Additional Information on Broadcast Chemical Site Prep
If perennial pasture grasses are present on the site, a chemical site preparation may be necessary. However, if the landowner wants to retain the pasture grasses with the longleaf pine, then scalping and or sub-soiling are sufficient for your site preparation. A good example is where some landowners will be planting longleaf pine in pastures with the intention of grazing cattle in the future (called Silvipasture).
If perennial grasses are unwanted, then they should be eliminated or controlled through the site preparation. In general, mechanical methods are ineffective at controlling perennial pasture grasses. Disking or plowing Bermuda grass is a really bad idea. Bermuda grass will have no problem reclaiming the site the spring following planting. Once longleaf seedlings are in place, it is very difficult to control Bermuda grass on the site.
Bermuda grass can be sprayed with high rates of Accord SP® or Roundup® (usually 5 quarts/acre) when the grass is actively growing. Alternatively, some people have had better luck with Arsenal® (usually 24 oz/acre) or Chopper® (usually 48 oz/acre). With glyphosate products (Accord SP® or Roundup®) there is no time delay in planting. You can spray in the morning and plant the same site that afternoon. With imazapyr products (Arsenal® and Chopper®) several weeks must pass between the herbicide application and planting your longleaf pine seedlings.
Bahia grass and fescue are more easily controlled than Bermuda. Usually, 3 quarts of Accord SP® or Roundup® will kill these grasses with a single application. As with Bermuda grass, make sure to spray the chemical while the grass is actively growing. Do not spray in the middle of a drought. Do not spray while heavy dew is still on the grass. And time the application so the chemical has time to dry before any subsequent precipitation.
Dr. Thomas G. Barnes with the Department of Forestry at the University of Kentucky reported on his research killing fescue in the February 2002 issue of Wildlife Trends. They found that imazapic at 12 oz/acre with a surfactant was extremely effective at killing fescue. Dr. Barnes suggested that imazapic be applied while the fescue is actively growing and about 4-6” in height.
Annual introduced grasses are oftentimes the worst competitors in agricultural sites. It is not uncommon to find longleaf survival rates of 10% or less beneath crabgrass. Any grass that grows rapidly and forms a “mat” or “carpet” has the potential to severely reduce longleaf seedling survival. If uncontrolled, both crabgrass and Bermuda grass (a perennial) will form mats that blanket the seedling. The root systems of the grasses compete for water and nutrients while the aboveground biomass covers the seedling, reducing the seedling’s access to sunlight. Crabgrass, buffalo grass, and other annual grasses are late germinants. These species will not be controlled by early season pre-emergent herbicide applications. If these species are present, at least one follow-up application of Arsenal®, Envoy®, or another grass herbicide should be applied shortly after the grasses start germinating. Don’t wait too long. Generally grass herbicides are most effective if applied the first couple weeks following germination. Typically, we will apply our second round of herbicides in or around mid-May to control crabgrass and or residual Bermuda grass.