Wednesday, April 12, 2017

Colorado potato beetle management

Dr. Ajay Nair
Department of Horticulture
Iowa State University

Ames, IA. Recently I was contacted by a fellow grower and good friend Ms. Laura Krouse from Abbe Hills Farm, Mt. Vernon, IA with a question regarding common enemy of ours: Colorado potato beetle (CPB). Given the mild winter we have had, CPB could pose a formidable challenge this year. If you follow strict crop rotation plans and have moved your potato plots around, hopefully 650 ft, you should be ok but it is always good to be prepared. Why is 650 ft? That is because research shows that CPB in their early development stages emerge from the soil and walk to find potato plantings and 650 ft is to much of a hike for them !

Anyways, let us briefly discuss few management aspects especially insecticides, both organic and conventional. Growers who use conventional insecticides are number of options, some commonly used insecticide classes include pyrethroids (Warrior, Mustang, Asana, Baythroid), carbamates (Sevin), and chloronicotinyl (Actara, Admire, Assail, Platinum), to name few. It is also important to rotate insecticides between different chemical classes. Repeated use of same insecticide can lead to resistance issues in CPB. 

Now, what about organic management. Bacillus thuringiensis products are effective but not all strains. Bacillus thringiensis var tenebrionis provides effective CPM control, however, it is only effective against small larvae (less than 1/4 inch) and should be applied at egg hatch or when larvae are first seen. When the larvae get larger than that, it is more difficult to control with Bt. A commercial OMRI approved product containing Bt tenebrionis is Trident® (Certis USA Inc.). One can also use neem-based products such as Azatin-O, which is OMRI approved. Botanical insecticides, such as neem, have limited persistence in the environment as the temperature, ultraviolet light, rainfall and other environmental factors can degrade neem. Repeated applications may be needed but apply based on label instructions to avoid any kind of phytotoxicity.

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