The Old World bluestems compete well with weeds, and many examples of good final development of these stands in the face of severe competition exist. However, weed control is required but is often neglected during establishment and management of first-year Old World bluestems. Weed control is multifaceted and should be integrated into the management of young stands, generally after germination and early seedling development.
In all herbicide applications, proper calibration and operation of sprayers and other equipment is essential.
Do not add legumes or sod-seeded small grains to young stands, since such an action constitutes weed competition.

Part of seedbed preparation can be weed control (see the section on seedbed preparation). Weed population can be reduced by tilling deeply initially, preparing the initial seedbed starting in fall to midwinter, completing the seedbed just before planting, and delaying final seedbed and planting until after the earliest planting date. However, it may be unwise to delay planting because of weed control. Plant at the best time and control weeds other ways.

Figure 18. A weedy young stand of 'Plains' bluestem just before being sprayed with 2,4-D (left) and later that year after production development (right).

Old World bluestem seedlings have tolerance to the preemergence herbicide atrazine, which controls a wide range of weedy grasses and broad-leaved plants. Research indicates potential for planting Old World bluestem and applying atrazine before weeds or bluestem germinates (Dalrymple, 1983; Stritzke, personal communication). When atrazine was labeled for use on Old World bluestem, stands were injured on high-pH soils at even proper rates and on any soil if high rates were applied. The usual rate was 1 pound of active ingredient per acre. This information is from research results only. It is unlikely that atrazine will be approved by the United States government for general use on grasses.

There are several postemergence herbicides that can be used on first-year stands, three of which are the major ones: 2,4-D, triasulfuron (Amber), and metsulfuron (Ally). Less extensively used are mixtures of 2,4-D and picloram (Grazon P+D), 2,4-D and dicamba (Weedmaster), and dicamba (Banvel) alone in special situations.

When broad-leaved weeds are a problem, Old World bluestem can be sprayed safely with 2,4-D (figure 18). This spraying should be done regardless of top-dressing but especially in conjunction with fertilization after Old World bluestem emergence if broad-leaved weeds are present and considered detrimental.

Follow these guidelines and precautions. Spray after Old World bluestem has developed an adequate stand and is in the tillering stages. The plants may be only 2 to 4 inches tall. If weed competition is too thick to allow tillering, the spindly untillered bluestem plants should be 4 to 6 inches tall. Weed canopy helps protect grass seedlings from spray, but it prevents early tillering. If weeds are so thick that a complete canopy exists, or competition is extremely severe, spray regardless of Old World bluestem stand. Try to salvage the best of a bad situation. Use only 2,4-D amine at the lowest recommended rate for control of the weeds present. Rates are usually not less than 1/2 pound per acre or more than 1 pound of active ingredient per acre. Do not use a spreader-sticker of any kind, because it increases the chance of damage to very small grass seedlings. Do not mix 2,4-D and liquid fertilizer and spray on Old World bluestem seedlings, because the liquid fertilizer tends to desiccate small grass seedlings.

This 2,4-D herbicide prescription has been used on many thousands of acres without serious detrimental effect on Old World bluestem seedlings. Studies with weeping lovegrass also support this procedure (Dalrymple, 1969). Young Old World bluestem seedlings may be slightly suppressed temporarily, and a few may be killed, but the advantages of release from competition, increased stand, and earlier production far outweigh the slight damage to the seedling stands. Follow other label guidelines for proper 2,4-D spraying.

Do not spray 2,4-D and picloram mixtures, dicamba, or 2,4-D and dicamba herbicides on young Old World bluestem stands that are not well tillered or are only in the early stages of tillering. All ofthese herbicides tend to cause greater plant damage to weeds and establishing grasses alike. Do not use herbicides unless the bluestem plants have at least six tillers or are well covered with weed canopy, or unless the weeds are too thick, mature, resistant, or the like. If you use these herbicides, apply them at the lowest label rate possible. They are normally used in Old World bluestem plantings only when there are severe problems. Refer to the rope-wick application information. You may use dicamba alone when it is unwise to use 2,4-D.

Metsulfuron and triasulfuron herbicides have pre- and postemergence activity on a wide range of broad-leaved weeds. They do not perform as well as 2,4-D and other herbicides on ragweed and broomweed. Follow-up control with another postemergence herbicide may be necessary. There are fewer problems with volatility and damage to susceptible crops such as cotton and tomatoes with these herbicides than with 2,4-D and the other mentioned postemergence herbicides. Follow the label instructions on all herbicides. Special permits may be granted for other herbicide uses in pasture establishment and management. Check with the proper United States Department of Agriculture agency.