No. 3/May 19, 2014
Bridalwreath Spirea and Insect Management
Bridal wreath spirea, or Vanhoutte spirea (Spiraea x vanhouttei), is blooming in throughout the state. This is a major phenology plant in Don Orton's book Coincide. With phenology, stages of plant development (usually bloom time) are used to predict stages in pest development. This method is more accurate than using calendar dates because the plant is exposed to the same climatic conditions as the insect.
Hydrangea leaftier, Olethreutes ferriferana, has been noticeable in central Illinois and is present in other areas of the state. Damage appears as two to four cupped leaves tied together with silk at the end of a branch. An attacked plant will typically have ten to twenty of these cupped leaf sets. Pulling the leaves apart reveals a slender greenish caterpillar up to one-half inch long with a blackish head.
Euonymus caterpillars are numerous in northeastern Illinois. This insect rarely occurs in Illinois south of Kankakee or west of Rockford. Its main host in Illinois is European euonymus, Euonymus europaea. It is listed as also attacking spreading euonymus, E. kiautschovicus, and winged euonymus, E. alatus; but I have not received reports of it feeding on those hosts. European euonymus is a slender, large shrub to small tree.
There are three sawfly species that commonly attack azaleas, two in the spring and one in the summer. We are apparently currently seeing Amauronematus azaleae. There is one generation per year with the adults emerging to lay eggs on expanding leaves in the spring. The larvae are feeding at this time in central Illinois and apparently prefer mollis hybrid azaleas, which are deciduous. Nearby evergreen azaleas are not attacked.
Dealing with Tree Seedlings in the Lawn and Landscape
The maples are currently on a mission to reforest the Earth. The ash, cherry, and mulberry trees are often on the same mission. What can you do?
Modified Growing Degree Days (Base 50°F, March 1 through May 15)
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.
Emerald Ash Borer Emergence Approaching
Historically, as we approach the Memorial Day weekend, we begin to be aware of the possibility of emerald ash borer (EAB) emergence. Emerald ash borer emergence is predicted to begin when the accumulation of degree days reach 450—500. Several areas of the state have reached or are closing in on that threshold.
Illinois Invasive Plant Phenology Report
Several invasive plant experts from around the state have started a new series or reports focusing on the phenology of invasive plants in Illinois. The intent of these reports is to provide an update on the development of invasive plants across the state of Illinois – what plants are in bloom, leafing out, setting seed, or senescing in different areas of the state.
Impatiens Downy Mildew
Impatiens Downy Mildew (IDM) continues to threaten one of the most popular shade-tolerant bedding plants used in American landscapes. At one point, impatiens was the number one bedding plant sold in the United States. However, as a result of IDM, many growers have opted to cut back on the number of impatiens grown or avoid them all together.
Basil Downy Mildew in 2014
A sample of basil from Wisconsin was diagnosed with downy mildew last week at the University of Illinois Plant Clinic. Basil downy mildew was a serious problem last year and, depending on the weather, we may be seeing more of it in 2014. This pathogen affects both homeowners growing a few basil plants for fresh harvest, and the producers who cultivate commercial basil in Illinois.