Comparing the pest-management power of conventionally grown cotton and organically grown cotton is like pitting the New York Yankees against local Little Leaguers.
Conventional cotton has genetic traits incorporated into its seeds that control crop-decimating bollworms and tolerate herbicides. Organic cotton has neither.
Conventional cotton has selective insecticides available that target the key economic pest of the crop – lygus bugs – while preserving the beneficial insects that control whiteflies, mites and other secondary pests that can flare up and harm the crop.
Organic cotton has a limited list of insect-killing soaps and oils that can be used on the crop and none of them are selective. Even if they do kill lygus, which is an open question, they also kill the beneficials that protect cotton plants from other pest insects.
Yields are higher in conventional cotton, and fertilizing conventional cotton is much easier and cheaper.
Terry Button grows organic cotton. He has his reasons.
“It’s a valuable rotational crop in our organics program,” explained Button, who farms about 4,000 acres south of Phoenix, Arizona. “It’s a way to manage our water resources and generate income in the summer to supplement the winter vegetables that are our primary cash crop.”
About 800 of Button’s 4,000 acres are certified for organic production, and many of those acres sat fallow in summer before he started planting cotton about six years ago. He’s applying a combination of neem oil and molasses to try to manage lygus and hasn’t had too many whitefly or bollworm problems.
“The molasses mixture is supposed to discourage lygus feeding but I’m not sure it works,” he said.
To answer that very question – and to potentially help other organic growers incorporate cotton into their rotations – Macey Keith, a University of Arizona assistant in extension, is using a Western IPM Center grant to gauge the effectiveness and cost-effectiveness of bio-insecticides in controlling lygus. She’s planted research stands of organic cotton in Yuma and Maricopa to test the products.
“To measure their efficacy, we do sweeps to measure the population of lygus in the fields and if it’s reached the standard threshold for treatment we spray the field,” Keith said. “We have plots within the fields where we apply different products or different concentrations, then we do sweeps again at one day, three days and seven days after application and count the insect pests and beneficials in the cotton.”
Once the numbers are counted (and they haven’t been yet) Keith’s goal is to be able to tell growers like Button definitively if and how well the organic soaps and oils work, and at what level of lygus infestation they’re worth applying.
“It’s taking the efficacy data and applying it to an economic injury level for organic cotton because we don’t have that,” she said. “That would determine thresholds, and we could have a higher tolerance to lygus in organic cotton because of the lack of efficacy in the products.”
One interesting and potentially important difficultly in Keith’s research is, ironically, attracting enough lygus into her research plots to then try to kill.
“Peter Ellsworth says no self-respecting lygus bug would be caught dead in my fields,” she said, referring to the University of Arizona entomologist who developed the integrated pest management program that’s so successful in conventional cotton. “And he’s not wrong, even if it hurts my feelings a little bit. In organic practices, we’re limited to the nitrogen sources that we can use and what’s available has a really high dollar cost. And strictly due to budgets, we can’t provide that organic nitrogen to match that of a conventional nitrogen source.”
So her fields, while green and flowering and producing bolls, don’t have the dense verdant canopy, flower or boll production of nearby conventional cotton stands. Yields would be in the two-and-a-half bales an acre range rather than the four-plus bales-an-acre of a good conventional cotton field. Keith’s organic cotton fields are, effectively, slim pickings for lygus who have bountiful buffets nearby.
And that may be Arizona organic cotton’s saving grace.
Because the conventional IPM system controls cotton pests so well on an areawide basis, and because the price premium organic cotton can fetch offsets lower yields, growing organic cotton might just pencil out nicely – even if the organic insecticides don’t work well at all. Keith’s research could eventually develop the integrated organic management system that makes organic cotton economical to grow and boosts domestic production of the valuable crop.
“In Arizona, we have 20,000 acres of certified organic land growing vegetables and other field crops,” she said. “With the low insect pressure, areawide IPM, and with the genetic technologies and selective chemistries controlling insects in the conventional acreage, I feel like organic land in Arizona is ready for optimization. Organic cotton could be the crop that gets us there.”