We have accumulated enough Growing Degree Days that small alfalfa weevil larvae should be active in fields. Generally this pest does not develop into a problem but there have been a couple of years out of the last 20 where a spray to control would be warranted. Alfalfa feeding should be focused at the growing tip of the crop. At this point the larvae will be very small with a black head as they develop the size and amount of feeding increase.
To sample for alfalfa weevil, gather 10 stems per area and shake the stem into a bucket dislodging the larvae and counting the number of larvae in the bottom of the bucket. The number of larvae are then compared to the height of the stem to determine if treatment is warranted using the chart below:
A fact sheet reference with more detail can be found at: http://ohioline.osu.edu/ent-fact/pdf/0032.pdf
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