I have several clients with crabapple trees that look beautiful in the spring, but have sparse and spotty foliage by mid summer. I have located cultivars that are disease resistant, yet these still exhibit leaf spots and drop their leaves. Is there a solution? — via e-mail
Crabapple trees' drought hardiness and tolerance of poor soils along with the wide variety of flower, fruit and foliage colors make them a standard in today's landscapes. You are correct to look for disease-resistant cultivars. There are at least four major foliar and twig blight diseases that attack crabapples, depending on region: cedar-apple rust, apple scab, powdery mildew and fireblight. Any one of these can wreak havoc on your trees, leaving them ugly for much of the growing season. The trick is to do your research. If the crabapple cultivar is resistant to even one of these problems, the label can state they are “disease resistant.” For example, a crabapple may be resistant to apple scab, but not to fireblight or cedar-apple rust. To help you out, some nursery catalogs supply a disease-resistance rating for each problem. Select only cultivars that have “good” or “excellent” resistance to each of the four disease problems. Fortunately, there is a totally disease-resistant cultivar to fit nearly any shape, flower color, foliage color and fruit needed for a particular landscape.
Many of my clients insist on growing geraniums in the same container, year after year. For the past several years, I have been fighting a worm that tunnels into the flower buds, leaving holes in the flowers or no flowers at all. I have tried contact and systemic insecticides and Bt with no luck. The same worm seems to be attacking my petunias, as well. Color beds for my clients are an important income source for my company. What can I do? — via e-mail
The damage you are describing sounds like the work of the geranium budworm, also known as the tobacco budworm and cotton budworm. Cotton growers have battled this pest for years, with only marginal success. The adult budworm moth has light green wings with lighter color bands. Eggs are laid singly on host plants during early evening. The budworms themselves are striped and can vary in color. Budworms take one month to grow to maturity and two to three generations per year are normal depending on region. They overwinter as pupae in the soil. Because the budworms are sensitive to temperatures below 20 F, they are not considered a northern pest. However, they may survive in containers brought in for the winter or in the soil close to the south side of buildings. On geraniums, the budworm is difficult to control because the small worm burrows into the flower buds, avoiding contact insecticides. Systemic insecticides may not be present in the flower buds in large enough concentration to control the budworm. Bt has provided only slight control. Because petunia flower buds are not as tight and the flowers less dense, control is more successful. Pyrethroids, Sevin or Orthene may provide control on petunias. If growing petunias are an integral part of your color program, vigilance in control may help to break the cycle.
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