No. 2/April 25, 2016

Fields and Lawns of Purple
It's been a great spring for the color purple. The redbud trees are in full bloom and looking glorious in the central part of the state now. But for several weeks, the ground has been purple as well due to a few cool season weeds that seem to be enjoying the moderate temperatures we've been having.

Spruce Needle Casts (Rhizosphaera and Stigmina)
Spring has barely sprung and the Plant Clinic has already received a number of samples this year. Most common have been spruce and pine samples with a variety of issues including the ever-present fungal needle casts (Rhizosphaera and Stigmina on spruce, Diplodia and Lophodermium on pine). Most evergreen samples have been diagnosed with environmental stress as a contributing factor. The last several years have been very stressful to plants, especially to evergreens with the historic wet spring last year, harsh winter the year before, and two years of drought a few years before that.

Gymnosporangium Rusts on Eastern Red Cedar
Three Gymnosporangium rusts commonly affect trees in Illinois landscapes: Cedar-apple rust, Cedar-hawthorn rust, and Cedar-quince rust.  As their name suggests, these pathogens require two hosts to complete their life cycles. A portion of each disease's life cycle occurs on Juniper (Juniperus spp.) hosts, while the remainder occurs on one of several deciduous host within the Rosaceae family.

Invasive Plant Phenology Report - April 2016
The University of Illinois Extension Forestry produces a monthly invasive plant phenology report that gives information on the development of invasive plants across Illinois, informing readers about what is in bloom, leafing out, setting seed, senescing in different regions of the state.

Modified Growing Degree Days (Base 50°F, March 1 through April 21)
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.

Woody Oak Galls
There are three common stem and twig galls on oaks that become woody. Gouty and horned oak galls cause tree dieback and can kill heavily infested trees. Oak bullet gall can cause some dieback, but is not likely to cause serious tree harm. All three are caused by gall-making wasps that attack the tree at this time of year during bud elongation.