Grassland mangers are often faced with an undesirable plant species that they are trying to control with the most cost-effective treatment out there. However, sometimes just by changing when you graze these species, you can have very effective results of managing them. In order to do this you need to know some of the growth characteristics in the species of plant you are targeting. Grasses can be divided into two groups based on their season of growth, cool and warm. Cool seasons grow in the early part of the growing season and then again in later fall. Warm seasons, on the other hand, produce most of their growth during midsummer.
In South Dakota, introduced cool season varieties are regularly the species of plant many producers try to control. In the eastern part of the state, smooth brome grass and Kentucky bluegrasses are a nuisance and on the western part it is crested wheatgrass and cheat grass.
I recently finished my graduate research project in Brookings looking at the effects of intensive early stocking (IES) on species composition of pastures. IES, also called double-stocking, essentially doubles the number of livestock on a given pasture for the first half of the grazing season, and then are removed allowing the pasture to rest the second half of the growing season. For example, we had two 20 acre pastures, one stocked season long (SL) with 10 head of yearlings for 4 months (June-September) and the other stocked IES with 20 head of yearlings for 2 months (June-July). The stocking rate remained the same on both pastures but the grazing pressure was increased during the early part of the summer with IES. By using IES we saw an increase in warm season grasses however the cool seasons were not negatively affected but if a higher intensity of grazing was accomplished perhaps we would see a decline in cool season.
A research project in Montana found that grazing can be used to successfully suppress cheat grass. The project demonstrated that intense, repeated grazing with sheep, early in the growing season could substantially reduce cheat grass production. However, grazing must be intense and occur early in the season before cheat grass begins to mature. Grazing must also be repeated because cheat grass is capable of recovering from a single defoliation and producing seed.
Keep in mind that grasses like Kentucky bluegrass, smooth brome grass, and crested wheat grass are perennial plants, while cheat grass is a winter annual. However, the fundamentals are the same. If you can obtain the grazing pressure on the species that you are trying to control, when that species is trying to grow, you can have varied success at managing it and utilize it at the same time. In SD cool season species often cause the problems so early grazing can help control them, but it is critical to know the species you are targeting and some of the characteristics associated with it. The more intense the grazing pressure is, the more likely you are going to supress the species you are trying to control. Nevertheless, it is equally critical that heavy grazing pressure be removed before desirable plants begin to grow, otherwise they will be damaged and their vigor reduced.
Source: Kyle Schell