Fluazifop-butyl {(±) butyl 2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid}, haloxyfop-methyl {methyl-2-[4-[[3-chloro-5-(trifluoromethyl-2-pyridinyl] oxy] phenoxy] propanoic acid}, and sethoxydim {2-[1-(ethoxyimino)-butyl]-5-[2-ethylthio)propyl-3-hydroxy-2-cyclohexen-1-one}exhibited soil herbicidal activity to annual grass species in greenhouse and field experiments. Control of forage sorghum [Sorghum bicolor (L.) Moench. ‘Rox Orange’] with all three herbicides was greater when seeds were planted at or near the soil surface than when planted 2, 4, or 6 cm deep. Imbibition of the herbicides by forage sorghum and soybean [Glycine max (L.) Merr.] seeds did not reduce germination at concentrations of 10-3 M or lower, but forage sorghum seedling survival and vigor were reduced by herbicide concentrations as low as 10-7 M. Fluazifop-butyl, haloxyfop-methyl, and sethoxydim were more phytotoxic when applied to the root zone than the shoot zone. Haloxyfop-methyl exhibited the longest soil residual control in the field followed by fluazifop-butyl and sethoxydim. Haloxyfop-methyl and fluazifop-butyl controlled simulated shattercane [Sorghum bicolor (L.) Moench. ♯3 SORVU] in soybeans with preemergence and early postemergence applications, whereas control from similar applications of sethoxydim was limited and variable.

Greenhouse and laboratory studies were conducted to examine certain characteristics of RPA 201772 and how they may affect its utility. 14C-RPA 201772 was used to determine the stability of RPA 201772 in various pH spray solutions over time. After 24 h, degradation of RPA 201772 was 20, 36, and 93% in spray solutions adjusted to pH 4.0, 7.0, and 10.0, respectively. The major metabolite was diketonitrile (DKN), which is herbicidally active. In addition, 9 and 15% of the RPA 201772 had degraded into an inactive benzoic acid derivative at pH 7.0 and 10.0, respectively. The differences in herbicidal activity of RPA 201772 and its metabolite DKN were also evaluated. Corn seeds and velvetleaf seeds readily imbibed RPA 201772, but only low levels of DKN were imbibed. Preemergence (applications of RPA 201772 and DKN were equally active on corn and velvetleaf. Further studies determined that the principal sites of uptake of RPA 201772 by corn was roots and seeds for four different corn hybrids. Another study determined that light was required for RPA 201772 activity. Corn shoots from seeds germinated under 14 h of light exhibited rate-dependent injury, while corn germinated and grown in the darkness was not injured.

A charcoal barrier was used to determine the importance of root, shoot, and seed exposure on the activity of nine acetanilide herbicides to peas (Pisum sativum L.) grown in a greenhouse. Greater reduction of plant weight occurred from root exposure than from shoot exposure. For all herbicides, the average reduction in shoot and root weight from shoot exposure was 7 and 20%, respectively; and root exposure reduced shoot and root weight 15 and 40%, respectively. The average reduction in shoot and root weight from exposing all plant parts to herbicides was 47 and 69%, respectively. Seed exposure had no influence on plant weight. This response indicates that pea roots are the primary site of activity for many acetanilide herbicides, and provides support to previous findings that showed rainfall was necessary to leach acetanilide herbicides down to the root zone of processing peas for maximum reduction of shelled pea yield. Field studies, conducted over a 2-yr period, were designed to evaluate annual weed control and pea injury from preemergence and early postemergence applications of seven acetanilide herbicides. Shelled pea yield was not reduced by any treatment. All treatments provided good to excellent grass control and fair to good broadleaf weed control.

Results from greenhouse and growth chamber studies indicated that alachlor [2-chloro-2′,6-diethyl-N-(methoxymethyl) acetanilide] injury to ‘Superior’ potatoes (Solanum tuberosum L.) was related to time of herbicide application and temperature. Injury to the ‘Superior’ cultivar was observed when alachlor was applied just before potato emergence. Necrosis of shoots near the soil surface, shoot dieback, stem swelling, leaf crinkle, and plant stunting were characteristic symptoms of alachlor injury. Cool temperatures appeared to intensify the injury. ‘Superior’ potatoes outgrew injury within 41 days after treatment. Herbicide placement studies in the growth chamber suggested that alachlor or its metabolites were absorbed by the shoots of emerging ‘Superior’ potatoes. Under growth chamber conditions the ‘Katahdin’ cultivar was injured by preemergence applications of alachlor when the herbicide was applied just before plant emergence. Injury symptoms were similar to those observed on the ‘Superior’ cultivar. ‘Pungo’ and ‘Norchip’ potatoes were tolerant to preemergence applications of the herbicide regardless of time of application.

In greenhouse studies, soil organic matter reduced the herbicidal activity of ethalfluralin (N-ethyl-N-(2-methyl-2-propenyl)-2,6-dinitro-4-(trifluoromethyl)benzenamine). Fifty percent inhibition (I5.0) values for barnyardgrass [Echinochloa crus-galli (L.) Beauv.] stand, injury, and shoot fresh weight increased as the soil organic-matter level increased. No difference in ethalfluralin tolerance was found among 16 cucumber (Cucumis sativus L.) cultivars. When grouped according to market type, fresh market cultivars tended to be injured more than pickling cultivars by excess ethalfluralin. Both shoots and roots of cucumber absorbed the herbicide, but exposure of roots to ethalfluralin was more toxic than exposure of shoots. Field studies indicated that with certain edaphic and environmental conditions, cucumbers can be injured by preemergence applications of ethalfluralin. Injury was greatest in a low organic-matter soil following a heavy rain. Ethalfluralin at 1.3 kg/ha gave adequate weed control in 1 and 3% organic-matter soils, but not in a 9% organic-matter soil.

A greenhouse study was conducted to determine the effectiveness of adjuvants on postemergence large crabgrass control with dithiopyr. Using barriers to isolate foliage or soil, the primary site of dithiopyr uptake was found to be via foliage. Laboratory and greenhouse studies elucidated the factors involved in enhancement of crabgrass control by dithiopyr with nine superior adjuvants. Two adjuvants increased dithiopyr absorption by 3.7 to 4.3% over the herbicide alone. However, none of the adjuvants increased dithiopyr translocation out of the treated leaf. Treatment of a single large crabgrass leaf indicated that enhancement of dithiopyr activity by adjuvants involved an effect on translocation, on spray retention, and on the external movement of the spray solution to the apical meristem, with the relative importance of any 1 factor depending on the particular adjuvant used. Because of the large losses of dithiopyr during absorption/translocation studies, a separate volatilization experiment determined that 70% of the applied dithiopyr volatilized within 24 h at 24 C. Dithiopyr absorption decreased and volatilization increased with each 10 C increase in temperature. Nonrecoverable dithiopyr ranged from 46 to 55% at 5 C to 92 to 95% at 35 C. Volatility losses of this magnitude may mitigate adjuvant enhancement of postemergence grass activity of dithiopyr.

Response of creeping bentgrass, annual bluegrass, and Kentucky bluegrass to foliar, soil, or foliar plus soil applications of bispyribac-sodium was evaluated in greenhouse studies. Soil-alone and foliar plus soil applications of bispyribac-sodium at 148 or 296 g ai/ha resulted in greater injury and shoot dry weight reduction of all species 28 d after treatment (DAT) compared to foliar-alone treatments. Creeping bentgrass was less injured than annual or Kentucky bluegrass regardless of application placement. Further studies evaluated foliar and root absorption and translocation of 14C-bispyribac-sodium in creeping bentgrass, annual bluegrass, Kentucky bluegrass, and roughtstalk bluegrass. Foliar absorption into creeping bentgrass was less than that of other species at most harvest timings from 4 to 72 h after treatment. Annual and roughstalk bluegrass translocated greater amounts of foliar-absorbed 14C to the crown and shoots compared to creeping bentgrass. Annual and roughstalk bluegrass accumulated approximately 47% more 14C per dry weight of plant tissue than creeping bentgrass and 74% more than Kentucky bluegrass after 72 h in nutrient solution containing 14C-bispyribac-sodium. Annual and roughstalk bluegrass translocated approximately 80% of root-absorbed 14C to shoots, whereas creeping bentgrass and Kentucky bluegrass translocated slightly less (66% of absorbed for both species). These studies suggest that bispyribac-sodium is readily absorbed by roots and translocated to shoots which may contribute to its total activity within a plant. In addition, creeping bentgrass displayed lower amounts of foliar and root absorption and subsequent translocation than annual and roughstalk bluegrass which may contribute to greater bispyribac-sodium tolerance displayed by creeping bentgrass.