Grassy weed management strategies are much more difficult than for broadleaf weeds in an oat crop.
Growers should consider increasing seeding rates, using weed control (tillage or herbicide) prior to seeding and varying seeding dates. There are a limited number of herbicides registered to control grassy weeds. Lorox/linuron are registered for controlling barnyard grass and suppression of green foxtail.
Wild oat is the most serious weed concern for oat growers (Figure 4.2). Wild oat is highly competitive with oat crops. Increasing numbers of wild oat increases the yield loss of oat. Wild oat does not emerge early in the spring (making pre-seeding applications of glyphosate less effective) and it continues to emerge over 4 to 6 weeks. The earlier the emergence, relative to the oat crop, the higher the yield loss. Wild oat seeds can last in the seed bank over many years and the awn on the wild oat can assist the seed to ‘find’ soil depressions and aid in weed establishment. Wild oat has been selected for resistance to many common grass herbicides, making control in rotational crops difficult. Finally, wild oat seed contamination can be a reason for downgrading in some markets. Using a single strategy for wild oat is insufficient but there are a number of integrated weed management strategies available to manage wild oat.
CULTURAL WEED CONTROL
Choose fields with low wild oat populations (see crop rotation). Wild oat control in most rotational crops can effectively deplete wild oat populations. However, because of herbicide resistant wild oat, the reliability of herbicides is decreasing for many growers.
Grow a competitive oat variety and manage the agronomy in the field to increase the vigor of the oat crop.
Increase the oat seeding rate in order to have a more competitive crop. Increasing the seeding rate has several benefits, including increasing crop competition, reducing the tillers and thus increasing the uniformity of maturity.
Seed oat early to increase the competitive advantage of the crop. Early seeding has many advantages, including reducing the yield losses of oat and earlier maturity.
Delaying seeding until wild oat have emerged and are controlled has been advised previously but has serious consequences.
The strategy to delay seeding reduces yield and can delay harvest. Because wild oat continues to emerge over 4 to 6 weeks, this strategy is not recommended.
Fertilize the crop, not the wild oat. Applying fertilizer in precision bands adjacent to the seed row in order to make the crop as competitive as possible or use a delayed release seed placed N to keep nutrients for later crop stages.
Consider seeding oat with a larger seed size. (See research article below)
CHEMICAL WEED CONTROL
There are no selective herbicides than can remove wild oat from oat crops, either preseeding or for in crop applications. Pre-plant herbicide to control emerged wild oat can be less effective because of the relatively late seed emergence and extended germination period.
PHYSICAL WEED CONTROL
Direct seeding has been shown to reduce the density of wild oat. Seeds left on the soil surface are removed by seed predation from insects and birds. Additionally, wild oat seeds are not buried by tillage. The mulch that covers most of the soil reduces light reaching wild oat seeds, reducing germination. Post-seeding tillage to control emerged wild oat is an option for organic production.
Research Paper (2005): Crop Science 45: 1410-1416 (2005)
“Oat Caryopsis Size and Genotype Effects on Wild Oat-Oat Competition”
Christian J. Willenborg, Brian G. Rossnagel, and Steven J. Shirtliffe
“Wild oat competition causes extensive yield and quality losses in… oat”
“Traditionally, wild oat was controlled by delaying planting so that emerged wild oat could be controlled by tillage. However, delayed planting of oat causes substantial declines in grain yield, test weight, plump seed and groat percentage with a corresponding increase in thin seed percentage.”
“A key component of integrated weed management systems is to grow competitive varieties.”
“Our main objective was to assess the relative importance of oat caryopsis [grain] size and genotype in affecting wild oat-oat competition in the greenhouse….We conducted this study in a greenhouse because it provided us with a high degree of experimental control, repeatability, and precision, allowing us to isolate the effects of seed size on oat competitive ability.”
This greenhouse study was conducted in 2002 and 2003 at the University of Saskatchewan in Saskatoon. AC Assiniboia, CDC Boyer and CDC Orrin were the varieties used. All seed was sourced from the same location. The seed groupings LARGE, MEDIUM and SMALL were determined on the basis of the groat size to eliminate the effects of the size of the hull.
Results And Discussion:
“Oat derived from large caryopses [grain] produced 17% more biomass and 15% more panicles per m2 than plants derived from small caryopses, irrespective of genotype or wild oat competition. Similarly, plants established from medium-seeded caryopses produced 11% more biomass and 9% more panicles than from plants established from small caryopses.” It was noted that statistically, the results for medium and large seed were not significantly different from each other.
Broadleaf weed management strategies include increasing seeding rates, tillage prior to seeding and varying seeding dates. There are also a number of herbicides available for weed control in oat.
Herbicides containing 2,4-D should be avoided on oat as it has been shown to cause a considerable yield reduction. Products containing dicamba should be used according to the crop stage restrictions on the label. Application of dicamba products under stress conditions, such as drought, should be avoided.
Chemical control options are available in the provincial crop protection guides and in an app for the Alberta BlueBook.