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Fighting Weeds with Microbes

Ragweed

We read many, many studies involving manipulation of DNA with as of yet uncalculated risks. It was quite refreshing to read new research employing DNA-based tools in tandem with common sense for the good of all forms of agriculture and the health of the soil.

Using high-powered DNA-based tools, a recent study at the University of Illinois published in Microbial Biology identified soil microbes that negatively affect ragweed and provided a new understanding of the complex relationships going on beneath the soil surface between plants and microorganisms.

“Plant scientists have been studying plant-soil feedback for decades,” said U of I microbial ecologist Tony Yannarell. “Some microbes are famous for their ability to change the soil, such as the microbes that are associated with legumes — we knew about those bacteria. But now we have the ability to use high-power DNA fingerprinting tools to look at all of the microbes in the soil, beyond just the ones we’ve known about. We were able to look at an entire microbial community and identify those microbes that both preferred ragweed and affected its growth.”

Researchers believe an effective strategy to suppress weeds might be to use plants that are known to attract the microbes that are bad for ragweed, and in so doing, encourage the growth of a microbial community that will kill it.

“We used the same soil continuously so it had a chance to be changed,” Yannarell said. “We let the plants do the manipulation.”

This encapsulation of the research is from the June 2014 issue of Acres U.S.A.

Fungus May Offer Natural Weed Control

Weed control AmaranthA naturally occurring fungus may prove useful in the weed control fight against Palmer amaranth, an aggressive southern weed that can grow at the rate of 2 inches a day and out-compete corn, cotton, soybean and other crops for resources, potentially reducing their yields.

Weed Control Important to Avoid Glyphosate Resistance

To make matters worse, some biotypes of the weed have become resistant to weed control using glyphostate herbicides. As a possible alternative, USDA scientists are exploring ways to formulate Myrothecium verrucaria, a fungus which attacks Palmer amaranth’s leaf and stem tissues, causing wilt, necrotic lesions, loss of chlorophyll and other disease symptoms that can kill young plants and weaken older ones. Studies at the Jamie Whitten Delta States Research Center operated by USDA’s Agricultural Research Service in Stoneville, indicate Myrothecium can wreak similar havoc on biotypes of Palmer amaranth that resist glyphosate and other herbicides such as triazines. Learn more about this possible weed control in the February 2014 issue of Acres U.S.A.

New Bale Unroller Design Proves Effective

Photo by USDA NRCS

Photo by USDA NRCS

John Wilhoit and Timothy Coolong from the University of Kentucky have introduced a new technology that can make the application of organic mulches more efficient. The team altered a conventional round-bale unroller and designed experiments to document its efficiency.

“We modified an unroller so that the new design would be offset a sufficient distance for the tractor to straddle the row of plastic and unroll the bale in the space between adjacent rows of plastic,” explained Wilhoit and Coolong. “Then, we tested the efficacy of the modified unroller with several types of organic mulches for between-row weed control in organic watermelon. Mulching between rows can be an effective practice for controlling weeds; our modification makes mulching with round bales of hay or wheat straw more efficient.”

For the experiments, the offset round-bale unroller was used to apply hay and wheat straw mulch to between-row areas of ‘Crimson Sweet’ watermelon in 2009 and 2010. The mulches were applied at two thicknesses: one or two layers unrolled from round bales. “The results showed a significant mulch-type by year interaction for weed control,” the authors said. “One-year-old hay had less impact on weed control in 2010 compared with 2009, whereas other mulches had improved weed control in 2010. One-year-old wheat straw and new hay had the lowest levels of weed biomass compared with new wheat straw and the no-mulch control.”

The experiments also proved that the thickness of the mulch affected weed control, with mulches applied in two layers resulting in significantly less weed biomass than those applied in one layer.

“These results suggest that hay and wheat straw mulches can be an effective weed control practice when used in conjunction with cultivation,” Wilhoit stated. “Weed control with all of the mulches was significantly better than the control. Our results also indicated that adequate weed control could be achieved with a single layer of mulch, reducing costs for mulching with round bales. The hay and wheat straw mulches were effective in weed control, even at application rates in the 15,000 to 20,000 pound-per-acre range.”

This report appears in the January 2014 issue of Acres U.S.A.

Vetch Cover Crop Recommended for Organic Zucchini

Illustration_Vicia_sativa0In a new study, the popular cover crop vetch (Vicia sativa L.) was used in a two-year field experiment designed to determine the effects on organic zucchini yield and quality of vetch residue management strategies incorporating green manure using a roller-crimper (RC) and organic fertilizers.

To allow for timely crop rotation in organic farming, the growing cycle of cover crops is often terminated before natural maturity using mechanical chopping and/or plowing, field disking, mowing or crushing with a roller-crimper. Innovative conservation tillage production systems using RC technology to end cover crops are gaining popularity. The technique uses one or two passes of the RC to flatten the cover crops, leaving a thick mulch layer into which the next crop is sown or transplanted. The thick mulch hinders the development of weeds during the critical growing period, contributes to reduced soil erosion and increases soil moisture and fertility.

Researchers used municipal solid waste compost, anaerobic digestate and a commercial organic fertilizer in the field experiments designed to determine yield, yield components, crop quality, and soil nutritional status in organic zucchini fields in southern Italy.

“Our results showed that zucchini yield was influenced positively by the vetch residue management strategy, although the response was significantly different between years,” the scientists said. “The vetch cover crop increased marketable zucchini yield in the first year by 46.6 percent compared with the fallow treatment, indicating that this fertility-building crop could reduce off-farm nitrogen (N) fertilizer input for subsequent crops. Averaging over two years of the experiment, marketable zucchini yield increased by 15.2 and 38 percent with the roller-crimper mulch and green manure plow-down, respectively, compared with the fallow treatment, although differences were significant only in the first year.”

The application of organic fertilizers in vetch management plots increased marketable zucchini yield by 21.8 percent in the first year compared with the unfertilized control.

This article appears in the December 2013 issue of Acres U.S.A.

Weed Control with Flame Cultivation

cranberry & flameUniversity of Massachusetts scientists designed a study using flame cultivation (FC) techniques for weed control in cranberry crops. The results, published in HortScience, show promise for integrating the weed control technique into “certain situations,” including organic farming. The team tested three types of handheld propane torches and varying exposure times on several species of perennial weeds. “We thought that flame cultivation would cause damage to cranberry plants and that damage would increase with increasing exposure duration and vary by flame cultivator tool used,” noted Hillary Sandler, the study’s corresponding author. Although the results showed minor response differences between the cranberry varieties tested, all varieties showed recovery from flame cultivation damage, irrespective of which tool was used or the duration of exposure.

Flame Cultivation Offers Economic Alternative to Glyphosate

“Our economic analysis showed that the time and cost of using an open flame torch for spot control of weeds was similar to that of the common practice of using a wick applicator to apply glyphosate to weeds,” the researchers noted.

This article appears in the November 2013 issue of Acres U.S.A.

Glyphosate-Resistant Pigweed Project

Weed control Amaranth-pigweedPalmer amaranth, commonly known as pigweed, is one of the most common — and problematic — weeds in soybean crops across the southern United States. Because it is difficult to control, it is best to combat the weed before it emerges. The journal Weed Technology offers results of field tests of resistant Palmer amaranth in glyphosate-resistant soybean crops in Arkansas conducted over a two-year period. In this study, 250,000 glyphosate-resistant pigweed seeds were incorporated into the soil, and their emergence was evaluated five times during the growing season. Three farming practices were tested — deep tillage, planting a cover crop of rye and doublecropping a field with wheat and then soybeans in the same growing season.

This article appears in the October 2013 issue of Acres U.S.A.