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Sulfur shortage, weed control
complicated by influences of drought

Aug. 30, 2012 | 0 comments

The increasing deficiency of sulfur on crop land, weed control during periods of drought, and the choices and effectiveness of herbicides were among the topics considered by speakers at the annual agronomy field day on Montsma Farms.

The event was sponsored by AgriPartners Cooperative and the Extension Service.

Even before the effects of the drought during the first half of the 2012 growing season became noticeable, the lack of sulfur in alfalfa fields stood out with short and yellowed plants on hilly spots and with yields only about one-half of average, AgriPartners agronomist Brian Madigan observed.

As has been documented in national data, the annual atmospheric deposits of sulfur in the area have fallen by about 10-15 pounds per acre in the past 25 years, Madigan pointed out.

Because the sulfur is carried in rain and snow, a shortage of these aggravates the problem, he noted.

In addition, Madigan continued, sulfur and nitrogen tend to mirror one another in availability through natural processes. Two of the parallels are that both of them can leach and that both are also crucial nutrients for corn and alfalfa, he indicated.

The downturn in the volume of sulfur, much of it as a byproduct of industrial smokestacks, that's available from the atmosphere means that another source is needed, Madigan explained.

Among the readily or regionally available sources for supplementing alfalfa with 40-50 pounds per acre are the quite expensive ammonium sulfate (100-200 pounds of product per acre), pelletized gypsum (an application rate of 300 pounds per acre of a product costing $120-$130 per ton), and byproducts of coal plant scrubbers ($20 per ton plus the costs of trucking and application), he said.

Liquid ammonium sulfate is another choice but it needs to be placed away from the seed rows or at rates of 5-10 gallons per acre as a sidedress application in corn, Madigan continued.

He also listed manure as another source both for sulfur and organic matter and noted that a gypsum application should be sufficient for two years on alfalfa.

In other observations from a service area that straddled the parts of Wisconsin that suffered moderately or severely from the effects of the 2012 drought and those which incurred relatively minor effects, Madigan mentioned how the abnormally early growth of weeds supported insect infestations.

He also noted the lower draw on fertilizer resources by crops during the drought, and the recent and rapid onset of anthracnose in corn whose roots are in dry soil.

In his view and experience, rain showers briefly broke up the life cycle of this year's plague of spider mites in soybeans and insecticide and miticide applications were effective for no more than 7-10 days.

Weeds Thrive in Annual Crops

The 2012 growing season was ideal for weed growth in annual crops, according to Extension Service weed management specialist Vince Davis.

He noted that the previous emphasis on weed resistance to glyphosate during his tenure had to be redirected during "a year you want to forget" and that was highlighted by "dismal weed control" in too many corn and soybean fields.

Without moisture to activate the ingredients of pre-emergent herbicide applications, only about 30-50 percent of the anticipated weed control occurred, Davis reported.

He acknowledged that the experience with the drought knocked the wind out of the standing recommendation, at least for this year, for residual products to control weeds early in the growing season.

Some weeds that began growing very early were very big and hardened by the time a herbicide was applied, dandelions were a serious problem on no-till land, and some weed seeds germinated outside of their normal time because of a lack of moisture for a couple of months, Davis stated.

If nothing else, he remarked, it is relatively easy this year to visually correlate crop yields with weed concentrations. Grassy weed species, lambsquarters, ragweed, and velvetleaf being the most prominent, he said.

Field Visits Sought

As a more direct followup to the 2012 experiences with weed control, Davis's graduate research assistant Ross Recker has been traveling the state since mid-July to gather more information on late-season weed escapes.

He's also looking at weed control comparisons on the use or non-use of atrazine, to monitor the increased use of glyphosate as the only mode of action, to identify geographic trends, and to collect seeds from suspicious weed plants that might indicate resistance to a herbicide.

Recker told the attendees that he has visited more than 100 fields, most of them in the western and central parts of Wisconsin.

Wishing for inclusion of the eastern counties, he's asking farmers there to identify one of their fields with weed control failures and to call him at 608-262-1392 or to send an e-mail to rrecker@wisc.edu.

To take part in the inspection, cooperating farmers will also be asked to complete a brief survey about the problem field(s), Recker stated. The survey form is available on the http://www.zoomerang.com/Survey/WEB22FSESTMEKJ web site.

Cover Crop Strategies

Despite the new dimension in the attention to weed control, Davis said the most questions posed to him in recent weeks have involved the growing and handling of cover crops this fall and next spring.

He said the first point in addressing that topic must be distinguishing between the intended use - either for harvesting as feed or merely as a crop for covering the soil to control erosion and provide organic matter and perhaps some nutrients.

If the intent is to harvest the crop, one needs to be aware of and honor the restriction, possibly of up to 18 months, that was attached to a herbicide applied to a previous crop, Davis stated.

In all cases, observe the labeling instructions on the product which was used, he stressed.

When the restriction on followup crops is relatively short term, there might still be some concern about herbicide carryover to what is planted in the spring of 2013, Davis observed.

He explained that a combination of warm and fairly wet weather during the coming months would alleviate most of those concerns.

Following the labels and the charts that identify restrictions pertaining to certain crops is crucial but, for the most part, "we're not at a point yet of changing crop rotations," Davis remarked. "But flexibility will help if you can switch crops in fields."

Weed Pressure in Soybeans

Weed control was fairly good in corn this year but this was not true in many cases with soybeans, Syngenta Crop Protection's regional agronomist Jeff Laufenberg reported.

He said this was due to an absence of rain for a long time after the soybeans were planted and in cases when weed control was attempted with one application of glyphosate.

What stood out in 2012 was the employment of a two-pass herbicide application on soybeans, Laufenberg pointed out.

Within that strategy, he said the best results on timing and for control of the entire spectrum of weeds was to have the first of the two passes consist of a non-glyphosate product - a tactic that was effective in dealing with broadleaf weeds.

Laufenberg's Syngenta colleague Justin Hopf shared a variety of updates on the company's products, including the planned introductions in 2013 of a non-GMO drought tolerant corn, which has a combination of a dozen traits and of a trait containing a higher dose of corn rootworm control.

He also cited a difference of about eight percent in the plant population, due to a black cutworm infestation, in the host Montsma Farm plots between Syngenta hybrids with and without the Viptera technology trait which controls that early season pest.

Hopf also reported that 2012 alfalfa yields were about a quarter dry matter ton per acre higher with the use of the company's Quadris fungicide.

He noted that it requires a 14-day waiting period before crop harvest, that the ideal application time is at six to eight inches of growth, and that, unlike some other fungicides, is suitable for application on both straight alfalfa and with a grass mix.

Asked about corn seed production for 2013, Laufenberg said Syngenta was among the companies that reacted to the experiences of 2011 by expanding its seed production to seven states, much of it on irrigated land.

He acknowledged, however, that significant production will be needed in the southern hemisphere in the coming months and advised corn growers to place their orders early in order to be in line for the particular hybrids and volumes that they want for their 2013 crop.

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