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ARS Home » Southeast Area » Dawson, Georgia » National Peanut Research Laboratory » Research » Publications at this Location » Publication #185103
Title: FIRST-YEAR HERBICIDE RELEASE OPTIONS FOR COGONGRASS CONTROL IN LOBLOLLY PINE PLANTATIONS

Author
item Faircloth, Wilson
item PATTERSON, M - AUBURN UNIVERSITY
item MILLER, J - USDA FOREST SERVICE
item TEEM, D - AUBURN UNIVERSITY

Submitted to: Proceedings of Southern Weed Science Society
Publication Type: Abstract Only
Publication Acceptance Date: 1/24/2005
Publication Date: 6/1/2005
Citation: v. 58.

Interpretive Summary: none required.

Technical Abstract: In the southeastern U.S., cogongrass [Imperata cylindrica (L.) Beauv.] is invading forest lands, especially loblolly pine (Pinus teada L.) plantations. These even-aged 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. Deep tillage and high rates of the herbicides glyphosate and imazapyr are known to suppress cogongrass in a variety of situations, including site preparation for reforestation. Often control is needed after plantation establishment, but before pines become large enough to tolerate the high rates needed for control or a directed application can be made. The objective of this study was to investigate first-year release herbicide options for loblolly pine with respect to cogongrass control and pine response. Release options were investigated on an existing field study that was designed to determine establishment options for loblolly pine into cogongrass. Field plots in the existing study were 100 loblolly pine seedlings spaced on a 25m x 25m grid (1600 trees/ha) planted Jan. 15, 2002. Field plots were subdivided, based on four prior site preparation (SP) types in the original study: 1) mechanical, 2) herbicide, 3) herbicide followed by (fb) mechanical, and 4) no SP. Release herbicides were imazapyr (0.17 kg/ha) applied alone, imazapyr (0.11 kg/ha) plus sulfometuron (0.11 kg/ha), and imazapyr (0.11 kg/ha) plus sulfometuron (0.11 kg/ha) plus metsulfuron (0.04 kg/ha). Four replications of each SP-release combination were used. Where no prior SP treatments were applied, release herbicides were compared in spring (May 21, 2002) and fall (Oct. 9, 2002) application timings. Where SP treatments had been implemented, release herbicides were applied on Oct. 9, 2002, only. Plant biomass was measured in August of 2003 and partitioned into 3 categories: 1) live cogongrass, 2) thatch, and 3) other remaining woody and herbaceous plants. Tree height (HT) and ground-line diameter (GLD) were measured at age 1 and 2, and diameter breast height (DBH) was measured at age 2. Mortality was recorded as percent survival. Contrasts were performed both within and between site preparation methods using Mixed Models analysis at the 0.05 level. Release treatments showed no significant differences in second year plant biomass when preceded by the following SP methods: mechanical SP only (P=0.9916), herbicide SP only (P=0.7114), and mechanical SP plus herbicide SP (P=0.5852). Release treatments were significant for plant biomass where no SP was used. Tree response, as measured by GLD and HT in the second year, showed no significant differences for the various release treatments when applied after either herbicide SP only (P=0.6444) or mechanical SP plus herbicide SP (P=0.5713). Release treatments were significant in pine growth response for both the mechanical SP only and no SP. Spring-applied herbicides decreased live grass biomass and thatch compared to fall-applied, regardless of herbicide or prior SP method. Application timing of imazapyr alone made no significant difference in live grass biomass, while the spring-applied combination of imazapyr plus sulfometuron significantly decreased live grass biomass 33% compared to fall application. Contrary to both live grass and thatch, other species biomass was reduced by fall application of imazapyr plus sulfometuron, indicating that spring-applied tank-mixes increased the recruitment of possible successional species, which aid in the rehabilitation process. The tank-mix combination of imazapyr plus sulfometuron yielded larger trees in GLD (both