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Late Herbicide Applications
What kind of precautions should be considered when applying herbicides at advanced labeled crop growth stages. That is the question facing many producers. It's a judgment call based on careful evaluation of the weed, density and size and on crop stage. Considerations listed below should be included in the decision process.
1. Low weed populations or late emerging weeds won't cause much yield loss under wet
conditions but may cause harvest delays. Don't risk late spraying for a few annual weeds.
2. Give perennials, like Canada thistle or field bindweed, a priority. Treat infested
areas. You're not risking much crop yield.
3. Decide to sacrifice some weed control for crop safety-- heavy crop growth will help.
4. Avoid the critical period, 5-7 days before and after pollination. Barley pollinates
in the boot; oats and spring wheat soon after the head emerges.
5. MCPA amine or ester have the greatest crop tolerance at all stages. Good choice if
it will handle the weeds in question.
6. Amine forms of 2, 4-D are considered less harsh than esters--you want to avoid
damage to the flag leaf.
7. Bromoxynil has adequate tolerance in late grain but weed control may be inadequate
because the dense crop canopy will not allow coverage on larger weeds.
8. Don't apply Banvel combinations after the 4-leaf or Tordon combinations after the
5-leaf stage. These are high-risk treatments for late spraying.
9. Ally, Express or Harmony Extra appear to have a wide crop stage tolerance. Injury
risk factor, at late application, is related considerably to the tank-mix partner of MCPA
or 2,4-D. Consider MCPA ester rather than 2, 4-D ester as it is safer at late application.
10. Recommendations are based on data from applications at specified stages.
Responsibility for crop injury or inadequate weed control is assumed by those applying at
non-recommended stages. Follow label guidelines for maximum growth stages for particular
herbicides.
For more information see W-564 "Identifying Leaf Stages in Small Grain at http://www.ext.nodak.edu/extpubs/plantsci/weeds/w564w.htm
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