Look out for summer pests

Courtesy photo by Adam Varenhors: An image of the differential grasshopper adult.

Sow and Grow

Hot, dry conditions across much of the state have put stress on crops. Although drought conditions are front of mind for many, we still need to be scouting fields watching for pest issues. Depending on your pre-emergent herbicide activation, you may already have sizeable weeds out in the field ready to be controlled. However, note that spraying during extremely hot conditions can cause drift and efficacy issues with some chemicals- take care to read labels and watch for proper application temperature ranges. For questions concerning what herbicides to use and when to use them, check out the ‘South Dakota Pest Management Guides’ that can be found in print at the nearest SDSU Extension Regional Center or on our website (extension.sdstate.edu – search for "pest guide").

Another pest issue that may be headed our way is grasshoppers. Large grasshoppers can cause economic loss in cash crops and substantially reduce forage yields. Drought conditions tend to make grasshopper infestations worse, as they seek any green plant materials they can find during the growing season. When pastures and ditches begin to dry down, they seek alternative plants as a food source.

Last year, large grasshopper populations caused damage to crops in central South Dakota; a 2020 USDA survey of central and western South Dakota indicated that many areas experienced populations above the threshold of eight grasshoppers per square yard. Considering the grasshopper pressure in 2020, populations in 2021 could be a serious issue in these areas again.

There are two methods that can be used to scout for grasshoppers to determine if they are at or above threshold. The first is visual count; estimate a square yard in front of you and count the grasshoppers jumping out of the area while you slowly walk towards it. The second is a sweep net method; use a 15-inch diameter sweep net and capture grasshoppers in four pendulum swings over about one square yard – count the grasshoppers in the net.

Regardless of the sampling method, it is best to repeat it several times in a pattern throughout the field, and then use your counts to calculate an average. The action threshold for grasshopper populations is 15-20 nymphs (immature insects) or 8-10 adults per square yard (USDA). SDSU recommends scouting for both nymphs and adults in field margins and within fields. In field margins, management should happen when nymph populations reach 50-75 per square yard and when adult populations reach 21-40 per square yard. Within the field, consider management when 30-45 nymphs per square yard are found or when there are 8-14 adults per square yard. If these thresholds are exceeded, an insecticide should be considered.

More specifically, in corn, watch for silk, ear tip, or developing kernel feeding – if this is happening insecticide management shoul.d occur. In soybean, if grasshoppers have caused 20% defoliation or more after flowering, or if pod feeding is occurring on developing pods, insecticide management is recommended. In range and pasture lands with large infestations, spreading poison grasshopper baits or baits containing the Nosema locusta spore can be used to reduce populations. If grasshoppers are still growing (early in the season), an insect growth regulator containing deiflubenzuron may be used to inhibit grasshopper development; note, this has no effect on adult grasshoppers. For a current list of pesticides appropriate for grasshopper control, see the SD Pest Management guides mentioned previously.

While we’re talking about pests, note that the annual pesticide container recycling days are coming up across the state beginning in July. This program is free to producers who bring in empty, triple rinsed pesticide containers to the appropriate local pick up site at the specified time frame. To see the full list of pick up times and locations visit danr.sd.gov and search ‘Pesticide Container Recycling Program’.

Resource: https://extension.sdstate.edu/will-grasshoppers-be-issue-2021

Upcoming Events and Announcements

• South Dakota Grazing Exchange – Short on grazing forage or hay? Check out the SD Grazing Exchange powered by the SD Soil Health Coalition. This free resource connects forage producers and livestock growers together across the state. www.sdgrazingexchange.com

• Summer Small Grain Variety Tours – SDSU Extension will host small grain variety tours beginning June 17 in Ideal with various location and dates to follow. Visit Extension.sdstate.edu/events for a full listing of locations and times. There is no cost or registration required.

• 2021 Garden Hour – every Tuesday evening from 7-8 p.m. CT through Sept. 28, join the SDSU Extension Horticulture team virtually to discuss garden and landscaping questions virtually. Register at extension.sdstate.edu/events. No registration fee.

• June 28, Drought Hour – 11 a.m. This webinar will include ‘Summer Drought and Climate Update’ as well as ‘Nitrate QuikTest for Standing Forages’ talks. Free to the public, sign up at extension.sdstate.edu/events.

• July 6, Summer Farm Stress Series – SDSU Extension is hosting a summer farm stress webinar at noon the first Tuesday of the month through September. This series is geared for producers, their families and the general public who might have an interest in supporting our rural communities. There is no cost; register at extension.sdstate.edu/events.



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