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Invasive plants change ecosystems from the bottom up

Researcher says Phragmites ‘farm’ their own soil communities

Date:
September 5, 2017
Source:
University of Rhode Island
Summary:
Even when two different Phragmite lineages are grown side-by-side in the same ecosystem, the bacterial communities in the soil differ dramatically. This is a discovery that will aid in understanding how plant invasions get started and the conditions necessary for their success.
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In a common garden at the University of Rhode Island, Laura Meyerson has been growing specimens of Phragmites — also known as the common reed — that she has collected from around the world. And while they are all the same species, each plant lineage exhibits unique traits.

Now Meyerson, a professor of natural resources sciences, and Northeastern University Professor Jennifer Bowen have revealed that even when two different lineages grow side-by-side in the same ecosystem, the bacterial communities in the soil differ dramatically. It’s a discovery that will aid in understanding how plant invasions succeed and the conditions necessary for their success.

“It’s almost like the different lineages are farming their own microbial communities,” said Meyerson. “What’s amazing is that an invasive Phragmites population in Rhode Island and California will have microbial communities more similar than a native and invasive population living right next to each other in Rhode Island.”

The Phragmites lineage native to North America has inhabited local wetlands for thousands of years, but a lineage introduced from Europe has begun to take over many North American marshes.

“I’m interested in bacteria within salt marshes, but I’ve never thought about these particular plant-microbe interactions and how microbes in the soil work to both facilitate plant success and inhibit growth,” said Bowen. “But it turns out that the evolutionary signatures of the different plant lineages are so strong that it results in similar microbial communities in related plants that are found across the country. And that’s incredible.”

In a research paper published this week in the journal Nature Communications, Meyerson and Bowen outline their field surveys and controlled experiments on native, invasive and Gulf of Mexico lineages of Phragmites. Both methods found that the bacterial communities in the soil are primarily structured by plant lineage rather than by environmental factors, as was previously thought.

“These findings go against the general dogma that says that the environment determines the microbial community you’re going to get,” Meyerson said. “Two populations growing close to each other should have microbial communities more similar than those living farther apart. But our results say that’s not true. In this case for these plants, it’s the plant lineage — below even the species level — that determines the microbial community.”These results are important for understanding more about the success and fitness of invasive species.

“Microbes are really important in terms of determining what happens in a plant community,” explained Meyerson. “By selecting for particular microbial communities, they’re engineering their ecosystem from the bottom up. What happens at the microbial level affects the fitness and chemistry of the plants, and that affects plant interactions.”

The researchers noticed that the microbes associated with the native Phragmites had more kinds of bacteria that are used to defend the plant from enemy attackers than the microbes associated with the invasive variety, which left most of its enemies behind in its native environment.

“The invasive plants didn’t need to cultivate these defense mechanisms among their microbial communities,” Bowen said. “What our research shows is that these plants are successful as invaders, in part, because they are freed from the need to cultivate a microbial defense shield.”

Meyerson said her results provide a new perspective for those managing land and trying to control invasive plants.

“It’s another reason to be cautious about invasive species,” she said. “We have to look beyond what’s going on above ground. We also have to look below at the microbial communities and how they affect ecosystems from the bottom up.”

Story Source:

Materials provided by University of Rhode Island. Note: Content may be edited for style and length.


Journal Reference:

  1. Jennifer L. Bowen, Patrick J. Kearns, Jarrett E. K. Byrnes, Sara Wigginton, Warwick J. Allen, Michael Greenwood, Khang Tran, Jennifer Yu, James T. Cronin, Laura A. Meyerson. Lineage overwhelms environmental conditions in determining rhizosphere bacterial community structure in a cosmopolitan invasive plant. Nature Communications, 2017; 8 (1) DOI: 10.1038/s41467-017-00626-0

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  • Bloomberg

Pesticide ‘Drifting’ Wreaks Havoc Across U.S. Crops

Photographer: Daniel Acker/Bloomberg

Pesticide ‘Drifting’ Wreaks Havoc Across U.S. Crops

‎August‎ ‎1‎, ‎2017‎ ‎4‎:‎04‎ ‎PM‎ ‎CDT ‎August‎ ‎2‎, ‎2017‎ ‎9‎:‎58‎ ‎AM‎ ‎CDT
  • Missouri, Tennessee, Arkansas have placed curbs on dicamba use
  • At least 2.5 million soy acres are impacted, researcher says

Larry Martin in Illinois says he’s never seen anything like it in his 35 years of farming. Arkansas soybean grower Joe McLemore says he faces the loss of his life savings.

They’re among farmers across the U.S. suffering from a pesticide “drifting” across from neighboring fields onto their crops, leaving behind a trail of damage. Although not a new problem, it’s re-emerged with a vengeance this year. At least 2.5 million acres (1 million hectares) have been damaged in this growing season through mid-July, according to estimates from Kevin Bradley, a professor of plant sciences at the University of Missouri.

Dicamba, the offending herbicide, is produced by seed and crop-chemical giants Monsanto Co., DuPont Co. and BASF SE. It’s been around for decades, but in recent years it gained a new lease of life after the companies developed new dicamba-resistant soybean and cotton seeds, allowing farmers to spray crops later in the growing process.

Dicamba is fine if you’re growing those genetically modified varieties, but not if you’re cultivating others and the chemical wafts over from another farm. The situation is so bad that states including Missouri, Arkansas, and Tennessee have placed restrictions on dicamba use at various times during the summer.

Martin, a third-generation farmer, says an 80-acre soybean field of his has been damaged by dicamba. McLemore, who started out on his own eight years ago, after two decades working on someone else’s farm, says 800 of his 1,026 acres of soybeans have suffered damage.

Stunted, Wrinkled

“I’m not really trying to whine or anything, but it’s my life savings on the line every year,” he said by phone.

 McLemore is among a group of growers that have filed a lawsuit in a federal court in Missouri against BASF, Dupont and Monsanto for compensation. Monsanto spokeswoman Christi Dixon said the suit is without merit, while BASF spokeswoman Odessa Hines said it’s reviewing the claim. Dupont spokeswoman Laura Svec said the company hasn’t seen the lawsuit and so can’t comment on it.

Non-resistant crops are left stunted with wrinkled leaves after coming into contact with dicamba. Frustratingly, there’s no way to gauge the impact of yield until the fall harvest, farmers and researchers say. And it’s not always clear where the chemical might have come from — McLemore says that, in his case, he can’t be sure. That leaves farmers angry but also unsure whether to blame neighbors or herbicide manufacturers, said Aaron Hager, a weed scientist at the University of Illinois.

Farmers planted 20 million acres of dicamba-resistant soybeans and 5 million acres for cotton this year, executives at St. Louis-based Monsanto said in a telephone interview Monday. The company attributes the drifting problem to farmers using illegal, off-label products that are more volatile — and thus more prone to drift — than the latest versions of dicamba. They may also be cleaning or using their spraying equipment incorrectly, or applying dicamba when it’s windy, said Robb Fraley, executive vice president and chief technology officer.

Monsanto, which is being acquired by Germany’s Bayer AG, says employees are out in the fields talking to farmers about the problem. Fraley said farmers want better weed-control tools, such as dicamba product, and that the company will learn lessons from what’s happened this season. “There’s always a few challenges in launching new technology,” he said.

Germany’s BASF referred questions on dicamba to a recording of a July 19 media briefing that cited possible explanations for drifting similar to those outlined by Monsanto.

“This year thousands of growers have used these products properly and successfully meeting their challenges with resistant weeds and productivity,” said Svec at DuPont, which has a supply agreement with Monsanto for the herbicide.

The Environmental Protection Agency says it’s reviewing the situation.

“EPA is very concerned about the recent reports of crop damage related to the use of dicamba in Missouri, Arkansas and other states,” an EPA spokesperson said in an emailed statement. “We are working with the states and the registrants to better understand the issue. We are reviewing the current use restrictions on the labels for these dicamba formulations in light of the incidents that have been reported this year.”

While farmers typically look to federal crop insurance for a myriad of issues, problems with dicamba aren’t covered, according to the Risk Management Agency. Country Financial, a farm insurer, based in Bloomington, Illinois, has seen an increase in the number of dicamba-related inquiries, said company spokeswoman Alexandrea Williams. Martin, the Illinois farmer, says he’s not confident his insurance coverage will pay out.

“This is the craziest thing I’ve ever seen,” he said in a telephone interview. “You know you’re going to have a loss of income.”

— With assistance by Jeff Wilson

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Lasers for weed control

 

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Combatting weeds with lasers

Date:
June 7, 2017
Source:
Universität Bonn
Summary:
A robot automatically identifies weeds in a field and combats them with a short laser pulse. Sustainable agriculture, which avoids the use of herbicides as far as possible, could benefit from this smart idea.
FULL STORY

A robot automatically identifies weeds in a field and combats them with a short laser pulse. Sustainable agriculture, which avoids the use of herbicides as far as possible, could benefit from this smart idea. Dr. Julio Pastrana and Tim Wigbels from the Institute of Geodesy and Geoinformation at the University of Bonn are convinced of this. With an EXIST Business Start-up Grant from the Federal Ministry for Economic Affairs and Energy, the scientists are now driving forward the development of this practical tool for field work.

Those who want a rich harvest need to drive back weeds so that the crops can grow better. In organic agriculture, herbicides are ruled out as they are considered toxic chemicals, and unwanted plants must be laboriously weeded out. If the expectations of Dr. Julio Pastrana and Tim Wigbels are correct, this time-consuming work can soon be taken care of by robots.

Laser-based weed control can eliminate herbicides

The computer scientists in the Photogrammetry Laboratory at the Institute for Geodesy and Geoinformation at the University of Bonn are currently developing a novel system: using cameras on an all-terrain robot vehicle or even a tractor add-on, unwanted wild weeds should be automatically identified in the various crops and combatted in a targeted way. “The robot shoots the leaves of the unwanted plants with short laser pulses, which causes a weakening in their vitality,” reports Dr. Pastrana. “It is thus predicted that we will no longer need to use herbicides on our fields and the environment will be protected,” adds Wigbels.

Before forming the start-up, Dr. Pastrana worked in robotics and researched automated image interpretation techniques with Prof. Cyrill Stachniss from the Institute of Geodesy and Geoinformation at the University of Bonn. Dr. Pastrana completed his doctorate on the detection and classification of weeds with the aid of statistical models at Leibniz Universität Hannover and built an earlier version of the robot there with a colleague. Wigbels studied Computer Engineering at RWTH Aachen University and then worked in software development within a company.

The researchers are now pushing forward their start-up “Escarda Technologies” for one year at the University of Bonn with an EXIST grant from the Federal Ministry for Economic Affairs and Energy. “It is now a case of finding investors and further developing the business plan for the start-up,” says Wigbels. The researchers are also using the funding from the Ministry to buy the parts needed to construct a prototype.

Prof. Stachniss is supporting the start-up in various ways: Pastrana and Wigbels can thus use laboratories at the institution and consult with colleagues there. What’s more, Rüdiger Wolf from Technology Transfer at the University of Bonn helped the start-up to submit the application for the EXIST funding. “The advice was very helpful,” says Dr. Pastrana, delighted. Both scientists would also like to participate in the start-up round tables organized by Technology Transfer in order to benefit from the experience of other start-ups. The EXIST grant also enables them to attend training programs to prepare them for the challenges of independence.

“The idea combines innovative robots with a current sustainability topic,” says transfer advisor Rüdiger Wolf. He says the analyses of the market and competition for such an application are sound. Pastrana is convinced of the benefits of the laser-based technique for new agricultural machinery: “Our aim is to contribute to achieving more sustainable agriculture.” At the Bonn Idea Exchange by the Bonn/Rhein-Sieg Chamber of Commerce and Industry, both founders won an award for the best start-up idea.


Story Source:

Materials provided by Universität Bonn. Note: Content may be edited for style and length.


Universität Bonn. “Combatting weeds with lasers.” ScienceDaily. ScienceDaily, 7 June 2017. <www.sciencedaily.com/releases/2017/06/170607094152.htm>.

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Asian-Pacific WS meeting

Dear colleagues and friends,

On behalf of the organizing committee, it is my pleasure and great honor to invite you to attend the 26th Asian-Pacific Weed Science Society Conference (APWSS 2017) Kyoto, to be held on  (refer to http://www.c-linkage.co.jp/apwss2017/). The theme of the conference is “Weed Science for People, Agriculture, and Nature.”

Weed science is a comprehensive research area that covers ecology, biology and chemistry related to weed control and management. Weed science is nowadays an advanced science that is closely linked to human societies. We should use interdisciplinary and multifaceted approach to address future weed science and management. I assure you that attending the 26th APWSS conference provides an excellent opportunity to meet experts in weed science and the respective fields and learn to apply your new-found knowledge when you return home.

The host city, Kyoto, is the ancient capital of Japan and is recognized worldwide as the country’s historical, cultural and spiritual heart. The city offers you numerous cultural and unique experiences with its countless shrines, temples, and architectural masterpieces including 17 UNESCO World Cultural Heritage Sites. Mid-September is one of the best times to visit Kyoto. We suggest you to take a nice walk and to enjoy the streets and local sightseeing spots before and after attending the conference.

We look forward to welcoming you in Kyoto, September 2017!

Dr. Hiroshi Matsumoto

Chairperson, the 26th Asian-Pacific Weed Science Society Conference (APWSS2017)

President, Asian-Pacific Weed Science Society

Professor, University of Tsukuba

*************************************************

The deadline of call for papers is on 31 May 2017.

(refer to http://www.c-linkage.co.jp/apwss2017/papers.html)

Other important links are as follows:

Registration details   http://www.c-linkage.co.jp/apwss2017/registration.html

Program    http://www.c-linkage.co.jp/apwss2017/programme.html

Secretariat e-mail: apwss2017@c-linkage.co.jp

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Southwest Farm Press Daily

Resistant Pigweed
Early control is crucial for successful management of resistant pigweed.

Have you noticed any flowering pigweed recently?

Recent research conducted at College Station and Lubbock by Texas A&M scientists has shown that Palmer pigweed plants can emerge and produce seed as late as early October at these locations. This means that pigweeds can emerge even after the harvest of row crops in August or September in South Texas, and manage to produce significant amounts of seeds in the fall.

Palmer amaranth and waterhemp are two pigweed species that have become problematic in row crop production fields in Texas. Palmer amaranth is widespread in the High Plains, Rio Grande Valley, Coastal Bend and Central Texas regions, whereas waterhemp is predominantly found in the Upper Gulf Coast as well as the Blacklands regions.

Herbicide resistance in these two species is an emerging issue and Extension specialists have emphasized the need for diversifying weed management tactics to prevent or delay resistance. Because pigweeds produce enormous amounts of seeds, preventing seed production from the escapes is a critical component of sustainable resistance management. Research has shown that a single Palmer pigweed plant can produce in excess of 1.5 million seeds under good growing conditions.

Recent research conducted at College Station and Lubbock by Texas A&M scientists has shown that Palmer pigweed plants

can emerge and produce seed as late as early October at these locations. This means that pigweeds can emerge even after the harvest of row crops in August or September in South Texas, and manage to produce significant amounts of seeds in the fall. The issue is likely of even greater importance in the southernmost regions of the state, where winter frosts may not always occur.

LATE-SEASON MANAGEMENT

In a previous row-crops newsletter, we have emphasized the importance of managing these late-season emerging pigweeds to minimize future weed issues.

 On April 6, 2017, we noticed flower heads in Palmer pigweed that emerged in early spring in College Station. By April 17, mature seed could be found on the flower heads of the group of seedlings that emerged first. These plants were of considerable size and produced ample seeds (at least several thousand seeds per plant) (Figures 1 to 3). This is the first time we ever noticed mature seed production in Palmer pigweed prior to summer in College Station, especially within the planting window for grain sorghum, cotton and soybean.

Muthu Bagavathiannan

Figure 1. View of a field with flowering Palmer pigweed in College Station (mid-April 2017)

 

At Corpus Christi, Josh McGinty observed Palmer pigweed seed maturity by mid-March this year.

This observation highlights the likelihood that Palmer pigweed can add seed to the soil even prior to planting the summer crops in some areas of Texas, and these mature weeds have caused many challenges for obtaining adequate control with the preplant burndown herbicides. It is likely that pigweed seed production has occurred prior to row-crop planting in areas south of College Station in the Upper Gulf Coast, Coastal Bend and Rio Grande Valley regions due to much warmer temperatures. We could not rule out the possibility for pigweed seed production in areas north of College Station as crop planting is usually delayed by few weeks.

EARLY SEASON CONTROL

This observation points to the need for robust early-season weed management practices implemented prior to planting. Application of effective burn-down or pre-plant incorporated residual herbicides is critical even when producers plan to disk the field prior to crop planting. If herbicide resistance is suspected, the burndown herbicides must include herbicides for which the pigweeds are still susceptible and must be applied prior to pigweeds reaching the 4 to 6 inch growth stage.

Figure 2. Growth of individual Palmer pigweed plants in College Station (mid-April 2017)

Continuous wet weather conditions can complicate herbicide application timings. Thus, applications must be made at the earliest possible window to achieve effective control of the pigweeds. If burndown applications did not provide sufficient pigweed control due to resistance, larger growth stages, or other reasons, consider disking the field prior to mature seed production if tillage is an option.

Keep in mind that pigweeds only need about two weeks from flowering to mature seed production. Pigweed flowers mature from the bottom of the seedhead upward, so look for dark brown to black seeds at the base of the flower head (see Figure 3). It is imperative to be vigilant in preventing seed production in pigweeds, and the importance of monitoring and managing early-season pigweeds should not be overlooked.

Figure 3. Presence of mature seed (black color) in Palmer pigweed plants by mid-April in College Station

It is unclear whether we are finding biotypes (or portion of a biotype) that have developed the ability to germinate and produce seed early in the season. Further, we are not sure what portion of these seeds can germinate immediately and produce seed again during late summer. Research will be conducted to answer these and other practically relevant questions.

Contributors: Muthu Bagavathiannan, Josh McGinty, Vijay Singh, Peter Dotray and Gaylon Morgan

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In this video, scientists and local people explain the dangers of Opuntia stricta,  an invasive cactus weed covering large tracts of land in Kenya’s semi-arid Laikipia County, and efforts in place to tame its spread and adverse impacts.

O. stricta, a native plant of South America, is causing problems for people, domestic animals as well as wildlife. It was introduced in Kenya as an ornamental plant but has since invaded community lands according to Arne Witt, regional coordinator for invasive species at the Center for Agriculture and Biosciences International (CABI).

In Laikipia, about 253 kilometres to the north of Nairobi, Kenya’s capital city, it is dominating thousands of hectares of land given its fast propagating nature. As a result it is reducing the area of agricultural farmlands, wildlife areas and ranches. It is also causing socioeconomic and health challenges.

But scientists are now using a bio-control method in the area to destroy the weed. They have introduced a sap-sucking bug called Dactylopius opuntiae, commonly known as cochineal. It was imported from South Africa where it is being used to control the cactus weed in Kruger National Park.

Bio-control is restoring the ecosystem’s natural balance and curbing the weed’s spread, Witt explains. The cochineal specifically feeds on the cactus and has gone through laboratory tests to ensure it has no non-target impacts, especially on other plants.

Since the introduction of cochineal in the Laikipia areas of II Polei, Naibunga and Dol Dol, infected plants have virtually stopped producing fruit, inhibiting further spread of this noxious weed. This is more so where communities have embraced the use of cochineal, according to Witt.

O. stricta cannot be suppressed through chemical and mechanical control because of the costs associated with those methods. The spread of the cactus in Laikipia, Witt explains, is fuelled by the fact that it adapts well to semi-arid regions.

He says bio-control is a long-term, sustainable and effective way of controlling widespread invasive species in Africa.  “Embracing bio-control in Africa, not only for controlling invasive plants but also for controlling crop pests is crucial as pests become resistant to chemicals over time,” says Witt. “Over 200 weeds species [are] resistant to herbicides, 500 weed species are resistant to chemicals.”

A survey has shown that O. stricta spread is getting worse, but Witt is optimistic that in four to five years cochineal will get established.

Invasive species is a growing concern in Kenya — 50 per cent of such plants are introduced intentionally into the country for ornamental or agro-forestry purposes.

“Invasive species [are] foreign species brought from somewhere else as a result of human activities, and once established in a new environment, their proliferation starts to have a negative impact on diversity, crop production and animal health,’’ Witt says.

He adds, “We need a strict surveillance in place such that any new invasive [species] can be detected very early and eradicated.”

Kimani Kuria, manager of the community development programme at Ol Jogi Game Reserve, says science is playing a big role in biological control. “When harvested, the plants stay in the green house for two months laced with cochineal”, he says, adding that using the green house is improves the control and speed of the process.

The impact of O. stricta extends to wildlife and livestock. When abandoned baby elephants are rescued, Kuria explains, their tongues are found to be septic as a result of damage from the plant, and they cannot feed well. He says this is also seen in livestock in neighbouring communities, as the majority depend on livestock production. “If we do not manage Opuntia stricta, we will lose millions of dollars in range land production and livestock production in Kenya.’’

Kuria explains that the cactus has a waxy layer on the leaves, which means that a high concentration of chemical or other methods are required to control it, which would pose a threat to non-target organisms.

This multimedia piece is part of a series on invasive species supported by CABI

This piece was produced by SciDev.Net’s Sub-Saharan Africa English desk

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AfricaRice News brief

Friday, January 27, 2017

An international team of researchers representing the Africa Rice Center (AfricaRice), the International Rice Research Institute (IRRI) and Wageningen University, has raised the alarm over the enormous economic impact of parasitic weeds on rice production in Africa, threatening the food security and livelihoods of millions of resource-poor rice farmers and consumers in the region.

Smallholder farmers in the continent are losing every year half a million tons of rice worth about US $200 million because of parasitic weeds. This is roughly equivalent to the annual rice consumption of Liberia, a low-income country, which is highly dependent on rice imports. If the rice lost due to the parasitic weeds had been saved, it would have been enough to feed the total population of Liberia (4.5 million people) for a whole year.

Parasitic weeds are among the most destructive and problematic weeds to control. “When these plants invade food crops, they turn into ferocious weeds,” said Dr Jonne Rodenburg, Agronomist at AfricaRice.  The most important parasitic weed species in rice are Striga asiaticaS. asperaS. hermonthica and Rhamphicarpa fistulosa. They are all endemic to Africa and can also parasitize other cereal crops like maize, sorghum and millet.

The team of researchers reveal that these parasitic weeds, which survive by siphoning off water and nutrients from host crops, have invaded 1.34 million hectares of rainfed rice in Africa, affecting an estimated 950,000 rural households. They are increasingly becoming severe due to an intensification of agricultural production and climate changes.

The areas affected by parasitic weeds are home to some of the world’s poorest farmers. Studies by AfricaRice and partners have shown that parasitic weeds seem to predominantly affect women farmers in Africa as they are often forced to grow rice on the most marginal and parasitic weed-infested plots.

Parasitic weeds threaten rice production in at least 28 countries in Africa that have rainfed rice systems. The most affected countries are Burkina Faso, Cameroon, Côte d’Ivoire, Guinea, Madagascar, Mali, Nigeria, Sierra Leone Tanzania and Uganda.

The researchers warn that these parasites are spreading fast in the rainfed rice area and if nothing is done to stop them in their tracks, the damage will increase by about US $30 million a year.

These findings were revealed in a recent article by Rodenburg, Demont, Zwart and Bastiaans, entitled “Parasitic weed incidence and related economic losses in rice in Africa,” published in Agriculture, Ecosystems and Environment 235 (306-317). It is published as open access (http://www.sciencedirect.com/science/article/pii/S016788091630528X).

Rice is the second most important source of calories in Africa. It is also critical for smallholder incomes. Demand for rice is growing at a rate of more than 6% per year – faster than for any other food staple in sub-Saharan Africa (SSA), because of changes in consumer preferences and urbanization. Rice production is increasing across SSA, but the continent still imports some 40% of its rice.

Until now, there has been little information on the regional spread and economic importance of parasitic weeds in rice in Africa. “We have presented in this article best-bet estimates on the distribution as well as the agronomic and economic impact of parasitic weeds in rice in Africa,” explained Dr Rodenburg. “In fact, this is the first multi-species, multi-country impact assessment of parasitic weeds in Africa.”

The article focuses on the four most important parasitic weeds in rice. Striga species – known under the common name “witchweed” – occur in at least 31 countries with rain-fed upland rice systems.  Rhamphicarpa fistulosa – known under the common name “rice vampireweed” – threatens rice production in at least 28 countries with rainfed lowland rice systems.

Dr Sander Zwart, AfricaRice Remote sensing and Geographic information systems specialist, explained that for this study, a map of rainfed rice production areas, compiled from different databases, was overlapped with parasitic weed observation data retrieved from public herbaria to visualize regional distribution of these four important parasitic weeds.

From this overlap, probabilities of actual infestation were estimated. These estimates together with secondary data on parasite-inflicted crop losses and efficacy of weed control were combined into a stochastic impact assessment model.

The knowledge acquired on the distribution as well as the agronomic and economic impact of parasitic weeds in rice in Africa underlines the importance of finding effective measures to control these pests through research.

AfricaRice and its partners have been investigating and developing efficient parasitic weed management strategies that are affordable and feasible for resource-poor rice farmers. “A range of high-yielding, short-cycle, farmer-preferred rice varieties have been identified with resistance or tolerance to different species and ecotypes of Striga, as well as varieties with good defense against R. fistulosa,” said Dr Rodenburg.

He explained that such varieties can be combined with different agronomic measures, such as late sowing (against R. fistulosa) or early sowing (against Striga), and the use of organic soil fertility amendments. Growing a leguminous cover crop such as Stylosanthes guianensisand following a zero-tillage approach also contribute to effective control of Striga, as demonstrated by agronomic experiments conducted by AfricaRice and its partners.

To study institutional and socio-economic constraints underlying the challenge posed by the parasitic weeds, and to raise awareness and improve communication on efficient management strategies, AfricaRice and its partners have brought together stakeholders, including national research institutes, extension services, crop protection services and private sector representatives in workshops in East and West Africa.

At a time where there is a decline in public sector investments in agricultural research, efficient targeting of resources is becoming increasingly important. “The results of our studies emphasize the importance of targeted investments in further research, the development and dissemination of control technologies and capacity building of farmers, extension agents and other stakeholders, to reverse the observed trend of increasing parasitic weeds in rice,” stated Dr Rodenburg.

http://africarice.blogspot.com/2017/01/africas-rice-farmers-lose-200-million.html

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