–by Jeff Whitworth–Field Crops Entomology
Alfalfa weevils continue to cause concern around the state, but that shouldn’t last much longer. After checking many fields in north central Kansas, from 20-23 May, it is obvious that alfalfa weevil infestations have been very problematic–but has run its course, for the most part. All fields sampled had alfalfa weevil larvae (see fig. 1), whether previously treated or not. All fields, including 2 untreated, had less than a 2% infestation of larvae and adults. There were still a few adults (see fig. 2) hanging around in these unswathed fields which is common as the uncut alfalfa canopy does provide shade for these adults until it is swathed. After swathing these adults usually emigrate from the alfalfa fields and not return until early fall. Adult alfalfa weevils do feed- but at a much reduced rate compared to larvae.
Alfalfa caterpillars (see Fig. 1) are also becoming more common in alfalfa fields throughout the state. These develop into the common white or yellow butterflies, again usually very common around both alfalfa fields and, later on, soybean fields. However, these larvae do not usually cause enough damage to be of any consequence.
Figure 1: Alfalfa weevil larvae (smaller larvae with dark heads) and Alfalfa caterpillar (larva on the left)
Figure 2: Alfalfa weevil adult