Entomology and Plant Pathology, Oklahoma State University
127 Noble Research Center, Stillwater, OK74078
Vol. 12, No. 3
Feb 1, 2013
Alfalfa Weevil Populations and Comments on Resistance
Phil Mulder and Kelly Seuhs,
Extension Entomologist and OSU Extension Associate
In an earlier news release we discussed alfalfa weevil egg populations for January (located in the attached table) and suggested that numbers were relatively low with moderate viability of those eggs (68%). Two locations (Grady and Tillman counties) had extremely high egg populations. An update on degree days through January 31, 2013 is presented in the last column of Table 1 and shows that in spite of current colder conditions, the higher temperatures earlier have resulted in a few locations nearing the 150 degree day point. Remember this level of degree days represents the point that serves as an indicator for growers and consultants to begin scouting for larvae. Although precipitation totals across the state remain low, some areas have experienced showers during the last front that came through. This rainfall will definitely help the alfalfa to grow and usually helps in suppressing aphid populations, particularly when the cold is accompanied by wet conditions. Currently, even with the moisture received last week, most of the state is still in an extreme drought with well below average rainfall.
I want to reiterate what was said in the last news release, that we must remain vigilant; early 2011 was a perfect storm for insect (aphid) development while a mild and dry 2012 showed an increase of alfalfa weevil populations. Also, in 2011, above average temperatures and below average rainfall equated to minimal to no alfalfa growth occurring in the spring allowing an explosion of insect populations prompting multiple sprays for control.