Vegetable Crops News

Straw Mulch and Bt Suppress Colorado Potato Beetle

The bioinsecticide Bacillus thuringiensis subsp. tenebrionis (Btt) is active against Colorado potato beetle, but often has not consistently controlled beetle populations as well as synthetic insecticides. Btt is most effective against small instars, making timing of applications crucial.

Another alternative management technique is the use of straw mulch in potato fields. Reduced beetle numbers and damage in mulched fields is due primarily to increased numbers of natural enemies. However, the use of mulch alone is usually not sufficient to reduce damage below economic thresholds.

Research in Indiana shows that these two approaches can be combined to provide good protection against Colorado potato beetle -- as good as an application of the commonly used synthetic insecticide esfenvalerate.

The use of straw mulch and no-mulch, the synthetic pyrethroid esfenvalerate (Asana XL), and Btt (M-Trak, Mycogen, Salinas CA) were compared for their effects alone and together on Colorado potato beetle on potato.

The mulch treatments had a significantly greater density of predators and fewer beetle larvae than no-mulch plots. Over the two year study period, twice as many predators were found in the mulched plots. The most abundant predators during the time 1st-generation Colorado potato beetles were present were ground beetles; two species of lady beetles, a predaceous bug and a lacewing were also found. At the time of the 2nd-generation, lady beetles and lacewings were the most abundant predators; only one ground beetle (Lebia sp.) was abundant. Twospotted stink bug was the 3rd most abundant predator in the first year of the study, but was scarce in the second year.

Potato yields in mulched plots were at least 33% greater than in no-mulch plots. Yields in the mulch + Btt plots were equal to insecticide treated plots, and were about 65% greater than Btt alone or the control plots.

This combined management strategy works because the two factors do not compete of interfere with one another.

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