Several precision postemergence-directed sprayers with different nozzle designs and arrangements were evaluated for potential use in sweet corn for wild-proso millet (PANMI) control in field trials from 1987 to 1989. Ametryn at 2270 g ha-1 plus oil-emulsifier mixture (OEM) at 1.3% v/v and sethoxydim alone or plus OEM applied postemergence-directed selectively controlled PANMI in sweet corn. Sethoxydim at 220 g ha-1 plus OEM controlled PANMI best when averaged over the 3-yr period. Ametryn plus OEM did not injure corn and sethoxydim at 110 g ha-1 plus OEM caused little or no corn injury and no yield reductions when applied with any of the sprayers. Generally, only sethoxydim at 220 g ha-1 plus OEM injured corn. The amount of injury was different among sprayers, with the nozzle designs and arrangements responsible for corn injury. Injury was minimized when sethoxydim was applied with a sprayer equipped with 150 degree dual orifice nozzles spaced 38 cm apart and mounted on skids that contacted the soil to assure constant nozzle height. This sprayer, or sprayers of similar nozzle design, show the most potential for use by sweet corn growers.

A series of greenhouse studies examined the effectiveness of PRE- and POST-applied sulfentrazone in controlling purple and yellow nutsedge as influenced by selective tissue exposure. In addition, 14C-sulfentrazone was utilized to contrast absorption and translocation resulting from these exposures. Consistent control with preemergence applications to germinating tubers was obtained with a combined root and shoot zone exposure. Yellow nutsedge was more susceptible than purple nutsedge. Performance of the separate root and shoot zone exposure was soil pH- and nutsedge-species dependent. POST-foliar applications to established nutsedge were more effective when sulfentrazone was allowed to contact the soil surface. 14C-sulfentrazone was readily absorbed by the roots and translocated to the foliage of both species in hydroponic culture.

Greenhouse and growth chamber experiments were conducted to determine the reasons for stunted growth and yield suppression of corn noticed sometimes in nicosulfuron-treated corn fields infested with heavy population of johnsongrass. Results indicated that in the absence of johnsongrass, nicosulfuron applied broadcast POST at 35 g ai ha−1 had no effect on corn. However, growth reduction of corn occurred when nicosulfuron-treated johnsongrass and corn were allowed to share the same rooting medium with their root systems intermingled. The reduction in growth was even greater when corn foliage or the soil surface were also treated with johnsongrass. The extent of growth reduction of corn growing with nicosulfuron-killed johnsongrass depended on weed density and herbicide application rate. Greater growth reductions occurred at four johnsongrass plants per pot compared to two and at a higher application rate of 100 μg nicosulfuron per plant. In general, johnsongrass killed by nicosulfuron appeared to be more phytotoxic to corn than plants killed by paraquat. Nicosulfuron provided excellent control of johnsongrass and improved corn growth by two to three times that of not controlling johnsongrass, but it could not elevate corn growth to the level obtained when johnsongrass was controlled by paraquat or in the absence of interference from johnsongrass.

Sweet corn (Zea mays L. rugosa 'Seneca Scout’) and soybeans (Glycine max L. Merr. ‘Kanrich’) were grown in nutrient solutions containing alachlor [2-chloro-2′,6-diethyl-N-(methoxymethyl)acetanilide] at 2.36 × 10-5 M, polyethylene glycol MW 6000 (PEG6000) at −2.5 bars osmotic potential, alachlor at 2.36 × 10-5 M plus PEG6000 at −2.5 bars osmotic potential or with no additions. Sweet corn and soybean roots exposed to alachlor plus PEG6000 accumulated significantly more PEG6000 than roots exposed to PEG6000 alone; increased shoot uptake occurred only in soybean. Alachlor was also shown to significantly increase root osmotic potential and decrease root electrolyte leakage.

Experiments were conducted to evaluate the occurrence and significance of release of herbicide through subterranean parts of nicosulfuron-treated johnsongrass. In a bioassay, the rooting medium of johnsongrass treated foliarly with 50 or 100 μg nicosulfuron plant−1 was inhibitory to the radicle elongation of sorghum and corn indicating the increased toxicity of the rooting medium of nicosulfuron-treated johnsongrass. The study with 14C-nicosulfuron indicated a basipetal translocation of foliarly applied nicosulfuron in johnsongrass to its roots/rhizomes and also into the rooting medium. By 30 DAT, around 23% of the 14C-label absorbed by johnsongrass was found exuded into the rooting medium. Radiochromatogram scans of thin layer chromatography plates of rooting medium indicated unmetabolized nicosulfuron as the major 14C-labeled compound (56%). The study also revealed a subsequent uptake of exuded 14C by corn roots sharing the medium. On the whole, the amount of 14C-label recovered from untreated corn amounted to 4.3% of the total applied to johnsongrass. In another experiment, the presence of nicosulfuron in the rooting medium was detrimental to corn growth. Reductions in corn growth occurred at concentrations of 10−8 M nicosulfuron or greater in the rooting medium. The sensitivity of corn to root uptake was attributed to greater accumulation of nicosulfuron at a faster rate in the growing parts.

Greenhouse experiments were conducted to evaluate seedling rice tolerance to haloxyfop and to determine soil moisture effects on root, shoot, and root plus shoot uptake. Visible injury to rice at 4 wk after treatment increased with each increase of haloxyfop rate from 40 to 160 g ai/ha, regardless of growth stage. Less injury was observed at equivalent rates in four-leaf than in younger rice. Similarly, equivalent haloxyfop rates reduced shoot fresh weight of one- to three-leaf rice more than shoot fresh weight of four-leaf rice. There was no interation between soil moisture levels (19 and 24%) and haloxyfop activity. Fresh weights were less when haloxyfop at 40 or 80 g/ha was absorbed by both roots and shoots than when absorption was by either roots or shoots alone. However, at 80 g/ha fresh weight was similar whether haloxyfop was absorbed by roots or shoots alone. Root uptake, in the presence of 160 g/ha haloxyfop, did not contribute to reduced fresh weight with root plus shoot treatments because of the initial foliar activity incurred.

Field experiments were conducted at two locations in North Carolina during the summer of 1992 to ascertain the reasons for stunted growth of corn noticed occasionally in fields treated POST with nicosulfuron to control dense infestations of johnsongrass. Treatments consisted of nicosulfuron at 35 g ai/ha sprayed POST, either over-top or post-directed only to johnsongrass in a single early application or in sequential applications of 17.5 g/ha. Checks included a hand-weeded, paraquat post-directed to johnsongrass, and non-weeded. Nicosulfuron provided satisfactory control of johnsongrass irrespective of whether applied once or sequentially. Corn yield in nicosulfuron-treated plots was as much as three times greater than in non-treated plots depending on hybrid and location. In the absence of johnsongrass interference, nicosulfuron caused a corn yield reduction of 6 to 9%. However, in the presence of johnsongrass interference, an additional 16 to 26% reduction in yield occurred with a POST application of nicosulfuron. Reductions in corn plant height and dry matter accumulation also were noticed for nicosulfuron treatments compared to post-directed application of paraquat and hand removal of johnsongrass.

Ground ivy is a stoloniferous, perennial weed that persists in lawn turf. With the widespread use of 2,4-D on turf sites, the development of 2,4-D–tolerant ground ivy is a possibility. Ground ivy populations showed a highly variable response to foliar 2,4-D application. Ground ivy from Nebraska (NE) was tolerant to 2,4-D, whereas Ohio (OH) ground ivy was susceptible. The 2,4-D–susceptible OH population absorbed 37% more foliar-applied 14C–2,4-D than the 2,4-D–tolerant NE population. Although OH and NE populations total translocation of applied 14C was similar and averaged 5%, the OH population translocated 42% more toward the apical meristem of the primary stolon than the NE population, primarily because of the OH population's higher 14C–2,4-D absorption. The variation in response to 2,4-D found between these two populations occurred after exposure of roots to 2,4-D, but the effect was less pronounced. These results suggest that the difference in foliar uptake may partially contribute to differences in response to 2,4-D between these two populations. Likewise, differences in acropetal translocation may contribute to the differential sensitivity of 2,4-D–tolerant and –susceptible ground ivy populations.

We examined the effect of a postemergence application of fluazifop-P on root uptake, translocation, and metabolism of 14C-terbacil in ‘Kent’ strawberry. Fluazifop-P had no effect on uptake of 14C-terbacil from a nutrient solution over 48 h, nor did it affect the proportional distribution of 14C-label in the plants. The 14C-label was readily translocated to the foliage where it tended to accumulate in vascular tissue. Fluazifop-P reduced the overall conversion of 14C-terbacil to metabolites by about 50%. Thin layer chromatography of methanol extracts of leaflets, petioles, crowns, and roots separated the 6-hydroxymethyl derivative, and several unidentified metabolites, including a major water-soluble metabolite at the origin. At least 50% of the latter could be converted to the 6-hydroxymethyl metabolite by β-glucosidase, but other metabolites could be separated in other solvent systems. The levels of metabolites were generally two- to threefold higher in plants treated with terbacil alone than in those pretreated with fluazifop-P. Therefore, we conclude that the interaction observed between these herbicides in the field results from fluazifop-P inhibiting detoxification of terbacil by strawberry.