, poorly sized fruit, or it swings between a huge crop one year and almost none the next. Plums, especially Japanese types, overset badly, and an unthinned tree divides its resources among too many fruit and locks into alternate-year (biennial) bearing. It is easy to assume the tree needs more feeding, but the limiting factor is fruit number, not inputs. The corrective action is thinning: remove young fruit early to about one plum every 4 to 6 inches so the remainder size properly and the tree bears more evenly year to year. Next season Thin the small fruit early to about one every 4 to 6 inches, more on Japanese plums. This one step does more for size and for evening out the crop than extra feeding.Thin young fruit early and firmly to one plum every 4 to 6 inches, heaviest on Japanese types; this does more for size and for evening out the crop than any feeding.

Sticky gum and sawdust at the bottom of the trunkGummy ooze and frass at the base of the trunk

04 of 04

What happened Sticky gum mixed with what looks like wet sawdust (frass) has shown up where the trunk meets the soil, sometimes in a little mound. This is the sign of the peachtree borer, which also attacks plums; the larvae tunnel in the bark at the base. Plums ooze gum for many reasons, so it is easy to shrug off as sap, but the sawdusty frass means larvae are inside, and they can kill a young tree. Scrape away the soil, find the holes, and kill the larvae with a wire, then keep the trunk base free of wounds.Gummy ooze mixed with sawdust-like frass has appeared at the soil line, sometimes mounded. This is the signature of peachtree borer, which also attacks plum; the larvae tunnel in the inner bark at the crown. Plums gum in response to many stresses, so the ooze alone is sometimes dismissed as sap, but the frass is the tell that larvae are inside, and a young tree can be girdled and killed. Expose the crown, locate the entry holes, and kill the larvae by hand, then protect the trunk base from the wounds that attract egg-laying. Next season Check the base of the trunk every late summer for fresh gum and frass, keep mowers and trimmers away from it, and dig out any larvae right away before they ring the trunk.Inspect the soil line each late summer for fresh gum and frass, keep mowers and trimmers off the trunk base, and worm out any larvae promptly before they girdle the tree.

The usual suspects

Pests & diseases

Pests

Plum curculio

P · 01

Symptoms On small developing plums, look for a curved, crescent-shaped scar, the mark the beetle leaves when it lays an egg. Damaged fruit often drops early, and some that stays on the tree ends up misshapen or has a grub inside. You see this soon after the petals fall, and it is the usual reason for wormy plums.Small developing fruit carries a distinctive crescent-shaped scar where the female cut a slit to lay an egg. Infested fruit often drops early; fruit that hangs on may be gnarled or have a grub tunneling inside. Damage appears shortly after petal fall and is one of the most common causes of wormy backyard plums. Cause A small beetle with a long snout called the plum curculio, which is named for this very crop. The adults show up around bloom and start damaging the little fruits right after the petals drop, laying eggs inside them. The larvae then feed within the fruit and later drop to the ground.The plum curculio (Conotrachelus nenuphar), a small snout beetle and a signature pest of its namesake crop. Adults emerge around bloom and attack fruit from petal fall onward, laying eggs in the developing fruit; the larvae feed inside, then drop to pupate in the soil. Organic treatment Early in the morning the beetles are slow. Spread a sheet under the tree, tap the branches so the beetles fall, and destroy them. Pick up and throw away any dropped fruit promptly so the larvae inside do not mature. A kaolin clay spray (a fine white mineral coating) starting at petal fall helps keep them off.For a backyard tree, jarring the limbs over a sheet in the cool early morning when the beetles are sluggish, then destroying what drops, reduces the population. Promptly gather and dispose of dropped infested fruit to break the cycle. Kaolin clay applied from petal fall is an organic deterrent. Prevention The main thing is cleanup. Pick up fallen fruit all season so the larvae inside cannot finish growing in the soil under the tree. Keeping the ground clear lowers the number of beetles the next year.Sanitation is the backbone: remove dropped fruit through the season so larvae cannot complete development in the soil beneath the tree. A clean orchard floor and prompt fruit pickup steadily lower pressure year over year.

The control ladder

The ladder troubleshoots from the gentlest solution to the strongest. Start with the gentlest option and only move on when and if it doesn't work.

Garden sanitation

Start here: pick up every dropped plum promptly and get it out of the garden, because the grub inside finishes growing in the soil under the tree. On a cool early morning, when the beetles are sluggish, spread a sheet under the branches, tap them so the beetles fall, and destroy what lands. Keeping the ground clear all season means fewer beetles the following year.Season-long removal of drops denies larvae the soil beneath the canopy, and the effect compounds year over year, which is why sanitation is the backbone rather than a supplement. Jarring limbs over a sheet at first light, while adults are still cold enough to drop instead of fly, physically strips the population that petal fall released.
Kaolin clay

Kaolin clay is a fine white mineral you mix with water and spray on, leaving a coating the beetles do not want to walk on. Start at petal fall, the moment they begin working the young fruit, and reapply through the season as the fruit expands and rain washes the film thin.Kaolin from petal fall is the organic deterrent this crop's guidance names, and it works as a particle barrier, so unbroken coverage on expanding fruit is what carries it. Heavy use can flare San Jose scale and mites, worth weighing on a tree that already carries scale.

No spray for this one. Prevention is the control.

Aphids (leaf curl plum aphid and mealy plum aphid)

P · 02

Symptoms In spring the new leaves at the shoot tips curl up tightly, and if you unroll one you find little green or waxy-gray insects, aphids, packed inside. They leave a sticky shine (called honeydew) that turns black with sooty mold. A bad early attack curls the leaves and slows the new growth.In spring, new leaves at the shoot tips pucker and curl tightly around colonies of small soft-bodied aphids (leaf curl plum aphid), while the pale, wax-dusted mealy plum aphid clusters on the undersides of leaves. Both excrete honeydew that turns leaves shiny and sticky and grows black sooty mold; heavy early infestations stunt shoots and can distort young fruit. Cause Two kinds of aphids that live on plum: one curls the new leaves, and the other is a pale, waxy gray one. They spend the winter as eggs near the buds, then multiply fast on the tender spring growth before flying off to other summer plants.Two aphids specific to plum: the leaf curl plum aphid (Brachycaudus helichrysi), which curls the spring foliage, and the mealy plum aphid (Hyalopterus pruni), whitish with a mealy wax coat. Both overwinter as eggs near the buds, build up on new spring growth, then migrate to summer hosts (leaf curl plum aphid to plants in the aster family, mealy plum aphid to reeds and cattails). Organic treatment Ladybugs and other helpful bugs usually clean aphids up by early summer, so avoid harsh sprays that kill those helpers too. Blast the colonies off with a hard spray of water, and for a bad case use insecticidal soap or a light horticultural oil on the curled shoots. A dormant oil spray in late winter kills the overwintering eggs.Natural enemies (ladybugs, lacewings, syrphid larvae, parasitic wasps) usually bring aphids under control by early summer, so protect them by not spraying broad insecticides. A strong jet of water knocks colonies off, and narrow-range horticultural oil or insecticidal soap on the affected shoots helps in a heavy infestation. A dormant or delayed-dormant oil spray targets the overwintering eggs. Prevention Go easy on spring feeding, since lush new growth attracts aphids. Keep ants off the trunk (they protect aphids) with a sticky band, and leave the helpful bugs alone. If aphids come back every year, a dormant oil spray in late fall or winter is the best prevention.Avoid heavy spring nitrogen, which pushes the soft flush aphids favor. Keep ants (which farm aphids for honeydew and drive off predators) off the trunk with a sticky band, and preserve natural enemies. A late-fall or dormant oil where aphids are a chronic problem is the most effective single measure.

The control ladder

The ladder troubleshoots from the gentlest solution to the strongest. Start with the gentlest option and only move on when and if it doesn't work.

Balance nitrogen

Go easy on nitrogen feeding in spring. Rich feeding pushes out soft new shoots, and that tender growth is what these aphids multiply fastest on.Restraining spring nitrogen limits the succulent flush that drives colony buildup at the shoot tips. It is a feeding habit set before the aphids arrive rather than a response once they have.
Water spray

Knock the colonies off with a strong jet of water from the hose, aimed up into the curled shoot tips where they hide. Do it early in the day so the leaves dry quickly.A forceful jet dislodges colonies on sturdy wood without the collateral a broad spray carries. Tightly rolled leaves shelter some of them, so expect to repeat as colonies rebuild, and spray early enough that foliage dries, since long leaf wetness favors disease.
Beneficial predators

Ladybugs, lacewings, hoverfly larvae, and tiny parasitic wasps usually clean up plum aphids by early summer on their own, so the most useful thing you can do is skip the harsh insecticides that kill those helpers along with the aphids. Ants farm aphids for their sugary honeydew and chase the helpers off, so keeping ants off the trunk protects your allies.Resident natural enemies typically bring both aphid species down by early summer, so conservation is the working control: decline broad-spectrum material, and deny ants access to the colonies they tend and defend.
Insecticidal soap

For a heavy infestation, spray insecticidal soap straight onto the aphids in the curled shoots. It kills only what it wets, so unroll the tips and coat them. Skip it on a dry, stressed tree or above 90°F, since it can burn leaves.Contact soap suits a heavy pocket the softer steps have not held, and the rolled leaf is the practical limit, since it shields aphids from coverage. It also kills soft-bodied beneficials it directly wets, so treat only the infested shoots, and avoid water-stressed trees or temperatures above 90°F.
Horticultural oil

A narrow-range horticultural oil helps two ways: on the curled shoots in season, and, more usefully, as a dormant or delayed-dormant spray in late fall or winter that smothers the eggs waiting near the buds. Where aphids return every year, that dormant timing is the strongest single step. Do not use oil above 90°F or on a drought-stressed tree, and once the tree has leaves keep it at least 30 days clear of any sulfur spray; check the oil label, because some say to wait longer.In-season oil gives contact control on exposed colonies; the delayed-dormant application is the higher-value use, taking the overwintering eggs before the spring flush rather than chasing colonies after it. Observe the oil constraints: not above 90°F, not on stressed trees, and not within 30 days of sulfur while the tree is in leaf, or longer if the oil label says so.

No spray for this one. Prevention is the control.

Peachtree borer

P · 03

Symptoms Look at the very bottom of the trunk where it meets the soil. The peachtree borer, which also attacks plums, leaves a sticky, gummy ooze mixed with what looks like wet sawdust (frass). You may see a small mound of gum and frass at the base. A young tree with several borers can be killed in one season, so catch this early.Gummy ooze mixed with sawdust-like frass at the base of the trunk, right around the soil line, often with a mounded look where the bark meets the ground. Plums, like other stone fruit, are a host. A heavily infested young tree loses vigor as the larvae girdle the inner bark; several borers in one trunk can kill a newly planted tree in a season. Cause The larvae (young grub stage) of the peachtree borer, a moth whose adults look like wasps and fly by day. The adults lay eggs on the lower trunk in summer, and the larvae burrow into the bark at and below the soil line. Trees with existing wounds are hit hardest.Larvae of the peachtree borer (Synanthedon exitiosa), a clearwing moth whose day-flying adults are wasp-like. Eggs are laid on the lower trunk in summer; larvae tunnel in the inner bark at and just below the soil line. Trees stressed by winter injury, mechanical wounds, or bacterial canker are attacked first. Organic treatment Once the larvae are tunneling inside, no spray reaches them. The backyard fix is to scrape soil away from the base in late summer or fall, find the holes marked by gum and frass, and kill the larvae with a thin, stiff wire pushed into each hole. Then smooth the soil back.There is no rescue spray once larvae are tunneling inside. The practical home control is to expose the crown in late summer or fall, find the entry holes by the gum and frass, and kill larvae by hand with a thin wire. Keep the trunk base free of wounds. Prevention Keep mowers and string trimmers away from the trunk; the wounds they leave attract the egg-laying moths. Keep grass and weeds cleared from the base so you can see the soil line, and check it every late summer for fresh gummy ooze.Protect the lower trunk from mechanical injury (the wounds that draw egg-laying females), keep the tree vigorous, and clear weeds and tall grass from the base so the crown stays open and easy to inspect. Check the soil line each late summer for fresh gum.

The control ladder

The ladder troubleshoots from the gentlest solution to the strongest. Start with the gentlest option and only move on when and if it doesn't work.

Garden sanitation

Clear the grass and weeds away from the bottom of the trunk so the soil line stays in plain view, and look it over once a year in late summer for fresh gummy ooze. Keep mowers and string trimmers off the bark down there, since the wounds they leave are what draws the egg-laying moths.A clear, open crown is both a scouting surface and one less shelter at the trunk base, so give the soil line a late-summer inspection for new gum and frass. Mechanical injury gives egg-laying females the wounded bark they favor, so keep machinery off the lower trunk and keep the tree vigorous.
Borer stem surgery

Once the larvae are tunneling under the bark, no spray reaches them, so this is the backyard fix. In late summer or fall, scrape the soil back from the base, spot each entry hole by the gum and the frass, which is the wet, sawdust-like droppings, push a thin stiff wire into it to kill the larva inside, then smooth the soil back.Worming out the larvae by hand is the practical home control at and just below the soil line, where the tunnels run in the inner bark and no rescue material follows them. Work the exposed crown in late summer or fall, follow each gum-and-frass entry, and probe with stiff wire. A few borers can girdle a young trunk in one season, so the labor is well spent there.

No spray for this one. Prevention is the control.

San Jose scale

P · 04

Symptoms Little gray, round, hard bumps crust over the bark of twigs and branches, and the fruit can get small reddish spots where the scales feed. A bad infestation makes the bark look ashy and can kill off twigs and branches, weakening the tree.Tiny gray, circular, hard-shelled scales encrust the bark of twigs and branches, sometimes so densely the bark looks ashy; feeding sites on fruit show as small red-purple haloed spots. Heavy infestations kill twigs and whole limbs from the top down and weaken the tree over a few seasons. Cause An armored scale insect called San Jose scale. After the tiny young 'crawlers' settle down, they stay put under a hard shell and suck sap, with several generations a year. Only the crawler stage moves around and can be targeted.San Jose scale (Diaspidiotus perniciosus), an armored scale insect. Immobile once settled, it feeds on sap under a waxy shell and passes several overlapping generations a year; crawlers (the mobile young stage) are the only vulnerable window and spread the infestation along the branches. Organic treatment The main control is a thorough spray of horticultural oil in late winter while the tree is leafless, coating all the bark to smother the scales. During the season, helpful insects keep light infestations down. Prune out and destroy branches that are heavily crusted with scale.A thorough dormant or delayed-dormant application of horticultural oil, wetting all the bark, smothers overwintering scales and is the mainstay of home control. In-season, natural enemies (tiny parasitic wasps, predatory beetles) suppress light infestations; prune out and destroy heavily encrusted wood. Prevention Prune for good airflow, use a dormant oil spray in areas where scale has shown up before, and check any new trees you buy, since scale often hitches in on nursery stock. Avoid harsh sprays that kill the helpful insects.Keep the tree vigorous and well pruned so airflow is good, apply dormant oil where scale has appeared before, and inspect incoming nursery stock, since scale often arrives on new trees. Preserve natural enemies by avoiding broad-spectrum sprays.

The control ladder

The ladder troubleshoots from the gentlest solution to the strongest. Start with the gentlest option and only move on when and if it doesn't work.

Garden sanitation

Prune out the twigs and branches that are heavily crusted with scale and destroy what you cut rather than leaving the wood by the tree. That takes out the densest colonies in one pass. Give any new tree a close look before you plant it, since scale often hitches a ride in on nursery stock.Removing and destroying encrusted wood strips the settled population where it is thickest and lowers the crawler load that spreads along the branches. Inspect incoming nursery stock as well, which is a common way an infestation arrives in the first place.
Beneficial predators

Tiny parasitic wasps and predatory beetles feed on scale and hold light infestations down on their own. Broad insecticides wipe those helpers out, so leaving them undisturbed is a control in itself.Resident parasitoids and predatory beetles suppress light populations, and the mobile crawler stage is the window they exploit, since a settled scale sits under an armored cover. Avoiding broad-spectrum material is therefore part of holding the population, not merely a courtesy to the garden.
Horticultural oil

This is the main home control: in late winter, while the tree is bare, spray horticultural oil so it wets every bit of bark on the twigs and branches. The oil smothers the scales under their shells, so coverage is the whole job. Do not spray oil on a drought-stressed tree or above 90°F, and once the tree has leaves keep it at least 30 days from any sulfur spray; check the oil label, because some say to wait longer.A thorough dormant or delayed-dormant oil applied to run-off over all bark is the mainstay here: the armored cover blocks most contact material, so the result rides entirely on wetting the shell. Repeat it in seasons following an infestation rather than waiting for encrustation to rebuild. Keep the oil constraints in view: not above 90°F, not on stressed trees, not within 30 days of sulfur while the tree is in leaf, or longer if the oil label says so.

No spray for this one. Prevention is the control.

Diseases

Black knot

D · 01

Symptoms Hard, black, warty lumps (called knots) grow along the twigs and branches, anywhere from an inch to six inches or more long. They start as a soft olive-green swelling one year and turn coal-black and hard the next. The branch beyond a knot often wilts and dies, and a badly infected tree gets stunted and gnarled. Black knot is the classic plum disease, the one to learn to recognize.Hard, black, elongated, warty swellings (knots) grow along twigs and branches, from an inch to six inches or more long, girdling and eventually killing the wood beyond them. A new gall starts as an inconspicuous olive-green, corky swelling one year, then hardens and turns coal-black by the second. Leaves on knotted branches may wilt and die, and a heavily infected tree becomes stunted and misshapen. This is the signature disease of plum. Cause A fungus (Apiosporina morbosa) that lives in the black knots over winter, on your tree and on any wild plums or cherries nearby. In cool, wet spring weather it shoots out spores that infect the new green shoots. You will not see anything the first year; the knot swells the next year and turns black the year after.The fungus Apiosporina morbosa (formerly Dibotryon morbosum). It overwinters in the galls on the tree and on nearby wild or ornamental Prunus, and in cool, wet spring weather releases spores that infect the new green shoots. Infection is invisible the first season; the gall swells the following year and blackens the year after, so the disease runs on a roughly two-year cycle. Organic treatment Cutting the knots out is the main fix, and when you do it matters: prune in late winter while the tree is bare, before it starts growing in spring. Cut each knot off 3 to 4 inches below the black lump, into clean wood, because the fungus reaches farther than you can see. Carry the cut pieces away and burn, bury, or bag them so they cannot re-infect the tree, and wipe your pruners with rubbing alcohol between cuts.Pruning is the core control, and timing is everything: in the dormant season, before growth resumes (before about April 1), cut out every knot, making the cut 3 to 4 inches below the visible gall into clean wood, since the fungus extends beyond what you can see. Remove the prunings from the area and burn, bury, or bag them, and disinfect tools between cuts. On a scaffold too valuable to remove, cut the gall out to healthy wood. A protective fungicide on the new shoots in early spring supports the pruning where pressure is high. Prevention Check the tree every winter and cut out any knots before spring, when they spread. Just as important, clean up or remove wild plums, chokecherries, and neglected ornamental plums nearby, because they keep re-infecting your tree. Some plum varieties resist black knot better than others, so ask when you buy, but cutting the knots out each year is the habit that matters most.Scout and prune out knots every dormant season before they can release spores, and deal with the reservoir: remove or clean up wild plum, chokecherry, and neglected ornamental Prunus within range, which sustain the disease. Choosing a less-susceptible cultivar and keeping the tree open and vigorous both help, but annual knot removal is the non-negotiable habit.

The control ladder

The ladder troubleshoots from the gentlest solution to the strongest. Start with the gentlest option and only move on when and if it doesn't work.

Resistant varieties

Some plum varieties shrug this off better than others, so ask which one you are buying before the tree goes in the ground. It lowers the trouble, but it does not take the place of cutting the knots out each winter.Cultivar susceptibility varies, so a less-susceptible selection lowers the pressure a tree carries for its whole life. It is a planting-time choice that supports the annual pruning habit rather than substituting for it.
Weed host control

Look past your own tree. Wild plums, chokecherries, and neglected ornamental plums and cherries in the neighborhood carry the same fungus and keep re-seeding your tree with spores each spring, so removing or cleaning up the ones within reach matters as much as pruning your own.The nearby reservoir governs how much pressure the tree sees: wild and neglected Prunus hold galls that shed spores into the same cool, wet spring weather your tree is pushing green shoots in. Clearing that reservoir within range is what lets annual knot removal actually hold.
Prune out infection

This is the fix, and the timing carries it: cut the knots out in late winter, with the tree still bare and before spring growth resumes. Place each cut into clean wood 3 to 4 inches beyond the lump you can see, because the fungus runs farther along the branch than the swelling shows. Then get the prunings out of the yard, by burning, bagging, or burying them, and disinfect the blades between cuts, for which rubbing alcohol works.Dormant removal ahead of spring growth, before about April 1, is the core control. Take each cut 3 to 4 inches into clean wood past the gall, since colonized tissue extends beyond what is swollen, and carry the prunings off site rather than piling them nearby. Disinfect between cuts, and where a scaffold is too valuable to lose, excise the gall back to healthy wood instead of taking the limb.

No spray for this one. Prevention is the control.

Brown rot

D · 02

Symptoms At bloom, infected flowers go limp and brown, and small gummy dead patches can form on the nearby twigs. As the plums ripen, brown spots appear and spread quickly, sometimes rotting a whole fruit in a day or two in warm, wet weather, with a dusty tan fuzz on the surface. Rotted fruit shrivels into a hard, dried mummy that hangs on the tree.At bloom, infected blossoms wilt and turn brown, and the infection can run back into the twig to form a small gummy canker. As fruit ripens, brown circular spots appear and spread fast, sometimes rotting a whole plum within a day or two in warm, wet weather, with a dusty tan spore mass on the surface. Rotted fruit dries into a mummy that clings to the tree or drops. Cause A fungus called Monilinia fructicola. It survives the winter in dried mummy fruit and in dead twig patches, then releases spores at bloom that infect the flowers. Those flower infections later cause the fruit to rot. Warm, humid, wet weather makes it spread fast, and any break in the skin lets it in.The fungus Monilinia fructicola. It overwinters in mummified fruit (whether hanging in the canopy or fallen) and in twig cankers; spores released at bloom infect flowers, and those infections later seed the fruit rot. Warm, humid, wet conditions drive rapid spread, and any skin break (curculio scar, hail, cracking) is an entry point. Organic treatment The main control is cleanup: take off and destroy every dried mummy from the tree and the ground, and prune out the gummy dead twig patches, since these hold the spores. If the weather is wet during bloom, an organic-approved spray at bloom helps protect the flowers. As soon as you see a plum rotting, pick it and throw it away, and thin the fruit so plums are not touching.Sanitation is the core control: remove and destroy every mummy from the tree and the ground, and prune out gummy twig cankers, because these are the spore sources. During a wet bloom, an organic-approved bloom-time fungicide reduces blossom blight. Once fruit is rotting, pick and dispose of it promptly, and thin fruit so plums do not touch, which slows spread through a cluster. Prevention Cleanup all year prevents most of the damage: never leave dried mummies on the tree over winter, pick up dropped fruit, and prune so the tree is open and the plums dry fast after rain. Keep pests like plum curculio in check, since their wounds let rot in. Pick fruit on time, handle it gently, and chill it soon after picking.Year-round sanitation prevents most loss: never leave mummies on the tree over winter, remove dropped and thinned fruit, and keep the canopy open with good pruning so fruit dries quickly after rain. Control plum curculio and other pests whose wounds open the door, harvest promptly, handle fruit gently, and cool it soon after picking.

The control ladder

The ladder troubleshoots from the gentlest solution to the strongest. Start with the gentlest option and only move on when and if it doesn't work.

Garden sanitation

Cleanup is the core of it. Take every shriveled, dried fruit, called a mummy, off the tree and off the ground, and clear away the dropped and thinned fruit too. Mummies are where the fungus waits out the winter, so leaving them hanging sets up next year's rot. Pick and dispose of any plum you see rotting as soon as you spot it.Mummies in the canopy and on the ground are the primary overwintering inoculum, so stripping them at dormancy and clearing drops and thinnings through the season removes what would otherwise meet bloom. In season, pull rotting fruit before the dusty tan spore mass develops and seeds the fruit around it.
Airflow spacing

Prune the tree so it is open and air moves through it. This rot runs on wet fruit, so a canopy that dries fast after rain gives it much less to work with.An open canopy shortens the wetting period on fruit after rain, which is the variable that decides how fast warm, humid weather turns a spot into a rotted plum.
Prompt harvest

Pick the plums as they come ready instead of letting them hang, handle them gently so the skins do not break, and chill them soon after picking. Any nick or split in the skin is a way in for the rot.Harvesting on time removes fruit before the ripe phase the pathogen exploits, and gentle handling protects the skin, since any break, whether a curculio scar, hail, or a growth crack, is an infection court. Cooling soon after picking slows what may already be underway.
Prune out infection

Cut out the small gummy dead patches on the twigs, the ones left where the disease ran back from an infected blossom, and destroy what you remove. Those patches hold spores over winter alongside the mummies.Twig cankers formed where blossom infections ran back into the wood are the second overwintering site, so excise them into clean wood and destroy the prunings, leaving next spring's bloom less inoculum to meet.

No spray for this one. Prevention is the control.

Bacterial spot

D · 03

Symptoms Leaves get small angular water-soaked spots that turn dark and fall out, leaving little holes, called a shot-hole look. Bad cases turn leaves yellow and thin out the tree. On the fruit, small sunken spots, pits, and cracks form. How badly a tree is hit depends a lot on the variety, and Japanese plums are often more affected than European ones.Small angular, water-soaked spots on leaves turn brown to purple-black and drop out, leaving a shot-hole look; heavy infection yellows and thins the canopy. On fruit, small sunken spots, pits, and cracks develop on the skin, downgrading the crop. Susceptibility varies sharply by cultivar, and Japanese plums are often hit harder than European. Cause A bacterium (a microscopic organism, not a fungus) called Xanthomonas. It spreads in warm, wet, windy weather and builds up when there are other susceptible plum or peach trees close by. The spots can look like spray damage.The bacterium Xanthomonas arboricola pv. pruni. It spreads in warm, wet, windy weather and builds up where susceptible plum, peach, and related trees grow nearby. Symptoms are sometimes mistaken for spray injury or nutrient problems. Organic treatment There is no good home cure once it shows up. Copper sprays help a little as prevention but can hurt the tree if overused, so they are not a dependable fix. The best you can do is keep the tree healthy and the canopy open so it shrugs off the damage.Home options are limited once symptoms appear: copper sprays help more as prevention than cure and can injure the tree if overused, so they are not a reliable home fix. Keeping the tree vigorous and the canopy open and dry helps it tolerate the disease. Prevention The best prevention is the variety you pick. Choosing a plum known to resist or tolerate bacterial spot avoids most of the trouble, so it is a decision to make before planting. Good airflow, going easy on nitrogen, and a healthy tree also help.The most effective measure is choosing a resistant or tolerant cultivar at planting; this is largely a variety decision made before the tree goes in. Good airflow, avoiding excess nitrogen, and tree vigor reduce severity.

The control ladder

The ladder troubleshoots from the gentlest solution to the strongest. Start with the gentlest option and only move on when and if it doesn't work.

Resistant varieties

This one is mostly decided before you plant. Varieties differ a lot in how hard they get hit, and Japanese plums often suffer more than European ones, so buy a tree sold as resistant or tolerant to bacterial spot.Cultivar susceptibility is the dominant variable and it is set at planting, with Japanese types generally taking it harder than European. Once a susceptible tree is in the ground, what remains manages severity rather than removing the disease.
Airflow spacing

Prune so air moves through the canopy and the leaves dry off after rain. This will not clear the bacteria, but an open, healthy tree carries the spotting with less damage.Canopy openness and tree vigor act on severity rather than on presence: faster drying cuts into the warm, wet, windy conditions the bacterium spreads in, and a vigorous tree tolerates the leaf drop better.
Copper fungicide

Be realistic about this rung. There is no dependable home cure once the spots are on the tree. Copper does more as a preventive than as a rescue, and overusing it can injure the tree itself, so it is not something to lean on. If you do reach for it, follow the label rate, and keep spray and runoff away from ponds and storm drains, since copper is highly toxic to fish.Copper is a limited protectant here rather than a cure, and phytotoxicity from repeated application is a real cost, which is why it does not amount to a reliable home answer for this disease. Where it is used, the label rate governs, the copper compound named on the label sets the acute hazard band, and the residue accumulates at the soil surface, so keep repeat use over the years restrained.

No spray for this one. Prevention is the control.

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