The future is now for rangeland grasshopper scouting
Monday, July 23, 2018
Most agricultural producers know grasshopper infestations can sweep over Oklahoma rangeland like a Biblical plague if conditions are right, and conditions are becoming increasingly favorable for the pests.
“Grasshoppers seem to be in an upward cycle for causing problems in Oklahoma over the past few years,” said Tom Royer, Oklahoma State University Cooperative Extension Integrated Pest Management coordinator. “They are always a difficult problem to deal with but this late in the year, they are nearly impossible to control.”
That is because the grasshoppers have sprouted wings, making effective control of the insects a “hit-and-miss” prospect, and a more expensive control endeavor.
“Be aware grasshoppers can eat 25 percent to 50 percent of their body weight in forage a day,” Royer said. “In contrast, a steer will eat 1.5 percent to 2 percent of its body weight in forage a day.”
Depending on the level of infestation, grasshoppers can have a significant negative effect on the health and availability of a producer’s pasture resources.
“For this year, it’s probably too late to effectively reduce numbers but success in controlling grasshoppers next year starts with what producers are doing now,” Royer said.
The first step is for producers to assess grasshopper population numbers on their properties. Royer suggests the producer study an area about one-square-yard in size as he or she walks through the pasture, counting the number of grasshoppers that jump out of the area as he or she passes. Repeat the process three or four times, leaving approximately 75 feet in between areas of study.
Royer added grasshopper control in rangeland is probably never justified until numbers exceed 12 per square yard.
“We suggest a threshold of 24 or more small grasshoppers – less than a half inch long – per square yard is a starting point for deciding whether to spray or not,” he said. “The threshold for larger grasshoppers is from 12 to 40 insects per square yard.”
Sprays are most effective if timely and practiced over large areas. The best time to control the pests is from mid-May through about July 1, while the grasshoppers are wingless.
“Once grasshoppers sprout wings they can fly for miles in search of food, and that is basically the challenge right now,” Royer said. “It’s important producers prepare now to mitigate their presence next year as the grasshoppers will be laying eggs this fall.”
Available control options
Royer explains there are three options that a producer might consider:
The first option is to spot treat hatching areas or spray the borders around a field with an approved pesticide. Grasshopper eggs are often deposited in concentrated egg-laying sites, in pastures, ditches and untilled field margins. Fortunately, grasshopper nymphs tend to remain in their hatching areas for some time after they emerge.
“This is why spot applications of a registered insecticide in those areas can effectively reduce grasshopper numbers,” Royer said. “No herding is required, and would be a challenge if it were.”
Another option is to use a Reduced Agent and Area Treatment with Dimilin. The active ingredient is diflubenzeron, which is registered for use in rangeland and pastures to control grasshoppers. It disrupts the molting process of grasshoppers.
“Because of its specific activity on the invertebrate molting process, it is very non-toxic to vertebrate wildlife but should not be applied to ponds or streams,” Royer said. “Birds can still eat the grasshoppers without suffering ill effects. In addition, diflubenzeron must be ingested to be effective plus it covers less pasture so it has minimal impact on beneficial or non-target insects.”
Using a RAAT treatment strategy, the rate of the chemical is lowered and applied in alternating treated and untreated strips. This strategy takes advantage of the grasshopper’s natural tendency to move as it feeds. Essentially, as grasshoppers move from untreated to treated areas and eat foliage treated with diflubenzuron, they are killed when they try to molt.
“RAAT applications can be made with an aerial or ground application, but diflubenzuron is the only insecticide that specifically allows a RAAT application against grasshoppers,” Royer said.
A RAAT treatment can reduce application costs by 50 percent to 60 percent, with 65 percent to 70 percent less insecticide being applied compared to conventional broadcast treatments.
Royer said he has received questions about using Coragen or Prevathon as a RAAT application. Both have chlorantraniliprole as an active ingredient.
“OSU data indicates this product is very effective at controlling grasshoppers, but we found it was not as effective at reducing grasshoppers in untreated areas,” he said. “Grasshoppers in untreated areas tended to stay there and not move, so the jury is still out on using it as a RAAT application. The good news is that it is a bit less dependent on timing for the proper growth stage of grasshoppers compared to Dimilin.”
However, producers should be aware that chlorantraniliprole is much more expensive to apply, even if applied as a strip crop. Even more importantly, it is not labeled for a RAAT application.
“In Oklahoma, you are not allowed to apply any pesticide in a manner not listed on the label, such as applying a lower-than-labeled rate or in this case as a RAAT application,” Royer said. “We appreciate people’s interest but know the rules, they are in place for good reasons.”
Broadcast applications represent the third option, A producer can apply a registered insecticide as a spray or bait to control grasshoppers.
“Another question we are getting regards the use of Nolo Bait or Semaspore for control,” Royer said. “Again, these biological treatments are most effective when applied to immature grasshoppers in May or June.”
Royer’s general recommendation to producers is control this late in the season may be justified in improved pasture where hay will be harvested as a cash crop. However, when it comes to grazing, producers should carefully consider the cost of supplying hay versus spraying before making such a decision to treat.
Rates and additional information about all insecticides registered for control of grasshoppers are listed in EPP 7193, “Management of Insect Pests in Rangeland and Pasture,” available online at http://facts.okstate.edu. Additional information is available by accessing EPP 7196, “Grasshopper Management in Rangeland, Pastures and Crops,” also available online at http://facts.okstate.edu.
The Oklahoma Cooperative Extension Service is one of two state agencies administered by OSU’s Division of Agricultural Sciences and Natural Resources, and is a key part of the university’s state and federally mandated teaching, research and Extension land-grant mission.