|Figure 1. Distribution of wild oat in the United States|
Wild oat causes yield reductions directly by competing with the crop for moisture, light, and nutrients. Such losses occur early in the growing season. Most of the yield loss occurs before the crop is 45 to 50 days old. In addition to yield losses, wild oat may cause dockage at the elevator, increased tillage, reduced yields from delayed seeding, and increased expenditures for herbicides. Compared to herbicides used to control broadleaf weeds in small grains, effective wild oat control herbicides are expensive.
Wild oat infests 28 million acres of land in the United States. North Dakota is the most seriously infested state, with annual losses ranging from $150 to $200 million annually. Wild oat is extremely competitive and difficult to control because:
Early identification and treatment of wild oat plants is essential for control measures to be successful, but identifying wild oat seedlings in small grains is often difficult. Accurate identification is based on several distinctive characteristics of the wild oat plant.
Wild oat has an elongating first internode and coleoptile. Because of this characteristic, wild oat seedlings can emerge from greater depths in the soil than wheat and barley, which have only an elongating coleoptile. Research indicates that, under certain conditions, wild oat is capable of emerging from depths as great as 9 inches.
Another characteristic useful for early identification is the absence of auricles in wild oat. The leaves of wheat and barley have auricles that grow outward from opposite ends of the leaf collar, but these are completely lacking in wild oat (Figure 2).
|Figure 2. Wheat, barley, and wild oat plants (left to
showing leaf formations.
A third distinctive characteristic is the twist of the leaf blade. The leaf blade of all grass plants has a characteristic twist. The leaf twist of wild oat is counterclockwise (Figure 3), while wheat and barley leaves roll clockwise. In addition, the inflorescence (arrangement of flowers) of a mature wild oat plant is a spreading open panicle that often droops.
|Figure 3. Wild oat plant seedling, showing|
counterclockwise twist of leaves.
Wild oat seed vary in color from yellowish white to different shades of grey, brown, or black. A prominent depression or scar, sometimes called a "sucker mouth," is found at the base of the seed (Figure 4). The seed have prominent hairs at their base, and a twisted and bent awn (a hair-like appendage, also called a "beard") rises from the middle of the back of each seed. Domesticated oat seed usually are lighter in color and do not have the hair.
|Figure 4. Wild oat seed, showing|
"sucker mouth," hairs, and awn.
Wild oat is an annual that reproduces from seed. It germinates best when soil temperatures are cool, so very little wild oat seed germinates during the warm summer months. The weed shatters its seed early, before most crops are harvested. Freshly shattered wild oat seeds are generally dormant and therefore protected from fall germination and subsequent winter kill. However, dormancy periods in freshly shattered seed vary with the growing conditions during development. Wild oat seeds also have secondary dormancy that keeps the seed from germinating under unfavorable conditions such as high summer temperatures.
Wild oat plants rarely produce more than 200 seed, but viable seed are produced rapidly, generally within 7 to 10 days after heading. The twisted, bent awn that rises from the back of each seed is straightened and rewound repeatedly by moist conditions and often serves as a mechanism for covering freshly shattered seed.
Wild oat is very competitive. Researchers from several states have presented information about the wild oat problem, indicating that heavy infestations could reduce wheat yield by one-third. Results from tests in Texas from 1991 to 1994 indicate wheat yield reduction as high as 80 percent. One wild oat head per square foot reduced wheat yield 6 percent, and the average wild oat plant can produce 3 to 6 heads. In badly infested fields, wild oat heads exceeded 25 per square foot and resulted in severe yield reductions.
Wild oat seed may lie dormant for up to 6 years if left near the soil surface. If worked deeply into the soil, seed may remain dormant for many years. Deep plowing does not rid an area of wild oat; it only prolongs the problem.
Wild oat is being spread in Texas in these ways:
Preventing wild oat from starting in clean fields is the most economical control method. Prevent the spread of seeds by following these precautions:
Cultural practices can reduce wild oat stands at minimal cost. Follow these steps:
Research and demonstrations with herbicides have shown that wild oat can be controlled. A recommended procedure is late fall seeding in fields with wild oat infestations. Then apply glyphosate (Roundup® and others) to kill emerged wild oat before planting the crop. If this method is used, it is important to minimize soil movement at the time of planting.
Fourteen herbicides are registered for wild oat control in wheat. These
Eight herbicides are registered for wild oat control in barley. These
No herbicide gives 100-percent control, but, if they are used in conjunction with good cultural practices, adequate control can be obtained and herbicide applications can be justified economically. Grazing and haying restrictions vary between herbicides and producers should refer to the label for complete information.
Far-go® is a preplant-incorporated herbicide which comes in liquid and granular forms. It may be applied immediately after planting but before emergence. Incorporate the herbicide no deeper than 1 inch. Planted wheat must be at least 1/2 inch below the treated layer or injury will occur. The soil should be loose and mellow. Clods or trash cause poor incorporation and poor wild oat control. Best results are obtained when incorporation is done twice in opposite directions. Incorporate the herbicide immediately after application with a spring tooth harrow (field cultivator), or a rolling cultivator set for shallow incorporation, in a well prepared seedbed. Incorporation with a tandem disk or offset disk plow is too deep and causes severe injury to wheat.
The remaining herbicides listed above are applied post-emergence over the top of the growing wheat or barley crop. Time the applications so that the wild oat plants are in the two- to five-leaf stage. Best control is achieved on smaller plants, but consideration must be given to the non-uniform emergence of wild oat. If the applications are made too early, many of the weeds may not have emerged. If the applications are made too late, control is reduced, and you must use higher rates of the herbicide to achieve effective control. Assert offers some control of broadleaf weeds such as mustards and may have residual soil activity, while Avenge and Tiller have no residual activity.
Before using any herbicide, always read the label and follow all the directions listed. Rates, amounts, and the nozzle angle necessary for effective control are described on labels.
The information given herein is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement is implied.