Wild oat control in winter wheat

Billy E. Warrick and Todd Baughman, Extension Agronomists, Texas A&M University, 02/25/2013


Wild oat, Avena fatua, is a severe problem in the Rolling Plains and the northern Blacklands of Texas Infestations range from scattered stands along ditches and edges of fields to severe infestations that prevent wheat harvest.

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:

  • It has delayed germination.
  • It shatters its seed before most crops are harvested.
  • Its growth habit is similar to that of wheat, barley, and domesticated oats.

Identification

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).

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.

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.

The Problem

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:

  • Planting seed contaminated with wild oat seeds. The Texas seed law allows up to 300 wild oat seed per pound of commercial seed, so simply purchasing seed does not ensure that it is wildoat-free.
  • Moving combines and other equipment from infested fields to clean fields. Many fields have a strip of wild oat around the edge and none in the center. As the combine moves across the field, wild oat seed is carried with it. In addition, seeds of wild oat are carried easily from field to field by other farm equipment.
  • Wind and water moving across fields.
  • Birds and fur-bearing animals transporting seeds as they move.



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