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Following Soybeans with ‘Flowers

Thursday, November 13, 2003
filed under: Rotation

A change in the federal crop insurance rules allows sunflower to be grown on fields planted to soybeans, dry peas, and lentils the previous year. Thus, acreage planted to soybeans, dry peas, and lentils in 2003 can be planted to sunflower in 2004, without affecting federal crop insurance coverage.

This change applies to all sunflower-producing states. Insurance restrictions remain when the previous crop is canola, crambe, dry beans, mustard, rapeseed or safflower. Sunflower planted on acreage where any of these crops were planted the previous year will not be eligible for federal crop insurance coverage.

The rotational restriction was in place primarily because of a concern about the risk of Sclerotinia. However, while growing sunflower after corn or small grains is still preferred, the disease risk in sunflower is less following pulse crops or soybeans compared to canola, crambe, dry beans, mustard, rapeseed and safflower.

And if weather conditions are favorable for Sclerotinia, the disease may take hold no matter what crop precedes sunflower.

John Sandbakken, who follows crop insurance issues for the National Sunflower Association, says the USDA’s Risk Management Agency made the policy change since head rot is caused primarily by windborne ascospores.

Thus, Sandbakken says it didn’t make sense to restrict the planting of sunflower after pulse crops, when the biggest risk of Sclerotinia head rot in sunflower is when weather is conducive for the development and spread of these ascospores, which may be blown in and infect sunflower regardless of crop rotation.

According to the North Dakota State University Extension Service bulletin on Sclerotinia head rot in sunflower (posted online at “Rotation is not as big a factor for reducing head rot as for reducing stalk rot. Spores that blow in from some distance can cause head rot on sunflower, even though it may be planted in a field with no broadleaf crop history at all. Rotation will not prevent head rot in sunflower but will be beneficial for other reasons.”

NDSU still recommends a minimal crop rotation interval of three or four years from highly susceptible crops such as crambe, canola, and dry beans.

Weed control benefit, N credit

In the absence of weather conditions favorable for disease, there is no risk in sunflower yield or quality planted on the previous year’s soybean ground, says NDSU extension agronomist Duane Berglund. In fact, there may be an agronomic benefit.

“Weed pressure should be greatly reduced following Roundup-Ready soybeans, or Roundup-Ready corn for that matter. It would clean up some of those perennial weeds in particular, especially Canada thistle."

Berglund says sunflower would also take advantage of a 40-lb/ac nitrogen credit following soybeans, peas, or lentils.

In the High Plains, much of the soybean acreage is irrigated. The revised federal crop insurance rotation rule allows High Plains growers greater planting flexibility in adding sunflower to their crop mix, and reduce water use and pumping costs at the same time.

Sunflower uses as much or more soil water as other crops, but uses about 15-20% less water than corn, and does well in dry conditions due to its deep, aggressive root system. Thus, more irrigated crop producers in the High Plains are growing sunflower under limited irrigation, prewatering if need be prior to planting, and watering again at stand establishment, just prior to flowering through seed fill.

Alternatively, some crop producers in the High Plains are combining irrigation and dryland farming on the same acreage: irrigating soybeans or corn, for example, then coming back the following year on the same ground and growing dryland winter wheat, sorghum, or sunflower.

Colorado State University extension agronomist Ron Meyer says that in all of the years he has been involved in production agriculture in eastern Colorado, he has seen white mold in sunflower only once. “It was sunflower following pinto beans, and there was excess irrigation and excess fertilizer applied to the sunflower crop.”

Still, Meyer advises not straying too far from the rotational rulebook. “Leave the soybean stubble stand and plant sunflower back into it the following spring. I would probably advise planting oils over confection. And if you follow soybeans with sunflower, do it only one cycle, then rotate a grass back into the mix.”

Berglund stresses too that while the new federal crop insurance rule allows sunflower to be planted following soybeans or pulse crops, granting greater planting flexibility, it should be viewed as a short-term rotation option.

“If you’re going to follow soybeans with sunflower, I’d like to see a grass crop back in the rotation after that, like barley if you don’t have good soil moisture recharge, or wheat or corn if you have good recharge.”

The USDA’s Agricultural Research Service in Fargo, working cooperatively with NDSU and South Dakota State University, has been testing sunflower hybrids to analyze genetic resistance to Sclerotinia head rot. Plants are inoculated with disease fed by a mist irrigation system, and evaluated for Sclerotinia disease resistance.

This year, USDA-ARS also initiated evaluation of sunflower hybrids for susceptibility to Sclerotinia wilt (root rot). Testing took place at three N.D. locations (Mapleton, Wahpeton, Carrington) Fisher, Minn., and Brookings, S.D.

Ultimately, the evaluation of experimental and commercial hybrids for both Sclerotinia head rot and wilt will provide farmers a good barometer of tolerance levels, according to Jerry Miller, USDA research geneticist.

Miller says researchers involved in the hybrid analysis are still refining protocol for reporting hybrid evaluation results. He advises farmers interested in planting sunflower on last year’s soybean or pulse ground, or who are otherwise concerned about Sclerotinia stem or root rot infection, to consult with commercial seed representatives about hybrids which provide the best tolerance. – Tracy Sayler

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