Elm leaf beetles can be serious pests of elm trees throughout Colorado. These insects feed on elm leaves and cause them to dry up and die. This gives heavily infested trees an unsightly, general brown color. Repeated injuries also weaken trees and make them prone to branch dieback and wind injury. Elm leaf beetles favor Siberian elms, but all elm species may be damaged during beetle outbreaks.
Elm leaf beetles also are common nuisance pests in houses. Large numbers of beetles may seek overwintering shelter in and around homes. Masses of beetles become active in late winter and spring and can be found crawling on windows and furnishings. Although elm leaf beetles don’t actually reproduce indoors, their presence often causes concern.
Preventive steps -first and foremost, beetle control on nearby trees – can reduce problems in homes.
Typically, adult beetles start to migrate to overwintering shelter in mid-August, but movements greatly increase by early September.
Weather probably is the most important factor that affects elm leaf beetle populations. Long winters, or a late spring freeze, may kill large numbers of overwintering beetles. In addition, small larvae are susceptible to being blown or rubbed off trees during wind storms. This may be particularly common when larvae are forced to feed on older, tough leaves. This increases their wandering, and many die in the process.
Several insecticides are effective controls when sprayed on foliage at the proper time in the life cycle. These treatments often are best applied after most eggs are laid by the overwintering females, but before the larvae start to cause significant injury to the leaves.
ArborScape’s curative sprays, timed twice a year to correspond with the destructive larval stage of the beetle, controls their numbers and disrupts reproduction. The number of affected leaves and subsequent infestation of nearby buildings drops sharply when these sprays are implemented.
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