Invasive weed threatens Midwest farm economy

University of Illinois News Bureau: An invasive weed that has put some southern cotton farmers out of business is now finding its way across the Midwest – and many corn and soybean growers don’t yet appreciate the threat, University of Illinois researchers report.

University of Illinois crop sciences professor Aaron Hager is warning Illinois farmers about Palmer amaranth, an invasive weed that can take over farm fields in a season or two. | Photo by L. Brian Stauffer

Palmer amaranth (Amaranthus palmeri), a flowering plant native to the Sonoran desert and southwest United States, has a laundry list of traits that make it a fierce competitor on the farm, said Aaron Hager, a University of Illinois crop sciences professor.

Palmer amaranth germinates throughout much of the growing season, starts earlier and grows faster than other weeds, and is a prolific seed producer, Hager said. It can tolerate drought and heat extremes that would kill other plants. And it is becoming resistant to the most common herbicides used to combat it, he said. Killing the plant before it can go to seed is the best way to control it, he said. That means treating young plants with herbicides when they are less than 4 inches tall. “Once it is taller than 4 inches, the effectiveness of herbicide treatments drops off very dramatically and very quickly,” Hager said.

Catching the plant that early is problematic, however. As a seedling, Palmer looks a lot like waterhemp, another problematic weed that is difficult to control. This means farmers have the dual challenge of determining whether Palmer has invaded their fields and, if it has, taking effective action to kill it before it takes over...

Photo by Aaron Hager. Palmer amaranth grows very fast, germinates throughout the season, produces lots of seeds, can tolerate heat extremes and is very adaptable, researchers report

Study shows invasive species in waterways on rise due to climate change

A press release in AlphaGalileo via Queen's University, Belfast: One of the most serious threats to global biodiversity and the leisure and tourism industries is set to increase with climate change according to new research by Queen’s University Belfast. Researchers at Queen’s have found that certain invasive weeds, which have previously been killed off by low winter temperatures, are set to thrive as global temperatures increase.

The team based at Quercus, Northern Ireland’s centre for biodiversity and conservation science research, predicts that invasive waterweeds will become more widespread over the next 70 years. The researchers say that additional management and legislation will be required if we are to stop the spread of these pest species.

Four species in particular could establish in areas on average 38 per cent larger than previously thought due to projected climatic warming. The water fern, parrot’s feather, leafy elodea and the water primrose, are already highly problematic throughout warmer parts of Europe. Invasive species are considered to be one of the most serious threats to global biodiversity, along with climate change, habitat loss and nutrient addition.

The estimated annual cost of invasive species (plants and animals) to the UK economy is £1.8 billion, with £57 million of impact on waterways including boating, angling and waterway management.

...Dr Ruth Kelly, from the School of Biological Sciences at Queen’s, who led the study, said: “Traditionally upland areas have been protected by low winter temperatures which kill off these invading weeds. Now these are likely to become increasingly vulnerable to colonisation....

Salvinia natans (L.) All. (Water Fern) and Nuphar lutea (L.) Sm. (Yellow Water-lily). Habitat: edges of an oxbow lake near Volgograd Reservoir (Volga). Engelssky District, Saratov Oblast, Russia. Shot by Le.Loup.Gris, Wikimedia Commons,  under the Creative Commons Attribution-Share Alike 3.0 Unported license 

Deadly striga weed spreading across Eastern Africa

Maina Waruru in SciDev.net: Rising soil temperatures are increasing the spread of a deadly, parasitic weed that significantly reduces crop yields in Sub-Saharan Africa, Striga, according to scientists. The noxious weed, also known as witch-weed, usually thrives in the warm and humid tropics but is now spreading to cooler and wetter highlands as a result of warmer soils driven by global warming and low soil fertility, which provides the right conditions for Striga to thrive.

This spread has threatened the livelihoods of around 100 million people, with more than four million hectares of maize crops infected. In general, Striga reduces maize and cowpea yields by up to 80 per cent in Sub-Saharan Africa.

Some farmers are now abandoning maize cultivation for cassava as the parasitic plant colonises areas at attitudes more than 1,500 metres above sea level, said Mel Oluoch, head of the Integrated Striga Management in Africa programme at the International Institute of Research in Tropical Agriculture (IITA), during a farmers' field day in Western Kenya last month (17 January) organised by ISMA.

"Striga currently remains the biggest threat to maize production, particularly in the East Africa region where corn is the staple for millions of inhabitants," said Oluoch, adding that the weed devastates plants by attaching itself at the root base, starving the host for nutrients.

"More worrying is that the weed is spreading fast to areas not traditionally known to be infected, owing to climate change-related impacts and the resulting rise in soil temperatures coupled with low soil fertility across most of Africa," Oluoch told SciDev.Net and added that they have been observing the weed for more than two years...

Corn in Kenya, from USAID's Africa bureau

Farm 'weeds' have crucial role in sustainable agriculture

Seed Daily via SPX: Plants often regarded as common weeds such as thistles, buttercups and clover could be critical in safe guarding fragile food webs on UK farms according to Researchers funded by the Biotechnology and Biological Sciences Research Council (BBSRC).

Published tomorrow in Science, researchers from the University of Bristol detail the interactions that occur between the different food webs commonly found on farms throughout the UK and the robustness of these interactions to species loss.

In one of the first studies to look simultaneously at multiple types of food webs, the researchers found that some plants such as thistles, cow-parsley, clover and buttercups were disproportionately well linked to animals through the food web.

The research also showed that bees, butterflies and other pollinators are more susceptible to changes in their environment making them more fragile than other networks. This research highlights the importance of ensuring an agri-ecosystem approach is taken in land management practice to enhance biodiversity on UK farmland.

Professor Jane Memmott, from the University of Bristol, who led the study, explains: "If ecologists, land managers and policy makers want to manage farmland diversity, they need to understand the way species are linked to each other, since these links can have a huge impact on a community's response to species loss, species restoration and the provision of ecosystem services such as pollination and pest control."...

Thistles, by John Singer Sargent, between 1885 and 18889

Weeds vital to farmland species

Science Daily: Weeds, which are widely deemed as a nuisance plant, are vital to the existence of many farmland species according to a new University of Hull study published in the journal Biological Conservation. Since many weeds produce flowers and seed, they are an integral part of our ecosystem and together with other crop and non-crop seeds found on farms, they provide food for over 330 species of insects, birds and animals.

Scientists at the Universities of Hull and Bristol examined the distribution of berries and soil-surface seeds collected over an entire year. They built up the first picture of its kind showing which farmland habitats are the most important seed producers and how the seed resources change in different seasons.

Whilst considerable research has linked agricultural intensification with dramatic declines of seed-feeding birds, surprisingly little is known about the wider importance of seeds for other farmland animals, especially insects. Moreover, understanding the dynamics of farmland seed food resources for species of conservation concern is of considerable research interest.

The team of researchers created complex 'food-webs' which linked all farmland insects, birds and mammals which are known to feed on the seeds recorded on a typical organic farm. They used the food-web to identify the key seed-producing plants favoured by most animals. This enabled them to model the impacts of increasing farm management on seed resources and food-web interactions.

Dr Darren Evans, a lecturer in Conservation Biology at the University of Hull and who led the research said: ... "We show that an increase in farm management intensity can lead to a decline of up to 19% in overall seed biomass and energy, which is presumably why agricultural intensification causes many farmland birds to suffer a 'hunger-gap' in mid-winter. Non-farmed habitats such as woodlands and hedgerows are important for seed resources, but we also show that some farmed areas are too."...

Photo by Brian Thomas

Battling superweeds with a lower volume of chemicals

Seed Daily: They pop up in farm fields across 22 states, and they've been called the single largest threat to production agriculture that farmers have ever seen. They are "superweeds" - undesirable plants that can tolerate multiple herbicides, including the popular gylphosate, also known as RoundUp - and they cost time and money because the only real solution is for farmers to plow them out of the field before they suffocate corn, soybeans or cotton.

Now, thanks to the work of researchers at Dow AgroSciences, LLC, who have been collaborating with a University of Missouri researcher, a new weapon may be on the horizon to eliminate superweeds. Zhanyuan Zhang, a research associate professor of plant sciences and director of the MU Plant Transformation Core facility, partnered with research scientists at Dow AgroSciences, LLC, to engineer soybean plants that can tolerate an alternative herbicide that may help slow the spread of superweeds, such as tall waterhemp.

According to an article in the New York Times, farmers considered RoundUp a "miracle chemical" when it was introduced because it killed a wide variety of weeds, is safe to work with, and broke down quickly, reducing environmental impact. However, weeds quickly evolved to survive gylphosate, and that threatened to reverse an agricultural advance known as minimum-till farming.

…Using a massive genetic database and a bioinformatic approach, Dow AgroSciences researchers identified two bacterial enzymes that, when transformed into plants, conferred resistance to an herbicide called "2,4-D," commonly used in controlling dandelions.…"Unlike glyphosate, which targets amino acid synthesis, 2,4-D is a hormone regulator. Because it has a different mode of action, 2,4-D is an ideal herbicide to deal with glyphosate-resistant weeds," said Zhang, who managed the soybean transformation portion of the study and contributed to some data analysis....

Conyza canadensis on the sidewalk in in Bonn-Beuel. Shot by Michael Becker, Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported license

Weed resistance could mean herbicide is futile

Bob Holmes in New Scientist: The world's most popular herbicide is losing its knockout punch. More and more weeds are evolving resistance to glyphosate - originally marketed by Monsanto as Roundup - but the problem could have been forestalled by farming practices enriched by a better understanding of evolution. This is a serious problem. "Glyphosate is as important to world food production as penicillin is to human health," says Stephen Powles, a plant scientist at the University of Western Australia in Perth.

In 1996, Monsanto began selling crop varieties genetically modified to contain a gene for glyphosate resistance. This enabled farmers to spray glyphosate - lethal to plants yet non-toxic to animals - on their fields to kill weeds without damaging the crops, even during the growing season.

Today nearly 100 million hectares worldwide are planted with glyphosate-resistant crops. In much of the south-eastern US, as well as Brazil and Argentina, farmers grow glyphosate-resistant corn, soybeans and cotton year after year and have come to rely almost exclusively on this herbicide. This has encouraged at least nine species of weed to evolve their own glyphosate resistance, to the point where some farmers can no longer control weed infestations.

The solution, as any evolutionary biologist will tell you, is for farmers to vary weed-control practices so that weeds face a number of evolutionary pressures instead of just one. Monsanto recommends precisely this in its instructions to farmers. But farmers have been reluctant to reduce their use of an effective herbicide for an intangible future benefit, especially when few have experienced glyphosate-resistant weeds….

Backlit spring weeds, shot by Downtowngal, Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported license

Weeds damage homes as the climate warms

Paul Kelbie in Guardian, via the Observer (UK): A combination of a warmer climate, increased rainfall and a ban on the use of chemicals has created an epidemic of weeds causing hundreds of thousands of pounds worth of damage to homes and public buildings. Homeowners are facing large bills due to weeds damaging pipes and buildings as climate change produces an explosion in plant life.

According to Peter Brownless, horticulturalist at the Royal Botanic Garden, Edinburgh, long periods of warm and wet weather combined with increasing volumes of detritus in gutters and drains is encouraging plants to grow out of control at a faster rate than ever before. "A recent change in European legislation means there are far less herbicides available for local authorities and home gardeners to use to control weeds," he said.

According to Brownless many problems are caused by alien species which are thriving in Scotland's increasingly mild climate. "One plant that's causing quite a bit of concern at the moment is the New Zealand waterweed which established itself on Duddingston Loch in Edinburgh a few years ago and has out-competed many of the native plants….

Overgrown weeds in the Algiers section of New Orleans, shot by Infrogmation, Wikimedia Commons, under the terms of the GNU Free Documentation License, Version 1.2