Thus, unless the value for the crop loss caused by the pests exceeds the cost of controlling them, it is not profitable to spray. On the other hand, some insect losses can be avoided if a spray is applied at the proper time. A good pest management program requires proper identification of the pest species causing the damage, and determination if the economic threshold has been exceeded. Get a copy of the publication A Pest Management Program for Alfalfa in Pennsylvania from your local extension office. This publication will aid you in deciding when it is profitable to control potato leafhopper and alfalfa weevil.
Pest identification requires knowing when and what to look for in the field.
Figure 8-1 shows the key periods of forage insect occurrence in Pennsylvania. Alfalfa blotch leafminer can be found in practically all alfalfa fields in the state. However, damage always looks worse than it actually is. The second cutting usually is most severely infested. The adult fly is about .13 inch long and resembles a common housefly.