Submitted to: Southeastern Exotic Pest Plant Council
Publication Type: Abstract Only
Publication Acceptance Date: 5/3/2005
Publication Date: 6/3/2005
Interpretive Summary: none required.
Technical Abstract: Cogongrass [Imperata cylindrica (L.) Beauv.] is a non-native, invasive weed that is disrupting economically and ecologically important plant communities in the southeastern United States. Cogongrass is invading forest lands, especially those growing loblolly pine (Pinus teada L.) plantations. These silvicultural systems are prone to cogongrass establishment and growth due to clear-cutting and site preparation treatments that expose soil on large, contiguous areas in a short period of time. Such disturbance may create a mineral seed-bed that favors cogongrass seedling establishment and movement of machinery between infested and un-infested areas may introduce vegetative propagules. Once established, cogongrass promotes fire and is assumed to reduce loblolly pine growth, though no published studies quantify this reduction. Cogongrass also affects secondary uses of plantations such as the leasing of land for hunting and other types of recreation. This could occur as the overall biological diversity of stands is reduced to a few species, including the grass and the pines, eliminating plant species needed by wildlife for food and shelter. Cogongrass has the potential to create vast monocultures in the Southeast, in which rehabilitation and reforestation will by necessity become increasingly intensified and expensive. In addition, property devaluation will become a serious problem where cogongrass is involved due to the high costs of rehabilitation and absence of productive land-use. The primary research objective of this project was to investigate options for the establishment or reforestation of loblolly pine into cogongrass-infested areas. Factorial combinations of herbicide and mechanical site preparation as well as first-year herbicide release treatments were tested. Cogongrass response and loblolly pine survival and production were the measured responses. The study site was located in Mobile County, near the town of Theodore, AL. Soil at the study area was a Bama fine sandy loam with high site index (90) for loblolly pine. The experiment was a factorial arrangement that tested two herbicide site preparation (SP) treatments, two mechanical SP treatments, and two pine release herbicide treatments. Herbicide SP levels were none and a broadcast-applied tank mixture of glyphosate at 3.3 kg ae/ha, imazapyr at 0.34 kg ae/ha, and nonionic surfactant at 0.5 % v/v. Application was on October 3-4, 2001. Mechanical SP levels were a scalping treatment and none. Scalping consisted of using a bulldozer and fire plow to remove the upper 10 to 15 cm of cogongrass rhizomes and roots, folding these back upon intervening grass to create a furrow in which seedlings were planted. Scalping was performed on December 19, 2001. Release treatment levels were band-applied herbicide and none and were applied after seedling planting. Visual inspection of the test area in the spring of 2002 (3 mo. after planting) indicated that plant species composition, including cogongrass, was greatly influenced by SP methods. Therefore, plots were subdivided for release treatment in order to investigate timing of release application, tank-mix partners for imazapyr, and release applications of varying cost. In addition to the eight plots in the factorial core, a ninth treatment, termed “complete control”, was added. Since a non-treated or negative control was part of the factorial arrangement, the intent of “complete control” was to provide a positive control to compare the responses from the factorial experiment. Because of persistent cogongrass regrowth, “complete control” was not actually achieved and risk of tree damage did not permit further treatments, however, a greater level of cogongrass suppression was added to the study by this treatment. The nine treatments were replicated four times in a randomized complete block design. Treatment plot