Cover crops attract pest predators who use pesticides


(Beyond pesticides, Nov. 2, 2021) Cover crops create habitat that attracts pest predators and help mitigate crop damage, according to research published in the journals Agroecosystems and Biological Control by scientists at the University of Georgia. Increased predator diversity can reduce pest pressure that prompts conventional chemical farmers to apply toxic pesticides, and the study authors find the practice to be economically viable in these cropping systems. “There is a change movement underway where growers are thinking more about using natural systems instead of just using pesticides,” co-author Jason Schmidt, PhD said in a press release. “Growers need to use all the tools available to make a profit, so if they can promote beneficial insects in the system to help with pest management, fewer inputs are needed and this should lead to lower production costs. “

To determine how beneficial cover crops were for cotton production, researchers began with two-year experimental crops established in 2016 and 2017 in Georgia. Twelve cover crop plots were established with crimson clover and rye, while an unplanted cover crop plot was used as a control. Researchers planted the cover crop in early November after harvesting the previous cotton crop, and completed and rolled the cover crop 2 weeks before a cotton planting in May. Cover crop residues were vacuumed up with an inverted leaf blower that the scientists created and sampled six times in random locations. An analysis was then conducted on the intestinal contents of the recovered pest predators to determine which pests they were consuming.

Predator communities were found to be much more diverse (7-10 times more) in the covered fields. While the cover crop fields contained a range of spiders and other predatory insects, the control fields mainly contained a specific type of beneficial beetle. The researchers found that the benefits of cover crops were most pronounced in early spring. But as the cover crop degrades, the differences between the cover crop predator communities and the control plots have started to level out.

“Cover crops have advantages early in the season when the cotton plants are small,” said Dr Schmidt. “Cover crop residues form a complex habitat matrix with cotton seedlings emerging from it and there are insect predators that can defend these young plants from pests.” Dr Schmidt says the change occurs when there is more cotton growing above the ground than there is a cover crop. “Later in the season you see similar communities. So even though there is some habitat on the ground from these cover crops, it doesn’t seem to matter in terms of the overall community in the system when cotton plants become the primary habitat available.

A closer look at the results shows that thrips populations, which can often hamper cotton crops in the early stages of growth, are mitigated by increased cover crops. Cover crops also bring predators that hamper stink bug damage to cotton bolls. An economic analysis revealed that cover culture was a cost effective approach comparable in cost to a completely conventional chemical management system. “These results suggest that conventional growers using cover crops could reduce insecticide inputs through natural reductions in pest pressure and, overall, do not incur additional production costs,” reads. one in the Biological Control study.

Scientists say they will continue their work to better understand the complex interactions that occur between pests and predators in cultivated fields. “This is our ultimate goal, to understand how diversity works and the beneficial roles that species play in production systems and to make the best use of these services for production systems, like cotton,” said Dr Schmidt.

The study results are probably not surprising to organic farmers and even many home gardeners who make sure to keep their soil covered with organic matter year round. The key to soil conservation is practices that minimize soil disturbance, increase plant diversity, and continually keep the soil covered with living plants or roots in the soil.

The results of the study are encouraging in the context of a system dependent mainly on chemical inputs. The end of the cover crop used an unnamed chemical herbicide, for example. Although herbicides are intended to target plant material, products like glyphosate threaten a wide range of species. A federal biological assessment released late last year found that glyphosate itself is likely to affect 93% of endangered species. Thus, a range of predatory insects that may have contributed to further or more sustained pest control may have been killed by the use of a chemical to terminate the cover crop. Options for stopping non-toxic cover crops include mowing or using a roller / crimper machine that folds plant residue evenly over the soil surface.

Study after study, the results show that creating a habitat that increases diversity improves plant productivity and reduces the use of toxic pesticides. Conventional cotton production can utilize these practices and see ephemeral benefits, but when properly maintained, these practices decrease pest pressure and create more stable ecological systems that provide long-lasting ecological and economic benefits. To truly break out of dependence on chemical inputs, conventional systems must evolve not only towards cover crop diversity, but also crop diversity in general, as multi-crop farming practices produce higher yields than land. farming in monoculture.

Most organic farmers, required to maintain or improve soil health according to organic standards, already have practices that work with natural systems. Help keep growing organically, so that more farmers adopt these safer practices, buying organic products where possible. To help be part of the organic solution, join Beyond Pesticides today and support our fight to maintain the integrity of organic standards against attacks from the conventional chemical industry.

All positions and opinions not attributed in this article are those of Beyond Pesticides.

Source: Agroecosystems, biological control, University of Georgia press release

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