Weeds could help to feed the world

Photo:Keng T/WikimediaPlants that cope better with changes in the environment – giving greater crop yields in the face of global warming – could be developed following a study into the weeds in the cracks in pavements.

Dr Giles Johnson and his team at The University of Manchester have identified a protein that helps plants 'track' the environment and increase their capacity to photosynthesise (capturing light energy through the leaves which enables them to grow). This protein is produced according to the expression of a particular gene.

Microbe may provide key to combating giant salvinia

Giant salvinia.Photo:Eric Guinther/WikimediaLouisiana Tech researchers say 'natural herbicide' could control destructive biomass

A team of researchers at Louisiana Tech University has found that a naturally occurring microorganism acts as a natural herbicide against giant salvinia. Giant salvinia is a noxious and invasive aquatic weed that can block all sunlight penetration into bodies of water, altering entire ecosystems. Under ideal conditions, it's been reported that giant salvinia can double in size every three days.

Organic weed control options for highbush blueberry

Researchers study mulching options for weed control at Blueberry Acres in Nova Scotia. Photo: Derek LynchResearch scientists at Nova Scotia Agricultural College have been working steadily to find effective organic methods to control weeds in cultivated blueberry crops. One resulting study, published in a recent issue of the ASHS journal HortScience, reported on the efficacy of three organic mulches used on highbush blueberry (HBB) produced under organic production practices. The research team determined that the major factor influencing weed suppression by compost mulches (for certain weed species) was likely mulch thickness and bulk density, which provide a barrier to weed growth and prevents light penetration to the soil surface.

Weeds are a widespread problem for the blueberry industry. North American commercial blueberry producers who took part in a recent survey indicated that weed problems were a concern in almost all production areas, particularly in young plantings when bushes are not fully established and most susceptible to competition.

Weed control is even more of a challenge for growers of organic products, including organic highbush blueberry (Vaccinium corymbosum L.). The current study was initiated as an attempt to find feasible, effective organic weed control methods to sustain Nova Scotia's growing blueberry industry.

A two-year field study was conducted in 2005 and 2006 in an established field of 5-year-old northern highbush blueberry at Blueberry Acres, a commercial blueberry operation in the Annapolis Valley of Nova Scotia. Mulches, applied in-row at a 20-cm depth, included pine needles, manure-sawdust compost, and seafood waste compost.

Dr. Derek Lynch, of the Department of Plant and Animal Science at NSAC, headed the research team. According to Lynch, organic materials such as pine bark, peat, and sawdust are commonly used as a pre-plant soil amendment to increase the organic matter content of mineral soils, but heavy applications of organic mulch can result in high soil salinity and impact plant yield and growth, even resulting in environmental impacts.

"Alternately", noted Lynch, "thickly applied organic mulches may be an effective weed management option. Mulch thickness is an important consideration because the emergence of weed seedlings is inversely related to seed depth, meaning the efficacy of weed control tends to increase with mulch thickness."

The study reported that pine needles (PN) were the most effective mulch in suppressing weed growth, with 55 per cent less and 73 per cent less aboveground weed biomass compared with the control in 2005 and 2006, respectively. Pine needle productivity effects were much more modest, however. One year after application, pine needles lost some efficacy at suppressing weeds but the treatment was still superior to both composts. The researchers recommend continuing to top-dress PN or similar mulches on a yearly basis to maintain mulch thickness.

Lynch summarised, "This approach can be cost-effective depending on local availability of mulch materials. However, precautions should be taken to avoid excess nutrients from heavy application of nutrient-rich mulches and weed-seed contamination of these types of mulch." He added that more research is needed to evaluate the long-term effects of different mulches on productivity and nutrient availability in these systems.

Organic weed control for dandelions

Photo: WikimediaMulched maple and oak leaves reduce dandelions in established Kentucky bluegrass

Spring and summer often find homeowners out in their yards, busily attempting to control the onslaught of dandelions in a quest for green, weed-free lawns. Dandelions, broadleaf perennial plants that have a questionable reputation as lawn wreckers, can make even the most patient gardener reach for chemical weed killers to control the onslaught of the ubiquitous weeds. Now, the answer to an environmentally responsible way to control dandelions could be right on the front lawn.

Responding to criticism that synthetic herbicides can be harmful to the environment, researchers around the world are experimenting with organically derived weed control methods.A team at Michigan State University recently studied the effectiveness of pesticide-free mulched maple and oak leaves on common dandelions in established Kentucky bluegrass comparable to residential lawns.

Previous research indicated that mulched maple leaves resulted in fewer dandelions when incorporated into established turfgrass, but the leaves used in that research may have contained herbicide residues. These findings triggered a subsequent study designed to compare the effects of mulched leaves from herbicide-free maple and oak species on established turfgrass as an organic broadleaf weed control method, according to Alexander R. Kowalewski, lead author of a study published in HortTechnology.

"The objectives of our research were to quantify the effectiveness of four maple and one oak species leaf mulch as an organic broadleaf weed control method in an established Kentucky bluegrass turfgrass stand, then to identify specific maple species that provide effective broadleaf weed control. The final two objectives of this research were to determine the optimum leaf litter particle size and rate per unit area for the most effective broadleaf weed control", Kowalewski explained.

The scientists compared the effects of pesticide-free mulched maple and oak leaves on dandelion populations in an established Kentucky bluegrass lawn in field experiments at the Hancock Turfgrass Research Center in East Lansing. The team tested red maple (Acer rubrum), silver maple (A. saccharinum), sugar maple (A. saccharum), high sugar content sugar maple, and red oak (Quercus rubra) in coarse and fine particle sizes and differing application rates.

Mulch applications were made in fall and data collected beginning in spring on Kentucky bluegrass spring green-up and common dandelion plant counts. The data showed that the high application rate, regardless of tree genus or species, resulted in the highest green-up ratings. Common dandelion plant counts after one and two mulch applications at the high rate showed that up to 80 per cent and 53 per cent reduction was achieved, respectively.

Although the results from the research do not suggest that mulched leaves can be used exclusively as an alternative to herbicides to provide high-end weed control, Kowalewski stated: "If home owners want to incorporate this practice into an annual maintenance program, the findings of this study suggest that an increased spring green-up and a reduction in common dandelion population could be observed."

The lurking menace of weeds

Photo: S B JohnnyToday more than a billion people in the world are hungry, the result of flawed policies mainly, but also of wars and revolutions and of natural hazards like floods, droughts, pests and diseases compounded, nowadays, by climate change. But one huge hunger-maker lurks largely unnoticed...

"Maybe it's because weeds are not very spectacular," says weed expert Ricardo Labrada-Romero. "Droughts, insects and diseases like Swine Flu are attention-grabbers because their effects are dramatic. Weeds are different. They play havoc quietly all year round, year after year."

Consider, he says, the damage caused by one weed alone, Broomrape (Orobanche spp), an aggressive root weed which attacks legumes and vegetables and can not only lead to complete crop failure but also make fields infertile for many years.

Huge production losses

Figures clearly show that weeds should be regarded as farmers' natural enemy No. 1. According to a leading environmental research organisation, Land Care of New Zealand, they cause some USD95 billion a year in lost food production at global level, compared with USD85 billion for pathogens, USD46 billion for insects and USD2.4 billion for vertebrates (excluding humans).

At today's prices, USD95 billion translates into some 380 million tonnes of wheat, or more than half of world production expected in 2009. And of those USD95 billion, USD70 billion are estimated to be lost in poor countries.

Economic losses may be even greater considering that more than half of the time farmers spend in the fields is devoted to weed control, says Labrada-Romero. It follows that if farms are to increase their productivity one of the first things they must do is improve weed management.

Stagnating yields

Nowhere is this more important than in Africa, where weeds are a major cause of stagnating yields and production. "With only manual labour available, African smallholders need to weed every day and that means a family physically can't handle more than 1-1.5 hectares," Labrada-Romero explains. "But proper management would allow them to farm more land and grow more food."

Modern integrated weed management involves much more than spraying herbicides. Crop rotation is one effective technique because weeds are often biologically adapted to a given food crop so that changing the crop can reduce weeds too.

Also important, says Labrada-Romero, is the use of certified, quality seeds. Many of the seeds produced and used by farmers are contaminated by weed seeds. If smallholders produce their own seeds, they should be taught to clean them so as to avoid planting weeds in their fields at sowing time.

Solarisation

Soil solarisation, a simple non-chemical technique, can be used to control weed seeds and seedlings as well as many soil-borne pathogens and pests. Transparent polyethylene plastic placed on moist soil during the hot summer months increases soil temperatures to levels that are lethal to weeds.

And as for water weeds - a separate but very menacing threat in many parts of the world - biological control methods can be used. Introduction of specific insects native to the Amazon has, for instance, proved successful in keeping disastrous water hyacinths infestations in check.

While appropriate use of modern herbicides is necessary to meet growing demand for food, greater use of non-chemical methods is desirable not only on general environmental grounds but because herbicide resistance is increasingly becoming a problem. In the United States for example, 13 weed species are now resistant to glyphosate, the herbicide most widely used.

After two decades fighting weeds, Labrado-Romero, a 62-year-old year-old Cuban, recently went into well-deserved retirement. "But the fight against weeds must go on," he says, "otherwise more people will starve".

Cape tulips – pretty but pests in pastures

Cape tulips, imported as attractive garden plants, are now pasture pests in Western Australia, South Australia, Victoria and New South Wales. Photo by: Paul Yeoh, CSIRO EntomologyCSIRO and the Department of Agriculture and Food Western Australia (DAFWA) are collaborating to try to outwit one of southern Australia’s worst agricultural weeds.

“We are initiating a one-year study to see if it would be feasible to control one and two-leaf Cape tulips (Moraea flaccida and M. miniata) using the rust fungus Puccinia moraeae as a biological control agent,” CSIRO Entomology’s Dr John Scott said.

Dr Louise Morin, CSIRO's experienced plant pathologist, will be testing various rust isolates to see how pathogenic they are on Cape tulips occurring in Australia as well as testing them on a few key closely-related, non-target plant species.
The tests will be conducted in the AQIS-accredited CSIRO Black Mountain Containment Facility in Canberra.

Dr Scott said Cape tulips appear to be suitable targets for biological control because there are only a few close relatives among Australian native species and no related crops.

The logical place to look for possible biological control agents for Cape tulips was their home range, South Africa. Earlier CSIRO surveys there identified three potential biological control agents, of which the rust appears the most promising.

This initial study, funded by DAFWA, will yield information on the aggressiveness of the rust on Cape tulips and assist in determining its biological control potential.

“It will also provide preliminary information on the susceptibility of key non-target plant species to the rust. This is an important first step in deciding if the rust should undergo future comprehensive host-specificity testing,” Dr Scott said.

Cape tulips were introduced to Australia from South Africa in the mid-19th Century as garden plants. Since then, they have become major pasture weeds in Western Australia, South Australia, Victoria and New South Wales. They are unpalatable and poisonous to livestock.

Cape tulips are also invading natural ecosystems and have the potential to be serious environmental weeds.