So much for spring, but in its wake we have a rash of problems, some of which you might already have encountered.
Ground covers seem to have come down with horticultural cancer and plants seemed to have been growing rapidly until two weeks ago. Bedding plants have not been spared -- some leaves have distorted, others have developed ugly blotches in the past two weeks.
On sunny lawns where folks have been sprinkling to take up the slack in rainfall, disease also has struck with lightning speed.
Hardest hit by disease has been English ivy, destroyed in some landscapes by a ravenous attack of bacterial leaf spot. Disease spores incited the infection in early May as rains poured over the soil. It took almost three weeks for bacteria to invade the pores of ivy leaves. The first signs of trouble were greenish-brown spots that expanded to quarter-inch diameter with a brown-black center. From this, bacterial decay spread throughout the ground cover, killing plants to the roots. The stench from dead ivy was overpowering.
Then, there is pachysandra. Ordinarily, the ground cover is seldom touched by disease, but there has been considerable dieback on neglected pachysandra over the past month. Weak plants are usually attacked by the blight.
Triggered by cool, wet weather, the spores enter pachysandra through wounds from previous insect attacks. The disease spreads quickly, leading to the formation of stem cankers that kill the plant within two weeks. Spores survive on dead leaves and organic matter until proper environmental conditions return for it to reinfect new pachysandra plants.
With ivy and pachysandra, plan on a major cleanup as soon as possible. Rake the garden clean of dead and diseased plants. Prune away all plants and stems touched by disease. Rake up all debris to reduce future outbreaks. Everything goes into the trash bag for sanitation pickup.
Even though we're out of the cool, wet weather, healthy plants will benefit from an immediate protective fungicide. Use only Bordo-Mix for this as other products won't work.
Put three ounces of water in a small plastic bucket, then slowly add four tablespoons of Bordo-Mix while stirring until the powder is completely dissolved. Next, add the mixture to a gallon of water. If the ivy or pachysandra garden is small, use a sprinkling can to apply the solution to healthy leaves. If you have a large area to protect, use a hand-pump sprayer, spraying leaves thoroughly to the point of runoff. Apply only if no rain is forecast within 24 hours of your treatment.
The void created by dieback of the ground cover can't be filled without addressing lurking disease spores in the old soil. Meanwhile, there is the threat of weed seeds invading the bare soil. Two solutions are feasible.
First, if you must plant immediately, use a steel rake to scoop up the top inch of old, contaminated soil, disposing of it in the same trash bag. Then, healthy ivy or pachysandra may be brought in and planted, with a generous layer of pine bark nuggets placed around the plants to promote rooting.
If replanting isn't feasible at this time, cover the bare soil with a thick layer of pine bark nuggets to prevent weeds from sprouting. Leave the mulch in place until new plants will be set into the soil.
Good horticultural practices will reduce chances of infection, the foundation of which is avoiding overhead watering. Try to lay down a soaker hose in the ground cover, strewing pine bark nuggets over the hose to force water into the soil without splashing on the foliage. As for next spring, spray Bordo-Mix to ivy and pachysandra in mid-April and early May to keep diseases in check.
Bedding plants escaped most of the traditional spring diseases, but you should check plants just to be sure. Here are the serious outbreaks:
Hollyhock leaves are dotted with rust (bright yellow or orange spots on top, brown pinhead spots on leaf bottom). Pick spotted leaves first to reduce infection, then spray healthy foliage with Ortho Multi-Purpose Fungicide containing Daconil. Shake the quart container first to put the Daconil in suspension, then add 2 1/4 teaspoons of the liquid to a gallon of water in a hand-pump sprayer, together with a tablespoon of sticker-spreader. Spray in late evening when no rain is forecast; a second spray two weeks later is suggested.
Diseased hollyhocks may not flower, but if they do, remember to cut stalks to the ground immediately after flowering. Pick up diseased leaves that have fallen to the ground. If you replant hollyhocks, plan on making biweekly Daconil sprays to the foliage from May 1 through the first days of July. Mallow is now believed to be the alternate host of the rust disease, so eliminating the mallow weed probably will eliminate the rust problem in future years.
Rust haunts other plants, among them coreopsis, buttercup, anemone, aconitum, clematis, lupine, monarda and liatris. Coreopsis is attacked by rust that grows in the winter on longleaf pine, so don't plant coreopsis near pines. Ornamental grasses are alternate hosts of rusts that attack buttercups, so avoid wild grasses entirely. Campanula and iris also come under attack by rust, in which case sanitation and Daconil sprays are the best controls.
Delphinium leaves show black spots on the top side, brown spots on the underside. Usually, bottom leaves are infected first by leaf spot and the disease then works its way up the stalk. Remove spotted leaves, being careful not to touch healthy leaves in the process. Plants growing in wet soils may seem to wilt, shrivel and release a pungent odor, in which case crown rot has destroyed the plant. Spade from the soil, and don't grow delphinium there again.
Petunias are generally healthy bedding plants, but occasionally are devastated by stem and root rot, which attacks the stem at the soil line, turning plants black. If petunias seem to wilt, spade them from the soil. The cure is to grow petunias in raised beds; they rarely come down with root rot.
Zinnia leaves may be badly spotted. Tops show red-brown borders, with gray-white centers. Stems may turn dark brown to black; if so, the plant should be pruned to the ground and stems added to a trash can. Pick off spotted leaves, then spray healthy leaves with powdered Maneb or Bordo-Mix in late evening.
Finally, there are the overworked, over-watered sunny lawns that have just come down with pythium disease. Homeowners with automatic underground sprinkling systems usually are charter members of the pythium club because of over-watering of the lawn. The combination of over-watering, daytime temperatures of 85 to 95 degrees, lack of calcium in plant tissue and high nighttime humidity trigger the disease.
Symptoms are unmistakable. In early morning hours, white cobwebs are found on newly infected blades of grass, the webs disappearing as morning temperatures rise. By 8 a.m. the webs have all but disappeared. Look for greasy spots on the soil, too, this giving rise to the "grease spot" alias for pythium disease. Dieback of turfgrass begins as a small circle, with the webs showing in healthy grass just beyond the circle of dead grass.
Stop watering altogether, shutting down the timer of the sprinkling system. Allow a week or more for the waterlogged soil to dry, after which, in the absence of rain, you should reprogram the timer for once- or twice-a-week soaking of the lawn to apply an inch of water a week. Consult sprinkler head information provided by the installer to determine how long the sprinklers should operate.
Apply pulverized limestone at 50 pounds for each 500-square-foot area to make calcium available to turfgrass plants. Also, consider treating diseased grass with Aliette or Subdue 2E. Unfortunately, both products are not available in granular form, therefore you will have to use a sprinkling can. Begin with a clean trash can, adding 10 to 12 gallons of water, then the required ounces of powdered Aliette or Subdue to treat 1,000 square feet. Make certain no rain is forecast when attempting to control pythium.
Jack Eden is the host of "Over the Garden Fence" Sundays from 10 a.m. to 1 p.m. on WTOP Radio (1500 AM).