No. 6/May 31, 2016
Modified Growing Degree Days (Base 50°F, March 1 through May 26)
Insect development is temperature dependent. We can use degree days to help predict insect emergence and activity. Home, Yard, and Garden readers can use the links below with the degree day accumulations above to determine what insect pests could be active in their area.
Oak Leaf Blister
Oak leaf blister symptoms are starting to become noticeable on oak trees. This disease is caused by the fungal pathogen, Taphrina caerulescens. Although all oaks are susceptible, red and black oaks are among the most affected by this foliar disease. White oaks are rarely infected.
Hosta Leaf Spots
Anthracnose is a common fungal disease of many deciduous plants. We've already seen a lot of ash and sycamore trees affected with anthracnose this year. The causal pathogens are not the same, but they are related and thrive under similar environmental conditions. Hosta anthracnose shows up as large, irregular, brown lesions on the leaves. The centers of older lesions may fall out, giving the leaves a tattered appearance. The disease is favored by moisture and warm temperatures.
Lecanium scale, more properly European fruit lecanium, Parthenolecanium corni, continues to build populations throughout the state. Along with borers, a couple of scale insects, scurfy scale and lecanium scale, take advantage of stressed trees. The severe drought of 2012 followed by another drought in the second half of the 2013 growing season caused severe root loss from which trees are still trying to survive.
Bagworms will be hatching in southern Illinois at this time. They will hatch in central Illinois by mid-June and in northern Illinois a week or two later. Upon hatching, young caterpillars crawl out of their mother's bag where the eggs were laid and crawl upward. They get to the top of the tree and spin out silk, creating a long streamer that catches in the wind, carrying the young bagworm to new hosts.