WHAT DO YOU DO WHEN YOU FIND FALL ARMYWORMS?

by: Kathy Flanders
Extension Specialist and Associate Professor Auburn University


In the last issue of Cattle Today, I explained where fall armyworms come from, how they live, and how to look for them. This article will focus on how we can work together to know when and where damaging populations of fall armyworms have been found. It will also discuss ways to control fall armyworms.

The hot dry weather we had during May and June makes it likely we will have problems with fall armyworms this summer AGAIN! It will be important to check your forage grasses this summer for the presence of fall armyworm. The Alabama Cattlemen's Association and the Alabama Cooperative Extension system have worked together to purchase sweep nets that you can borrow to look for fall armyworms. Regional Animal Science Extension Agents and most county offices of the Alabama Cooperative Extension System have sweep nets that can be borrowed to look for armyworms in forages (see http://www.aces.edu/directory). To find out which cattlemen have sweep nets, you can contact your regional extension agent, or use the information tool on the map located at this link: http://maps.acesag.auburn.edu/alabama_armyworm_watch. You can also purchase a sweep net from mail order supply stores that specialize in farm, forestry or pest management supplies. A sweep net costs approximately $25. There is a video showing how to use a sweep net on the Alabama Cattlemen YouTube Channel (www.youtube.com/alabamacattlemen).

The best places to start looking for fall armyworms are in your most valuable hayfields, as well as in areas of fields that have been attacked by fall armyworms in previous years. If you find fall armyworms using the sweep net, the next step is to count how many caterpillars you have per square foot. Look on the grass itself, as well as in the leaf litter (thatch) on top of the soil. If you find more than two to three caterpillars per square foot, it is probably time to apply an insecticide or to cut the field for hay. The best time to look for fall armyworms is when they are most likely to be feeding. This is from late evening through early morning. If you don't find any armyworms using the sweep net, you should look again in about seven days.

If you have enough armyworms that they need to be controlled, please send an e-mail to flandkl@auburn.edu so that I can let other cattlemen and extension agents know when armyworms have been found. A map showing where and when armyworms have been found is located at: maps.acesag.auburn.edu/alabama_armyworm_watch. You can also watch for information on the Alabama Cattlemen Facebook page and in communications from Alabama Cooperative Extension System.

Management Tactics for Fall Armyworm

Early harvest: If damaging populations of armyworm are discovered when a hayfield is close to harvest, you may be able to cut the field to keep from losing any more biomass. The harvesting operation kills some caterpillars directly. However, most caterpillars probably die from exposure to the high soil surface temperatures that occur after harvest. If extremely high numbers of caterpillars are found, harvesting alone may not be enough to stop the armyworms. In that situation, apply an insecticide then observe the appropriate interval between application and harvest.

Using an insecticide: At the time of writing this article, there are eleven insecticides that can be used for controlling fall armyworm caterpillars in perennial grass forages. Some, but not all of these, can also be used in annual grass forages. It is important to read the directions for use (the label) of an insecticide carefully to make sure that the product can be applied to a particular type of forage. The label also contains information on how to mix and apply the product for maximum efficacy. Insecticides have two names. Most of us are more familiar with the trade name of the insecticide, because that is the marketing name. However, it is important to be familiar with the common name, or active ingredient, of the insecticide, which can be found in the active ingredient section of the product label. The common name is written in lower case letters, to distinguish it from the trade name. The same insecticide may be sold under several trade names. Alabama Cooperative Extension System Circular ANR-1019, Management of Fall Armyworms in Pastures and Hayfields, available from your county Extension office, or at http://www.aces.edu/ pubs/docs/ A/ ANR- lO19/ANR-1019.pdf, provides details on the insecticides that are currently legal to use in perennial grass pastures and hayfields. The circular includes the common names and examples of trade names. Those insecticides are beta-cyfluthrin, e.g., Baythroid XL; carbaryl, e.g., Sevin XLR Plus; chlorantraniliprole, e.g., Coragen; cyfluthrin, e.g., Tombstone Helios; diflubenzuron, e.g., Dimilin 2L; lambda-cyhalothrin, e.g., Karate Z; methamidophos, e.g., Lannate LV 2.4; methoxyfenozide, e.g., Intrepid 2F; methyl parathion, e.g., Cheminova Methyl 4EC; spinosad, e.g., Tracer SC; and zeta-cypermethrin, e.g., Mustang Max.

The insecticides vary in price; grazing and harvesting intervals; mode of action; speed of action; and safety to the environment and to the applicator. You will find that the insecticide label usually recommends a range of application rates. In general use higher rates of insecticides (and higher volumes of water): when the grass is thick, when fall armyworm populations are high, when caterpillars are large, and to get the longest residual effect. Some insecticides will only kill smaller caterpillars, so check the comments provided about each insecticide.

The following generalizations may help you match your circumstances to the right insecticide.

These insecticides have the longest residual: methoxyfenozide, diflubenzuron, and chlorantraniliprole. Insecticides with longer residuals help in outbreak years where generations of fall armyworms overlap, resulting in almost continuous egg laying. Caterpillars sprayed with methoxyfenozide quickly stop eating and will die in a few days as the insecticide causes the caterpillar to molt too soon. Caterpillars sprayed with chlorantranilip-role also quickly stop eating, become paralyzed, and then die within a few days. Caterpillars sprayed with diflubenzuron do NOT stop eating until the next time they molt. That is why it is essential that diflubenzuron be applied when the fall armyworm caterpillars are 0.25 inches long or less, well before they get to their last molt. As noted in the last article, about 80 percent of the total feeding is done after the last molt, in the last four days of the caterpillar stage.

The following insecticides have the shortest grazing interval (grazing interval in parentheses): beta-cyfluthrin (0), cyfluthrin (0), chlorantraniliprole (0), diflubenzuron (0), lambda-cyhalothrin (0), methoxyfenozide (0), spinosad (0), and zeta-cypermethrin (0).

The following insecticides have the shortest interval between the time of application and harvest (preharvest interval): beta-cyfluthrin (0), cyfluthrin (0), chlorantraniliprole (0), zeta-cypermethrin (0), diflubenzuron ( 1 ), methomyl (3 ), and spinosad (3).

The following insecticides do not require a pesticide applicators license: carbaryl, chlorantraniliprole, methoxyfenozide, spinosad.

Other Tips: Apply insecticides early or late in the day, because the caterpillars are more active at these times. Use as large a spray volume as you can. Never apply the insecticide in less water than is recommended on the label. By scouting for armyworms you may find that you don't have to treat the whole of each field. Apply insecticides where you find the caterpillars. If caterpillars are marching into a field, you may be able to stop the advance by applying several swaths of the insecticide on either side of the "front line." Finding the caterpillars when they are small can also save money, as you can often use a lower rate of the insecticide.

Last but not least: Use pesticides only according to the directions on the label. Follow all directions, precautions, and restrictions that are listed. Do not use pesticides on plants that are not listed on the label. The pesticide rates in this article are recommended only if they are registered with the Environmental Protection Agency and the Alabama Department of Agriculture and Industries. If a registration is changed or canceled, the insecticide is no longer recommended. Before you apply any pesticide, check with your county Extension agent for the latest information. Trade names are used only to give specific information. The Alabama Cooperative Extension System does not endorse or guarantee any product and does not recommend one product instead of another that might be similar.







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