No. 4/May 16, 2016

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

Brown Boxwoods
Each spring we receive questions and concerns regarding browning boxwoods. The browing foliage is often the result of winter injury, and weak pathogens infecting the winter injured tissues. More recently, however, callers have been concerned about Boxwood Blight, a new and devastating disease to boxwood. Boxwood blight has been identified in 18 states, mostly along the eastern seaboard and Oregon. In the Midwest, it has been confirmed in Ohio and Missouri.

Roundheaded Appletree Borer
At this time of year, roundheaded appletree borer adults emerge from infested trees. The adult beetles are elongate, one-half to one-inch long, brown to black beetles with white undersides, two white stripes down the back, and long antennae. Females fly for about 40 days, making one-inch long longitudinal slits through the bark, usually just above the soil line. Within each slit, she lays a single egg.

Flatheaded Appletree Borer
Flatheaded appletree borer generally attacks trees or parts of trees under stress. It commonly attacks older rose family trees, assisting in their death. Particularly in the northern two-thirds of Illinois, serviceberry, mountain ash, flowering cherry, purple-leaf plum, and Bradford and Callery pears are short-lived trees, frequently dying within 30 years. As these trees decline, flatheaded appletree borer frequently attacks them. With homeowners and other clientele commonly assuming that all trees live for a hundred years or more, this natural decline and borer attack is difficult for them to understand.

Viburnum Crown Borers
Viburnum crown borers are several species of clearwing moth borers that attack at the base of viburnum shrubs. Younger plants and those that have just been transplanted or put under similar stress appear to be more susceptible to attack. Vibrurnum opulus, particularly Vibrunum opulus compacta, appears to be considerably more susceptible to attack than other species. Commonly, new plantings of Viburnum opulus compacta are severely attacked, resulting in severe dieback and even the death of half or more of the planting. Other species of Viburnum are attacked but are usually not severely damaged.

Grass Sawfly
Grass sawfly larvae have been found feeding on turf in northwestern Illinois. In the past, they have been found feeding on various species of Lysimachia, sometimes called loosestrife or creeping jenny. The sawfly larvae are whitish to pale green with light tan heads and obvious black eyes. Fully grown larvae are a little over one inch long. We're not sure which species this is, but it is likely Dolerus nitens as it is common as adults in late spring.