By Roger Don Gribble
Enid News and Eagle
ENID, Okla. —
Oklahoma State University entomologist Phil Mulder and his associates have been covering northwest Oklahoma trying to determine what type of alfalfa weevil pressures producers will be facing in the spring.
Along with determining weevil pressures, Mulder is looking at the eggs laid by the adult weevils and determining just how viable those eggs will be.
Mulder is sampling three locations in northwest Oklahoma. Counties being sampled are Kingfisher, Major and Alfalfa. These sites have been in alfalfa production for several years and the sites are not grazed so researchers can obtain good numbers. There are 10 sampling sites statewide for this research project.
Statewide there appears to be more alfalfa weevil eggs this year (100.5/square foot) than in 2012 (65.68/square foot). If we look at northwest locations for egg counts, we see different patterns. For example, in Kingfisher County there were 36.4 eggs per square foot in 2013 and 77.6 in 2012. At the Major County site, there were 77.2 eggs per square foot in 2013 and 74.8 eggs in 2012. The Alfalfa County site near Cherokee had 72.4 eggs per square foot in 2013, and in 2012 there were 198.0 eggs.
Each location is somewhat unique to itself and makes it difficult to make hard and fast statements about the potential for alfalfa weevil to be a major impact on our alfalfa crop. It is thought the dry fall of 2012 might have had a negative impact on the alfalfa weevil adults and their egg laying patterns. The negative impacts on egg laying activities plays right into the hands of alfalfa producers in northwest Oklahoma.
Mulder and his associates will again survey the state for additional eggs this month. Those counts also will include the viability of the eggs that were laid. Not all the eggs laid will create a weevil, and by looking at the January numbers calculated by Mulder, we see that the 2013 eggs laid at the Major County site are 81.5 percent viable, and the Alfalfa County site have 64 percent of those eggs capable of producing weevils.
One other note to mention, here is the degree day calculations for alfalfa weevil. We know that when a site reaches 150 degree days, we can expect to see weevil eggs begin to hatch. At that point in time, producers will need to start their scouting activities to determine if they reach the economic thresholds for controlling alfalfa weevil larvae. At the Kingfisher County site, they have reached 125 degree days. There are 120 degree days in Major County and 109 degree days in Alfalfa County.
You can watch your degree day calculations on the Oklahoma Mesonet. To do so, navigate in the crops menu to alfalfa. Move to Alfalfa Weevil Heat Units and select the statewide map and then move to your closest Mesonet Station to view the current calculations.
Please feel free to visit with your Oklahoma Cooperative Extension Service ag educator about this information. They can help direct you to where you can find this information and help determine your degree day level for your farm.
Gribble is Oklahoma Cooperative Extension Service northwest area agronomist.