Northern Prairie Wildlife Research Center
Burning at the time of tiller elongation also affects smooth brome. For example, in eastern Nebraska, Willson (1991) found about a 50-percent reduction in smooth brome tiller density after a prescribed burn in early May, at the time of tiller elongation. Working in North Dakota, Kirsch and Kruse (1972) also found that basal cover of smooth brome decreased by half or more following a May burn. Similarly, Old (1969) reported that smooth brome burned in late April produced less than one-half the biomass produced in unburned areas.
Herbicides also affect smooth brome. In pastures dominated by smooth brome, Waller and Schmidt (1983) discovered that atrazine applied in late April at 1.9 lbs./acre reduced smooth brome by 91 percent and shifted the dominance from cool- to warm-season grasses. Dill and his colleagues (1986) also found that atrazine applied at a higher rate (2.9 lbs./acre) in the spring reduced smooth brome dominance in pastures with remnant native grasses.
Other factors affecting smooth brome are related to possible inter-specific interactions (McElgunn and others, 1972, Smith and others, 1973). For example, Hertz (1962) suggested that the number of smooth brome tillers per plant was determined to a large extent by competition from other species and adjacent smooth brome plants. He found that removing nearby individuals of a companion crop increased the number of tillers produced by smooth brome when compared to stands where a companion crop was not removed.
Our own studies (Willson and Stubbendieck, 1996; Willson and Stubbendieck, 1997) at Mead and at Pipestone have led us to several conclusions. At Meadwhere we studied the effects of spring burning at four stages of smooth brome growth: tiller emergence, elongation, heading, and floweringwe found that burning at emergence does not affect secondary tiller (tillers that grow following treatment) density or biomass in years when precipitation is normal or below normal, although in years with above normal precipitation smooth brome biomass increases dramatically. On the other hand, burning during the other three growth stages significantly reduces both tiller density and biomass, especially when repeated year after year.
In May 1990 and 1991 at Pipestone, we tested (Willson and Stubbendieck, 1996) four treatments: 1) single application of atrazine at 1.9 lbs./acre; 2) mow smooth brome to 1.5 in. height and rake off clippings; 3) burning; and 4) control. We found that only atrazine was effective in reducing the smooth brome tiller density, possibly because the herbicide killed the whole plant. Burning had a minor effect, but was not significantly different from the control. We suspect that the lack of success we had with burning at Pipestone as compared to Mead, and to the results obtained by other researchers, was due to differences in interspecific interactions - namely, at Pipestone there was not enough competition from big bluestem, which was a co-dominant with smooth brome at Mead, to inhibit the initiation and growth of secondary smooth brome tillers.