Jointed goatgrass is a troublesome weed in winter wheat. It is estimated that jointed goatgrass is spreading at a rate of 50,000 acres per year and that even light infestations of this weed can have a significant impact on crop yield. Overall, jointed goatgrass costs producers more than $145 annually due to reduced yield, increased grain dockage, and reduced land values.
Several factors make jointed goatgrass a nuisance in winter wheat systems. First, it emerges at almost the same time as the crop. Second, the resemblance between jointed goatgrass and winter wheat makes early infestations very difficult to identify in time for optimal management. Third, jointed goatgrass produces spikelets (sometimes called joints) that are about the same size as wheat, increasing the difficulty in cleaning. Finally, it can produce large number of seeds that may survive in the soil for up to five years.
Management practices used over the past 20 years are also responsible for the spread of jointed goatgrass. For example, the use of less competitive semi-dwarf wheat varieties, shorter crop rotations, increased fertilizer, and adoption of minimum tillage create environmental conditions that favor the spread of jointed goatgrass. Moreover, because jointed goatgrass and wheat are genetically related, chemical control is not possible in conventional winter wheat fields without unacceptable levels of crop injury.
The Clearfield wheat system offers growers the opportunity to control jointed goatgrass in winter wheat with an herbicide. It combines herbicide-tolerant wheat varieties with the Beyond herbicide (imazamox). Clearfield was developed through traditional breeding techniques and no foreign, non-wheat DNA was introduced or inserted into the wheat plant. Thus, Clearfield wheat is not a genetically modified crop and should not face national or overseas marketing problems.
Beyond is a broad-spectrum herbicide that provides post-emergence and in-season residual weed control of several grasses including jointed goatgrass, feral rye, downy brome, Japanese brome, cheat, Italian ryegrass, wild oats and volunteer cereals. It also provides control of several annual broadleaf weeds such as chickweed, shepherd's-purse, field pennycress, common lambsquarters, pigweed and wild buckwheat.
Preventing the selection and spread of herbicide-resistant weed biotypes is a challenge to the Clearfield technology. Herbicide weed biotypes resistant to Beyond could arise by either selecting for resistance among weed populations or by direct transfer of the resistant gene into jointed goatgrass populations.
Beyond inhibits the activity of the acetolactate synthase (ALS) enzyme, the first step in the biosynthesis of the branched chain amino acids valine, leucine and isoleucine. The lack of these amino acids restricts the building of proteins and results in the slow death of the treated plant. ALS inhibiting herbicides have been used in crop production since the 1980's. Unfortunately, it was quickly learned that the likelihood of selecting resistant weed biotypes with the continuous use of this class of herbicides is very high. Worldwide, there are 86 weed species reported to be resistant to ALS inhibiting herbicide, 37 of them occurring in the USA.
Another avenue by which jointed goatgrass may develop resistance to Beyond is through the direct transfer of the resistant gene into jointed goatgrass populations. Winter wheat and jointed goatgrass are genetically related and out-crossing from wheat to jointed goatgrass can occur. Although the natural out-crossing rate of these two species is very low, it is possible to develop herbicide resistance due to the transfer of the herbicide tolerance gene from wheat into jointed goatgrass.
A few simple steps will help producers protect and prolong the usefulness of the Clearfield technology.
First, producers should not continuously use Clearfield wheat on the same land. Rotation to spring crops such as corn, sorghum, sunflowers or peas provides a unique opportunity to rotate herbicides with different mode of actions and use alternative cultural and mechanical methods to break the cycle of winter weeds, including jointed goatgrass.
Second, the use of ALS-inhibiting herbicides should be limited to no more than two out of four years, unless other weed management practices are implemented. If possible, producers should use sequential or tank-mix partner herbicides with multiple modes-of-action on the target weed species.
Third, producers should properly manage weeds in the fallow year. During this period, the best option is to use tillage or a non ALS-inhibiting herbicide for burn-down to control weeds before they produce seeds.
In conclusion, Clearfield system provides a unique opportunity to chemically manage jointed goatgrass, a problematic weed of winter wheat. However, it is necessary to develop an integrated management system to insure the long-term usefulness of this technology. Please visit the National Jointed Goatgrass Research Program website at www.jointedgoatgrass.org for additional management information.
Disclosure. Common chemical and trade names are used in this publication for clarity by the reader. Inclusion of a common chemical or trade name does not imply endorsement of that particular product or brand of herbicide and exclusion does not imply non-approval.
Categories: Weed, Integrated Weed Management, Herbicide Resistance, Jointed Goatgrass