Posts Tagged: weeds
Over the last three millennia, the practice of growing rice has evolved and spread throughout much of the globe. From China, through India, to Greece and parts of the Mediterranean and from Europe to the Americas, rice has demonstrated its versatility in desert regions and wetland deltas alike. Abundant in carbohydrates, it is today one of the world’s most widely eaten foods.
While University of California researchers develop rice varieties more tolerant to the modern challenges of climate change — flooding, heat stress, drought — California rice farmers each year discover more new threats in the form of non-native and herbicide-resistant weeds. So well adapted are these weeds that if left unmanaged, they cause rice yields in some places to plummet to nearly nothing.
The introduction of rice to California in 1912 was fraught with weed challenges from the start. The traditional dry-seeding method allowed barnyard grass to quickly overrun fields. While a new water-seeding technique suppressed the weed, it led to a whole other set of problems. In continuously flooded fields — still the most widely used practice in California today — an imported weed, late watergrass, flourished. Aquatic weeds took advantage of the new environment while others gradually became more flood tolerant. For many years, advanced herbicides allowed farmers to gain ground over these weeds.
Then, beginning in the early 1990s, several weed species, including late watergrass, were found to be evolving resistance against the most powerful herbicides. A metabolic resistance to one herbicide, researchers discovered, could lead to resistance for another.
Weeds also found new ways to outcompete rice. One invasive weed, Ludwigia, grows fast and tall — as high as 10 feet. Shadowing the rice plants, it spawns tiny seeds that travel well in water. Other weeds, meanwhile, are small and run along the ground to avoid combines and some emerge earlier in the season than rice, dominating resources.
In the Department of Plant Sciences at UC Davis, professor Albert Fischer’s laboratory is battling rice weeds on a variety of fronts: by researching the evolution and mechanisms of herbicide resistance, finding traits that make rice varieties more competitive, developing resistance techniques through field testing at the industry-supported Rice Experiment Station in Biggs, Calif., and by encouraging farmers to diversify management methods.
One system Fischer encourages is the stale seedbed technique, which allows weeds to emerge first from a reserve of seeds in the soil. Once that flush is up, farmers use a general herbicide to kill the weeds. At least one local farmer with a bad weed problem has controlled late watergrass this way. By replacing herbicides with shallow tilling, organic farmers can use this method.
With each management system is a different combination of growing techniques and herbicides, depending on weather, soil moisture and soil temperature, among other factors. Fischer’s team at the experiment station spends much of its time testing these herbicides on new weeds.
UC Cooperative Extension farm advisors encourage growers to also sanitize equipment, rotate crops, scout for surviving weeds and apply herbicide only when necessary, easing selection pressure on weeds while reducing environmental impact. Along that line, Fischer’s team is discovering how switching growing techniques and irrigation systems may be helping farmers meet higher environmental standards, addressing a trend of steeper water prices in California. Other researchers see this as an opportunity to reduce greenhouse gases released from decaying rice stalks post-harvest.
For each strategy, researchers weigh costs over benefits to select the right weapons for arming farmers entangled in this ongoing war with weeds.
You may wonder about this practice of ‘sheeping off’ or grazing alfalfa fields, as sheep are most associated with rangelands in the coastal foothills or the Sierras. Basque sheepherders have historically managed sheep grazing in the Sierra Nevada mountains, which is a legacy that still remains in arborglyphs, or drawings in aspen trees, and in current grazing leases on federal lands. But sheep grazing in alfalfa fields has also been a long-time practice, probably for as long as there’s been alfalfa in our valley.
Alfalfa growers also benefit from sheep grazing in their fields during wintertime when the alfalfa is dormant. Alfalfa is a perennial crop which means that the root system remains alive below ground throughout the year even when the stems and leaves die during winter dormancy. Sheep feed on winter weeds, helping to control them in both seedling as well as established alfalfa stands that may negate the need for an herbicide treatment. Sheep grazing also reduces the alfalfa vegetation that dies back in winter, producing cleaner hay, the following spring. Sheep also help control weevil insect pests by feeding on older alfalfa stems, where the weevils lay eggs. This practice may help reduce weevil pressure and feeding damage to the first alfalfa cutting when weevils are actively feeding, a positive benefit, especially for organic growers.
The correct timing of alfalfa grazing is especially important for sheep producers since incorrect timing can result in a potentially lethal condition in sheep called bloat. Bloat occurs when a ruminant, such as a sheep, consumes too much fresh alfalfa with a high concentration of leaf proteins called saponins. When saponins are digested in the rumen, they create foam that prevents the sheep from burping up gases that are a produced from digestion in their stomach. Grazing too early in the fall or too late in the spring increases the risk of bloat, which is another reason why alfalfa grazing is done during the winter months.
Studies in California have documented economic benefits for both sheep producers and alfalfa growers. Sheep producers benefit from high quality feed during wintertime. Alfalfa growers benefit from weed and weevil control, as well as cleaner hay that can result in higher quality forage compared to non-grazed alfalfa stands.
Next time you come upon an alfalfa field full of sheep, know that they’re there for a purpose, providing feed for sheep and weevil and weed control for the alfalfa, in an environmentally sound manner. And, see if you can get in a game of ‘I Spy’ and find those Great Pyrenees dogs.
For more information, see the articles listed below:
- Bell, C.E. and J.N. Guerrero. 1997. Sheep grazing effectively controls weeds in seedling alfalfa. California Agriculture 51(2):19-23. http://ucce.ucdavis.edu/files/repositoryfiles/ca5102p19-67649.pdf
- Doran, M.P., L. Hazeltine, R.F. Long and D.H. Putnam. 2010. Strategic grazing of alfalfa by sheep in California’s Central Valley. Technical Report. http://cesolano.ucanr.edu/files/63758.pdf
- Pelton, R.E., V.L. Marble, W.E. Wildman and G. Peterson. 1988. Fall grazing by sheep on alfalfa. California Agriculture 42(5): 4-5. http://ucce.ucdavis.edu/files/repositoryfiles/ca4205p4-68804.pdf
'Sheeping off' an alfalfa field.
For conventional growers, chemical herbicides have taken the drudgery out of weed control. For organic farmers, weeds continue to be a perennial headache.
Many large-scale organic growers have turned to mechanical cultivators to dislodge weeds. However, standard cultivation systems leave an untouched band of soil around the seedlings that must be cleared by hand. This hand labor often represents a large part of total production expenses.
Richard Smith, a UC Cooperative Extension advisor in Monterey County who specializes in vegetable production and weed control, heard about “finger weeders” while at a conference in Germany.
“There is a brand available in the U.S., but the European design is much better,” Smith said.
He purchased a finger weeder from the German Kress Company and conducted trials on commercial farms in Monterey County to assess their effectiveness in organic vegetable production. With this system, hard plastic discs with long fingers are pulled by a tractor horizontally down the field, dislodging recently germinated weeds while leaving transplanted vegetables unharmed.
The timing of cultivation is critical. For transplanted vegetables, the cultivation must be done after the plants are firmly rooted and weed seedlings have just one small, tender root. Soil moisture also influences the effectiveness of the finger weeder.
In a trial Smith conducted on organic leeks, the finger weeder removed 80 percent of weeds, while the standard cultivator removed 29 percent. Hand weeding time was reduced by 45 percent, from 19 hours per acre to 10 hours per acre. The yield of the leeks was not affected by the finger weeder cultivation.
On an organic radicchio farm, the finger weeder removed 81 percent of weeds, while the standard cultivator reduced 48 percent. Hand weeding time was reduced 44 percent, and the yield was unaffected.
In six out of eight trials, the finger weeder significantly reduced hand weeding time compared to standard cultivation.
“We want to raise awareness among our growers that this is a viable option for weed control on organic farms,” Smith said.
Smith is also studying other high-technology organic weed control systems, such as computer-guided cultivation equipment.
“There is tremendous potential in this technology, but it is very expensive,” Smith said.
For more information on organic weeding options, see the video below:
Many funding sources for weed eradication have been reduced or completely eliminated. According to the California Assembly Budget Committee’s annual Preliminary Review of the Governor’s Proposed 2012-13 State Budget, the California Department of Food and Agriculture will absorb a permanent budget reduction of $12 million in program cuts, in addition to a $19 million budget reduction in 2011-12. Funding for weed management areas (WMAs) has been reduced to the point that many WMAs have become inactive or are being managed voluntarily as an adjunct to other duties.
http://www.cal-ipc.org/) annual symposium at Lake Tahoe in October, it was stressed that competition for limited funding will pit us against ourselves and each other. Only by working together, creating collaborative projects, will we be able to benefit from the limited funding opportunities available.
Enter the collaborative grant-funded project. Agencies are looking for applications that demonstrate community support from a diverse range of stakeholders. For example, the Sierra Nevada Conservancy (SNC) is currently reviewing proposals received in response to their Healthy Forests initiative. Proposition 84 — The Safe Drinking Water, Water Quality and Supply, Flood Control, River and Coastal Protection Bond Act of 2006 — will fund approved projects. Five million dollars is available this year for healthy forest projects; next year an equal amount will be available for rangeland projects.
Two weed control projects created by UC Cooperative Extension Central Sierra received SNC invitations to submit complete grant applications. One project is a collaboration between UCCE, the U.S. Forest Service, and Yosemite National Park; another works in partnership with Cal-IPC.
As an example of the collaborative partnerships being sought by funding agencies, the National Fish and Wildlife Foundation is offering the ‘Pulling Together Initiative’ which “seeks proposals that will help control invasive plant species, mostly through the work of public/private partnerships such as Cooperative Weed Management Areas.” Successful projects must “have a project Steering Committee composed of local cooperators who are committed to working together to manage invasive and noxious plants across their jurisdictional boundaries.”
Clearly, in light of decreased federal and state funding, a strategic direction for weed-control projects will be to leverage resources, working together to do what no one agency can accomplish alone.
Two additional collaborative projects, created by Wendy West of UCCE Central Sierra, are highlighted here:
- A Weed-Free Forage List providing California resources for weed-free feed and erosion control materials will soon be posted on Cal-IPC’s website. The site will also contain explanatory information about weed-free certification, along with links to inspection procedures and noxious weed lists.
- Workshops designed to help prevent the spread of weeds during construction, aggregate production and maintenance activities are being offered throughout the state. The workshop is hosted and sponsored by U.S. Forest Service, National Park Service, California Department of Food and Agriculture, University of California and University of Nevada Cooperative Extension, and the California Invasive Plant Council.
A Fresno County workshop was held in January and a sold-out workshop is scheduled for March in Los Angeles County. If you are located in the central California region that includes Amador, Calaveras, El Dorado, Madera, Mariposa, San Joaquin, Stanislaus or Tuolumne counties, please consider attending the next workshop, scheduled for April 9 in Sonora. The final workshop will be held in Truckee on May 2. Register for the workshops here./span>
Weeds, weeds, weeds! Have you noticed? This has been a banner year for weeds. Puncturevine where I’ve never seen it before. Garden soil covered with common purslane (at least it’s good in salads). And solid stands of yellow starthistle everywhere!
What can be done? First of all, identify your weeds. Different weeds require different treatments. Is it an annual or perennial? Does it propagate by wind-blown seeds or by runners? The University of California Integrated Pest Management website, has weed-identification guides that are fun and easy to use. The website also offers treatment guidelines.
In the California foothills, yellow starthistle (YST) is perhaps the most common weed of concern. It impacts much of our open space - agricultural and rangeland - and intrudes into our neighborhood landscapes. Yellow starthistle currently infests more than 15 million acres of land in California. Not only does it prevent recreational use, like walking or hiking, but it chokes out native grasses and wildflowers. It is also poisonous to horses, causing a neurological disorder called "chewing disease” which can be fatal once symptoms develop.
That said, yellow starthistle can be hand-pulled at any time in its lifespan. In its present dry and spiny stage, pulling the weeds can inflict pain, so be sure to wear gloves. Double-bag the plants and burn them later in the fall.
There is a fairly new herbicide (2009) on the market from Monterey Chemical called Star Thistle Killer.
Local pest control companies are also available to provide a one-time herbicide application for yellow starthistle. For more information, go to the Central Sierra Cooperative Extension website or call the Yellow Starthistle Leading Edge Project in the UC Cooperative Extension office at (530) 621-5533 or (209) 533-6993.
Information adapted from the University of California Integrated Pest Management Program and from “Yellow Starthistle: Brief Homeowner Information Sheet” by John E. Otto, Amador County Master Gardener.
Also see the following video on yellow starthistle control.