Pests
Symptoms Clusters of tiny soft green or gray insects on the growing tips and undersides of leaves, sometimes with curled, sticky foliage.Colonies on growing tips and leaf undersides, one of the pests UC IPM lists for mint; honeydew and the insects themselves contaminate a crop eaten fresh, and soft, overfed growth is the most susceptible. Cause Aphids are small sap-sucking insects that breed fast, especially on soft growth from too much fertilizer, and they can spread plant viruses.Several aphid species feed on mint; they reproduce rapidly and favor the lush growth that excess nitrogen and rich soil produce. Organic treatment Blast them off with a strong spray of water, or use insecticidal soap or neem oil on the leaf undersides, repeating every few days. Rinse cut sprigs well before use.Dislodge colonies with a water jet or spray insecticidal soap or neem, covering leaf undersides, and repeat every few days; conserve ladybugs, lacewings, and parasitoid wasps. Prevention Welcome ladybugs and lacewings, go easy on nitrogen, and check new growth often.Scout the tips early, avoid overfeeding, and conserve natural enemies; because you eat the leaves, lean toward a strong water spray before anything else.
Symptoms A fine stippling or speckling on the leaves, sometimes with faint webbing on the undersides, worst in hot, dry weather. Leaves look dull, sandy, or bronzed.Twospotted and related spider mites, which UC IPM lists for mint, stipple the foliage with pale flecks and spin fine webbing on the undersides; they flare in hot, dry, dusty conditions and on drought-stressed plants, which is why mint's moisture love is also its best mite defense. Cause Tiny sap-sucking mites, not true insects, that explode in hot, dry, dusty conditions and are easy to miss until the leaves are speckled.Spider mites feeding with piercing mouthparts; populations build fastest in heat and drought and on dusty, water-stressed plants. Organic treatment Spray the undersides of the leaves with a strong jet of water to knock them off, keep the plant well watered, and use insecticidal soap or neem if they persist.Hose the undersides forcefully and repeat, maintain steady soil moisture, and apply insecticidal soap or a miticidal oil to the leaf undersides; conserve predatory mites and minute pirate bugs. Prevention Keep mint evenly moist and mulched, since drought stress invites mites, and rinse dusty foliage in hot spells.Do not let mint dry out or get dusty, mulch to hold moisture, and scout the undersides in hot weather when mites move fastest.
Symptoms Young shoots cut off at the soil line, notched or shot-holed leaves, or plants that weaken and thin out from grubs feeding on the roots and rhizomes.Utah State lists flea beetles and cutworms among mint's insect pests; cutworms sever young shoots at the soil line and mint flea beetles chew small holes, while soil and rhizome feeders thin an established patch from below. On a home planting numbers are usually modest. Cause A mix of chewing pests, cutworms and mint flea beetles above ground and root-feeding larvae below, that damage leaves, stems, and the underground runners.A complex of foliage feeders (cutworms, mint flea beetle) and root/rhizome feeders (root and rhizome larvae); the perennial, spreading root mass is what harbors the below-ground stages. Organic treatment Handpick cutworms at dusk and use cardboard collars on new transplants, hose or handpick flea beetles, and keep the bed clean; dividing and resetting a tired patch in fresh ground breaks root-pest cycles.Handpick and use collars against cutworms, dislodge flea beetles with water or row cover on new plantings, and manage root pests culturally by dividing and resetting the patch in clean soil; reserve any spray for the labeled edible-herb products. Prevention Clear plant debris where cutworms shelter, rotate a heavily infested patch to fresh ground, and keep plants vigorous so they outgrow light feeding.Sanitize debris, keep plants vigorous, and reset an infested patch into fresh ground on a multi-year cycle, the same renewal that keeps mint from getting woody.
Diseases
Symptoms Small orange, yellow, or rust-brown powdery pustules on the undersides of the leaves and on the stems, with pale spots on the upper surface. Badly affected leaves curl, brown, and drop, and rusty leaves are not good to eat.Puccinia menthae, the classic mint rust: orange to brown powdery pustules on leaf undersides, stems, and petioles, with defoliation in a bad year (NC State lists rust among the main mint diseases). It overwinters in the rhizomes, so an infected patch reinfects itself, and warm humid crowding drives it. Cause A rust fungus, the signature mint disease, that thrives in warm, humid, crowded conditions and lives over on the roots and rhizomes from year to year.The rust fungus Puccinia menthae, favored by warm, humid, crowded conditions and carried over in the root and rhizome mass. Organic treatment Pick off and destroy rusted leaves as soon as you see them, thin and space plants for airflow, water at the soil line, and cut a badly infected patch to the ground; in a severe case, start a fresh planting from clean, rust-free cuttings in a new spot.Remove and destroy infected leaves, open up the planting for airflow, switch to soil-line watering, and mow or cut a heavily infected patch to the ground and clear the debris; renew from clean cuttings in fresh ground where it recurs. There is no reliable home cure once it is established. Prevention Space plants for good airflow, avoid wetting the foliage, keep the patch from getting congested, and start new plantings from clean stock.Airflow, dry foliage, and uncongested spacing are the defenses; propagate only from rust-free plants and reset a chronically infected patch elsewhere.
Symptoms Stunted, off-color plants whose lower leaves yellow and wilt, often on just one side of a stem, with whole shoots or plants dying back in warm weather. It does not wash off and there is no spray cure.Verticillium wilt (a soilborne Verticillium), the disease that most limits mint's longevity: slow, bronze-cast spring growth, one-sided branch development, lower-leaf yellowing and wilt in warm or dry weather, and dieback. The Connecticut Experiment Station and Utah State both flag it for mint. The fungus persists in soil for years and has a wide host range, so it is managed by site selection and renewal, not treatment. Cause A soil-borne fungus that clogs the plant's water-conducting tissue; it builds up in the ground and is the disease that shortens the life of a mint patch.A soilborne Verticillium fungus that invades the vascular system; it survives for years in soil and infects many crops (tomato, potato, strawberry, other mints). Organic treatment There is no cure for an infected plant, so remove it. Start fresh plantings from clean cuttings in a new bed, and do not follow tomatoes, potatoes, or strawberries, which host the same fungus.Rogue out affected plants and manage by prevention: propagate disease-free cuttings, establish new patches in clean ground away from prior verticillium hosts, and rotate the mint bed on a multi-year cycle where the disease appears. Prevention Plant clean stock in ground with no recent history of the disease, avoid siting mint after verticillium-susceptible crops, and move the patch to fresh ground every few years.Use clean stock, avoid ground that grew tomatoes, potatoes, eggplant, or strawberries, and reset the patch in fresh soil periodically, since there is no rescue for an infected plant.
Symptoms A white, powdery dust on the leaves and stems (powdery mildew), or dark sunken spots and blotches on leaves and stems (anthracnose leaf spot). Heavily spotted or coated leaves are not good to eat.Powdery mildew (white powdery patches that brown and shrivel heavy foliage, listed for mint by UC IPM) and anthracnose or leaf spot (Utah State and NC State list leaf-spotting fungi for mint), both favored by crowded, humid conditions and wet leaves. Cause Fungal leaf diseases that spread in crowded, humid plantings and on wet foliage, worse where air does not move.Foliar fungi (powdery mildew; anthracnose and other leaf-spot fungi) driven by high humidity, crowding, and prolonged leaf wetness. Organic treatment Remove affected leaves, thin the planting and water at the soil line to keep the leaves dry, and cut a badly hit patch back to encourage clean new growth.Improve airflow by thinning and dividing, water at the soil line, remove infected foliage, and shear a badly affected patch to force clean regrowth; drip irrigation and avoiding overnight leaf wetness are the practical controls Utah State recommends. Prevention Space for airflow, water at the base rather than overhead, and avoid crowding.Open the canopy, keep the foliage dry, and do not let the patch get congested; renew a chronically diseased stand from clean cuttings.
