June 5, 1991
The frequent rains this spring have created ideal conditions for the development of apple scab on crabapples. Apple scab is a serious problem on susceptible crabapple varieties. Scab appears on leaves as roughly circular, velvety, olive-green spots on both the upper and lower leaf surfaces. The spots eventually turn dark-green to brown. Margins of these spots are feathery rather than distinct. Heavily infected leaves may curl up, become distorted in shape, turn yellow and fall off. Highly susceptible crabapple varieties may lose almost all their leaves by midsummer.
The rainy weather this spring has delayed the planting of field crops across much of the state. The heavy rainfall has also interfered with the plans of many home gardeners. Fortunately, there is still time to plant many vegetables, annuals, perennials, trees and shrubs.
The last practical dates to plant specific vegetables in central Iowa are listed below. The last practical planting dates are one week earlier in northern Iowa. The dates for southern Iowa would be one week later.
June 20 -- tomatoes, peppers, eggplants, muskmelons*, watermelons*
Right now is the time to apply preventive borer sprays if you have an infested white birch tree that you are trying to protect from demise by the bronze birch borer. Dursban and lindane insecticides are available as trunk sprays to prevent the entry of new borers (beetle larvae) into the tree. Three sprays at two week intervals are required to get us through the adult emergence and egg laying period. Read and carefully follow label directions, especially personal protection precautions listed on lindane labels.
The following list highlights some of the commonly diagnosed diseases during May. Disease Host
peach leaf curl peach
Rhizosphaera needle cast spruce
anthracnose maple, ash, sycamore
cedar-apple rust cedar, juniper
slime molds turf
Coniothyrium leaf spot maple
For those of you ready for something different, try growing orchids as houseplants. Orchids can be grown by anyone able to grow African violets. Orchids are fascinating because of their extraordinary variety of sizes, colors, shapes, and habits, as well as their variety of fragrances. There are some 30,000 species and even more hybrids.
Peach leaf curl, caused by the fungus Taphrina deformans, is a common springtime disease of peaches. The disease is easy to recognize. Infected leaves are thickened and puckered and often turn a reddish color. The symptoms may be limited to small areas of the leaf or may involve the entire leaf. Infected leaves turn gray and eventually wither and fall from the tree. The disease may also occur on the fruit, blossoms, and young twigs. Infected shoots appear stunted, swollen, and chlorotic. Diseased fruits exhibit raised, wrinkled areas and often fall prematurely.