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Used in cuisines all over the world, onions are known for either their sweet and savory flavor or strong and pungent flavor that enhances dishes from casseroles to curries. Consumers in the U.S. eat a lot of onions — this vegetable only trails potatoes, tomatoes and sweet corn in popularity, according to the Cornell Chronicle.
Bulb onions can be cultivated in almost all parts of the country, professor of entomology at Cornell AgriTech Brian A. Nault told EcoWatch in an email.
Nault is the senior author of a new study, “Impact of Reducing Synthetic Chemical Inputs on Pest and Disease Management in Commercial Onion Production Systems,” published in the journal Agronomy.
Nault told EcoWatch that most of the bulb onions produced in America are grown in Washington, Oregon, California and eastern Idaho. On the East Coast, onion production is concentrated in New York and Georgia.
They may be easy to grow, but onions are also susceptible to common insects that enjoy them as much as we do.
“As onions’ leaves expand, they may be found by tiny onion thrips, which suck sap from onion leaves. These are hard to see because they hide down in the folds and neck of the leaves,” warned Bonnie Plants.
In addition to consuming the onion plants, thrips carry a virus that has the ability to kill onions and spread bulb-rotting bacteria, the Cornell Chronicle reported.
According to SFGATE, natural methods — such as spraying the plants with water, surrounding plants with mulch, planting crops like vegetables, herbs and flowers around the onions or using a nitrogen-based fertilizer — may be used to deter thrips.
Nault told EcoWatch that the natural methods he and his team have tested haven’t proven as effective as synthetic chemicals in keeping down population numbers of onion thrips.
“Members of my research program and I have investigated many natural alternatives to synthetic pesticides for onion thrips control in onion that might be easier on the environment. Unfortunately, none have proven as effective as some [of] the best synthetic pesticides except spinosad (Entrust SC), which is an OMRI-listed product that can be used in organic onion production. We have evaluated reflective mulch, straw mulch, onions bred for thrips suppression and naturally occurring biological control. In a few cases, we have seen slight reductions in onion thrips densities using these alternative practices, but in most cases they have either failed or have been inconsistent,” Nault said.
The study found that when farmers used “action thresholds” — the density level of a crop pest at which the population needs to be controlled in order to keep it at a level that doesn’t result in economic loss — and applied insecticides 2.3 fewer times to control onion thrips; onion bulb size and yields were maintained, reported the Cornell Chronicle.
Following three years of trials in the field, the researchers found that 50 to 100 percent less fertilizer could be used without a reduction in crop yields.
“Plots with no fertilizer had no difference [compared to plots with full and half amounts],” said Max Torrey, whose 12th generation family farm in Elba, New York, was one of the study’s trial sites, the Cornell Chronicle reported. “People were skeptical, but this evidence gives us a lot more confidence in what we need to use.”
Almost all of the 7,000 acres of New York’s dry bulb onions are grown in the fertile “muck soil” of drained swamps. The climate of western New York demands rigorous cultivation for growing onions, and farmers use a great deal of synthetic chemicals like pesticides and fertilizer on their onion crops.
“Muck soil is an excellent soil type for growing onions. However, there are other soil types that are also very good for growing onions (e.g., sandier soils). For example, most onions that are grown in the western U.S. are not grown on muck soils,” Nault told EcoWatch. “[M]uch less synthetic fertilizer is needed to grow onions in muck soil, but completely eliminating fertilizer will not likely be the answer long term.”
Though onion growers in New York have a geographical advantage in being close to sizable East Coast markets, demand, growing conditions, pests and diseases factor into their profits each year, reported the Cornell Chronicle.
“[T]he use of synthetic chemicals [is] still necessary for most NY onion growers to produce a profitable onion crop. This is especially true for large-scale commercial production of bulb onions because they are grown in large monocultures and there are many weeds, insects and diseases that negatively affect onion,” Nault told EcoWatch.
Nault said that beginning in the late 1990s, onion farmers depended more and more on insecticide spray programs to keep the numbers of onion thrips down, the Cornell Chronicle reported. Then, thrips quickly became resistant to the pesticides.
In order to maintain the efficacy of the insecticides that are still being used, Nault has been adjusting the action thresholds so that onion farmers in New York can spray only when needed, while continuing to be profitable.
“By reducing the frequency of insecticide applications in general and reducing the use of each insecticide in particular, resistance development in thrips populations should be mitigated. Essentially, the goal is to minimize the probability that an onion thrips mutates giving it the ability to resist a particular insecticide active ingredient,” Nault told EcoWatch. “Let me use a baseball analogy. If a pitcher only throws fastballs to a batter, eventually that hitter will learn to hit a fastball. However, if you throw fastballs, sliders, change-ups, splitters, etc. and mix them up when throwing to the batter, the batter will have a much lower chance of hitting any of the balls. And if you never throw the ball, the batter can’t hit it!”
Resistance to insecticides is so prevalent that it incentivizes farmers to employ action thresholds in their cultivation management practices.
“The No. 1 reason farmers give for using action thresholds is mitigating the development of insecticide resistance,” said Nault in the Cornell Chronicle. “The next new, good chemical tool may not come until 2025. They can’t afford to lose this one.”
Nault discovered studies showing that using less fertilizer had the potential to lower the number of pests in some crops and decided to add that factor to the study’s test trials.
Nault and the onion growers involved in the study found that it didn’t matter how much fertilizer was applied to an onion at the time of planting. The number of thrips, size of the onion bulb, bulb rot and overall yield were not affected.
“We didn’t expect this, but it has an even bigger potential impact,” said Nault, as reported by the Cornell Chronicle. “Reducing fertilizer use in commercial farming is beneficial to the environment for so many reasons, especially water and soil health.”
Each year, $420,000 in the cost of pesticides could be saved by onion growers in New York if they used action thresholds, Nault said. Nault has seen a number of onion growers cut down their use of fertilizers from 25 to 50 percent, instead of applying a standard amount to each field.
“[T]he most effective sequence of products was combined with the use of action thresholds to optimize onion thrips control. Rather than spraying onions weekly with insecticides, onion growers have reduced the number of applications substantially,” Nault told EcoWatch.
Using less synthetic chemicals on onion crops has a host of ecological benefits.
“Reducing the use of synthetic pesticides can benefit the environment by conserving non-target organisms. Examples may include beneficial insects that feed on insect pests that live either above or below ground. In some cases, a reduction in pesticide use may improve soil health by conserving microorganisms and arthropod fauna in the soil. Other benefits could include reducing runoff of pesticides into water systems that could be detrimental to aquatic organisms,” Nault said.
Torrey explained that, although taking soil samples and looking for thrips requires more work, he expects to save a minimum of $100 per acre in the cost of synthetic chemicals on 2,200 acres of onion crops, not to mention the benefits it has for the environment, the Cornell Chronicle reported.
“The muck is our livelihood and our future,” said Torrey in the Cornell Chronicle. “We must take care of it. Now we finally have a proven way to reduce costs and make New York onion growers even more competitive and sustainable.”