Old-field planted longleaf pine (Pinus palustris) survival and growth response to various herbaceous weed control herbicides and application timings after 11 years

Chemical herbaceous weed control (HWC) is frequently used to improve the early survival and growth of planted longleaf pine (Pinus palustris). Reports on long-term survival and growth response of longleaf pine to commonly used HWC herbicides and spring first year application timings are limited. The objectives of this study were (1) evaluate survival and growth of longleaf pine in response to three common herbicides, (2) evaluate three HWC application timings, and (3) determine if defect and disease prevalence are increased by faster growth rates following banded, overtop HWC treatments. Three study areas were installed as randomized complete block designs in Treutlen and Laurens County, Georgia, USA. Imazapyr [Arsenal (R) Applicators Concentrate (AC)] (A4 treatment) was applied during late March, mid-April, and mid-May of the first growing season, and a premixed blend of hexazinone and sulfometuron methyl (Oustar (R)) (10OS treatment) was applied on the same dates. The last treatment was a split application of sulfometuron methyl (Oust XP (R)) and imazapyr (2OA4 treatment). Survival post-establishment was greatest in the control treatment (no HWC) when the March application timing was included in the analysis, but with March timings removed, the 10OS treatment had the greatest survival after 11 years (April and May applications). March application timing resulted in significantly lower survival than April or May applications with 10OS and A4 treatments. Diameter and height were greatest in the 10OS and 2OA4 treatment, while the 10OS and control treatment had the greatest average green weight and basal area ha(-1) at age 11-years-old. When herbaceous weeds present competition issues in newly established longleaf pine stands, the 10OS treatment applied in April or May on similar Coastal Plain sites may offer satisfactory long-term longleaf pine growth.

Automated summary

The study evaluates the long-term survival and growth response of longleaf pine to commonly used herbicides and application timings. It found that different herbicides and application timings can significantly affect the survival and growth of longleaf pine, with some treatments resulting in higher survival rates and better growth parameters after 11 years.