Joanne Whalen, Extension IPM Specialist; firstname.lastname@example.org
Continue to scout fields for both alfalfa weevil and pea aphids. Both can be found in fields throughout the state. Fields should be scouted for these two insect pests until the first cutting. Examine 5‐10 stems for damage and weevil larvae until damage or larvae are found on the plants. Once larvae are found, a decision to treat should be based on collecting a minimum of 30 stems throughout a field and checking for the number of larvae per stem. The following thresholds, based on the height of the alfalfa, should be used as a guideline when making a treatment decision for alfalfa weevil: (a) up to 11 inches tall – 0.7 per stem; (b) 12 inches tall – 1.0 per stem; (c) 13 to 15 inches tall – 1.5 per stem; (d) 16 inches tall – 2.0 per stem and (e) 17 to 18 inches tall – 2.5 per stem. The following thresholds should be used as a guideline when making a treatment decision for aphids : (a) alfalfa less than 10 inches tall treat if you find 40-50 aphids per stem, and (b) alfalfa 10 inches or taller in height treat if you find 75- 100 per stem.
Low levels of cereal leaf beetle adult (eggs and small larvae), armyworms and grass sawfly larvae have been found in an occasional field in Kent and Sussex counties. Cereal leaf beetle populations are often unevenly distributed within a field so it is important to carefully sample so that you do not over or under estimate a potential problem. Eggs and larvae are also found on leaves near the ground so careful examination of the entire plant is critical. The treatment threshold is 25 eggs and/or small larvae per 100 tillers/stems, with more larvae than eggs present to justify a spray. More information on sampling and treatment thresholds for grass sawfly and true armyworm can be found at the following link