After a miserable dry hot summer, we have finally received some good rainfall and in most areas the fields are slowly recovering. Many folks took advantage of the moisture and have already planted some small grains.
This is all great news, but now that we have some grass we are going to have to contend with a couple of pests.
The dry weather provided the perfect environment for every grasshopper nymph to survive as a result we have a very large grasshopper population. These grasshoppers are now large enough that they can really do some damage to everything from grass to leaves on trees. Fall Armyworms are becoming more widespread, and we can expect numbers to increase.
Unfortunately, the pests are here to stay until late fall, the worm numbers seem to drop off when the nights get cool, but a frost is really the only thing that will stop both pests.
The larvae of the fall armyworm are green, brown, or black with white to yellowish lines running from head to tail. There will be a white line between the eyes that forms a “Y” pattern on the face. At first thefallarmywormcaterpillar or larvae are very small about 1/8”, at this stage they cause very little damage and usually go unnoticed. The larvae will feed for 2 to 3 weeks growing to 1 to 1.5”. Once the armyworms reach ¾” in length they quantity of forage they eat increases dramatically. During the final 2-3 days of feeding, armyworms consume 80% of the total forage during their entire development. Once the armyworm completes feeding it tunnels into the soil and enters the pupal stage. The moth emerges from the pupa in about 10 days and repeats the lifecycle.
Scouting is the key to controlling damage associated with the fall armyworm. It is best to check fields late in the evening or early in the morning; this is when they will be feeding in the upper canopy. Damage from the small larvae will leave a clearing or windowpane effect on the leaf, as the larvae grow, they will begin eating on the edges of the leaves.
There are several products that will work on both grasshoppers and armyworms but may have different requirements for stage of treatment and different residual times. Though it is more expensive, I think Vantacor is going to be the better product to use this year, it has up to a 6-week residual and will work on mature grasshoppers and armyworms. If you just need a quick knockdown and do not require a long residual, any of the lambda cyhalothrin products are less expensive and will work well at killing mature worms and grasshoppers but offer only about a 7-day residual.
The following is a list of insecticides for fall armyworm control, I encourage you to check with your good local pesticide dealers and applicators to see what is working best in your area.
Insecticides Labeled for Armyworm and Grasshopper Control in Pastures and Hayfi elds.
Always read and follow all label instructions on pesticide use and restrictions. Information below is provided for educational purposes only. Read current label before use.
Karate Z. 13.1% lambda cyhalothrin. Fall armyworm and grasshoppers. Pasture and rangeland grass, grass grown for hay and silage and grass grown for seed. Pasture and rangeland grass may be used for used for grazing or cut for forage 0 days after application. Do not cut grass to be dried and harvested for hay until 7 days after the last application. Restricted use insecticide.
Lambda- Cy. 11.4% lambda cyhalothrin. Fall armyworm and grasshoppers. Pasture and rangeland grass, grass grown for hay and silage and grass grown for seed. Pasture and rangeland grass may be used for used for grazing or cut for forage zero days after application. Do not cut grass to be dried and harvested for hay until 7 days after the last application. Restricted use insecticide.
Mustang Max. 9.6% zetacypermethrin. Fall armyworm and grasshoppers. Applications may be made up to 0 days for forage and hay, 7 days for straw and seed screenings. Restricted use insecticide.
Tombstone Helios. 25% cyfluthrin. Fall armyworm and grasshoppers. Pasture, rangeland, grass grown for hay and seed. Zero days to grazing or harvesting hay. Restricted use insecticide.
Warrior II. 22.8% lambda cyhalothrin. Fall armyworm and grasshoppers. Pasture and rangeland grass, grass grown for hay and silage and grass grown for seed. Pasture and rangeland grass may be used for used for grazing or cut for forage 0 days after application. Do not cut grass to be dried and harvested for hay until 7 days after the last application. Restricted use insecticide.
Baythroid XL. 12.07% cyfluthrin. Fall armyworm and grasshoppers. Pasture, rangeland, grass grown for hay and seed. Zero days to grazing or harvesting hay. Restricted use insecticide.
Dimilin 2L. 22% diflubenzuron. Fall armyworm and immature grasshoppers. Dimilin must be applied before armyworm larvae reach ½ inch or larger. Provides residual control for up to 2-3 weeks, as long as forage is not removed from the field. Label does not list a restriction on grazing.
Prevathon or Vantacor. 5% chlorantraniliprole. Fall armyworm and grasshoppers. Prevathon has a 0-day waiting period for harvest or grazing and is not a restricted use insecticide. Up to 6 weeks of residual control.
Besiege. 9.26% chlorantraniliprole and 4.63% lambda cyhalothrin. Fall armyworm and grasshoppers. Pasture and rangeland grass may be used for grazing or cut for forage 0 days after application. Do not cut grass to be dried and harvested for hay until 7 days after the last application. Restricted use insecticide.
Sevin 4F, Sevin XLR, Sevin 80S, Generic Carbaryl. Fall armyworm and grasshoppers. When applied to pastures, there is a 14-day waiting period before grazing or harvesting.
Malathion 57% and Malathion ULV. Fall armyworm and grasshoppers. Zero days to harvest or grazing.
Intrepid2F. Fallarmyworm (not grasshoppers). Begin applications when first signs of armyworm feedings appear. Use higher rates for heavier infestations. Do not harvest hay within 7 days of application. No pre-harvest interval for forage. 0 days to grazing.
Tracer. Treat when armyworm eggs hatch or when larvae are small. Use higher rates for larger larvae. Do not graze until spray is dry. Do not harvest hay or fodder for 3 days after treatment.
Comanche Extension Agent Michael Berry