An unexpected discovery from a new study looking at pest and disease control in New York City's commercial onion fields will allow the state's growers to reduce their use of synthetic chemicals without compromising crops, according to the portal. phys.org.
A study by scientists at Cornell Agriturismo Tech and recently published in the journal Agronomyshowed that by meeting thresholds for determining when to apply insecticides to control onion thrips—a major crop pest—farmers sprayed 2,3 fewer sprays per season, maintaining bulb yield and size. The threshold value is the density of the pest in the crop, which requires measures to be taken to prevent the increase in numbers to a level that will lead to economic losses.
The results of more than three years of field trials have also shown that farmers can use 50-100% less fertilizer without compromising yields.
“The no-fertilizer plots were the same [compared to full- or half-fertilized plots],” said Max Torrey '13, whose 12th generation family farm in Elba, NY, was a trial plot for the study. “People were skeptical, but this data gives us a lot more confidence.”
Growing onions in New York's western climate requires intensive cultivation and is heavily dependent on synthetic fertilizers and pesticides. It is also done exclusively on swampy soils. New York farmers grow almost all of the state's 7000 acres of onions on manure.
Onions are an important food item and are the fourth most consumed food in the US after potatoes, tomatoes and sweet corn. Growers of this crop in New York City have the added advantage of being close to major markets along the East Coast. But diseases and pests, especially onion thrips, greatly affect the profits of onion growers.
Onion thrips, tiny winged insects that feed on onion plants, have been on the radar of Brian Nault for many years. Nault, senior author of the study and professor of entomology at Cornell Agriturismo Tech, said farmers have come to rely on cost-effective weekly insecticide application programs to control thrips. Then, in the late 1990s, insecticide resistance began rapidly developing in thrips, as five to eight generations of the pest can be produced in a year. Thrips also transmit a virus that can kill plants and spread bacteria that cause bulb rot.
To help keep the insecticides effective, Nault calculated thresholds precisely so that onion growers in New York could only spray when the pest population required it.
“The #1 reason farmers use thresholds is to reduce the development of insecticide resistance,” Nault says. - The next new, good chemical agent may not appear until 2025. And we need to act now.”
In their new study, Nault and Carly Regan sought to further refine the onion thrips integrated management strategy. They knew that growers who continued to use weekly spraying programs instead of thresholds were at significant risk, increasing the likelihood of resistance developing. But Nault also found study results showing that reducing the amount of fertilizer can potentially reduce pests on certain crops. He added this factor in test trials.
Nault and his growing partners were amazed to find that the amount of fertilizer applied at planting had no effect on thrips population levels, rot, or bulb size and yield.
“We did not expect this, but it has an even greater potential effect,” Nault said. “Reducing the use of fertilizers in commercial farming is good for the environment in many ways.”
Nault is convinced that if all of New York's onion growers used the thresholds, they would see a cumulative $420 annual pesticide cost savings.