Apple scab has developed in central Illinois on susceptible crab apples. We are now seeing brown to black velvety leaf lesions that are 3/4 inch long. Leaf drop has not yet occurred. Reports from The Morton Arboretum in the Chicago area indicate that lesions are also present in the northern parts of Illinois on crab apples. For more information on scab, consult Report on Plant Disease No. 803 (available on the Web at http://www.ag.uiuc.edu/~vista/horticul.htm) or in issue number 2 of this newsletter.
Anthracnose has occurred throughout the state as we predicted. The disease was discussed in last week’s newsletter. Many homeowners are concerned about ash anthracnose because of the massive leaf drop it has caused. Remember, in years with prolonged cool, wet spring weather, the disease may kill almost the entire first flush of leaves. This happens often on sycamore, but not so frequently on ash. The trees will recover soon with a new flush of leaves. Sycamores have been heavily infected this year. Northern Illinois is seeing anthracnose on both ash and sycamore. So far, there have been no reports of maple or oak anthracnose, but these may occur later.
Rhizosphaera needle cast continues to come into the Plant Clinic on spruce. Refer to last week’s newsletter for the details. If your tree has this disease, there may still be time for the first fungicide spray. The first application is made when new needles are half grown.