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Crabgrass’ secret: The despised weed makes herbicide to kill neighboring plants

June 26, 2013 — Contrary to popular belief, crabgrass does not thrive in lawns, gardens and farm fields by simply crowding out other plants. A new study in ACS’ Journal of Agricultural and Food Chemistry has found that the much-despised weed actually produces its own herbicides that kill nearby plants.

Chui-Hua Kong and colleagues point out that crabgrass is not only a headache for lawns and home gardens, but also a major cause of crop loss on farms. Scientists long suspected, but had a hard time proving, that the weed thrived by allelopathy. From the Greek “allelo-,” meaning “other,” and “-pathy,” meaning “suffering,” allelopathy occurs when one plant restricts the growth of another by releasing toxins. They set out to determine if crabgrass has this oppressive ability.

Kong’s team isolated three chemicals from crabgrass that affect the microbial communities in nearby soil and did indeed inhibit the growth of staple crops wheat, corn and soybeans. “The chemical-specific changes in [the] soil microbial community generated a negative feedback on crop growth,” the scientists said, noting that the chemicals also would have a direct toxic effect on other plants.

The authors acknowledge funding from the National Natural Science Foundation of China.

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The above story is reprinted from materials provided by American Chemical Society.

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Journal Reference:

  1. Bin Zhou, Chui-Hua Kong, Yong-Hua Li, Peng Wang, Xiao-Hua Xu. Crabgrass (Digitaria sanguinalis) Allelochemicals That Interfere with Crop Growth and the Soil Microbial Community. Journal of Agricultural and Food Chemistry, 2013; 61 (22): 5310 DOI: 10.1021/jf401605g

Note: If no author is given, the source is cited instead.

ScienceDaily: Agriculture and Food News

Clove oil tested for weed control in organic Vidalia sweet onion

Weed control is one of the most challenging aspects of organic crop production. Most growers of certified organic crops rely heavily on proven cultural and mechanical weed control methods while limiting the use of approved herbicides. A new study of herbicides derived from clove oil tested the natural products’ effectiveness in controlling weeds in Vidalia® sweet onion crops.

“Cultivation with a tine weeder and hand weeding are the primary tools currently used for weed control in organic sweet onion (Allium ceps),” explained scientist W. Carroll Johnson, III. “However, conditions frequently arise that delay the initial cultivation; weeds that emerge during the delay are not effectively controlled by cultivation.” Johnson tested herbicides derived from natural products as a way to control these emerged weeds in organic Vidalia® sweet onion production. Johnson said that, although these types of herbicide have been studied previously, the majority of the studies were performed on warm-season crops and weeds. Vidalia® sweet onion is a dry bulb onion grown in Georgia as a cool-season (winter) crop.

To test the efficacy of the clove oil-derived herbicide, the researcher conducted irrigated field trials at the Vidalia Onion and Vegetable Research Center near Lyons, Georgia. One treatment factor was sprayer output volume, with the sprayer calibrated at 25 and 50 gallons/acre. Herbicide treatments were applied with a carbon dioxide-pressurized tractor-mounted plot sprayer using spray tips of differing sizes.

The other treatment factor in the trials was adjuvants used with clove oil. An OMRI-listed clove oil herbicide was evaluated and applied at 10% by volume spray solution. The adjuvants for clove oil evaluated were a petroleum oil adjuvant at 1.25% by volume, a commercial product containing 20% citric acid at a rate of 0.375% by volume, a commercial adjuvant containing 20% saponins extracted from Yucca schidigera at 0.03% by volume, an emulsified petroleum insecticide at a rate of 1% by volume, clove oil alone (no adjuvant), and a nontreated control.

“The field experiments showed that weed control was not consistently improved by applying clove oil (10% by volume) with a sprayer calibrated at 50 gallons/acre compared with sprayer calibrated at 25 gallons/acre,” Johnson said, adding that occasional improvements in weed control did not affect onion yield, and that adjuvants provided minimal improvement in weed control from clove oil and did not consistently improve onion yield. “All clove oil herbicide treatments, regardless of adjuvant, had difficulty in maintaining an emulsion in the spray tank and needed near-constant agitation. This tendency proved to be very problematic and suggests another disadvantage to using clove oil for weed control in certified organic crop production,” Johnson noted.

“Given the lack of weed response and onion yields to clove oil applied in higher sprayer output volumes and the corresponding increase in clove oil cost when increasing sprayer output volume, we cannot recommend clove oil in organic Vidalia® sweet onion production systems,” Johnson said. The full report of the experiments was published in HortTechnology.

Story Source:

The above story is based on materials provided by American Society for Horticultural Science. Note: Materials may be edited for content and length.

Agriculture and Food News — ScienceDaily

New biological agent to fight invasive weed

Sep. 27, 2013 — University of Rhode Island entomologists reached a milestone in their efforts to control the invasive weed swallow-wort this month with the first release of a biological agent to fight the pest.

Last week, the URI scientists, led by Professor Richard Casagrande and Research Associate Lisa Tewksbury, sent 500 larvae of the moth Hypena opulenta to partners in Canada for release in patches of swallow-wort near Ottawa.

“Swallow-wort is an aggressive invasive perennial weed that forms dense patches in a wide variety of habitats and may have negative impacts on monarch butterfly populations,” said Casagrande. “But we believe that this moth has potential for keeping the weed in check.”

In 2006, URI doctoral student Aaron Weed discovered the moth larvae feeding on swallow-worts in southern Ukraine. He brought the larvae to partners at the Commonwealth Agricultural Bureau International (CABI) in Switzerland for rearing and initial testing. Research on the biology, impact, and host range of these insects was conducted at CABI and in the URI Insect Quarantine Laboratory over the next six years by Weed, now a postdoctoral researcher at Dartmouth College, and a second URI graduate student, Alex Hazlehurst.

After finding that the moth larvae will only attack and survive on swallow-worts, the URI scientists and colleagues in Canada and Switzerland petitioned the U.S. Department of Agriculture in 2012 to allow field release of this biological agent in North America. The review panel recommended it for USDA approval on September 4, 2013. The USDA has additional steps in its approval process before the agent can be released in the United States next spring, but the Canadian government granted permission for immediate release.

The URI team sent larvae to partners at Canada Agriculture late last week for the first release. According to Naomi Cappuccino of Carleton University, the release appeared successful and larvae were already pupating in preparation for the Canadian winter.

Pale and black swallow-wort were accidentally introduced into the United States from Europe over a century ago and have since spread throughout the Northeast and well into Canada and the Midwest. These toxic vining plants are major pasture pests and serious weeds in many agricultural, ornamental, and forest environments. In addition to their invasiveness, swallow-worts are closely related to milkweeds and threaten monarch butterfly populations. Monarchs readily lay eggs on swallow-worts, but all larvae that hatch on the plant perish.

“We believe that swallow-worts are particularly problematic in North America because they left all their natural enemies behind in Europe, and indeed, several European insects attack these plants in their native range,” said Casagrande. “In addition to the moth just released, a second moth with populations found from Finland to Ukraine is under evaluation in our quarantine laboratory.”

These agents will be compared with a related species under study by USDA scientists to select the next best species if there is need for further releases.

According to Casagrande, the approval and release of a new weed biocontrol agent is a major accomplishment for the URI program, as it required six years of study on the biology and impact of the agent as well as testing against 76 potential host plants, all of which came out favorable. The USDA has a very careful review process that so far this year has only recommended two new agents for release.

Biological control programs of this type require a great deal of cooperative research. In addition to the URI team, the project involved Ukrainian plant taxonomists, Swiss, French, and Canadian biocontrol specialists, and faculty and USDA researchers at Cornell University. It was funded by several grants from the USDA, U.S. Forest Service, and Agriculture Canada.

URI has several other biological control programs under way, including distributing and evaluating biological control agents against the lily leaf beetle, purple loosestrife, and mile-a-minute vine.

ScienceDaily: Agriculture and Food News

New biological agent to fight invasive weed

Sep. 27, 2013 — University of Rhode Island entomologists reached a milestone in their efforts to control the invasive weed swallow-wort this month with the first release of a biological agent to fight the pest.

Last week, the URI scientists, led by Professor Richard Casagrande and Research Associate Lisa Tewksbury, sent 500 larvae of the moth Hypena opulenta to partners in Canada for release in patches of swallow-wort near Ottawa.

“Swallow-wort is an aggressive invasive perennial weed that forms dense patches in a wide variety of habitats and may have negative impacts on monarch butterfly populations,” said Casagrande. “But we believe that this moth has potential for keeping the weed in check.”

In 2006, URI doctoral student Aaron Weed discovered the moth larvae feeding on swallow-worts in southern Ukraine. He brought the larvae to partners at the Commonwealth Agricultural Bureau International (CABI) in Switzerland for rearing and initial testing. Research on the biology, impact, and host range of these insects was conducted at CABI and in the URI Insect Quarantine Laboratory over the next six years by Weed, now a postdoctoral researcher at Dartmouth College, and a second URI graduate student, Alex Hazlehurst.

After finding that the moth larvae will only attack and survive on swallow-worts, the URI scientists and colleagues in Canada and Switzerland petitioned the U.S. Department of Agriculture in 2012 to allow field release of this biological agent in North America. The review panel recommended it for USDA approval on September 4, 2013. The USDA has additional steps in its approval process before the agent can be released in the United States next spring, but the Canadian government granted permission for immediate release.

The URI team sent larvae to partners at Canada Agriculture late last week for the first release. According to Naomi Cappuccino of Carleton University, the release appeared successful and larvae were already pupating in preparation for the Canadian winter.

Pale and black swallow-wort were accidentally introduced into the United States from Europe over a century ago and have since spread throughout the Northeast and well into Canada and the Midwest. These toxic vining plants are major pasture pests and serious weeds in many agricultural, ornamental, and forest environments. In addition to their invasiveness, swallow-worts are closely related to milkweeds and threaten monarch butterfly populations. Monarchs readily lay eggs on swallow-worts, but all larvae that hatch on the plant perish.

“We believe that swallow-worts are particularly problematic in North America because they left all their natural enemies behind in Europe, and indeed, several European insects attack these plants in their native range,” said Casagrande. “In addition to the moth just released, a second moth with populations found from Finland to Ukraine is under evaluation in our quarantine laboratory.”

These agents will be compared with a related species under study by USDA scientists to select the next best species if there is need for further releases.

According to Casagrande, the approval and release of a new weed biocontrol agent is a major accomplishment for the URI program, as it required six years of study on the biology and impact of the agent as well as testing against 76 potential host plants, all of which came out favorable. The USDA has a very careful review process that so far this year has only recommended two new agents for release.

Biological control programs of this type require a great deal of cooperative research. In addition to the URI team, the project involved Ukrainian plant taxonomists, Swiss, French, and Canadian biocontrol specialists, and faculty and USDA researchers at Cornell University. It was funded by several grants from the USDA, U.S. Forest Service, and Agriculture Canada.

URI has several other biological control programs under way, including distributing and evaluating biological control agents against the lily leaf beetle, purple loosestrife, and mile-a-minute vine.

ScienceDaily: Agriculture and Food News

New biological agent to fight invasive weed

Sep. 27, 2013 — University of Rhode Island entomologists reached a milestone in their efforts to control the invasive weed swallow-wort this month with the first release of a biological agent to fight the pest.

Last week, the URI scientists, led by Professor Richard Casagrande and Research Associate Lisa Tewksbury, sent 500 larvae of the moth Hypena opulenta to partners in Canada for release in patches of swallow-wort near Ottawa.

“Swallow-wort is an aggressive invasive perennial weed that forms dense patches in a wide variety of habitats and may have negative impacts on monarch butterfly populations,” said Casagrande. “But we believe that this moth has potential for keeping the weed in check.”

In 2006, URI doctoral student Aaron Weed discovered the moth larvae feeding on swallow-worts in southern Ukraine. He brought the larvae to partners at the Commonwealth Agricultural Bureau International (CABI) in Switzerland for rearing and initial testing. Research on the biology, impact, and host range of these insects was conducted at CABI and in the URI Insect Quarantine Laboratory over the next six years by Weed, now a postdoctoral researcher at Dartmouth College, and a second URI graduate student, Alex Hazlehurst.

After finding that the moth larvae will only attack and survive on swallow-worts, the URI scientists and colleagues in Canada and Switzerland petitioned the U.S. Department of Agriculture in 2012 to allow field release of this biological agent in North America. The review panel recommended it for USDA approval on September 4, 2013. The USDA has additional steps in its approval process before the agent can be released in the United States next spring, but the Canadian government granted permission for immediate release.

The URI team sent larvae to partners at Canada Agriculture late last week for the first release. According to Naomi Cappuccino of Carleton University, the release appeared successful and larvae were already pupating in preparation for the Canadian winter.

Pale and black swallow-wort were accidentally introduced into the United States from Europe over a century ago and have since spread throughout the Northeast and well into Canada and the Midwest. These toxic vining plants are major pasture pests and serious weeds in many agricultural, ornamental, and forest environments. In addition to their invasiveness, swallow-worts are closely related to milkweeds and threaten monarch butterfly populations. Monarchs readily lay eggs on swallow-worts, but all larvae that hatch on the plant perish.

“We believe that swallow-worts are particularly problematic in North America because they left all their natural enemies behind in Europe, and indeed, several European insects attack these plants in their native range,” said Casagrande. “In addition to the moth just released, a second moth with populations found from Finland to Ukraine is under evaluation in our quarantine laboratory.”

These agents will be compared with a related species under study by USDA scientists to select the next best species if there is need for further releases.

According to Casagrande, the approval and release of a new weed biocontrol agent is a major accomplishment for the URI program, as it required six years of study on the biology and impact of the agent as well as testing against 76 potential host plants, all of which came out favorable. The USDA has a very careful review process that so far this year has only recommended two new agents for release.

Biological control programs of this type require a great deal of cooperative research. In addition to the URI team, the project involved Ukrainian plant taxonomists, Swiss, French, and Canadian biocontrol specialists, and faculty and USDA researchers at Cornell University. It was funded by several grants from the USDA, U.S. Forest Service, and Agriculture Canada.

URI has several other biological control programs under way, including distributing and evaluating biological control agents against the lily leaf beetle, purple loosestrife, and mile-a-minute vine.

ScienceDaily: Agriculture and Food News

New biological agent to fight invasive weed

Sep. 27, 2013 — University of Rhode Island entomologists reached a milestone in their efforts to control the invasive weed swallow-wort this month with the first release of a biological agent to fight the pest.

Last week, the URI scientists, led by Professor Richard Casagrande and Research Associate Lisa Tewksbury, sent 500 larvae of the moth Hypena opulenta to partners in Canada for release in patches of swallow-wort near Ottawa.

“Swallow-wort is an aggressive invasive perennial weed that forms dense patches in a wide variety of habitats and may have negative impacts on monarch butterfly populations,” said Casagrande. “But we believe that this moth has potential for keeping the weed in check.”

In 2006, URI doctoral student Aaron Weed discovered the moth larvae feeding on swallow-worts in southern Ukraine. He brought the larvae to partners at the Commonwealth Agricultural Bureau International (CABI) in Switzerland for rearing and initial testing. Research on the biology, impact, and host range of these insects was conducted at CABI and in the URI Insect Quarantine Laboratory over the next six years by Weed, now a postdoctoral researcher at Dartmouth College, and a second URI graduate student, Alex Hazlehurst.

After finding that the moth larvae will only attack and survive on swallow-worts, the URI scientists and colleagues in Canada and Switzerland petitioned the U.S. Department of Agriculture in 2012 to allow field release of this biological agent in North America. The review panel recommended it for USDA approval on September 4, 2013. The USDA has additional steps in its approval process before the agent can be released in the United States next spring, but the Canadian government granted permission for immediate release.

The URI team sent larvae to partners at Canada Agriculture late last week for the first release. According to Naomi Cappuccino of Carleton University, the release appeared successful and larvae were already pupating in preparation for the Canadian winter.

Pale and black swallow-wort were accidentally introduced into the United States from Europe over a century ago and have since spread throughout the Northeast and well into Canada and the Midwest. These toxic vining plants are major pasture pests and serious weeds in many agricultural, ornamental, and forest environments. In addition to their invasiveness, swallow-worts are closely related to milkweeds and threaten monarch butterfly populations. Monarchs readily lay eggs on swallow-worts, but all larvae that hatch on the plant perish.

“We believe that swallow-worts are particularly problematic in North America because they left all their natural enemies behind in Europe, and indeed, several European insects attack these plants in their native range,” said Casagrande. “In addition to the moth just released, a second moth with populations found from Finland to Ukraine is under evaluation in our quarantine laboratory.”

These agents will be compared with a related species under study by USDA scientists to select the next best species if there is need for further releases.

According to Casagrande, the approval and release of a new weed biocontrol agent is a major accomplishment for the URI program, as it required six years of study on the biology and impact of the agent as well as testing against 76 potential host plants, all of which came out favorable. The USDA has a very careful review process that so far this year has only recommended two new agents for release.

Biological control programs of this type require a great deal of cooperative research. In addition to the URI team, the project involved Ukrainian plant taxonomists, Swiss, French, and Canadian biocontrol specialists, and faculty and USDA researchers at Cornell University. It was funded by several grants from the USDA, U.S. Forest Service, and Agriculture Canada.

URI has several other biological control programs under way, including distributing and evaluating biological control agents against the lily leaf beetle, purple loosestrife, and mile-a-minute vine.

ScienceDaily: Agriculture and Food News

Flame cultivation promising as weed control method for cranberry

Sep. 16, 2013 — Cranberries are important agricultural commodities in states such as Massachusetts, Wisconsin, New Jersey, Washington, and Oregon. But cranberry-growing operations are challenged by weeds, which compete for precious resources and often decrease fruit yields and revenues. Producers currently rely on weed management strategies such as flooding and sanding cranberry beds, hand-weeding, or applications of pre- and postemergence herbicides. Recent interest in reducing chemical inputs into cranberry growing systems has led researchers to evaluate alternative methods such as flame cultivation as a potential nonchemical weed control option.

University of Massachusetts scientists Katherine Ghantous, Hilary Sandler, Wesley Autio, and Peter Jeranyama designed a study using flame cultivation techniques for weed control in cranberry crops. The results, published in the July 2013 issue of HortScience, showed promise for integrating the weed control technique into “certain situations,” including organic farming. The team tested three types of handheld propane torches (one open flame and two styles of infrared 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. Surprisingly, although the results showed minor response differences between the cranberry varieties tested, all varieties showed recovery from flame cultivation (FC) damage, irrespective of which tool was used or the duration of exposure.

“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. “In addition to being as cost-effective as glyphosate wipes, the non-fatal response to flame control indicates that it will cause less damage to cranberry plants that are incidentally exposed during spot treatment of weeds than glyphosate.”

The experiments determined that flame cultivation could be integrated as a sustainable and economical approach for weed control in some situations. “This technology could be applicable for conventional production as well as organic production, and would ideally be used as a spot treatment for weeds growing in the cranb

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Story Source:

The above story is based on materials provided by American Society for Horticultural Science.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.


Journal Reference:

  1. Katherine M. Ghantous and Hilary A. Sandler1 University of Massachusetts, Amherst, Stockbridge School of Agriculture, UMass Cranberry Station, 1 State Bog Road, P.O. Box 569, East Wareham, MA 02538 Wesley R. Autio Stockbridge School of Agriculture, University of Massachusetts, Amherst, MA 01003 Peter Jeranyama. Damage and Recovery of Cranberry Vines from Exposure to Handheld Flame Cultivators. HortScience, 2013 [link]

Note: If no author is given, the source is cited instead.

ScienceDaily: Agriculture and Food News

How rice twice became a crop and twice became a weed — and what it means for the future

July 17, 2013 — The evolutionary biologist Stephen Jay Gould once asked whether the living world would be different “if the tape were played twice.” If there were a duplicate Earth evolving quietly beside ours, would we observe the emergence of creatures like ourselves and of plants and animals familiar to us, or would the cast of characters be entirely different?

It’s an intriguing question.

So far replicate Earths are in short supply, but cases of parallel evolution (the same trait evolving independently in related lineages) allow scientists to ask some of the same questions.

One beautiful case of parallel evolution is the double domestication of rice in Africa as well as Asia, which was followed by its double “de-domestication,” or reversion to a wild form, all within the roughly 10,000 years since hunter-gatherers became settled farmers.

With the help of modern genetic technology and the resources of the International Rice GeneBank, which contains more than 112,000 different types of rice, evolutionary biologist Kenneth Olsen, PhD, associate professor of biology in Arts & Sciences at Washington University in St. Louis, has been able to look back in time and ask whether the same mutations underlay the emergence of the same traits in both cultivated and weedy rice.

His latest findings, which take a close look at the genetics of hull color, appear in the July 17, 2013, online issue of the Journal of Evolutionary Biology.

The answers are interesting in their own right but also have practical importance because modern agriculture is radically changing the selection pressures acting on rice, the most important food crop for most of the world’s populations.

In response to these pressures, weedy forms that evolved from the crop forms are taking on traits more like those of wild ancestors. “They’re very aggressive competitors,” Olsen says, “and they’ve become a huge problem both here in the U.S. and all over the world.”

“In some parts of the world farmers have given up trying to grow rice and just market the weedy stuff that’s infested the fields as a health food,” he says. You sometimes see red rice from the Camargue, the delta region in southern France, in stores, he says. “Red rice is full of antioxidants, which tend also to be plant defense chemicals,” Olsen says, “but it is basically a weed.”

Double domestication

Worldwide, most of the cultivated rice is Asian rice, Oryza sativa which was bred from its wild progenitor Oryza rufipogon in southern Asia within the past 10,000 years.

Whether the familiar indica and japonica subspecies of Asian rice also represent independent domestications is controversial. Most of the rice grown in the U.S. is japonica rice, Olsen says, which is genetically pretty different from indica rice, the rice grown in a lot of the tropics.

In any event there was a second unambiguous domestication event about 3,500 years ago when African cultivated rice (O. glaberrima) was bred from the African wild species O. barthii in the Niger River delta.

Scientists are now in a position to examine the genetic basis of both the Asian and African domestications, Olsen says. In a way it’s like being able to go back to check DNA fingerprints at the scene of a crime committed well before DNA testing first became available.

When a plant is domesticated, it acquires a suite of traits called the domestication syndrome that made it easier to grow as a crop. In rice, the syndrome includes loss of shattering (the seeds don’t break off the central grain stalk before harvest), increase in seed size, and loss of dormancy (the seeds all germinate at once and can be harvested at once).

Do the same genetic mutations underlie the emergence of these traits in both the Asian and African domestication events, or did domestication result from different mutations in the same genes, or even from mutations in different genes?

In a series of articles in the Journal of Evolutionary Biology and other journals, Olsen, postdoctoral researcher Cindy Vigueira, and their colleagues have shown that different mutations of the same genes underlie the loss of shattering, and the straw-colored hulls and white grains of both Asian and African cultivated rice.

So both Asian and African cultivated rice “broke” at roughly the same places under selection pressure from early farmers.

Double de-domestication

Like domestication, de-domestication, or evolution from the crop species of unpalatable weedy species that have many wild-like traits, also seems to have happened twice. One weedy strain resembles an Asian rice variety grown only in a small part of the Indian subcontient and the other strain resembles a rice grown in the tropics.

Because the weedy forms are closely related to rice varieties that were never grown in the U.S., they probably arrived as contaminants in grain stocks from Asia instead of evolving directly from the tropical japonica crops grown here.

The question, Olsen says, is whether crops reverted to wild forms by reversing the genetic changes that resulted in their domestication or through mutations that circumvented domestication in other ways.

At the genetic level the history of the weedy forms turns out to be messier than that of the crop forms.

For example, the weeds carry the crop form of the loss-of-shattering gene, which means that they branched off from the crops sometime after people selected for loss of shattering. The weedy forms shatter, but they’ve re-evolved this ability by some other, as yet unknown, pathway, he says.

Weeds stealing crop genes

The most important part of this story, Olsen says, is that the genetic histories of the crops and the weeds are closely intertwined. This means the weedy forms can draw on both ancestral genes and crop genes as they respond to the selection pressures of modern agriculture.

Even though both weedy strains arose in Asia, he says, weedy rice became a problem in southeast Asia only in the last few decades. The reason is that rice seedlings were traditionally grown in paddies and then transplanted to the fields by hand. As they worked in the fields, farmers would recognize and pull weeds growing there.

But on industrialized farms, rice is sprouted directly in the field, so there’s no opportunity to remove weeds. Because the seedlings of both weedy and cultivated rice look alike, farmers often don’t realize they have a problem until the field is really infested.

Weedy infestations can drop the yield by as much as 80 percent, Olsen says. If a field is heavily infested, the farmer’s only recourse may be to abandon it.

In the U.S. weedy rice is increasingly combatted by growing herbicide resistant crop strains, Olsen says. In recent years more than a third of U.S. rice fields have been planted with herbicide-resistant rice.

But that places huge pressure on the weeds to acquire herbicide resistance by hook or by crook.

The mechanism of herbicide resistance that is bred into the crop is pretty simple, Olsen says. It’s basically a single amino-acid change in a particular gene, although newer varieties are getting a bit fancier and multiple genes may be involved. So it would be pretty easy for random mutations to confer resistance on the weeds.

The other possibility is that resistance genes will migrate from the crop to the weeds. Because both cultivated rice and weedy rice tend to self-fertilize, there hasn’t been a lot of gene flow going on in rice in general, Olsen says.

But the crop and the weeds — which are, after all, the same species — could easily hybridize now that selective pressure is favoring gene flow.

“We’re already seeing more and more hybridization occurring,” Olsen says. “It’s going to change the overall composition of the weeds in U.S. rice fields and presumably elsewhere in the world as well.”

ScienceDaily: Agriculture and Food News