It’s easy to blame plant loss on pests, but it’s not always insects that destroy a garden. Viruses and fungal problems can be just as damaging – and sometimes worse. Here’s a look at some common disease symptoms you may notice on your plants, as well as possible causes and remedies.
Mosaic virus is an incurable plant disease. Remove infected plants from the garden and dispose of them in household waste or burn them. Avoid composting.
Photo Credit: ©2002 Dolezal Publishing/John M. Rickard
A common plant disease that might infect your vegetables is powdery mildew.
Photo Credit: ©2002 Dolezal Publishing/Donna Krischan
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.
Remedies: Remove infected leaves and branch tips. Collect and destroy infected fallen leaves. Thin excessive growth to promote air circulation. Spray with bordeaux mixture – a copper sulfate and lime-based fungicide.
Symptom: Leaves are mottled with black spots, then eventually yellow and die. Powdery
black or brown dusting on foliage and blossoms. Leaves may drop.
Cause: Black spot and/or leaf spot – fungal diseases found on many plants. Both spread by spores blown onto moist plant leaves. Common in shady, crowded plantings.
Remedies: 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 – a copper sulfate and lime-based fungicide.
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 containing bacteria is splashed onto cut and bruised foliage or is carried to flowers by pollinating insects.
Remedies: 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 – a copper sulfate and lime-based fungicide.
Symptom: Flowers and foliage collapse under a heavy fuzz of brown or gray fungal spores.
Cause: Botrytis rot, also known as gray mold.
Remedies: 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.
Remedies: Strip affected fruit from plants. Fertilize with a 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.
Remedies: Rarely curable. Remove infected foliage, dipping pruning shears in isopropyl alcohol solution between cuts. 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.
Remedies: 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 are sometimes 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 or mineral deficiency.
Remedies: Space plantings to allow good air circulation. Remove shading foliage. Strip and destroy infected leaves. Fertilize with a 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.
Remedies: Remove and destroy affected plants. Promptly control aphid, spider mite and thrips infestations, which can spread viral infection. Plant resistant cultivars.
Symptom: Leaves have white to grayish, powdery patches, as though they’ve been dusted with flour.
Cause: Powdery mildew, a fungal disease prevalent when days are hot and nights are cool, with high humidity. Mostly attacks new leaves.
Remedies: Thin branches to improve air circulation. Spray with a 0.5 percent solution of baking soda (sodium bicarbonate): 1 teaspoon baking soda per 1 quart of water. Rotate plantings annually to new beds.
Symptom: Foliage is marked with pale spots above, and brown, red, round spots on the undersides. Leaves may brown and drop.
Cause: Rust, a fungal disease, common on corn. Wipe affected foliage on a white cloth (which will stain orange or pink).
Remedies: Plant resistant cultivars. Fertilize with nitrogen monthly until symptoms subside. Rotate plantings annually to new beds.
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.
Remedies: Plant resistant cultivars. Remove and destroy affected plants. Rotate plantings annually to new beds.
