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Chemical vs. Cultural Control

Chemical Control

 

Selective chemical control of jointed goatgrass in conventional winter wheat is not available to growers. The genetic similarities and similar life cycles between wheat and jointed goatgrass have made selective herbicide development very difficult.  However, BASF has developed the Clearfield wheat system, which used conventional breeding methods to identify a gene that confers resistance to imazamox (Beyond) in wheat plants containing the gene. Beyond provides excellent control of jointed goatgrass in Clearfield winter wheat varieties, but it will kill conventional wheat varieties. Recently released two-gene Clearfield varieties provide extra crop safety and allow the use of crop oil concentrate or methylated seed oil as additives to increase the activity of Beyond on weeds. The use of these additives on single-gene Clearfield wheat varieties can result in unacceptable crop injury. Because jointed goatgrass and winter wheat share the D genome, it important to follow the Clearfield stewardship guidelines to prevent the transfer of the resistance gene from wheat to goatgrass.

 

Cultural Control

 

Strategies
Click on each individual control method to learn more about each factor.

  1. Use crop rotations that extend the period between winter grain crops to at least three years.
  2. Plant certified or jointed goatgrass-free seed.
  3. Delay seeding in the fall.
  4. Plant tall, fast growing winter wheat varieties.
  5. Plant wheat at recommended or above normal seeding rates and in narrow rows.
  6. Maintain healthy, vigorously growing winter wheat.
  7. Apply fertilizer so that it is available to the wheat, not the goatgrass.
  8. Prevent new seed production in fallow, readsides, or waste areas.
  9. Properly adjust the combine.
  10. Use tarps to cover trucks during grain transport.
  11. Do not transport contaminated straw to goatgrass-free areas.
  12. Grind contaminated grain before feeding to livestock.
  13. Deep plow fields in late fall or early spring once every 5 or 6 years.
  14. Burn wheat stubble to kill most JGG seed on the soil surface.

 

1.  Use crop rotations that extend the period between winter grain crops to at least three years. In predominately winter wheat-fallow areas, this can be accomplished by switching one year to a spring wheat.  Because the soil is moist in early spring, tillage by itself will not kill all of the jointed goatgrass.  Therefore, infested fields should be sprayed with glyphosate several weeks before they are tilled.  Consider rotating with late spring-planted warm season crops such as corn, grain sorghum, proso millet, or sunflower.  Cool-season crops such as spring wheat and spring barley must be planted early to give them time to germinate and produce seed.

The use of tillage was once thought to enhance jointed goatgrass germination after wheat harvest and during fallow periods.  Recent studies in Kansas indicated that no differences in JGG germination were seen for mechanical fallow (tillage) or chemical fallow (herbicides; no-till) during most years.  However, using tillage in fallow during a dry season may promote more JGG germination compared to using only herbicides.  The thought behind this is that tillage provides better soil seed contact and allows the JGG seeds to better access subsurface soil moisture compared to using only chemicals (no-till).  In addition, western Kansas typically receives enough rainfall during germination periods in the fall and spring to promote JGG emergence in no-till, chemical fallow fields.  Keep in mind that this practice may not work for all regions where jointed goatgrass is a problem.

 

2.  Plant certified or jointed goatgrass-free seed. Certified seed will assure growers their seed source is not contaminated with jointed goatgrass spikelets.  Contaminated seed is likely the primary source of new jointed goatgrass infestations.  If using bin-run or brown bagged seed, always check to be sure your seed is free of jointed goatgrass. 

 

3.  Delay seeding in the fall. If a rain occurs near planting time, wait a few days for the jointed goatgrass seed to germinate.  Use tillage or non-selective herbicides to kill goatgrass seedlings before planting wheat.  Delaying the time of planting may allow more jointed goatgrass seedlings to emerge and be controlled.  Following planting, the ideal scenario would see winter wheat emerge several weeks before the next flush of jointed goatgrass seedlings.  Delayed emergence relative to winter wheat will reduce competition from jointed goatgrass.  A Colorado study showed that 15 jointed goatgrass plants per square yard reduced wheat yields 27% when it emerged with winter wheat, 17% when it emerged 42 days later, and 6% when it emerged in March, 150 days after winter wheat.  Similar studies showed that delayed emergence of jointed goatgrass dramatically reduced jointed goatgrass tiller and spikelet production.  With less competition, winter wheat yields were generally greater when jointed goatgrass emergence was delayed for several weeks or months.

 

4.  Plant tall, fast growing winter wheat varieties. The tall characteristic alone will not ensure the maximum competitive advantage for the crop.  Varieties that are most competitive will emerge quickly, have rapid shoot and root growth, and constantly shade jointed goatgrass throughout the growing season.  Soil moisture and early growth rate are important factors for crop competitiveness.  A USDA-ARS study in Washington state showed that some varieties are more competitive with jointed goatgrass than others.  This study also demonstrated how jointed goatgrass is much more competitive with winter wheat under dry conditions.

 

5.  Plant wheat at recommended or above normal seeding rates and in narrow rows. Higher plant populations can increase crop competition with goatgrass.  Producers in high rainfall areas may see increased competition with little risk to wheat yield.  However, low rainfall areas may be precluded from increasing seeding rates due to a higher risk of reduced yields and test weights.  Winter wheat seeding rate should not be below the recommended rates.  Narrow row spacing can also increase crop competitiveness.  High seeding rates and narrow row spacing will not always increase yield, but when combined with other cultural practices including a tall, fast growing variety will minimize jointed goatgrass competition and weed seed production.

 

6.  Maintain healthy, vigorously growing winter wheat. A healthy crop can be the most effective and economical weed control practice.  Crops suppress weeds primarily by shading.  Management strategies that hasten shading of weeds will ultimately lead to a more competitive crop and less weed seed production.

 

7.  Apply fertilizer so that it is available to the wheat, not the goatgrass. Research in Wyoming has showed that jointed goatgrass was most competitive when fertilizer was broadcast applied compared with banding or spoke-wheel injection.  Jointed goatgrass likely profits from the broadcast treatment because it usually germinates in the top inch of soil where broadcast fertilizer is readily available.  Placing fertilizer deeper into the soil profile allows winter wheat roots to access the fertilizer more quickly and fully than jointed goatgrass roots.  Research in Colorado suggested that timing of fertilizer application is important for reducing the impact of annual grass weeds in a winter wheat-fallow rotation.  These studies showed that a fertilizer application in April of the fallow season, rather than at fall planting, favors winter wheat over annual grass weeds.  Nitrogen applications in the spring of the fallow season leach deeper into the soil profile than nitrogen applied later in the season.  This deeper nitrogen is less available to surface germinating weeds, such as jointed goatgrass and downy brome, than to winter wheat.

 

8.  Prevent new seed production in fallow, roadsides, or waste areas. Hand rogue scattered plants or use non-selective sprays to kill small patches before the weed produces viable seed.  Timing of jointed goatgrass control is critical for eliminating seed production.  Jointed goatgrass should be controlled before flowering (anthesis) to prevent seed production.  A study in the Pacific Northwest showed that mowing or treating JGG seed heads (50% emerged from the flag leaf) with glyphosate or paraquat eliminated viable seed production.  However, gradual delays in treatment timing after flowering resulted in progressively higher numbers of viable goatgrass seed produced.  For very late goatgrass control, paraquat or mowing may be preferred over glyphosate, which kills the plant more slowly and may allow more viable seed to develop.  Treatments of paraquat or mowing at early post-anthesis, reduced seed production to less than 20% of the glyphosate treatment.  Clean combines and other machinery before entering goatgrass-free fields.

 

9.  Properly adjust the combine. Proper combine adjustment can help in removing additional JGG seed from the field.  This is purely up to the individual!  You need to decide if it is more important to deal with added JGG seed to the field or if removing as much as possible would benefit you in the long run.  These are some issues that one needs to consider if total crop failure is evident.

 

10. Use tarps to cover trucks during grain transport. The lightweight spikelets, which are easily confused with wheat straw, can blow off the truck and start new infestations.

 

11. Do not transport contaminated straw to goatgrass-free areas. This point really needs no explanation.

 

12. Grind contaminated grain before feeding to livestock. Run contaminated grain through a hammer mill before feeding to livestock.  A Nebraska study showed that 20% of goatgrass spikelets germinated after 24 hours of rumen digestion.  Spikelets processed through a fin-grind hammer mill before feeding eliminated goatgrass germination.  Chemical analysis of jointed goatgrass spikelets showed that protein content was 11.7% and crude fiber was 26.1%.  A study in Oklahoma showed that when cattle were allowed to graze wheat in the fall, jointed goatgrass seed production increased and wheat yields decreased by 20%.

 

13. Deep plow fields in late fall or early spring once every 5 to 6 years. About 90% of JGG seedlings emerge from the top inch of soil, whereas very few emerge from below 3 inches.  This may be one reason why jointed goatgrass seems to flourish under shallow tillage compared to deep tillage.  Compared to sweep tillage, moldboard plowing has reduced populations in the following crop by 60%.

Frequent plowing may only serve to bring more goatgrass seed to the surface.  Deep plowing helps bury jointed goatgrass seed to the point where seedlings have a hard time emerging.  However, one has to think about possibly promoting germination during fallow periods to reduce the amount of JGG seed already in the soil.  This is obviously a management decision that needs to be made.

 

14. Burn wheat stubble to kill most JGG seed on the soil surface. For burning to destroy jointed goatgrass spikelets, there must be enough surface residue to sustain high temperatures and straw must be uniformly distributed.  Post harvest burning of wheat stubble during dry field conditions has killed 90% or more of the goatgrass seed lying on the soil surface.  Spikelets in soil cracks and or covered by a thin layer of soil may not be destroyed.  Because of air pollution and the potential for soil erosion following the loss of straw cover, burning should be restricted to small, isolated goatgrass infested areas.  Large areas of wheat stubble should be burned only as a one-time event as part of a long-term management program that includes other cultural control practices such as a temporary change in crop rotation.