–by Dr. Jeff Whitworth and Dr. Holly Schwarting
Alfalfa continues to cause concern throughout north central and south central Kansas due to defoliation by “worms”. There seems to be a combination of garden (alfalfa) webworms, fall armyworms, armyworms, yellow striped armyworms, etc. feeding on the foliage. Generally, if the alfalfa is within 10 days of swathing or if the “worms” are mature, (maybe ½ inch long for webworms which are naturally smaller than the others; or ¾ inch long for the others), it probably is best to just cut the field and not treat. If treatment is justified, please pay attention to the pre harvest interval (PHI) for whatever product is used. These worms won’t feed on the foliage after it is cut, but they may feed under the windrows holding back the regrowth and causing striping in these fields. For more information on these insects and their control options, as well as PHI’s, please visit: http://www.bookstore.ksre.ksu.edu/pubs/MF809.PDF