Tech Tuesday

New Way to Stop Invading Weeds?

Study makes use of herbicides in a new way, misdiagnosed stem canker a soybean risk and new research aims at food vs. fuel debate.

Herbicides, by their very name, mean they kill plants. But researchers at USDA's Agricultural Research Service are looking at an approach that would sterilize weedy grasses rather than kill them. The work may show this approach a more economical and environmentally sound approach.

Rangeland ecologists at ARS Fort Keogh Livestock and Range Research Laboratory in Miles City, Mont., conducted a study in two locations - Miles City and with a colleage at Dow AgroSciences in Indianapolis, Ind. They looked at exotic annual grasses including Japanese brome, cheatgrass and medusahead, which are causing damage to millions of acres of grassland in the West. The challenge comes from herbicides that not only stop invasive weeds, but also kill desirable perennial grasses.

However, if growth regulator products are used they don't usually hit those desirable perennial grasses so hard. This class of herbicide is usually used to control broadleaf weeds in wheat and other crop grasses, and on rangelands. The ARS researchers knew that when dicamba and other growth regulator herbicides are applied to cereal crops late in their growth stage, before seed formulation, the plants produce a lot fewer seeds.

They tested to see if these herbicides had the same late-stage application impact on Japanese brome, an invasive weed. In greenhouse experiments, they tested dicamba (Banvel/Clarity), 2,4-D, and picloram (Tordon) at typically used rates. They found that picloram reduced seed production nearly 100% when used at the late growth stage of the weed; dicamba was slightly less effective, but nearly eliminated all seed production; and 2,4-D was much less effective.

Since annual grasses only survive in soil a year or two, it should take only one to three years of herbicide treatment at the right growth stage to reduce the soil seed bank of annual weedy grasses without harming perennials, the researchers say.

In field tests, beyond the greenhouse, researchers found similar results. They also added aminopyralid (Milestone) to the field tests and found it as effective is picloram. The next stage of the research will look at lower-dose applications to cut costs and reduce non-target damage to broadleaf plants.

Watching for Stem Canker. Stem canker is becoming an increasing worry for soybean producers, in areas where the disease had disappeared for years. That's what South Dakota State University plant pathologist Thomas Chase is finding. A disease he says he stopped teaching about in class, started turning up in fields in 1998, and he sees it as a problem to scout for in 2010.

Stem canker, caused by a fungus, is divided into two types Northern and Southern. For South Dakota only the Northern version has been found - and it was a disease that caused a lot of trouble in the 1940s through the early 1950s until extremely susceptible varieties were removed from production. Southern stem canker arouse in the South and is a significant problem for those growers.

Chase says the resurgence of stem canker in the past few years in Northern states may be related to deployment of highly susceptible varieties, changes in farming practices, changes in pathogen population. Or it may have something to do with seed sources.

The SDSU Row Crops Pathology Project is looking at the question of how the host, pathogen and environmental factors contribute to stem canker epidemics in South Dakota and the surrounding region. So far, the impact of this disease is scattered and intermittent. That makes it hard to find as Chase notes he has to count on farmers calling them to find the infected fields.

For 2010, Chase advises scouting for the disease in early to mid-August and look for symptoms that include cankers or discolored areas centered on lower leaf nodes, dead and dying petioles, rapid wilting resulting in shriveled gray to brown colored leaves. You can confuse white mold or Phythophthora root and stem rot for stem canker. You can rule out white mold if the plants don't have the white moldy growth, and there's an absence of sclerotia on and in stems. Phythophthora can be ruled out by location of stem lesions - which are found on the base of the stem and are continuous with the soil line.

Chase recommends that infected fields be rotated out of soybeans for several years, select a resistant variety or consider using a fungicide seed treatment. You can learn more by visiting Stem Canker Basics.

Breeding Away Food vs. Fuel Debate. Researchers at the University of Minnesota may have a better answer on that food versus fuel debate that raged during 2008. They did genetic studies of corn and found varieties that can be bred to optimize properties for cellulosic ethanol without hurting grain yield.

USDA and the U.S. Department of Energy are promoting development of plant feedstocks suitable for producing cellulosic ethanol. In this scenario, plant materials rich in cellulose are broken down into sugars that are fermented into ethanol. Corn grain would then be harvested for feed and food while plant residues are captured for fuel production.

Since the 1920s, hybrid corn varieties grown by U.S. producers have been bred for high grain yield and superior agronomic performance. But these varieties have not been bred for qualities that would make their stover suitable for producing cellulosic ethanol.

The U of M genetic studies show that dual-purpose corn hybrids are feasible. Their work - funded by the USDA-DOE Plant Feedstock Genomics program - was reported in the March-April 2010 issues of Crop Science published by the Crop Science Society of America.

The research team found either neutral or favorable relationships among grain yield, stalk lodging, and stover-quality traits considered most important for producing cellulosic ethanol. Even though current corn lines have not been bred for cellulosic ethanol, they exhibited a significant amount of genetic variation for the stover-quality traits. DNA fingerprints indicated the lack of "silver-bullet" genes for cellulosic ethanol: instead, stover-quality for cellulosic ethanol is controlled by many genes that need to be accumulated in a corn hybrid by selective breeding.

Work now turns to DNA fingerprints and year-round breeding to fast-track a dual-purpose corn. The researchers note there are other questions to answer - including the big one: How much stover can be taken off of a field without hurting soil quality? But scientists are hard at work at those kinds of questions too.

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