No. 5/May 28, 2013

Tree and Shrub Borers
Most borers attack trees that are under stress. Roundheaded beetle borers typically chew niches through the bark to lay their eggs, although flat-headed beetle borers lay their eggs in bark crevices and under loose bark flakes. Moth borers typically lay their eggs in pruning and other wounds. Healthy trees have enough sap flow that borer eggs are flushed out of niches and young borer larvae drown. It is thought that the internal sap pressure in healthy trees squashes soft-bodied borer larvae.

Scouting Watch
Several borers are susceptible to control at this time throughout the state. Roundheaded appletree borer, flatheaded appletree borer, peachtree borer, and viburnum borers are all susceptible to control.

Maple Blight Mania
This has been an interesting week at the Plant Clinic, with many samples and calls coming in regarding leaf blights on maple. The symptoms appear as brown to black spots and blotches on leaves, bordered by veins, as well as dark black blister spots and blotches that eventually take over the entire leaf.  Eventually, the leaves will drop from the tree, which can cause the tree's appearance to be very, unsightly, and can be alarming to homeowners.

Modified Growing Degree Days (Base 50°F,  March 1 through May 23)
Insect development is temperature dependent. Of particular interest this week, degree day accumulations are nearing or have reached levels where we could see the beginning of emerald ash borer adult emergence (450-500 DD). Peak adult emergence usually coincides with the accumulation of 1000 DD, which is still several weeks off.

Is It Giant Hogweed?
Giant Hogweed is an invasive, exotic plant that has been found in a couple of locations in Illinois. As the summer season quickly approaches, the inquiries I receive about possible giant hogweed sightings begin to increase. Often, this invasive is confused with a very similar looking cow parsnip.