The growth responses of cogongrass [Imperata cylindrica (L.) Beauv.] were studied in a controlled-environment greenhouse with a day/night temperature of 29/23 C, under full available light and 56 and 11% of full light. The cogongrass plants were grown from stem and rhizome propagules originating from an interstate highway median, a pecan [Carya illinoensis (Wangenh.) K. Koch] plantation, and a pine (Pinus spp.) forest. After 89 days, the plants from all three populations produced, on average, three times as much total dry weight and leaf area in full available sunlight as in 56% full light and 20 times as much as in 11% full light. The distribution of plant biomass into rhizomes decreased with shading, whereas the distribution into leaves increased. The distribution of leaf biomass as leaf area also increased with shading, with the result that the plants grown in 11% full light had leaf area ratios about 2.5 times greater than those grown in full light. Reductions in dry matter production with shading were due to significant reductions in both net assimilation rate and leaf area duration or total amount of leaf area present. The plants from the shaded and exposed habitats generally did not differ significantly in their responses to shading. Thus, there is little evidence for the presence of sun and shade ecotypes in the populations of cogongrass studied.

Canopy cover of false broomweed (Ericameria austrotexana M.C. Johnston) on the Rio Grande Plains of Texas was initially reduced by 96% by glyphosate [N-(phosphonomethyl)glycine] applied at 2.2 kg/ha in the spring. Acceptable control of this shrub with glyphosate lasted at least 4 yr. Glyphosate severely reduced basal cover of perennial grasses during the year of treatment, but grasses completely recovered within 2 yr after treatment. Standing forage crop increased by an average of 83%, compared to untreated areas, and livestock carrying capacity increased from 1 animal unit (AU)/13 ha to 1 AU/7 ha. Picloram (4-amino-3,5,6-trichloropicolinic acid), paraquat (1,1′-dimethyl-4,4′-bipyridinium ion), and paraquat plus atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] applied in the spring were less effective than glyphosate. Canopy reductions of false broomweed 6 months after applications of 2.2 kg/ha of picloram, paraquat, or paraquat plus atrazine were equivalent to that from 1.1 kg/ha of glyphosate, and control with these herbicides was usually restricted to the season of application. Dicamba (3,6-dichloro-o-anisic acid), 2,4-D-[(2,4-dichlorophenoxy)acetic acid], atrazine, and 2,4-D plus atrazine were not effective when applied in the spring or fall. Time required for recovery of false broomweed canopy apparently varied with amounts of rainfall received after herbicide application.

Application of NH4+-bearing fertilizer in field and pot experiments increased triallate [S-(2,3,3-trichloroallyl)diisopropylthiocarbamate] activity on oats (Avena sativa ‘Harmon’). The effect was consistent in the growth chamber, but field results were more variable, depending on soil moisture and temperature conditions. Because the pot experiments showed that the major effect was in shoot-zone-treated soils, the increased triallate activity was attributed to a reduction in triallate adsorption to the soil colloids. However, a smaller effect was measured in root-zone-treated soil, thus a physiological effect is also possible.

In field and greenhouse experiments, liquid or granular formulations of EPTC (S-ethyl dipropylthiocarbamate) applied by hand directly in the row with seed of alfalfa (Medicago sativa L. ‘Vernal’), controlled grass seedlings in bands, usually 5 to 8 cm wide, without injuring alfalfa significantly. Grass was similarly controlled selectively when a mixture of alfalfa seed and clay granules, similar in size to alfalfa seed and containing 10% EPTC, was seeded mechanically.

Picloram (4-amino-3,5,6-trichloropicolinic acid) injected directly into a small, central-Arizona stream was lost by normal stream flow actions, such as the mixing of fast- and slow-moving water, and the interchange of surface and subsurface water in gravel and sand beds along the stream. Picloram was injected at a concentration of 6.26 ppmw; the maximum amount detected was 2.362 ppmw at 0.4 km downstream, 0.943 ppmw at 0.8 km, 0.316 ppmw at 1.6 km, 0.014 ppmw at 3.2 km, 0.001 ppmw at 6.4 km, and none further downstream. Picloram was detected near the limits of detection (0.001 to 0.004 ppmw) 2 days after injection at the 0.4-, 0.8-, and 1.6-km sites. In photodegradation tests, sunlight decomposed 57% of the picloram in containers after 8.8 h of exposure.