Cut, Bale, Scout!

Richard Proost, University of Wisconsin, Nutrient and Pest Management Program

Over the past few years some extension agents have reported a troubling trend. It seems that in some areas of the state, farmers are practicing a potato leafhopper (PLH) management program on alfalfa that can be best coined as the “Cut, Bale and Spray System” (CBS). Just as it sounds, alfalfa is cut, baled and then an insecticide is applied shortly after the bales have been removed. This is not a recommended practice for a variety of reasons.

First, PLH are usually not present immediately after harvest due to having been killed and/or chased out of the field by the harvest operations. Scouting the field is the only way to know if PHL is present in populations large enough to cause damage to alfalfa regrowth, justifying an insecticide application.

Second, due to the non-selectivity of the insecticides, the reduction of beneficial insect populations in alfalfa is a concern. Beneficial insects that remain in the stubble, such the larvae of lady beetles and lacewings, are at risk of being killed by the insecticide application.

A final problem with CBS is that it can give farmers a false sense of long term control. Insecticides used for PLH control have relatively short residual properties, providing control for perhaps 10 to 14 days. However, if farmers believe PLH are being controlled for a longer period of time, they may not be conscientious about scouting their alfalfa fields for them. Consequently PLH can migrate back into fields and build up quickly, causing additional damage to the alfalfa stand.

In an effort to reverse this trend, a joint effort of UW-Madison’s Department of Entomology, Nutrient and Pest Management Program, Integrated Pest Management Program, and UWEX Agriculture Agents started an educational program with the simple objective of providing farmers with the information and training necessary to properly manage PHL.  As part of this project, a PLH scouting and identification guide was developed by the NPM and IPM programs. This easy to use guide is a one page publication that identifies the potato leafhopper adult and nymph, plant damage, describes the scouting method for PLH, and the threshold levels. It can be downloaded at the IPCM web.

cut-bale-scout2007.pdf For further information regarding the PLH educational program, contact either Bryan Jensen at 263-4073 or Richard Proost at 262-7845.