August 11, 1995
Spider mites are an occasional pest of spruce and pine trees in Iowa. Mites feed externally on conifer tree needles with piercing-sucking mouthparts that puncture the plant tissue and suck out the liquid within the cells. In light infestations the foliage will appear to be speckled with very tiny yellowish-green spots. If the population of mites increases the damage can become severe enough to turn the foliage entirely greenish-yellow and eventually brown. Heavily infested branches will drop their needles.
The fungi Verticillium and Fusarium can cause infectious wilt diseases of tomato. A number of plant samples have tested positive for wilt diseases this year. These soilborne fungi enter the root system of the plant and eventually plug the plant's vascular tissue. This leads to yellowing and wilting of plants leaves, usually working from the bottom of the plant upward. Infected plants die early, often producing little or no fruit.
Again this year we are experiencing a bumper crop of hackberry lace bugs. Lace bugs are present every year on several of our common deciduous trees, but only occasionally are the populations large enough to be noticed. Other trees besides hackberry have lace bugs, but hackberry seems to suffer the most sever and noticeable symptoms. Though lace bugs from different trees all look alike, each tree species is infested with a different species that is named after the host plant; for example, hackberry lace bug Corythucha celtidis is on hackberry, sycamore lace bug C.
After a few years of above average rainfall and a wet beginning to 1995, irrigation has been the last thing on many gardener's minds. At this time, however, many parts of the state could use a good rain. One way to provide water when Mother Nature doesn't is through the use of drip irrigation. Drip irrigation systems use flexible polyethylene tubing with devices for dripping water (emitters) and low volume sprays. These systems are quite easy to install. They require no trenching and the only tools needed for installation are a pruning shears and punch.
The Plant Disease Clinic has been inundated with sick grapes this summer. The culprit is the very wet spring and early summer we experienced, which created ideal conditions for infection by two fungal diseases, anthracnose and black rot.
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While spring is the traditional planting season in Iowa, late summer and early fall is an excellent time to plant trees, shrubs, perennials, and spring-flowering bulbs. Late summer and early fall is also the best time to seed lawns.
We have received a number of hawthorn and crabapple samples with quince rust in the Plant Disease Clinic. Quince rust is common on these hosts and often results in severe deformation of plant tissue. This rust is often seen with its cousin--another Gymnosporangium rust called cedar-apple rust.