No. 7/June 16, 2014

Black Knot
Black knot is a common fungal disease that affects at least 25 Prunus species, both edible and ornamental.  The disease is caused by the pathogen, Dibotryon morbosum, which infects the new twigs, branches, and fruit spurs during the spring.  Trunks also can become diseased.

May Beetle
True white grubs, also known as 3-year white grubs and May beetles, consist of many species in the genus Phyllophaga in Illinois. Their life cycle varies from 1 to 3 years. At least one 3-year species is present as adults at this time. These 1-inch-long, reddish-brown to dark brown, stocky May beetles are active at night, feeding on the foliage of oak, ash, crabapple, and other deciduous trees.

Japanese Beetle
Many Japanese beetle larvae did not survive the winter, particularly in the northern half of the state. Research has shown that Japanese beetle grubs do not migrate deeper than 11 inches into the soil for the winter. They die if the soil temperature reaches 15 degrees F or if they are subjected to freezing temperatures for 2 months.

Modified Growing Degree Days (Base 50°F,  March 1 through June 12)
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 to determine what insect pests could be active in their area.

Emerald Ash Borer Activity
Degree day accumulations have reached levels where we would expect adult emerald ash borer activity in infested areas of the state.