Planning ahead for pest problems in 2006

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Scheduling can become a headache for arborists, landscapers, city foresters and even homeowners that don't know the best time to treat for a pest problem. Here are some of the major insect pest problems and the best time to treat for them.

Emerald ash borer
New test results from a timing study shows that imidacloprid can be used as basal soil drench from mid-October to mid-November, or from mid-April to early June. Any of those times worked well to protect small ash trees from EAB during the season after the drench, but the best results came from the early June application time. The timing is the same for soil injection around the base of ash trees. Imidacloprid trunk injections have worked well any time from late May to mid-July. Onyx, Tempo or Astro sprays have been effective when applied twice: in early and late June.

The imidacloprid drenches have worked best on small trees, but recent test results also look promising for larger trees if drenches are started when the trees are healthy and after two years of drenching (results have not been good on large trees after one year). Results for all of the treatments listed above are best when they are started before ash trees are compromised from borer attack and when trees are kept healthy with adequate water and fertility. (see images)

Bronze birch borer on European white birch
Treatments and timing are the same as for emerald ash borer. Native North American birch trees do not need insecticide treatment.

Mimosa webworm
This caterpillar pest of honeylocust trees caught many by surprise last year in the Detroit area and most of southern Michigan. Another mild winter means they will be back again in 2006. Any insecticide that works well on caterpillars will work for mimosa webworm (bifenthrin, carbaryl, cyfluthrin, deltamethrin, diflubenzuron, lambda-cyhalothrin, permethrin, spinosad and others). There are two generations of larvae during the summer, beginning in late June and again in August. The second generation tends to cause the most damage. Infested trees can be sprayed at the first sign of brown foliage and webbing caused by the webworms.

Japanese beetle
Japanese beetles will defoliate lindens and other favorite plants in July and August in some places in southern Michigan. Beetle pressure seems to be decreasing in Battle Creek and Kalamazoo as natural enemies become established and spread. The foliage of valued trees can be protected with a Tempo or Sevin spray applied in late June or early July when the first Japanese beetles emerge. Trees may have to be sprayed once or twice more at two week intervals in areas with intense pressure.

Euonymus scale

If you are fortunate enough to still have healthy Euonymus fortunei, plan on spraying them with a 2% horticultural oil in early June and for heavy infestations, again in early August for Euonymus scale.

Other insect pest problems
We have many insect pests that occasionally cause damage to trees and shrubs in the landscape. But most of these are best managed by scouting on a regular basis and only treating when necessary. In the Landscape Alert this year we will give you a list of insect pests to watch for, when they are active, and which ones seem to be causing the most problems. Stay tuned for another exciting season (no doubt!).

Did you find this article useful?