No. 4/May 18, 2015

Modified Growing Degree Days (Base 50°F,  March 1 through May 14)
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 in this article with the degree day accumulations listed to determine what insect pests could be active in their area.

Diplodia Tip Blight on Pine
The Plant Clinic has received a number of pine samples with various ailments this spring. Diplodia (also known as Sphaeropsis) Tip Blight has continued to be a common diagnosis on Austrian, Scots, and other pines. It can also affect spruce, fir, Douglas fir, cedar, arborvitae, and juniper plants, though the disease is much less common on these hosts. Diplodia Tip Bight is considered a stress disease because it is much more common on plants under stress.

Bronze Birch Borer
Bronze birch borer is a native species in the same genus as emerald ash borer and attacks the tree in a similar manner, except that it attacks birches instead of ash. Bronze birch borer attacks mostly nonnative, white-barked birches as their growth starts to slow down, typically when the trees reach 10 or more years old. It attacks younger trees that are mechanically damaged or planted in poor sites. Native white-barked birches are attacked much later in life, as they decline into old age.

Pine Needle Scale
Pine needle scale is a serious pest of pines throughout the state, killing branches and entire trees. It is most prevalent on Scots and mugo pine but is common on many other pine species. It also is found on spruce and hemlock and is likely to cause dieback on spruce. It is probably most serious to Christmas tree growers but commonly kills landscape plants as well.

Elm Leaf Beetle
Elm leaf beetle larvae are present in southern and central Illinois. This pest is less common in northern Illinois but larvae should be present by the end of the month. These larvae can be serious leaf skeletonizers of elm and zelkova. In general, European elms are attacked heaviest.