Healthy pastures and forages are often some of the most productive pastures and forages, but there are several factors that can work against our efforts in maintaining the health of these systems.
Plant diseases and pests actively reduce the health and productivity of our forage and pasture plants, and accordingly, may impact the quality of the forages being made available to our livestock.
With the amount of attention given to forage quality for the sake of maximizing the flow of nutrients to our livestock, giving some effort towards identification and management of disease and pest presence in these systems is an important component of the ability to protect and maintain the quality we strive for in our forages.
The focus of this article will be on the insect pests that may be found in forage systems.
There are several major insect pest species to be aware of. One group of pests, commonly referred to as lepidopteran pests, feed as larvae (caterpillars) in a wide range of crops that includes many of our forage species.
Armyworm
Lepidopteran 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 during late summer 2021.
These pests do not overwinter here, so their variability can also depend upon their success in migrating from the south. The adults (typically moths, although some species of butterflies as well) do not do any feeding, and are nocturnal, meaning they can be difficult to scout for.
Using pheromone traps to indicate presence and pressure of these pests is the best way to be timely with your observations and know when to scout for larval feeding, thus allowing for timely and precise pest management decisions. This is especially important when dealing with armyworm species, as they can decimate forages in the matter of hours, and as they enter later in-star stages, they become increasingly difficult to control.
Leafhopper
A few other primary pests in Ohio, especially in alfalfa, include the alfalfa weevil and potato leafhopper. At this point in the year, we are past the primary generation of alfalfa weevil, which typically only has one generation per year. However, in abnormally warm years, a second generation of weevil may develop, so this may need to be watched closely.
We are currently in the prime season for potato leafhopper. Potato leafhoppers do not overwinter here and are instead blown into our area on southerly winds and storm fronts from the south, which we have had plenty of this year.
These small insects are considered a sucking insect that use their piercing-sucking mouthparts to feed on the plant sap, and in doing so, damage the alfalfa leaves resulting in damage referred to as hopper burn. Hopper burn appears as a wedge-shaped yellow pattern on the leaves, typically moving from the leaf tip toward the mid-vein of the leaf.
I would encourage anyone with alfalfa to be scouting for potato leafhopper, the potential for damage and loss of quality in your alfalfa is high this year with the currently observed elevated populations of this pest. Information on scouting for both the alfalfa weevil and the potato leafhopper can be found in Ohio State University Extension factsheets ENT-32 and ENT-33 respectively.
More pests
A few other pests that are worth mentioning and can cause locally significant damage to forages include Japanese beetles, grasshoppers, spider mites, aphids, cereal leaf beetles, blister beetles, spittle bugs, plant bugs and other lepidopteran caterpillars such as clover worms, loopers and the diamondback moth (primarily a pest of brassica forage crops like rape and turnips).
There are numerous other species of insect pests that are not covered here but can be observed occasionally causing damage to forages. While these pests may be viewed by some as “minor” pests, they should still be given attention and may need to be managed if action thresholds are met.
Management decisions
A lot of factors go into making a management decision.
There are several questions that you should evaluate before deciding to make an insecticide application:
• How soon are you going to graze/harvest the forage?
• What stage is the forage at?
•What stage are the insect pests at in their life cycle?
• Is their population increasing or decreasing?
• Are there beneficial insects and natural enemies present that may be acting as biological pest control?
• If I do make an application, what are the label restrictions for utilizing the forage?
• Is the forecast favorable for rapid insect development and reproduction?
• Is the forecast showing conditions less favorable for rapid progression of insect pest populations?
• Have I thoroughly scouted my pastures and forages to accurately evaluate pest presence, population size, damage potential and any current feeding damage?
• Is this area newly seeded or many years established?
• Is cutting the forage an effective management decision for this pest?
This may seem like a lot to consider, but every pest management decision should be a well-informed decision and made with tact and intention.
No good pest management decision is made without proper identification of the suspected problem. Especially in perennial production systems, we can often find that our agroecosystem has developed somewhat of an ecological balance.
Beneficial
I frequently find large populations of beneficial insects such as spined shoulder bugs and lady beetles in pastures and forage fields. These are not just there by chance. I have consistently observed them feeding on pests such as alfalfa weevil larvae and aphids.
Making an insecticide application can wipe out beneficial insects along with the pests, sometimes resulting in flare ups of other pests like spider mites. The natural enemies and beneficial species are often slower to rebound after an application, meaning the pests may have a longer window of opportunity to build up population numbers and cause damage after the efficacy of a product has worn off.
There are certainly times that an application is warranted and will need to be made to preserve and protect the quality of the forage, and sometimes save the field or pasture altogether, as we observed with the fall armyworm.
As always, work with your county extension educator if you have questions about identification of insect species present in your pastures and forage fields.
Additional information about insect pests in forages can be found in the Field Crops Insect Pest Management Guide, published by Michigan State University and Ohio State University. The “Forage” section of the field guide begins on page 51.
Scouting is foundational to integrated pest management, and although time consuming, allows you to make the most effective and efficient pest management decisions for your farm. It is critical to the success of your pest management decisions that you get out, scout your pastures, and forage fields and evaluate your situation.
Always remember to read and carefully follow all labels on any pesticide. The label is the law.
