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Getting a jump on weeds in small grains: Best defense against weeds is a vigorous, competitive crop By Dr. Michael Peel
NDSU Extension Small Grains Specialist
mpeel@ndsuext.nodak.eduThe combination of proper crop rotation, good cultural practices, and using effective, approved herbicides in a timely manner are
key defense mechanisms to minimize weed problems in small grains.
So too is getting small grains off to a vigorous start. The importance of seedbed preparation, seeding date, seeding rate, and fertility to small grain yields is much
heralded. These factors are important to successfully combating weeds as well, because they allow small grains to get a leg up on weeds. Yield loss and market discounts can be directly attributed to lack of weed
control in small grains, so indeed, practices that improve weed control also improve crop productivity and crop quality. Yield loss in small grains can occur directly as a result of competition with
weeds. Wild oat and wild mustard at 10 plants per square foot can reduce wheat yields by 35%. Two to three kochia plants per square foot
can reduce yields by 30%. The presence of weed seed in grain increases dockage and results in additional loss. Weed control is obviously important, especially with the currently depressed markets.
Use of weed-free seed should obviously be every producer's first management strategy for weed control. Using weed-infested seed, even if it comes at a reduced price, is poor economic management, especially if
new weed species are introduced. Allowing as many weeds as possible to germinate and removing them with tillage, or herbicides, can aid in eliminating some weed problems. This is
most effective when conditions are favorable for germination of weeds; when weed seeds are non-dormant and germinate quickly. The down side of this is that delaying seeding beyond the optimum planting date can
drastically reduce the yield potential of a small grain crop. Tilling the soil immediately before planting will kill weeds that have germinated, giving the
crop a competitive advantage and often improving weed control from chemicals that do not control weeds that have germinated. Seed bed preparation that favors uniform crop stands is important. No
matter what tillage system is used, a good seed bed is required. Seed should be placed in moist soil at a depth of one to two inches with soil
firmed around the seed. This will allow rapid water absorption and germination. Unfavorable conditions include soil that is dry, cloddy, or
too wet. Seeding into these conditions generally results in poor stand establishment, which favors weed infestation in areas of a poor crop stand.
Probably the best defense against weeds is a vigorous, competitive crop. In addition to good seed bed preparation, critical factors in successfully
establishing a small grain crop are timely planting, a planting rate that optimizes productivity, and adequate fertility. Spring-seeded small grains
should be planted as early as possible. Generally this is when the soil can be worked without causing undue compaction and is in the 50 F temperature range. Optimum seeding rates for wheat and barley in the
Northern Plains should be based on a final plant population of 1.25 million plants per acre. Adequate soil fertility ensures good seedling vigor and
rapid crop canopy establishment that inhibits germination and growth of many weed species. See NDSU Extension bulletins SF712 and SF723
for additional information on fertilizing wheat and barley or on the web: www.ext.nodak.edu/extpubs/plantsci/soilfert/sf882w.htm.
Cultivation or mechanical weed control with a harrow or rotary hoe can be used to control young annual weeds in established wheat and barley crops. These weeds include lambs-quarters, kochia, nightshade,
pigweed, wild mustard, green and yellow foxtail, and barnyard grass. The optimum time to control these weeds is soon after germination before they
have emerged. Wheat and barley are easily injured, so mechanical weed control should only be done when the crop is young, the 1 to 3 leaf stage, and should only be done once.
Even after everything possible is done to prevent weed infestations, environmental conditions can result in certain weed problems (i.e., cool wet weather favoring wild oat). Scouting fields should be done twice
weekly during early crop growth to determine the need for chemical weed control. When herbicide treatment is necessary, your choices will depend
on the type of weeds present, their stage of growth, crop growth stage, and crop rotational plans. For more comprehensive information, consult the 2000 North Dakota Weed Control Guide W-253. This and other
NDSU Extension publications can be obtained by calling (701) 231-7882. |
