How To Battle Insects And Disease In Snap Beans

European corn borer damage

The list of insects and diseases that plague processing snap bean growers in the Northeast and upper Midwest hasn’t changed much over the years. Some of the crop protection options, however, are evolving.

In the area of insects, two that continuously show up in snap beans are the European corn borer (ECB) and the potato leafhopper (PLH). According to Russ Groves, a professor in the department of entomology at the University of Wisconsin, these pests are reasonably easy to control with the products currently available. What researchers are trying to do, he explains, is make some inroads and bring more reduced-risk technology into the mix.

Zeroing In On ECB

ECB overwinters in the upper Midwest and has two generations per year. As its name implies, this insect is principally a pest of sweet corn and field corn, and spends its first generation attacking those particular crops.  

The second generation, however, is what concerns snap bean growers. “ECB can get into peppers and other crops, such as snap beans,” explains Groves. “Females will lay eggs on plants at flowering and pin bean stage of development and those eggs then hatch. They don’t cause a lot of overt damage to the plant or significant yield drag, but they have an unlikable behavior of boring into the pods. So when the processing beans go to the plant, the electronic sorters have a hard time kicking out the corn borer-infested beans. One infested bean in a thousand is sufficient to reject an entire load.”

The industry currently bases the timing of insecticide applications on planting date and when the crop is at a susceptible stage for damage. For late-planted beans, for example, which are put in the ground in early to mid-July, the susceptible stage occurs in early to mid-August, when they are flowering and the adult corn borer moths are flying and laying eggs. “It is at the flowering stage when applications of pyrethroids are made,” he explains. “It is a very definable treatment window.”

Some new control options for ECB, however, are being investigated. Reduced-risk products classified as the anthranilic diamides, which includes DuPont Crop Protection’s Coragen, are currently being looked into as possible seed treatment options in snap beans. “Trials that were conducted in Wisconsin in 2010 showed that both rynaxypyr (e.g. Coragen) and the new cyazypyr (e.g. Verimark), both in the above-mentioned class of chemistry, show promise as future potential seed treatments,” says Groves.
“During the past couple of years, we have been looking at seed treatment and in-furrow applications of these products,” he adds. “They are systemically mobile and will move up into the plant. We are now trying to learn how to position them to use in the snap bean IPM program.”

Targeting PLH

Unlike ECB, PLH overwinters in the south and then makes the trek
northward each year. PLH colonizes potatoes, snap beans, and a number of other commodities.

Offering growers a cultural control method, Groves points out that one way to avoid leafhoppers is to plant early. As the pest has to migrate to Wisconsin, leafhoppers often haven’t made their way to the northern area of the country in time to attack the earliest planted snap bean crop.
Pyrethroids provide good control, but Groves says that about 90% of growers now use an at-plant seed treatment such as Cruiser (thiamethoxam, Syngenta Crop Protection). This seed treatment also helps control another key pest of snap beans, seed maggots.

“We look forward to the future possibility of having a snap bean seed treatment premix that contains both cyazypyr and thiamethoxam. And in this instance, several pests — including ECB, PLH, and seed maggots — would be targeted in one seed treatment,” adds Groves. “This area of investigation remains under way and new control options could be available in just a few years.”

Disease Management

In the area of disease control, a couple of the biggest disease threats growers deal with are root rots and white mold. There are some exceptions to that list, though, says Amanda J. Gevens, professor and Extension plant pathologist in potatoes and vegetables in the University of Wisconsin’s Department of Plant Pathology. In very wet years when foliage remains damp for long periods of time, growers will see more bacterial blight and brown spot.

The root rot complex — which consists of the fungal and fungal-like pathogens aphanomyces, pythium, rhizoctonia, and fusarium — and white mold, however, are issues each year. Root rot problems can be an issue early in the season when there is high soil moisture and cool conditions.
Offering some cultural control tips, Gevens says one way to discourage root rot pathogens from taking over fields is to rotate snap beans with small grain crops and cereals, which are not good hosts for the disease. She also says growers can reduce the risk of root rot problems by planting later in the season, such as in mid to late June or into July.

For growers who need to plant early in the season, Gevens advises them to do a shallow seeding, especially if weather conditions are expected to be cooler with high soil moisture (under 55°F). If high-pressure fields are anticipated, she encourages growers to use seed that is treated with a protectant fungicide.

Limit Moisture, Disease

   Moisture also is conducive to white mold problems. To reduce the instance of this soil-borne disease, Gevens suggests that growers keep the plant canopy as dry as possible.

Increasing between-row spacing and situating rows parallel to prevailing winds will also help reduce moisture levels. Growers must also pay attention to their irrigation schedule and avoid overwatering situations, she adds.
Managing nitrogen late in the season is another way for growers to reduce the incidence of the disease. “Excessive nitrogen will create a denser plant and that can help increase leaf wetness under the canopy, creating a good environment for white mold,” warns Gevens.

Chemical Controls

To successfully keep this disease at bay, growers need to have a foliar management plan in place using specific fungicides with strategically timed applications. Gevens says there is a short list of fungicides (thiophanate methyl and boscalid) that are registered and commonly used in Wisconsin for white mold on snap beans.

 The timing of applications, she says, should be at 30% bloom, and seven days later or at 100% bloom. “If growers spray prior to 30% bloom, they will lose quality of control,” she adds.

That short list of products, however, may be growing in the coming years, says Gevens. New chemistries are in the pipeline for white mold control that are anticipated for registration within the next few years. She mentions the fungicide Fontelis from DuPont Crop Protection, which received registration in March, as one of the controls.

“BASF and Bayer CropScience have submitted registrations for new white mold materials in dry beans, that, in time, may have a place in snap bean
disease control,” she concludes. 

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