Herbicide carryover a concern for vegetable growers

The reality of herbicide resistance has created the need to use multiple modes of action on large acreage row crops and the side-effect has created some management challenges for vegetable farmers, who also grow grain, cotton and peanuts in the Southeast.

Speaking at the recent Southeastern Fruit and Vegetable Growers annual meeting, University of Georgia Weed Scientist Stanley Culpepper said carryover is THE single biggest weed control issue that vegetable growers in the Southeast will face in 2009.

While there are a number of excellent new herbicides available to growers, most have come from cotton, grain or other large acreage crops. Though these new herbicides have a different name, often slightly different formulations, if the mode of action is the same — the risk of resistance is the same.

“Sinbar is a really good herbicide for watermelons — either seeded or transplanted. At 2-3 ounces per acre, it is low volume and can be broadcast directly onto plastic row covers. This allows growers to wash off the Sinbar and transplant. It’s very economical, very easy to apply and provides over 90 percent control of Palmer pigweed in some situations.

“The problem comes with the two-year carryover restriction of Sinbar. On some crops, like corn, oats, wheat and even squash, there may not be much damage. However, on collards, six months after Sinbar use, we have seen the whole crop killed,” Culpepper says.

He notes that Sinbar is not generally recommended as a stand-alone product, rather an excellent complement to ongoing weed control herbicide programs. One of the most common comibinations is Sinbar and Curbit.

“Sinbar is a good product, almost an ideal herbicide tool for vegetable growers, but growers must understand the rotational limitations, otherwise they risk big problems with crop failure and further restrictions for use,” Culpepper adds.

Reflex is another very effective weed management tool for vegetable growers. Ever increasing resistance by Palmer pigweed to glyphosate herbicides has spiked the use of Reflex in cotton and other crops. Culpepper points out that over 300,000 acres of cotton in Georgia alone was treated with Reflex in 2008.

On snap beans, Reflex is highly effective when applied at 12-16 ounces per acre applied within one day of planting. It is important to irrigate within two days after application.

Growers should avoid application in times of heavy dew and high temperatures and should apply Reflex to snap beans only after plants reach the two-leaf stage.

With so many acres of cotton treated with Reflex, and cotton coming and going out of production so rapidly these days, it is especially critical that vegetable farmers growing crops on new land know the history of this land.

“Reflex on vegetables is a phenomenal herbicide, and when you hear me say a product is phenomenal, you can know that means you have to be careful about rotation and carryover,” the Georgia specialist says.

While new products are coming into vegetable production, others are going out of the market. Registration for Alanap, a long-time successful vegetable herbicide will not be renewed for use on vegetables. Culpepper says the last supply will be available in 2009. Chemtura Chemical Company, marketers of Alanap, contends the vegetable registration is not economically feasible at this time. A spokesperson for the company also adds that the three-year shelf life is only under ideal storage conditions and that growers may want to use supplies no later than the 2010 season.

Vegetable growers may have a new soil fumigant, Paladin (dimethyldisulfide) in 2009, if label clearance goes as expected. This product will provide excellent control of nutsedge. It will need help with some annual weeds common in the Southeast, so new herbicide programs will be needed to go along with Paladin.

Paladin is a novel pre-plant soil fumigant for the treatment of weeds, soil-borne plant pathogens and nematodes in soils to be planted with vegetable and fruit crops where plastic-culture is used for fumigation.

Select Max, a relatively new grass herbicide brings a subtle, but potentially important, new twist to grass control for vegetable growers. The advantage for Select Max is that it allows growers to use a crop surfactant versus a crop oil in the tank-mix.

The combination of Select Max and a crop surfactant gives vegetable growers the best opportunity to control grass with the least risk of crop injury.

Poast and Select are both good grass herbicides, but control is reduced when tank-mixed with a crop surfactant. The new formulation of Select Max allows growers to avoid crop foliage burn, if that is important, says Culpepper.

“The next 3-5 years should be exciting for vegetable growers because of the new tools that are coming your way. The critical issue is to understand the potential crop injury issue with rotation. It will be absolutely critical to know the rotation liabilities with these new products to vegetable production,” Culpepper stresses.

Though knowing the mode of action of the herbicide and the herbicide history of the land is the best way to avoid carryover problems, there are some common-sense tips that can help in making herbicide use and weed management decisions, including:

• Apply labeled rates and follow rotational restrictions. Exceeding the rates listed on the label is illegal and can result in herbicide persistence. Crop rotational restrictions for particular herbicides can vary by application rate and timing, geography, and soil type and pH, so be sure to read the label thoroughly.

• Keep future cropping plans in mind when planning herbicide programs. Avoid the use of long-residual herbicides when including sensitive crops in the rotation.

• Note climatic conditions from the time between herbicide application and the next crop. Low moisture and temperature, in particular, can slow herbicide degradation and increase the risk of crop damage.

“Third party state labels held by the Georgia Fruit and Vegetable Growers Association (GFVGA) will bring a number of new products (15 or more) to growers in Georgia. Whether or not these can be extended to other states, via state labels and managed by the Georgia Fruit and Vegetable Growers Association is not clear.

For Georgia growers it is important to have third party labels on hand when the product is used. And, it is critical for growers to support management of these labels by the GFVGA. Without financial support, the association will not be able to continue this program for growers,” Culpepper says.

One product currently available to growers through the third party program is Chateau. This herbicide is especially good for control of purslane and pigweed — two of the biggest and most difficult weed problems faced by vegetable growers in the Southeast.

In addition to new vegetable labels, Chateau is labeled nationally for use on alfalfa, asparagus, blueberries, corn, cotton, potatoes, grapes, onions, stone fruit, strawberries and tree fruit and nuts.

In addition to pigweed and purslane, Chateau has shown efficacy on controlling chickweed, lambsquarters, fleabane, henbit, marestail, morningglories, nightshade, wild mustard, and selected annual grasses.

Culpepper stresses Chateau cannot touch the mulch when used on vegetables grown under plastic, because the material will not wash off the plastic.

The high cost of herbicides, combined with the small market nature of vegetable herbicides make it essential for growers to use weed and grass control materials wisely to insure future availability of these valuable tools.

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TAGS: Vegetables
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