PHOTO: © Neil Soderstrom

problem solver

Anthracnose

IDENTIFICATION — When anthracnose strikes after a cool, wet spring, you’ll find irregular dark blotches on leaves. Sometimes buds or small twigs will also be infected — symptoms vary with the host plant. Infected parts, especially leaves, eventually drop off.

DAMAGE — Anthracnose, caused by several types of fungi, attacks mainly shade trees, such as sycamore, ash and maple; also some small ornamental trees, like the dogwood in this photo. Spores overwinter on twigs, move through the air and begin to grow in cool, wet weather. Anthracnose rarely kills the tree, but repeated defoliation weakens the plant and makes it unsightly.

PREVENTION — Plant trees in sites with good air circulation and prune dense growth to improve air movement. Keep trees fertilized and vigorous so they can grow new foliage quickly. When choosing a new tree, read tags or ask for resistant cultivars.

problem solver

Septoria leaf spot

IDENTIFICATION — Septoria leaf spot is a common fungal disease that can affect black-eyed Susans. It begins with brown-black spots on the leaves then progresses to where the leaves may turn completely brown and fall off. Symptoms usually appear on lower leaves first.

CONTROL — This disease is tricky to get rid of but won’t kill your plants. Septoria spores are spread by water droplets, so watering at the base of the plant will reduce the spread. Rake up diseased leaves and burn or bury them. Don’t put them in the compost pile.

You can apply fungicides before any symptoms appear, but keeping the area clean will keep the plants looking better next year.

problem solver

Botrytis on peonies

IDENTIFICATION — Peony bushes can suffer from a variety of fungal diseases and botrytis is a big one. Fungal diseases thrive in warm, moist conditions like those in excessively rainy springs or humid summers. Small brown spots on the leaves will eventually spread to cover the entire leaf surface. Infected buds may shrivel up and fail to bloom.

CONTROL — Copper-based fungicidal soap sprays, such as Soap-Shield, may help. You may not need to treat the disease though; this fungus rarely kills the plant. As a preventative measure, cut the plants back to the ground after frost. Don’t compost infected material; discard it to get rid of fungus spores.

problem solver

Verticillium wilt

IDENTIFICATION — If the leaves of your annual flowers and vegetable plants seem to be yellowing and curling, your garden may be infected with verticillium wilt. Older, lower leaves fall off first, as younger, higher leaves become discolored and distorted. Only a few healthy leaves will remain at the top of the plant until it eventually dies.

To make sure wilt is the culprit, cut open an infected plant stem horizontally, near the soil line. Look for a narrow tan ring between the center and stem wall, or dark streaks shooting up the middle of the stalk.

CONTROL — Plants infected with verticillium wilt should be destroyed promptly because there is no control. The disease-causing fungus can live in the soil many years after the plant has died, so rotate your crop every four to six years. And make sure to keep it far away from your compost pile.

Protect your garden from wilt by buying resistant plants. Look for kinds that are labeled “VFN resistant.” These plants are less susceptible to verticillium wilt (V), fusarium wilt (F) and nematodes (N), which are all common pests.

Verticillium wilt also attacks some trees and shrubs. In large woody plants, the fungus causes leaves to yellow and curl and branches to die suddenly. If you suspect verticillium wilt has infected a tree or shrub, cut a twig from the infected area. Look for the ring in the cross section; there may also be streaking along the length of the twig if you peel back the bark. Before removing a valuable tree, consult with a plant pathologist to be sure of your diagnosis.

problem solver

Damping off

IDENTIFICATION – Damping off can be a problem for gardeners who start seeds inside. It is usually caused by cool, damp soil. The fungi that cause this disease can attack seeds before they germinate, although the most common symptom is seen on seedlings. An otherwise healthy seedling suddenly tips over. If you look closely at the stem near the soil level, you will find a pinched-in area. In a day or two the top part of the seedling will wilt and die. Damping off can kill an entire flat of seedling in just a few days.

CONTROL – It’s easier to prevent damping off than “cure” it. To start, sterilize everything – flats and tools – with a 10-percent bleach and water solution. Be sure to use sterilized seed-starting mix that is fresh. After sowing your seed, keep the flats in a warm area. Once the seedlings are up, slow down the watering. Let the top layer of soil feel dry to the touch before watering again. Also, don’t mist the flat between waterings. You can also turn on a fan to keep the air moving; just don’t aim it directly at the seedlings.

Commercial greenhouses use fungicidal soil drenches to prevent damping off, but home gardeners don’t have access to those chemicals. Good sanitation is the best bet for healthy seedlings.

problem solver

Stinkhorn fungus

IDENTIFICATION – It might look like an alien life form, but it’s just a stinkhorn fungus, either an elegant stinkhorn (Mutinus elegans) or a dog stinkhorn (Mutinus caninus). Though not harmful or poisonous, stinkhorns are aptly named — these things smell bad! The rotting-meat scent attracts flies, which spread the spores around.

FAVORITE CONDITIONS – Stinkhorns grow from egglike structures underground, and you can find them anywhere there’s decaying plant material — in lawns, under trees or in mulch.

CONTROL – There’s no prevention or control for this harmless fungus. And though it’s odd-looking, it will shrivel away in a day or two. It may appear in your lawn again as long as there’s decaying organic material to feed on. Look at this as an exciting encounter with nature — not everyone gets to see (or smell) one of these peculiar fungi!

problem solver

Black knot fungus
Apiosporina morbosa

IDENTIFICATION – When the leaves are off the trees, these grotesque, black swellings are easy to spot. You’ll find them mainly on members of the Prunus family — cherries, plums and peaches. Fungus spores spread by wind, insects, birds or humans. Black knot grows in warm (55 to 75 degrees), humid spring weather. The swellings develop over a two-year period. Even though infection begins the first year, no real symptoms appear until the following spring. Then the bark on a stem splits and a green fungus appears. It could cover an area 12 inches long and be several times thicker than the branch it infects. This green fungus hardens and turns black and knotty.

DAMAGE – These growths, or knots, shut off water and nutrients to the branch, which eventually wilts, dries up and dies.

CONTROL – The best defense against black knot is to plant resistant varieties. Check with your extension service or nursery for recommendations. During the fall and winter, prune and destroy infected branches. Cut at least 4 inches below the swollen, black area. To prevent spreading, dip pruning tools in a 10-percent bleach solution between cuts.

problem solver

Lawn rust

Late summer and fall is prime time for rust, a fungal disease of turf grass. It happens during warm, humid weather, and when the grass is stressed at the end of a long, hot summer. This fungus won’t kill your lawn, but it will make it more susceptible to other problems. But by improving the overall health of your grass, you can get rid of rust.

Dethatching and fertilizing with a high-nitrogen fertilizer will make your grass healthier. Don’t mow your grass shorter than 3 in. Rake up rust infected clippings and get them off the lawn. Water in the morning so leaf blades don’t stay wet. Once you’ve improved the condition of your lawn, the rust should disappear in a week or two. Dry fall weather will help too.

Having rust on your lawn once doesn’t mean you’ll have it again, but some grass cultivars are more susceptible than others. Check the bag when you buy grass seed to see if it’s a rust-resistant cultivar.

problem solver

Pink snow mold
Fusarium nivale

IDENTIFICATION – Ever notice a pink slime on your lawn in spring? It might be snow mold. This fungus attacks grass at temperatures between 40 and 60 degrees. It needs prolonged dampness from cold fogs, drizzle or melting snow to infest blades that have been damaged under heavy snow or traffic. The grass blades first appear slick and brown in 6- to 8-in. circles. The disease then spreads outward, leaving pink-bordered white patches in a ring effect.

DAMAGE – Under ideal conditions, the grass inside a ring sometimes grows back, but the usual result is a dead spot in the lawn.

CONTROL – Prevention is the most effective control. Keep turf mowed very short through late fall, and don’t apply fertilizers containing nitrogen within six weeks of the lawn going fully dormant. The fungi thrive on succulent new growth. Dethatching and a regular raking will also help. Home-use fungicides, such as Ornathal, Rubigan and Bromosan, work well on spots where snow mold has shown up before. But you’ll need to apply them early in spring before the symptoms appear.

pest watch

Powdery mildew

IDENTIFICATION – In mid- to late summer, you may notice a gray-white film on a plant, and the plant may begin to lose leaves. The culprit is powdery mildew. You’re most likely to see this problem on roses, phlox, zinnias, bee balm and lilacs (in the illustration).

This condition won’t kill the plant, but it’s not very attractive. Symptoms look the same, but specific fungi cause powdery mildew on different plants. In other words, the fungus that causes these symptoms on roses won’t cause the same disease on zinnias.

FAVORITE CONDITIONS – Humid weather, with warm days and cool nights, encourages powdery mildew.

CONTROL – As with many plant diseases, the easiest way to control powdery mildew is to plant resistant cultivars. But there are a few things you can do to help your existing plants. The spores survive the winter in leaves and plant debris, so clean up around infected plants to get rid of as many spores as possible. Make sure your plants have enough sun and good air circulation, as this will cut down on powdery mildew.

Fungicides are very effective for preventing this fungus. Read the label to make sure the fungicide controls powdery mildew, not downy mildew, a different disease. You’ll probably need to apply it more than once, starting before you see symptoms. You can’t “cure” powdery mildew — prevention is key. Spraying horticultural oil on plants until the leaves are covered, top and bottom, cuts down on the problem. Test this on a few leaves first, to make sure the leaves don’t burn. Wait for a cloudy day to spray anything on your plants — the combination of sun and sprays can damage foliage.