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Pigweed continues to outflank herbicides

TAGS: COTTONHERBICIDEWEEDSDICAMBARESISTANT PIGWEEDCulpepper-PPO-Greenhouse-Pigweed-W.jpgUniversity of Georgia ExtensionPre-emergence, residual herbicides — including PPO products — remain the best frontline defense if activated timely for a sound weed program, but a greenhouse study in Georgia throws caution flags.Scientific evidence collected this year and last confirms Georgia now has a concerning population of pigweed resistant to PPO-inhibitor Group 14 herbicides.

Brad Haire | Nov 11, 2020https://4648f008829c7812f536ae527c9eb0dd.safeframe.googlesyndication.com/safeframe/1-0-37/html/container.html

The plants in the greenhouse looked a little beat up but remained rigidly upright, almost boastful. That was a problem, but not too surprising. The pigweeds showed their natural agility.

Stanley Culpepper, University of Georgia Extension weed specialist, says scientific evidence collected this year and last confirms Georgia now has a concerning population of pigweed resistant to PPO-inhibitor Group 14 herbicides. PPO-resistance has been confirmed in other Southern states.

The plants in the greenhouse were part of a test Culpepper’s graduate student, Taylor Randell, conducted. Seven days prior, one set of plants, which were emerged at the time, was hit with a 125-ounce rate of Cobra with a crop oil concentrate. Another set, again already emerged, received a 240-ounce rate of Blazer with a nonionic surfactant. Another set got a 240-ounce rate of Reflex with a nonionic surfactant. Though stunted compared to the check plants, the tested plants looked OK and ready to continue growth.

Pre-emergence, residual herbicides — including PPO products — remain the best frontline defense if activated timely for a sound management program, he said, but the greenhouse study throws caution flags.

“If we get tolerance, or lose PPOs with our residuals, we will be in big trouble. That is not a place we want to be,” he said.

Research to determine how the pigweed in the greenhouse will respond to residual PPO activity began in November, he said.

Labels Back

With an EPA decision in October, cotton and soybeans growers again have access to use in-season dicamba technologies through 2025. Regulatory access to the technology again is a good thing, he said. Without continued sound weed management decisions, however, the technologies could play out before the labels expire or a court ruling stops them again.

The pigweed has proven again and again its naturally built to outmaneuver herbicides. One pigweed female competing with cotton for the entire season can produce 250 grams of seed, ready to be picked up and blown to the wind. Through natural selection, what if that one female is resistant to dicamba or 2,4-D? Pigweed resistance to dicamba and 2,4-D has been confirmed in Kansas, he said.

Culpepper has a picture he uses to make a point in some Extension presentations. It shows a spot in a field where emerged pigweeds were hit with Roundup plus dicamba. The pigweeds lay dead. But one stands firm, rigidly upright, almost boastful. That picture, he says, says it all.

Culpepper-Pigweed-after-roundup-dicamba-w.jpg
The lone pigweed survives application of Roundup and dicamba in a Georgia field. (University of Georgia Extension)

Numbers Game

It’s a numbers game, and the numbers are in the pigweed’s favor. Studies in Georgia and Tennessee confirm residuals at planting when activated can provide almost 98% control of season-long pigweed management. That’s impressive but that 2% of escapes can total as many as 19,000 pigweed plants per acre that a post application must eliminate, or “pigweed can still eat your lunch,” he said.

Cover crops can further reduce the number of pigweed plants a post application must eliminate. A cover biomass of 4,500 pounds per acre works well but 7,000 pounds per acre works even better to suppress pigweed emergence.

Cotton growers know the mantra, he said, but it is always worth repeating:

  • Pigweed-free at planting
  • Residuals at planting with two effective active ingredients.
  • Sequential post-emergence application.
  • Layby with directed or hooded application.
  • Remove escapes.

The game against herbicide resistance is not going to get easier. Growers carry much of the burden against weed resistance and have done an exceptional job over a relatively short period of time to regain solid ground against pigweed. But resistance is an industry-wide issue. Crop protectant companies, academia and growers, along with science-strong regulatory policy decisions, will need to coordinate resources and information to stay ahead.

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Red-headed cockchafer pasture damage.

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By Spencer Gibbs, Cradle Coast NRM April 17, 2014, 9 a.m.9, 2014

See: http://www.theadvocate.com.au/story/2225468/farmers-learn-new-skills-to-control-pests/?cs=130

WHAT if you could grow more grass, prevent pastures from becoming weedy and patchy and reduce the amount of spraying you do on your property?

You can beat pasture pests by doing a few things differently.

Integrated Pest Management (IPM) in pasture considers biological and cultural control practices to give stable, long-term pest control with minimal chemical support.

Biological measures tend to focus on the natural enemies of the pasture pest species while cultural measures include pasture or grazing management actions taken by the farmer to create an unforgiving environment for the pests.

Jason Lynch from Macquarie Franklin and Cradle Coast NRM are running a series of workshops for graziers in Tasmania’s North- West as part of a Pasture Pests program.

The workshops are designed to assist farmers and graziers in monitoring and controlling pests with minimal costs.

Significant pasture pest infestations can occur every few years.

IPM shows farmers how to look for problems before they start, for example: seeking out adult pasture pests in summer, which then relieves the issue of discovering the problem too late and having little alternative but to spray.

The ryegrass dominant pastures of the Cradle Coast region are susceptible to damage from pasture pests, three in particular: the black- headed and red-headed cockchafers (BHCC and RHCC) and corbie grubs.

When these pests are present in sufficient numbers they can devastate ryegrass pasture and create large areas of bare ground.

These bare areas are vulnerable to erosion and infestation by broadleaf and grass weeds, which reduces pasture productivity and requires the use of herbicides.

Treatment of BHCC and corbie grubs is heavily reliant on the use of synthetic pyrethroid and organophosphate broad spectrum pesticide applications.

Some organophosphates are currently under review and in the future the use of these products may become more restricted.

RHCC can’t be controlled by these methods, because it feeds below ground.

The Pasture Pests program offers the opportunity to reduce reliance upon agricultural chemicals in order to manage these pasture pets, reduce soil erosion and improve pasture productivity.

The first workshop will be run at the beginning of winter, followed by another in spring and then again in autumn 2015.

Participants will visit sites demonstrating the preferable heights that pastures should be grazed, see examples of damage from the previous winter, and also visit demonstration sites that are being used by growers.

The workshops are open to farmers as well as agricultural advisors.

There are limited spaces in the program so early registrations are recommended.

To find out more about the Pasture Pests program contact Spencer Gibbs, Coordinator: Productive Landscapes, at Cradle Coast NRM on 6431 6285.

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