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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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pigweed-butterfly-ga-field-2016 Brad Haire  Feb 06, 2017
Herbicide-resistant weeds didn’t fall from the sky or rise from fields in a mutant mutiny, but they are here nonetheless. With new herbicide technologies going mainstream this season, growers must continue dogged resistant-weed management programs to preserve viable chemistries for as long as possible.

Herbicide-resistant weeds didn’t fall from the sky or rise from fields in a mutant mutiny, but they are here nonetheless. With new herbicide technologies going mainstream this season, growers must continue dogged resistant-weed management programs to preserve viable chemistries for as long as possible.

“In general, herbicide-resistant weeds become a problem over time when they are selected to survive by the overuse of a single herbicide or single mode of action. In all weed populations, there are very low levels or frequencies of herbicide-resistant plants in comparison to susceptible plants,” said Eric Prostko, University of Georgia Extension weed specialist during an American Society of Agronomy webinar “Growing for Tomorrow: How Weed Resistance Management Can Lead to Sustainability”Feb. 1 sponsored by BASF.

The U.S. leads the world with 156 unique cases of herbicide-resistant weeds. “If you grew up in the U.S. like me, you are likely always proud to see American athletes win Olympic gold medals. The more the better, right? Unfortunately, the U.S. is also the gold medal winner for herbicide resistant weeds,” Prostko said.

Australia currently comes in second place with 84 unique cases of herbicide-resistant weeds, and Canada takes third with 64 cases.

Worldwide there are 478 unique cases of herbicide-resistance weeds. The most frequent modes of action that weeds have developed resistance to are the ALS inhibitors (SUs and IMIs), PS II inhibitors (triazine and ureas)  and the ACCase inhibitors (dim and fop grass herbicides), he said.

The over-use of glyphosate on glyphosate-tolerant crops has led to the rapid development of glyphosate-resistant weeds over the last two decades, he said. Today, there are 36 weed species worldwide with resistance to glyphosate with 16 of those species in the U.S.

PPO-resistance is now a growing concern, too. “The evolution of PPO resistance is scary because many growers have been relying on herbicides with this mode of action to help manage herbicide-resistant pigweed. Currently, three weed species have evolved PPO-resistance in the U.S., including tall waterhemp, Palmer amaranth and giant ragweed. PPO-resistant Palmer amaranth is under investigation in Alabama, Mississippi, North Carolina and South Carolina,” he said.

But resistant weed problems do not necessarily result in yield loss. In Georgia where farmers have dealt with glyphosate-resistant pigweed for more than a decade, cotton and peanut yields have continued to increase. But it has come at great cost.

The cost to fight resistant weeds with herbicides in Georgia cotton, for example, has increased since 2004 from $28 per acre to $68 per acre plus a 10 percent to 20 percent increase in cost of mechanical cultivation and an increase in the need for hand weeding going from just under $3 per acre to almost $24 per acre today.

So what can growers do or do better, especially in handling herbicide-resistant Palmer amaranth?

1 – Start weed-free at planting using a combination of tillage, cover crops and herbicides. Although the benefits of reduced tillage systems are many, they have also helped contribute to some of our resistant weed problems. “The deeper and longer Palmer amaranth seeds are buried, the less seed germination will occur. Burying pigweed seed with a moldboard plow every three years or so can be beneficial, particularly in problematic fields. In some cases, deep tillage may not be a practical option,” he said.

2 – For growers who cannot or will not use deep tillage, well-managed cereal cover crops can be used to help reduced the emergence of some weeds. Since Palmer amaranth seed requires light for germination, a heavy rye biomass, for example, can prevent light from reaching the soil surface which ultimately influences germination and emergence. Getting an adequate crop stand in extreme cover crops can often be challenging and requires diligence and practice.

3 – Another tactic that exploit’s the influence of light on weed seed germination and emergence is narrow-row planting. Studies in many crops show narrower rows typically result in better overall weed control.

4 – Use herbicides with multiple effective modes of action. Most, if not all, herbicide labels today have their modes of action listed in plain view. “You no longer have to be a weed scientist to identify different modes of action,” he said.

5 – A strict crop rotation “can be extremely beneficial for the management of herbicide-resistant weeds because multiple herbicide modes of action can be used over time. In the case of a typical cotton-and-peanut rotation in the Southeast, eight different herbicide modes of action can be used over a two year period,” he said.

6 – Don’t cut rates to save money or for any other reason. “The use of reduced herbicide rates has been proven to be one of the factors that can increase the rate of herbicide resistance development. … The bottom line: only full-labeled rates should be used for weed control.”

7 – Reduce the seed bank in field. Many growers know it but it’s worth saying again: pigweed is a ‘seedy’ plant, producing 500,000 to 1 million seeds per plant.

Cotton and soybean seed traits tolerant to new formulations of dicamba and 2,4-D, which are on track to be widely available and legal to spray over the top of crops this season, are expected to be planted in some regions. Both herbicides are in the same auxin herbicide family. “First and foremost, these new auxin technologies are not a miracle cure for all your current weed problems. You will still need to start clean, use residuals and make timely postemergence applications,” he said.

“Although much is being said about the new auxin technologies these days, I am not hearing very much about the fact that auxin resistance in weeds has already occurred,” Prostko said. “These herbicides are not new. Currently, eight weed species in the U.S have already developed auxin-resistance. Auxin technology stewardship will be even more important as we head into the future.”

Chad Asmus, technical marketing manager for BASF, spoke during the webinar and echoed Prostko’s concerns and recommendations for growers to reduce the risk of herbicide resistance developing in their fields, highlighting the company’s newly formulated dicamba herbicide Engenia, which can be sprayed over the top of dicamba-tolerant cotton and soybean.

The new herbicide has a BASF patented molecule called BAPMA, which, Asmus said, is the lowest volatility salt of dicamba with the highest loading and lowest use rate at 12.8 fluid ounces per acre; and it’s rain fast in 4 hours.

The Engenia label comes with many requirements, including buffer areas. Asmus stressed that growers must follow the label requirements thoroughly. Here are a few of the general federal requirements for Engenia:

  • Use the TTI11004 spray nozzle.
  • Boom Height: ≤ 24” above the target.
  • Application Volume: ≥ 10 GPA.
  • Ground Speed: ≤ 15 MPH.
  • Wind Speed and Direction: 0 to 15 MPH
    • For wind speeds ≤ 3 MPH confirm there is no field level temperature inversion.
    • Do not spray with wind speeds >10 MPH blowing toward neighboring sensitive non-specialty crops.
    • Do not spray with any wind blowing towards neighboring specialty crops.

Asmus said growers need to also pay special heed to any state-specific label requirements that might apply to Engenia this year. An updated list of EPA-approved tank-mix products for Engenia can be found at http://www.EngeniaTankMix.com.

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mersie

Dr. Wondi Mersie of Virginia State University, PI of the IPM Innovation Lab’s “Biological control of the invasive weed Parthenium hysterophorus in East Africa” project.

Feed the Future IPM Innovation Lab and Invasive Weed Species

The IPM Innovation Lab presented two papers at the “International Conference on Biodiversity, Climate Change Assessment and Impacts on Livelihood” in Kathmandu, Nepal. Dr. R. Muniappan, Director of the IPM Innovation Lab at Virginia Tech presented on the ecological distribution of the four alien invasive weed species, Ageratina adenophora, Chromolaena odorata, Lantana camara, and Parthenium hysterophorus. He pointed out the adoption of Ageratina adenophora to humid and temperate conditions, Chromolaena odorata to humid and tropical areas, and Parthenium hysterophorus to arid and tropical situations. However, several taxa of Lantana camara found in the tropics have adopted all the three conditions mentioned above.

Dr. Wondi Mersie of Virginia State University, PI of the IPM Innovation Lab’s “Biological control of the invasive weed Parthenium hysterophorus in East Africa” project, presented a paper on the adverse effect of Parthenium hysterophorus on biodiversity of above ground vegetation and the seed soil bank of rangelands in Ethiopia.

Stephanie Parker

IPM Innovation Lab

sparker1@vt.edu

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Scientists Use Insects to Control an Invasive Weed

An arundo gall wasp depositing eggs into the main stem of a giant reed. Photo by John Goolsby.

The release of tiny insects to combat an invasive weed is paying off, according to a recent study by the U.S. Department of Agriculture.Scientists from the USDA’s Agricultural Research Service released arundo gall wasps (Tetramesa romana) and arundo scale insects (Rhizaspidiotus donacis) several years ago as part of a biocontrol program to kill a weed called “giant reed” (Arundo donax) along the Rio Grande in Texas. The weed, also known as “carrizo cane” and “Spanish reed,” clogs streams and irrigation channels, weakens river banks, stifles native vegetation, affects flood control, reduces wildlife habitat, and impedes law enforcement activities along the international border.

Recent research conducted by entomologist John Goolsby demonstrates that these insects have helped control giant reed over more than 550 river miles. Measurements taken in 2014 documented a 22-percent decrease in plant biomass along the Rio Grande since the insects’ release in 2009. Measurements in 2016 show a further decrease of 28 percent and significant recovery of native riparian vegetation.

Giant reed grows between three and seven inches a day and reaches heights of 30 feet along the Rio Grande. The weed increases the population of cattle fever ticks by creating an ideal habitat for them, which makes it difficult for USDA inspectors to detect tick-infested cattle and deer. As the riverbank transitions back to native vegetation, the plant community supports greater abundance and diversity of tick-feeding ants and beetles that act as biological control agents.

To accelerate weed removal, scientists have combined “topping” — mechanically cutting cane — with insect releases. Topping suppresses growth for more than a year and makes plants more susceptible to insect attacks. Combining topping and insect releases gives a high, long-term suppression of cane and allows native trees to grow and start shading giant reed.

“We’ve thinned the cane out significantly,” Goolsby said. “The biggest decline in plants correlates with the greatest number of our biocontrol agents—the wasp and scale.”

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Science News
from research organizations

Sustainable alternative to methyl bromide for tomato production

Anaerobic soil disinfestation determined effective for controlling weeds, nematodes in Florida fresh-market tomato

Date:
August 25, 2016
Source:
American Society for Horticultural Science
Summary:
Field studies in two Florida locations evaluated and compared anaerobic soil disinfestations (ASD) and chemical soil fumigation (CSF) performance on weed and nematodes control, and on fruit yield and quality of fresh-market tomato. Results indicated that ASD (applied using a mixture of composted poultry litter and molasses as carbon source) may be a potentially sustainable alternative to conventional CSF for controlling plant-parasitic nematodes and weeds without causing negative effects on fruit yield and quality.

Tomatoes were grown in field studies to compare anaerobic soil disinfestations (ASD) and chemical soil fumigation (CSF). ASD applied using a mixture of composted poultry litter and molasses as carbon source was shown to be an promising alternative to conventional CSF.
Credit: Photo courtesy of Francesco Di Gioia

Following the phase out of methyl bromide, scientists continue to explore effective, viable, and more sustainable options for vegetable crop production. Among nonchemical alternatives, anaerobic soil disinfestation (ASD) is considered to be one of the most promising methods. ASD has been determined to be effective with a range of crops and environments against several soilborne fungal and bacterial plant diseases, plant-parasitic nematodes, and weeds.

A study in the June 2016 issue of HortScience focused on the effects of ASD in an open-field, fresh-market tomato production system. Field studies were conducted to evaluate and compare ASD with chemical soil fumigation (CSF) treatments for controlling weeds and nematodes, as well as for influence on tomato fruit yield and quality. In experiments conducted in southwestern (Immokalee) and northern Florida (Citra), conventional CSF was compared with two ASD treatments, which consisted of amending the soil with 22 Mg·ha-1 of composted poultry litter and two rates of molasses (13.9 and 27.7 m3·ha-1) as a carbon source.

Analyses showed that the application of ASD did not negatively affect commercial tomato fruit quality, and that quality and the mineral content of fruit produced with ASD was comparable or higher than that of fruit produced in CSF plots.

In both locations, the application of ASD provided a level of root-knot nematode control equivalent to, or more effective, than the CSF. Additional results showed that, in Immokalee, the CSF provided the most significant weed control, “but ASD treatments also suppressed weeds enough to prevent an impact on yield,” the authors said. In Citra, all treatments, including the CSF, provided poor weed control relative to the Immokalee site.

“Overall, the results of the two locations demonstrate that the ASD technique may be a valid and sustainable alternative to the conventional CSF, and could be transferred at commercial level,” the authors said. “Molasses rates showed similar performance in terms of root-knot nematode and weed control, yield, and fruit quality; therefore, the lower molasses rate could be suggested to reduce the cost of the ASD treatment.”

On-going research is focused on substitutions for composted broiler litter and minimizing nutrient inputs in an ASD system.


Story Source:

The above post is reprinted from materials provided by American Society for Horticultural Science. Note: Content may be edited for style and length.


Journal Reference:

  1. Francesco Di Gioia et al. The Effects of Anaerobic Soil Disinfestation on Weed and Nematode Control, Fruit Yield, and Quality of Florida Fresh-market Tomato. HortScience, June 2016

Cite This Page:

American Society for Horticultural Science. “Sustainable alternative to methyl bromide for tomato production: Anaerobic soil disinfestation determined effective for controlling weeds, nematodes in Florida fresh-market tomato.” ScienceDaily. ScienceDaily, 25 August 2016. <www.sciencedaily.com/releases/2016/08/160825113223.htm>.

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From Pestnet@yahoogroups.com

Three resources on line for weed identification. All from the US. This is taken from “Help with weed identification” http://www.whav.net/cms/help-with-weed-identification/

Start with University Weed Identification sites such as those at Michigan State University (http://www.msuturfweeds.net/id-tool/broadleaf/), The University of Missouri (http://weedid.missouri.edu) and New Mexico State University (http://weeds.nmsu.edu/weedid.php).

 

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