Pesticide resistance highlighted at field day

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(02/15/18) DELHI, La. — More than 100 agricultural producers heard from LSU AgCenter experts on how to manage for herbicide, insecticide and fungicide resistance at the Northeast Louisiana Crops Forum held Feb. 8 at the Delhi Civic Center.

AgCenter entomologist Sebe Brown said farming may get harder before it gets easier.

Insecticides are not 100 percent effective, and insect resistance is a growing concern, he said.

New insecticides are rare, and no new modes of action have been developed in nearly a decade, Brown said, adding that any new technologies will not be released for five or six years.

Brown urged growers to rotate insecticide chemistries with different modes of action to help preserve the current products.

Beneficial insects don’t get enough credit and can reduce reliance on insecticides in cropping systems, Brown said.

“If you can get free control from Mother Nature, I would welcome any help I could get,” he said.

To combat tobacco thrips, cotton growers will need to add an imidacloprid seed treatment, Brown said. He also advised against using pyrethroids on plant bugs and boll worms.

If Mother Nature were going to put resistance in a perfect weed, it would be Palmer amaranth, AgCenter weed scientist Donnie Miller said.

“Once it gets in your field, it just takes over,” Miller said.

Palmer amaranth is a prolific seed producer and can produce 200,000 to 600,000 seeds per plant, so control becomes a numbers game, he said.

Herbicides do not cause resistance in weeds, Miller said, but repeatedly applying herbicides with the same mode of action increases the problem.

“You have to overlay residual herbicides to essentially never let this plant get off the mat,” Miller said.

In cotton and soybeans, Miller recommended rotating herbicides with different modes of action no fewer than 10 days between applications to prevent the weed from ever producing seed.

Sometimes you have to get completely out of a crop for a year in order to select a mode of action that will give you that control,” he said.

AgCenter plant pathologist Trey Price said producers should be conservative in their approach to disease management in light of low commodity prices and fungicide costs.

Price said knowing which fungicides are applied to seed is important and told farmers to avoid planting “naked cotton seed.”

Base fungicide treatments are usually sufficient, and there is no need to over treat seed unless a specific treatment is not already applied by the company, he said.

Northern corn leaf blight, a foliar disease that has caused problems in corn over the past two years, can become a yield-limiting issue and can be managed by avoiding the use of susceptible hybrids and not following corn with corn in minimum or no-till situations, Price said.

The top 15 soybean-producing parishes in the state, many of which are in northeast Louisiana, fall short when it comes to maintaining soil fertility, AgCenter soybean specialist Todd Spivey said.

“This has been a trial by fire year,” he said, citing issues with redbanded stink bug, green stem syndrome and weather-related factors that affected some seed quality.

Spivey cautioned growers to soil test on a consistent basis and follow fertility recommendations to avoid mining essential nutrients from the soil.

Spivey said soil testing every three years is recommended, but pulling soil samples every two years is better, and every fall is optimum.

Because soil types can change many times within a 20-acre block and different soil types affect nutrient availability, Spivey suggested using a grid-sampling method to pull samples from 2- to 5-acre blocks within a field to get truly representative samples.

AgCenter agronomist Josh Copes said drill seeding will establish a more uniform stand and reduce seed waste when planting cover crops.

“One of the biggest problems in the fall is glyphosate-resistant Italian ryegrass,” he said.

Copes discussed a series of protocols with fall-applied residual herbicides to combat resistance in Italian ryegrass and other broadleaf weeds that become a problem at termination.

On four cover crop species, including cereal rye, tillage radish, crimson clover and winter pea, Copes said Zidua application resulted in little to no injury, reduced weed pressure in the cover crops and improved cover crop ground cover.

Copes said late cover crop termination is more difficult to control and recommended cover crops be terminated four to six weeks before planting the cash crop.

AgCenter extension agent Dennis Burns said crop yield maps are a scorecard for showing profitability within field management zones.

“Every field is not the same and will not yield the same,” Burns said.

Yield maps are used to divide fields into smaller units to reflect zones that need specific management and allow producers to improve control to match yield goals to inputs and maximize both yield and revenue potential, he said.

“It doesn’t save you money; it makes you money,” Burns said.

Establishing management zones is a long-term project that becomes more refined and stable over time, he said.

AgCenter extension agent Carol Pinnell-Alison provided updates on Worker Protection Standards that were fully implemented beginning Jan. 1, 2018.

Pinnell-Alison reminded producers that Louisiana Department of Agriculture and Forestry officials may begin random selections for on-farm inspections to ensure compliance.

She discussed expanded consideration and exemptions for immediate family workers, record keeping and information exchange, new posting requirements and spray drift management guidelines.

Pinnell-Alison also reviewed stewardship recommendations for pollinator health and urged producers to work with hive owners to avoid pesticide application that could result in bee kills.

AgCenter associate vice president Rogers Leonard said three key agriculture positions will soon be filled in cotton production, entomology and soil health to provide much-needed assistance in the region.

Remissioning efforts among extension agents will increase communication and focus on agronomy, animal science, horticulture, and forestry and wildlife throughout the state, Leonard said.

LSU AgCenter weed scientist Donnie Miller talks about herbicide-resistant weeds at the 2018 Northeast Louisiana Crops Forum held Feb. 8 at the Delhi Civic Center. Photo by Karol Osborne/LSU AgCenter

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