How to combat pasture and forage pests
How to combat pasture and forage pests

Autumn armywormAutumn armyworm
Fall armyworm is on the hunt in food plots. (Photo by Alabama Cooperative Extension System)

Healthy pastures and forage lands are often among the most productive pastures and forage lands, but there are several factors that can work against our efforts to maintain the health of these systems.

Plant diseases and pests actively affect the health and productivity of our forage and pasture crops and can consequently compromise the quality of the feed provided to our livestock.

With so much attention paid to forage quality to maximize nutritional delivery to our livestock, it is important to also put some effort into identifying and controlling diseases and pests in these systems in order to protect and maintain the forage quality we strive for.

The focus of this article is on the insect pests that can occur in feeding systems.

There are several important insect pest species to watch out for. One group of pests commonly referred to as lepidopterans feed as larvae (caterpillars) on a wide variety of crops, including many of our forage plants.


Lepidoptera species such as the common armyworm and fall armyworm can cause significant damage depending on the year and the population size of the pest. You may have experienced such damage during the fall armyworm outbreak in late summer 2021.

These pests do not overwinter here, so their variability may also depend on their success in migration from the south. The adults (usually moths, but also some butterfly species) do not feed and are nocturnal, meaning they can be difficult to detect.

Using pheromone traps to indicate the presence and pressure of these pests is the best way to time your observations and know when to look for larvae in order to make timely and accurate pest control decisions. This is especially important when dealing with armyworm species, as these can decimate forage plants in a matter of hours and become increasingly difficult to control as they advance into the stage.


Other major pests in Ohio, especially on alfalfa, include the alfalfa weevil and the potato leafhopper. At this point in the year, we are past the primary generation of the alfalfa weevil, of which there is usually only one generation per year. However, in unusually warm years, a second generation of weevils can develop, so this may need to be watched closely.

We are currently in the peak season for potato leafhoppers. Potato leafhoppers do not overwinter here, but are blown into our area by southerly winds and storm fronts from the south, of which we have had plenty this year.

These small insects are considered sucking insects that feed on plant sap using their piercing-sucking mouthparts, damaging the alfalfa leaves in the process, causing damage known as hopper scorch. Hopper scorch appears as a wedge-shaped yellow pattern on the leaves, typically moving from the leaf tip toward the midrib of the leaf.

I would recommend that anyone growing alfalfa be on the lookout for potato leafhoppers, as the risk of damage and quality loss to your alfalfa is high this year as increased populations of this pest are currently being observed. For information on looking for the alfalfa beetle and potato leafhopper, see Ohio State University Extension fact sheets ENT-32 and ENT-33.

Other pests

Other pests of note that can cause significant local damage to forage crops include Japanese beetles, locusts, spider mites, aphids, grain beetles, oil beetles, leafhoppers, plant bugs and other lepidopterans such as cloverworms, geometer moths and the cabbage moth (mainly a pest of brassica forage crops such as rapeseed and turnips).

There are numerous other types of insect pests not covered here, but may occasionally be observed causing damage to forage crops. Although these pests are considered by some to be “minor” pests, they still deserve attention and may need to be controlled if action thresholds are reached.

Management decisions

Numerous factors play a role in a management decision.

Before you decide to use an insecticide, you should consider several questions:

• How soon will you graze/harvest the forage?

• What stage is the feed in?

•What stage of their life cycle are the pests in?

• Is their population increasing or decreasing?

• Are there beneficial insects and natural enemies that could act as biological pest control?

• If I apply, what labelling restrictions apply to the use of the feed?

• Is the prognosis for rapid development and reproduction of insects favorable?

• Do the forecasts show less favourable conditions for the rapid spread of pest insect populations?

• Have I thoroughly inspected my pastures and forage areas to accurately assess pest presence, population size, damage potential and any current grazing damage?

• Has this area been newly seeded or has it been established for many years?

• Is cutting the feed an effective control measure for this pest?

While this may seem like a lot to consider, any pest control decision should be well-informed and made with tact and intention.

Without proper identification of the suspected problem, no good pest control decision can be made. Especially in perennial production systems, we can often see that a certain ecological balance has developed in our agroecosystem.


I often find large populations of beneficial insects such as spiny bugs and ladybirds in pastures and forage fields. They are not there by chance. I have repeatedly observed them feeding on pests such as alfalfa weevil larvae and aphids.

Applications of insecticides can kill beneficial insects as well as pests, sometimes causing flare-ups of other pests such as spider mites. Natural enemies and beneficial species often recover more slowly after an application, meaning pests may have a longer window of opportunity to increase their population numbers and cause damage after a product’s effectiveness wears off.

Certainly there are cases where application is justified and must be done to maintain and protect the quality of the forage and sometimes to save the field or pasture as a whole, as we have observed with the fall armyworm.

As always, work with your local district extension agent if you have questions about identifying insect species present in your pastures and forage fields.

For more information on insect pests in forage crops, see the Field Crops Insect Pest Management Guide published by Michigan State University and Ohio State University. The Forage Crops section of the field guide begins on page 51.

Scouting is the foundation of integrated pest management and, although time consuming, allows you to make the most effective and efficient pest management decisions for your operation. Getting out there, exploring your pastures and forage fields, and assessing your situation is critical to the success of your pest management decisions.

Always remember to read all labels on pesticides and follow them carefully. The label is the law.

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