June 9, 1995

Scab on Crabapples

Why are the leaves falling from my crabapple? This has been a common question. The answer in most cases is scab. Scab is a disease caused by the fungus Venturia inaequalis. In early stages, spots on occur on leaves as small olive-green to black areas. The spots may coalesce, especially along the midvein of the leaf. Infected leaves will eventually turn yellow and fall from the tree. The extended wet conditions this spring have favored the development of the disease.

Frost Injury to Shade Trees

Over the last three weeks or so, Iowans throughout the state have been wondering what's wrong with their trees. Leaf samples sent to the Plant Disease Clinic showed a wide variety of brown spotting, marginal browning, and water soaking. Many species have been affected, including maple (most common), oak, hackberry, and ash. Leaf damage often occurs throughout the tree.

Change in Milorganite Label

For many years Milorganite, a biosolid fertilizer product, has had warnings on its label not to use the product on food crops. The reason for this labeling was because Milorganite and other biosolid fertilizers had high labels of cadmium, which could cause health problems.

Oak Tatters

An occasional problem of oaks has showed up more often than normal this spring. You or your clients may notice oak leaves that have little or no blade surrounding the main veins, resulting in a skeletal appearance more reminiscent of an asparagus leaf than an oak leaf. Frequently, this damage is mistakenly attributed to leaf-chewing insects.

Summer Care of Hybrid Tea Roses

To successfully grow hybrid tea roses in Iowa, gardeners must give them considerable care. Important cultural practices during the summer months include watering, fertilizing, deadheading, and pest control.


Summer Care of Lawns

Sound mowing practices are necessary for a good quality lawn. This is especially true during the summer months. Improper mowing during hot, dry weather may seriously damage the turf.

Mow Kentucky bluegrass lawns at a height of 3 to 3 1/2 inches during the summer months. During cool weather in spring and fall, bluegrass lawns should be mowed at a height of 2 to 2 1/2 inches. The additional leaf area during summer shades and cools the crowns of the turfgrass plants. Extremely high temperatures at crown level can kill turfgrass.

Anthracnose of Shade Trees

Symptoms of anthracnose, primarily on ash and sycamore, have been evident on samples arriving in the Plant Disease Clinic. The disease may occur on sycamore, ash, maple, oak, walnut, linden, hickory, and other deciduous trees. Anthracnose is caused by a number of different but closely related fungi. Each fungus is specific to the host tree if affects.

Compost for Disease Control

For 20 years, scientists have been exploring the possibility that compost may help control some diseases. The addition of compost has reduced disease levels in potting mixes. Damping off and root rot diseases were reduced significantly with the addition of compost. Compost added to alfalfa fields resulted in healthier root systems and thicker plant stands. Phytophthora, a serious disease in soybeans and numerous other plants, has been reduced through the addition of compost and other cultural practices.