Cottonwood Leaf Beetle: Monitoring & Control

Cottonwood Leaf Beetle: Monitoring

The cottonwood leaf beetle, Chrysomela scripta F., can be a major defoliator in young poplar plantations. Defoliation (Fig. 1) can result in height and diameter decreases as well as increased lateral branching and terminal forking which will significantly reduce biomass of cottonwoods used for pulp and biofuels.

Research is underway to develop a sustainable management system that relies on multiple tactics to manage cottonwood leaf beetle in poplar plantations. Current management utilizes the broad-spectrum insecticide, Sevin, which honey producers believe is causing loss of foraging bees and hives. In addition, Sevin will kill foraging lady beetles which feed on cottonwood leaf beetle eggs. We are studying whether other pesticides can kill cottonwood leaf beetles and conserve lady beetles.

A field survey was done during 2002 in four poplar plantations near Alexandria, MN to count the number of cottonwood leaf beetles (Figs. 2 and 3) and predatory lady beetles. We are studying whether lady beetles, Coleomegilla maculata and Harmonia axyridis, can manage cottonwood leaf beetle populations. We are developing degree-day calculations to associate beetle activity with accumulated heat units for better pesticide application timing (Table 1).

Figure 1

Figure 2

Figure 3

Table 1

	Gen. 1		Gen. 2		Gen. 3
Site	Date	DD	Date	DD	Date	DD

1	June 4	109	July 20	617	Aug. 15	977
2	June 4	109			Aug. 7	793
3			July 10	495	Aug. 15	867
4	June 4	109	July 10	495	Aug. 28	977

Date

Benefits

We will develop alternative and sustainable management plans for cottonwood leaf beetle.
These tactics will offer more sustainable long-term control of the beetle and reduce conventional pesticide use.

Future Aims

Evaluate alternative pesticides for management of cottonwood leaf beetle. Determine if these pesticides are captured in the flavonoid pinocembrum, the residue on Populus leaves that bees use for propolis.
Determine if the entomopathogenic fungus, Beauveria bassiana can increase overwintering mortality.
Determine whether release of Harmonia axyridis, Asian lady beetle, or Coleomegilla maculata, twelve spotted lady beetle, will significantly reduce egg numbers.