Pests
Symptoms This tiny brown insect rests on new leaves at an angle, rear end raised, which is your clue. The young ones make little waxy white threads and curl the new leaf tips. The real danger is not the feeding but a fatal disease it spreads, citrus greening, so it is worth acting on even where the pest is uncommon.A tiny mottled-brown insect, about an eighth of an inch, that feeds tilted up at a 45-degree angle on new flush, a posture no other citrus pest shares. Nymphs make waxy tubules and curl tender growth. The insect matters less for its feeding than for what it carries: it is the vector of Huanglongbing (citrus greening), the most serious citrus disease worldwide. Scout the youngest flush. Cause The psyllid breeds on fresh new leaves, so it builds up fastest when the tree is pushing tender growth in warm weather. It has spread across the southern states, and any psyllid you find could be carrying the disease.Adults lay eggs only on new flush, so populations track flushing cycles and build fastest in warm weather when the tree pushes tender growth. The pest is established across much of the southern United States, and any psyllid should be treated as a potential disease carrier. Organic treatment Spray horticultural oil or insecticidal soap on the new growth to knock back the young psyllids, repeating each time fresh leaves appear. Hold off on oil when it is above about 95°F or the tree is short on water, or the oil can burn leaves. Also report any psyllids or signs of the disease to your local farm advisor.On a backyard tree, horticultural oil and insecticidal soap on the new flush reduce nymphs; thorough coverage is key, repeated as each flush emerges. Do not apply oil above 95°F or to a drought-stressed tree. Most important, report suspected psyllids or greening symptoms to your county agricultural office, since this is a regulated pest. Prevention Buy certified citrus from a trusted nursery, and never carry citrus plants or cuttings out of a quarantine zone, since that is how the pest and its disease spread. Check new leaves often in warm weather, and follow local guidance if greening is in your area.Buy only certified citrus from a reputable nursery and never move citrus plants or leaves out of a quarantine area, the main way the pest and disease jump regions. Inspect each flush in the warm season, and conserve the parasitic wasp Tamarixia and general predators that suppress it.
Symptoms You will see squiggly silver trails snaking through the new leaves, often with the leaf edge curled. A tiny caterpillar makes these tunnels inside young leaves only. It looks alarming but rarely hurts a grown tree, though it can set back a small young one.Silvery, serpentine tunnels winding through new leaves, with a thin dark frass line down each mine and leaf margins that curl around the damage. The larva mines only young, expanding foliage; hardened leaves are not attacked. On an established tree the injury is cosmetic, but on a young mandarin pushing lots of flush it can slow growth. Cause A tiny moth lays eggs on the newest leaves, and the larvae tunnel inside them. They breed fast in warm weather, so the worst damage shows on the late-summer growth.A small moth lays eggs on tender new flush, and the larvae mine between the leaf surfaces. Generations cycle quickly in warm weather, so damage peaks on the late-summer and fall flushes rather than spring growth. Organic treatment Usually no treatment is needed, and spraying can kill the good bugs that control it. On a small young tree you want to protect, light horticultural oil on the new leaves discourages the moth. Only spray in mild conditions, not in high heat or on a thirsty tree, and leave the tunneled leaves on.Chemical control is rarely warranted, and broad-spectrum sprays undermine the parasitic wasps. On a young tree where mining slows establishment, a light horticultural oil at bud break discourages egg-laying on the new flush; repeat as each flush emerges. Follow label heat limits and do not spray above 95°F. Leave mined leaves in place. Prevention Do not over-fertilize or prune a lot in summer, because that creates the tender leaves the moth needs. On a healthy grown tree it is best to live with the trails, since helpful wasps keep it in check.Avoid forcing excess tender flush with heavy nitrogen or unnecessary summer pruning, since the moth needs young leaves to breed. Tolerate cosmetic mining on bearing trees; resident parasitic wasps usually provide good control when broad-spectrum sprays are avoided.
Symptoms Scale look like little hard or waxy lumps that sit still on twigs and leaf undersides, so it is easy to mistake them for part of the branch. The soft kinds make leaves sticky and grow a black sooty coating, and ants are often crawling around them.Fixed, non-moving bumps clustered on twigs, along the leaf midrib, and beneath leaves. Armored types form firm gray or brown shells like raised bark; softer types are plumper and glossy and secrete honeydew that leaves foliage tacky and grows black sooty mold, with ants patrolling for the sugar. Heavy numbers bring mottled yellow leaves, early leaf fall, and twig dieback. Cause Scale are little insects that feed on the tree's sap. They get worst when ants are around, since the ants protect them from the helpful bugs that eat scale.A mix of armored and soft scale species tap into the tree and feed on sap. They gain the upper hand on trees that are dusty, crowded, or patrolled by ants, since ants drive off the ladybugs and parasitic wasps that would thin the colony. Organic treatment Coat the lumps with horticultural oil, reaching the backs of leaves and the twigs. Save the spray for cooler, well-watered days, never above roughly 95°F or on a stressed tree, or it can scorch the foliage. Spray again later as new ones appear.A thorough horticultural oil application, narrow-range petroleum or neem, smothers scale; the key is wetting every surface, especially twig undersides and leaf backs. Skip oil above roughly 95°F or on a drought-stressed tree. Plan a follow-up as fresh crawlers hatch. Prevention Keep ants from climbing the tree with a sticky band around the trunk, which lets the good bugs control the scale, and look over any new tree for lumps before planting it.Keep the tree vigorous, rinse dust off the canopy, and cut off ants with a sticky trunk band so resident beneficials can work. Inspect any incoming nursery tree, since scale often hitchhikes on new stock.
Symptoms Look for clusters of tiny soft-bodied insects, often green or black, packed onto the newest leaves and flower buds, curling the tips. They leave a sticky coating that ants follow and that grows a black sooty film. Mandarins are most vulnerable during the spring and fall flushes.Clusters of soft green, black, or brown aphids on the youngest flush and flower buds, with curled, distorted new leaves and sticky honeydew that draws ants and grows sooty mold. Spring and fall flushes are the targets. The brown citrus aphid is also a vector of citrus tristeza virus, which raises the stakes where that disease is a concern. Cause Aphids multiply very fast on soft new growth in mild weather, and ants protect them. Too much fertilizer makes extra tender leaves that draw them in.Aphids reproduce explosively on tender new growth in mild weather and are tended by ants for honeydew. Lush, over-fertilized flush is especially attractive, and ant protection lets colonies outrun their natural enemies. Organic treatment Spray them off with water, or use insecticidal soap or horticultural oil, getting under the curled leaves. Keep oil for mild days only, not in high heat or on a stressed tree, and avoid harsh sprays that kill the good bugs.A forceful water spray, insecticidal soap, or horticultural oil controls aphids; cover the undersides of curled leaves and repeat as needed. Observe oil heat limits (not above 95°F or on stressed trees), and preserve natural enemies by skipping broad-spectrum insecticides. Prevention Do not over-fertilize, which makes the soft growth aphids love, and keep ants out so ladybugs and other helpers can eat them. A blast of water from the hose usually clears them off.Avoid forcing excess tender flush with heavy nitrogen. Control ants so ladybugs, lacewings, and parasitic wasps can suppress colonies. A strong jet of water knocks aphids off new growth and is often all that is needed.
Symptoms Look for leaves that turn a dull, speckled, silvery color, sometimes with tiny red dots moving on them (a hand lens helps). Mites get worse when it is hot, dry, and dusty. A lot of them can bronze the leaves and drop some.Fine stippling or silvering on leaves and sometimes the rind, with tiny dark-red mites and cast skins visible under a hand lens. Heavy populations bronze the foliage and can drop leaves. Mites flare in hot, dusty, dry conditions and after broad-spectrum sprays remove their predators, so an outbreak often signals a dust-stressed or over-sprayed tree. Cause These mites love hot, dusty conditions and build up fast on stressed trees. Dusty trees and trees sprayed with strong insecticides (which kill the helpful mites) get the worst of it.Citrus red mite thrives in heat and dust and reproduces rapidly on stressed trees. Dusty roadside trees and trees sprayed with broad-spectrum insecticides, which remove predatory mites, are the most prone to damaging populations. Organic treatment Usually the damage is just cosmetic and needs nothing. If there are a lot of mites, horticultural oil works, but timing is tricky: mites peak in hot weather, the riskiest time to oil a tree. Only spray once it has cooled off, never on a hot, dry, stressed tree.Damage is usually cosmetic and rarely needs treatment. If populations run heavy on a stressed tree, horticultural oil provides control; observe heat limits strictly, as mite outbreaks coincide with the hot weather when oil is riskiest. Do not apply oil above 95°F or to a drought-stressed tree. Prevention Rinse dust off the leaves during hot, dry weather and keep the tree watered, because a healthy tree handles mites better. Avoid strong insecticides that kill the good mites.Hose dust off the canopy in hot, dry spells and keep the tree well watered, since vigorous trees tolerate mites better. Avoid broad-spectrum insecticides that destroy the predatory mites providing natural control.
Diseases
Symptoms The classic sign is a leaf yellow in a blotchy, uneven pattern, with the yellow on one side not matching the other (a nutrient problem is usually even on both sides). Fruit stay small, lopsided, green on the bottom, and taste bad. There is no cure, and the tree slowly dies. It is the worst citrus disease there is.Blotchy, asymmetric leaf yellowing that does not mirror across the midrib (distinguishing it from a symmetric nutrient deficiency), yellow shoots, and corky, enlarged veins. Fruit are small, lopsided, fail to color fully, stay green at the bottom, and taste bitter and salty; seeds often abort. The tree declines over years and there is no cure. This is the most destructive citrus disease worldwide. Cause Bacteria spread by the Asian citrus psyllid as it feeds on new shoots clog the tree's plumbing, blocking food to roots and fruit. No treatment reverses it; an affected tree is a permanent source of spread. Management is preventing psyllid feeding and removing any confirmed tree.Candidatus Liberibacter asiaticus, the bacterium behind greening, spreads tree to tree by the Asian citrus psyllid feeding on new growth, then clogs the phloem so nutrients cannot reach roots and fruit. No treatment clears an established infection, so management is entirely suppressing the psyllid and removing confirmed trees before they seed further spread. Organic treatment There is no treatment that saves an infected tree. Focus entirely on prevention: keep the psyllid off with regular inspection and treatment, and if a tree is diagnosed with greening, remove it promptly to protect nearby trees. An infected tree left in place becomes an ongoing source of psyllid pressure.There is no cure and no organic remedy for an infected tree. Management is prevention and vector control only: protect trees from the psyllid, and remove and properly dispose of confirmed-infected trees promptly so they cannot serve as a reservoir. Prevention Buy only certified clean trees, never move citrus out of a quarantine zone, and control the psyllid that spreads it. Check your tree often, and report anything that looks like greening to your local agricultural office, because removing infected trees quickly protects everyone's citrus.Plant only certified disease-free nursery trees, never move citrus out of quarantine areas, and control the psyllid aggressively where it is present. Inspect regularly and report suspected greening to your county agricultural commissioner, since coordinated removal of infected trees is the only effective area-wide defense.
Symptoms Look for gum oozing near the base of the trunk and a dark, sunken, slimy patch under the bark, along with a thinning, yellowing canopy. A key clue is leaves that wilt and do not perk up when you water, because the roots are rotting from too much water.A trunk lesion at or near the bud union, appearing first as a drop of gum, then a brown, necrotic, slippery area under the bark that can girdle the trunk. Below ground, dark, rotted feeder roots go with a thinning, yellowing canopy and leaves that wilt but do not recover after watering. It is one of the most serious threats to a citrus tree, and it follows wet feet and a buried graft union. Cause A soil fungus attacks the roots and trunk base when the soil stays too wet. Poor drainage, overwatering, and burying the graft knob are what let it in.Soil-borne Phytophthora species attack roots and the crown wherever soil stays saturated. A buried or mulch-packed graft union, poor drainage, and overwatering are the drivers; heavy clay and standing water are the classic setups. Organic treatment There is no easy fix once it takes hold. Improve the drainage, clear soil and mulch away from the trunk base so it can dry out, and water less. The best control is preventing it with good drainage and planting the tree high in the first place.There is no quick cure once the crown is girdled. Correct the cause: improve drainage, pull soil and mulch back from the crown to let it dry, and cut back irrigation. Minor bark lesions can sometimes be exposed and allowed to callus. Prevention through drainage and planting depth is the real control. Prevention Plant on a raised mound with the graft knob above the soil, make sure water drains fast, keep mulch off the trunk, and let the soil dry between waterings. Buying a tree on a root-rot-resistant rootstock also helps a lot.Plant high on a mound with the graft union well clear of the soil, guarantee sharp drainage, keep mulch off the trunk, and water with a soak-and-dry rhythm rather than constant moisture. Choose a Phytophthora-resistant rootstock, which most trifoliate and citrumelo stocks provide.
Symptoms Small brown or black spots with a yellow ring show up on young leaves and shoot tips, and dark, slightly sunken spots appear on small fruit, which may then drop. This one mainly troubles certain tangerine-type mandarins and tangelos (like Minneola and Murcott); satsuma and clementine are not among the types UF lists as susceptible.Small brown-to-black necrotic spots, often ringed by a yellow halo, on young leaves and shoot tips, plus small, slightly depressed dark spots on young fruit that can cause premature drop. It is a mandarin-and-tangerine-hybrid disease: Dancy tangerine and Minneola tangelo are most severely affected, with Murcott, Orlando, Lee, Nova, and Sunburst often hit. Fruit becomes more resistant as it matures, so mostly young fruit is affected. Cause A fungus infects the young leaves and small fruit of susceptible mandarin hybrids, spreading in warm, wet, humid weather. It cannot infect older leaves or older fruit.The tangerine pathotype of the fungus Alternaria alternata infects only young, susceptible tissue and spreads on warm, wet, humid weather, so it is most damaging in the humid Southeast and on the susceptible hybrid cultivars. Older, hardened leaves and older fruit are not infected. Organic treatment If you grow a susceptible type, copper sprays on the new growth during warm, wet weather help protect it, following the label. Spots already there will not heal. On satsuma or clementine you generally do not need to spray at all.On a susceptible cultivar, time copper fungicide applications to protect the new flush and small fruit during warm, wet spells, following label rates; there is no rescue for tissue already spotted. On a tolerant variety no treatment is needed. Prevention The easiest fix is picking the right variety: satsuma and clementine are not among the susceptible types, so choose those in humid areas instead of a susceptible one like Minneola. Otherwise, prune for good airflow, avoid wetting the leaves, and rake up fallen leaves.The strongest control is variety choice: satsuma and clementine are not among the varieties UF lists as susceptible, so plant those in humid regions rather than a highly susceptible hybrid like Minneola or Murcott. Prune for airflow, avoid overhead wetting, and clear fallen leaves. Copper fungicides on the susceptible flush are the fallback where a prized susceptible variety is grown.
Symptoms Yellow blotches on top of the leaf with a greasy-looking brown or black blister underneath, followed by leaves dropping, mostly in winter and early spring. It shows up mainly in warm, humid places like Florida and the Gulf Coast.Yellow mottling on the upper leaf surface with a matching blister-like swelling underneath that collapses into a brown-to-black, greasy-looking spot. Infected leaves drop, mostly in winter and early spring, thinning the canopy. It is a warm, humid-climate disease, most troublesome in Florida and the Gulf where relative humidity is high. Cause A fungus infects the undersides of the leaves in warm, humid weather, and it builds up on old fallen leaves under the tree. It is mainly a problem in humid climates, not dry ones.A fungus infects the underside of leaves during warm, humid, wet weather, with spores building on decaying fallen leaves on the ground. High relative humidity and warm nights are what drive it, so it is a Southeastern and Gulf concern rather than an arid-West one. Organic treatment A summer spray of horticultural oil (with copper if needed) controls it on a backyard tree, along with cleaning up fallen leaves. In dry climates you usually do not need to do anything.Horticultural oil, alone or with copper, applied in early to mid-summer gives good backyard control by smothering the developing infection; sanitation of fallen leaves supports it. In arid regions it rarely warrants treatment. Prevention Rake up and remove the fallen leaves under the tree, since that is where the fungus builds, and keep the canopy open for airflow. In humid areas a summer oil or copper spray helps if it is bad.Rake up and remove fallen leaves to cut the spore source, prune for airflow, and keep the tree vigorous. A summer horticultural-oil or copper application, timed to the main infection period, reduces it where pressure is high.
