> Next: Plant Pests
Diseases and Symptoms
On this page, find symptoms of various plant diseases, identification of the disease likely to be causing the condition, and options for treating or controlling the disease.
Using the Plant Disease Identification Table
Scan this table listing common plant diseases. Click on each disease name to reveal common symptoms for the disease and treatments or cures.
If the cure requires application of sprays or other treatments, follow the control’s package directions and label instructions, and review the step-by-step demonstration of how to apply dry and liquid sprays to vegetable plants [See: Applying Garden Chemicals].
Remember to choose first the least-toxic control measure, and limit treatment to areas of active disease infections.
To control difficult-to-treat, resistant, or recurring infestations of treated plant diseases, follow the principles, practices, and methods of Integrated Pest Management [See: Integrated Pest Management].
Plant Disease Identification Table
Symptom: Black, tan, or red spots on leaves; leaves yellow and drop. Black cankers on stems, with a general wilt of branch tips.
Cause: Anthracnose, a fungal disease that occurs in late spring and summer, typically after humid conditions.
Cure: Remove infected leaves and branch tips. Collect and destroy infected fallen leaves. Thin excessive growth to promote air circulation. Spray with Bordeaux mixture, available at many nurseries and garden retailers.
Symptom: Leaves are mottled with black spots, eventually yellow and die. Powdery black or brown dusting on foliage and blossoms; leaves may drop.
Cause: Black spot and leaf spot, fungal diseases, found on many plants. Spreads through spores that blow onto moist plant leaves. Common in shady, crowded plantings.
Cure: Space plantings to allow good air circulation. Remove shading foliage. Apply water at base of plant. Strip and destroy infected leaves. Spray with Bordeaux mixture, available at many nurseries and garden retailers.
Symptom: Flowers wilt and foliage tips curl, yellow, and die. Oozing cankers form at base of shoots with main stem. Affected foliage may have a strong odor.
Cause: Blight and scab, several bacterial diseases caused when soil that contains bacteria is splashed onto cut and bruised foliage or is carried to flowers by pollinating insects.
Cure: Remove and dispose of affected plants. Apply water at base of remaining plants. Install floating row covers and pollinate by hand. Rotate plantings annually to new beds. Spray with Bordeaux mixture, available at many nurseries and garden retailers.
Symptom: Flowers and foliage collapse under heavy fuzz of brown or gray fungal spores.
Cause: Botrytis rot, also known as gray mold, a fungal disease.
Cure: Remove affected blossoms, foliage, or entire plant; space plants for more air circulation; reduce nitrogen fertilizer.
Symptom: Gray scabs form on the blossom ends of maturing tomatoes and peppers.
Cause: Blossom-end rot, a developmental and cultural disorder rather than bacterial or fungal infection caused by stress and mineral deficiency.
Cure: Strip affected fruit from plants. Apply water containing 1 tbsp. (1/2 oz. or 15 ml) garden lime per gallon (3.8 l) for 7–10 days to increase soil calcium. Fertilize with 5–10–10 formula and mulch soil surface with organic compost. Water deeply and regularly. Shade affected plants from hot midday sun.
Symptom: Brown stains and softened tissue near base of stem or crown of plant; leaves may yellow or drop.
Cause: Crown or stem rot. Look for decaying stems. Usually associated with keeping soil overly moist.
Cure: Rarely curable; remove infected foliage, dipping pruning shears in isopropyl alcohol solution between cuts to sterilize them and avoid spreading the disease to healthy plants. Reduce watering. Repot to soil-free, well-drained mix. Root cuttings of healthy growth.
Symptom: Gray, cottony masses shroud brown-spotted, dying foliage. Stems are discolored.
Cause: Downy mildew, a fungal disease common in cool, moist conditions.
Cure: Space plantings to allow good air circulation. Remove shading foliage. Apply water at base of plant. Strip and destroy infected leaves. Rotate plantings annually to new beds.
Symptom: Flowers wilt and foliage tips curl, yellow, and die. Gray, powdery spores and fibers sometimes are seen on leaf undersides.
Cause: Fusarium wilt, a fungal disease common in cool, moist conditions caused by spores in soil entering plants through roots. Most prevalent in plants experiencing stress, mineral deficiency.
Cure: Space plantings to allow good air circulation. Remove shading foliage. Strip and destroy infected leaves. Fertilize with 0–5–10 formula and mulch soil surface with organic compost. Apply water at base of plant. Rotate plantings annually to new beds.
Symptom: Streaked and mottled foliage, deformed blooms; stunting; loss of vigor.
Cause: Mosaic virus, an incurable plant disease.
Cure: Remove and destroy affected plants. Promptly control aphid, spider mite, and thrip infestations, which can spread viral infection. Plant mosaic-virus resistant cultivars.
Symptom: Leaves have white to grayish, powdery patches, as though they have been dusted with flour or gray powder.
Cause: Powdery mildew, a fungal disease prevalent when days are hot and nights are cool, with high humidity. Mostly attacks new leaves.
Cure: Thin branches to improve air circulation. Spray with a 0.5% solution of baking soda (sodium bicarbonate): 1 tsp. (5 ml) baking soda per quart [1 l] of water. Rotate plantings annually to new beds.
Symptom: Foliage is marked with pale spots above, brown, red, round spots on their undersides; leaves may brown and drop.
Cause: Rust, a fungal disease, common on corn. Wipe affected foliage on white cloth, which stains orange, pink.
Cure: Plant resistant cultivars. Fertilize with nitrogen monthly until symptoms subside. Rotate plantings annually to new beds.
Symptom: Fruit develops bald, dry patches on its flesh in hot weather and direct sunlight. Fungal disease may rot fruit on margins of the patches, but the problem is cultural, not the result of fungal or other disease.
Cause: Sun scald, a cultural problem that resembles disease caused by overheating of fruit of peppers, tomatoes, and other thin-skinned vegetables in direct, hot sun.
Cure: Shade susceptible vegetables with 70% shade cloth or white, reflective, non-woven, floating-row-cover material of plants in direct sun during daylight hours over 103°F (40°C).
Symptom: Plants lose vigor and wilt in hot weather. Leaves drop. Plants die.
Cause: Verticillium wilt, a fungal disease caused by spores in soil entering plants through roots.
Cure: Plant resistant cultivars. Remove and destroy affected plants or dispose of them in household garbage. Rotate plantings annually to new beds.
Plant Disease Resistance Codes
Reference to Plant Disease-Resistance Codes Found on Some Seed Packs and Plant Tags
- A | Anthracnose | Fungus |
- Colletotrichum lindemuthianum (Bean)
- Colletotrichum orbiculare (Cucurbitaceae)
- AB | Alternaria Blight | Fungus | Alternaria dauci (Carrot) [See EB for Alternaria Blight of Tomato]
- ALS | Angular Leaf Spot | Bacterium | Pseudomonas syringae pv. lachrymans (Cucumber)
-
AS | Alternaria Stem Canker | Fungus | Alternaria alternata f. sp. lycopersici
(Tomato) - B | Bacterial Wilt | Bacterium | Erwinia tracheiphila (Cucumber)
- BB | Bacterial Blight | Bacterium | Xanthomonas hortorum pv. carotae (Carrot)
- BBS | Bacterial Brown Spot | Bacterium | Pseudomonas syringae pv. syringae (Bean)
- BLS | Bacterial Leaf Spot | Xanthomonas campestris pv. vesicatoria (Pepper)
- BMV | Bean Mosaic Virus | Virus | (Bean)
- BO | Botrytis Blight or Rot of Onion | Fungus | Botrytis allii (Onion)
- BR | Black Rot | Bacterium | Xanthomonas campestris pv. campestris (Brassicaceae)
- BS | Black Speck | Fungus | Rhizoctonia ssp
- C | Cercospora Blight | Fungus | Cercospora carotae (Carrot)
- CMV | Cucumber Mosaic Virus | Virus | (Cucurbitaceae)
- CR | Club Root | Fungus | Plasmodiophora brassicae (Cabbage)
- CRR | Corky Root Rot | Fungus | Pyrenochaeta lycopersici (Tomato)
- CS | Cavity Spot | Water Mold | Pythium spp. (Carrot)
- CTM | Curly Top Beet Mosaic Virus | Geminivirus spp. (Beet)
- Cv | Cladosporium Leaf Spot | Fungus | Cladosporium variabile (Spinach)
- CVYV | Cucumber Vein Yellowing Virus | Virus | (Cucumber)
- DM | Downy Mildew | Water Mold
- Bremia lactucae (Lettuce)
- Hyaloperonospora parasitica (Arugula)
- Hyaloperonospora brassicae (Broccoli, Cabbage, Chinese Cabbage)
- Peronospora belbahrii (Basil)
- Peronospora destructor (Onion)
- Peronospora effusa (Spinach)
- Peronospora viciae (Pea)
- Pseudoperonospora cubensis (Cucumber)
- EB | Early Blight (Alternaria Blight) | Fungus | Alternaria solani (Tomato)
- F | Fusarium Wilt | Fungus
- Fusarium oxysporum f. sp. basilici (Basil)
- Fusarium oxyporum f. sp. lycopersici (Tomato)
- Fusarium oxysporum f. sp. melonis (Melon)
- Fusarium oxysporum f. sp. niveum (Watermelon)
- Fusarium oxysporum f. sp. pisi (Pea)
- FBR | Fusarium Basal Rot | Fungus | Fusarium oxysporum f. sp. cepae (Onion)
- FLB | Foliar Late Blight | Water Mold | Phytophthora infestans (Potato)
- FOR | Fusarium Crown and Root Rot | Fungus | Fusarium oxysporum f. sp. radicis–lycopersici (Tomato)
- FY | Fusarium Yellows | Fungus | Fusarium oxysporum f. sp. conglutinans (Brassicaceae)
- GLS | Gray Leaf Spot | Fungus | Stemphylium solani (Tomato)
- HB | Halo Blight | Bacterium | Pseudomonas savastanoi pv. phaseolicola (Bean)
- LB | Late Blight | Water Mold | Phytophthora infestans (Tomato)
- LM | Leaf Mold | Fungus | Cladosporium fulvum also known as Fulvia fulva (Tomato)
- LMV | Lettuce Mosaic Virus (Lettuce)
- MDMV | Maize Dwarf Mosaic Virus (Corn)
- MT0-10 | Indicates that no Lettuce Mosaic Virus was found in a sample of 10,000 or more seeds tested.
- MT0-30 | Indicates that no Lettuce Mosaic Virus was found in a sample of 30,000 or more seeds tested.
- N | Roundworm | Nematode | Meloidogyne arenaria, M. incognita, M. javanica (Tomato)
- NCLB | Northern Corn Leaf Blight | Fungus | Exserohilum turcicum (Corn)
- Nr | Lettuce Leaf Aphid | Insect | Nasonovia ribisnigri (Lettuce)
- Pb | Lettuce Root Aphid | Insect | Pemphigus bursarius (Lettuce)
- PC | Phytophthora Blight | Water Mold | Phytophthora capsici (Pepper)
- PEMV | Pea Enation Mosaic Virus (Pea)
- PLR | Pea Leaf Roll Virus (Pea)
- PM | Powdery Mildew | Fungus
- Erisyphe heraclei or Leveillula taurica (Carrot)
- Erisyphe pisi (Peas)
- Erisyphe polygoni (Beans)
- Oidium neolycopersici (Tomato)
- Podosphaera xanthii (Cucurbitaceae)
- PMV | Pepper Mottle Virus | Potyvirus (Pepper)
- PR | Pink Root | Fungus | Phoma terrestris (Onion)
- PRSV | Papaya Ringspot Virus (Curcubitaceae)
- PU | Purple Blotch | Fungus | Alternaria porri (Leek)
- PVY | Potato Virus Y (Pepper)
- R | Common Rust | Fungus
- Puccinia allii (Leek)
- Puccinia asparagi (Asparagus)
- Puccinia sorghi (Corn)
- Uromyces appendiculatus (Bean)
- RS | Corky Root | Bacterium | Rhizomonas suberifaciens (Lettuce)
- RZ | Rhizoctonia or Black Scurf | Fungus | Rhizoctonia solani (Potato)
- S | Scab |
- Bacteria | Streptomyces scabies and other Streptomyces ssp. (Potato)
- Fungus | Cladosporium cucumerinum (Cucumber)
- SCLB | Southern Corn Leaf Blight | Fungus | Bipolaris maydis (Corn)
- SW | Stewart’s Wilt | Bacterium | Pantoea stewartii (Corn)
- TBSV | Tomato Bushy Stunt Virus (Lettuce Dieback Complex [Lettuce])
- TEV | Tobacco Etch Virus (Pepper)
- TLB | Tuber Late Blight | Phytophthora infestans (Potato)
- TM | Tobamovirus (Pepper)
- TMV | Tobacco Mosaic Virus (Solanaceae)
- ToANV | Tomato Apex Necrosis Virus (Tomato)
- ToMV | Tomato Mosaic Virus (Tomato, Pepper)
- TSP | Target Spot | Fungus | Corynespora cassiicola (Cucumber)
- TSWV | Tomato Spotted Wilt Virus (Tomato)
- TYLCV | Tomato Yellow Leaf Curl Virus (Tomato)
- V | Verticillium Wilt | Fungal | Verticillium albo–atrum and other Verticillium spp. (Potato, Tomato)
- WMV | Watermelon Mosaic Virus (Cucurbitaceae)
- WR | White Rust | Water Mold
- Albugo occidentalis (Spinach)
- Albugo spp. (Cabbage)
- WT | White Tip | Phytophthora porri(Spinach)
- ZYMV | Zucchini Yellow Mosaic Virus (Cucurbitaceae)