Loblolly pine or slash pine response and vegetation colonization are summarized for a region-wide study that included five locations on coastal soils in the southern United States. The objective was to evaluate timing of postplant herbaceous weed control (HWC) treatments following preplant site preparation with imazapyr applied at two timings (August and November) and at three rates (0.56, 0.84, and 1.12 kg ha−1). All imazapyr site preparation treatments were applied after bedding. Site preparation treatments resulted in fast-growing stands without HWC at all locations with average Year 3 dominant tree height ranging from 2.6 to 3.7 m. Imazapyr plus sulfometuron was an effective HWC treatment on loblolly pine. Vegetation control and pine response varied by surface soil texture. On coarser-textured soils, the site preparation treatments resulted in <10% vegetation cover in June of the first pine growing season. On these coarser-textured soils, loblolly pine growth was increased by second-year and not first-year HWC. On finer-textured soils, vegetation colonization was aggressive, with >20% cover in June of the first pine growing season, such that early first-year HWC provided the largest loblolly pine response of single-pass HWC treatments. Pines were highly tolerant to imazapyr site preparation treatments as evidenced by the lack of differences in slash or loblolly pine survival and growth from the doubling of imazapyr rates for applications in either August or November. There was little meaningful residual control of herbaceous vegetation into the second pine growing season from site preparation treatments or first-year HWC regardless of location. There was no consistent pine response benefit from increasing the imazapyr site preparation rate for included treatments. Cost-effective treatments would utilize low site-preparation herbicide rates followed by the appropriate timing of HWC if longer-term vegetation control is the objective.

An experiment was established in 1961 to determine the influence of bearmat (Chamaebatia foliolosa Benth.) competition on ponderosa pine (Pinus ponderosa Laws.) survival and growth. Ponderosa pine seedlings were planted in bearmat which was: (A) untreated, (B) sprayed with a mixture of 2,4-D [(2,4-dichlorophenoxy)acetic acid] and 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], and (C) eliminated by a combination of herbicide, clipping sprouts, and trenching to prevent root and rhizome invasion. Ponderosa pine survival after 19 yr averaged 9%, 66%, and 90%, respectively, for the three treatments. Tree height after 19 yr averaged 1.6, 1.9, and 5.7 m for treatments A, B, and C, respectively. Soil moisture use was initially less on the herbicide-treated than on the untreated plots, but bearmat quickly sprouted after application to compete with the pine seedlings for moisture. After 19 yr the bearmat was more dense and appeared to be more vigorous on the sprayed plots than on those receiving no treatment. We estimate that 75% reduction in net wood production could result after 50 yr on this site from bearmat competition.

Burning and 2,4-D [(2,4-dichlorophenoxy)acetic acid] were used on the early stages of beaked hazel (Corylus cornuta Marsh.) understory to prevent development of a dense, continuous understory. At this early stage beaked hazel understories consisted of seedlings, small clones, and large clones. The application of 1.12 kg/ha of 2,4-D in July and August killed 84 to 100% of the seedlings and small clones, 86 to 98% percent of the large clones; while the application of 0.56 kg/ha of 2,4-D in June, July, or August caused 77 to 98% mortality of seedlings and small clones, but only 57 to 83% of large clones. Effects of burning were much more variable and generally mortality was less than with 2,4-D. One or two burns killed 23 to 100% of seedlings and small clones, and an average of only 13% (range 0 to 93%) of large clones.

The use of aminopyralid combined with metsulfuron for western snowberry control was evaluated with field trials conducted near Rushville, NE. Herbicides treatments consisted of aminopyralid plus metsulfuron, aminopyralid plus metsulfuron plus 2,4-D, 2,4-D alone, and metsulfuron plus chlorsulfuron plus 2,4-D plus dicamba. All treatments were applied in May and June. Sixty days after treatment (DAT) western snowberry control with aminopyralid plus metsulfuron at 0.073 + 0.012 kg ai ha−1 applied in May was 64%, whereas when applied in June, control was 97%. Meanwhile control with 2,4-D was 99 and 78% for the May and June applications, respectively. No major differences between application timings were observed 60 DAT for the rest of the treatments, with control levels ranging from 85 to 99%. One year after application, differences in control between application timings only persisted for 2,4-D. At 365 DAT, western snowberry control with aminopyralid plus metsulfuron at 0.073 + 0.012 kg ai ha−1 was 76 and 78% for May and June applications, respectively. The addition of 2,4-D at 1.1 kg ai ha−1 to aminopyralid plus metsulfuron provided excellent control and was similar to the combination of metsulfuron, chlorsulfuron, 2,4-D, and dicamba for both May and June applications. Grass production and animal carrying capacity were higher after western snowberry control with the majority of the treatments. Aminopyralid plus metsulfuron applied at the lower rate was the exception. The increase in the carrying capacity after western snowberry control ranged from 2.2 to 4.5 animal unit month (AUM). The control of western snowberry resulted in an increase in net income per hectare when compared with the untreated checks, ranging from $4 to $47.9 ha−1. Several options are available for effective western snowberry control during a broader time of application with increased grass production.