Scouting Alfalfa For Insects

Stuart Carlson, Northern Product Agronomist
June 25, 2021

Alfalfa is a host for many kinds of insects that can hurt tonnage and quality. It is extremely important to scout on a regular basis to discover any potential problems early enough so it can be managed to maintain regular cutting intervals.

Scouting frequency and methods

To maximize high-yielding and high-quality alfalfa I recommend scouting your fields once a week.  Sampling may need to be more frequent in hot weather, under crop stress conditions or if populations were high in a previous sample.  Insects will grow and feed faster when conditions are warm. Also, when alfalfa is under stress the plant will grow at a slower pace allowing the insects to do more damage more quickly because the plant can’t grow ahead of the insects feeding.

I like to use an insect sweep when scouting for thresholds. A sweep is a hoop that is 15 inches in diameter with a white colored net attached to it on a handle. Most scouting guides will reference thresholds as so many insects per 10 sweeps.  With this method you can cover more area in a shorter amount of time. If you don’t have a sweep you can use the stem sampling method or ground area sampling using a hoop.  In these methods you will be looking for the pest directly on the plant itself. I recommend scouting early in the morning before the heat of the day.

What are you looking for? You will come up with several different pest when you run a sweep through the field. Each insect has its own threshold level that needs to be taken into consideration when deciding how to manage the field. Here are a few of the more common pests for you to watch out for when scouting your field.


Alfalfa is a great feed and cash crop with the ability to have several harvest opportunities throughout the growing season. Management of insects is key in maximizing tonnage and quality when you know what to look for. Take the time to scout your fields once a week and stop these pests from damaging your stands and potentially shorting up the crop’s life span.


  • UNL Cropwatch – Alfalfa Insect Pests
  • U of M – Alfalfa insects: What to look for and how to scout