Scout Alfalfa for These Damaging Pests

As with all crops, scouting alfalfa acres is key to controlling pests. Each pest has a different life cycle based on different variables, such as heat and moisture. While weather plays a key role, there are still cyclical patterns in which pests are more common. Below is a chart showing the most damaging pests to scout for according to season.

Potato Leafhopper and Pea Aphids are the two pests that cause the most damage annually across Latham Country. Many farmers question how to judge when spraying an insecticide is a wise choice. Below are some tips to help you scout fields and arrive at a decision.

1. WHAT TO LOOK FOR. Scouting should begin five to seven days after the first cutting is taken and should continue weekly or bi-weekly if population counts reach close to threshold on a particular day. When scouting for Potato Leafhoppers, look for stunted plants, yellowing leaves in a v-shaped pattern beginning at the leaf tip, as well as “hopperburn,” or a red edge found on the leaf. This red burn can be easily confused for Boron deficiency. Pea Aphids will cause plants to lose their green color and wilt.
2. HOW TO TAKE SWEEP SAMPLES. The easiest way to scout for these insects is to use a small sweep net. Walk a W-shaped pattern in the field, taking samples from five randomly selected areas. Leafhopper infestations generally begin on the edges of the field, so include these areas in your checks. Tips for Taking Sweep Samples:
   •  Swing the sweep net in a 180-degree arc, so the net rim strikes the top 6 to 8 inches of growth. Each 180-degree arc is one “sweep.”
   • Take a sweep from right to left, walk a step, take another sweep from left to right, and so on.
   • After taking five sweeps, quickly close the net and count the number of each insect.
   • Divide this number by five to get the average for that area; record the average for each of the five areas in the field.
3. THRESHOLDS AND TREATMENT. A plant’s immune system tends to handle more pressure as alfalfa matures, however, the harmful compounds that each insect species injects while feeding can reduce yields. When left unmanaged, severe cases can shorten the life cycle. Treatment for Potato Leafhoppers and Pea Aphids can follow these guidelines.

Early harvests often can be used to control both leafhoppers and aphids. Insecticides are a tool to help alter the life cycle of a pest and are especially helpful if thresholds are reached when alfalfa is small. Several insecticides are labeled for alfalfa with different classes and modes of action. Most have a harvest wait period depending on class and rate used. Be sure to follow the label guidelines closely. As with herbicides, alternating modes of action reduces the risk of resistant pests.