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.

Over 9 yr, bandane (polychlorodicyclopentadiene isomers) at 67 kg/ha, bensulide [O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide] at 11 and 22 kg/ha, DCPA (dimethyl tetrachloroterephthalate) at 22 kg/ha, and terbutol (2,6-di-tert-butyl-p-tolyl methylcarbamate) at 22 kg/ha applied preemergence controlled 94 to 100% of large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSP] in a lawn of common bermudagrass [Cynodon dactylon (L.) Pers. # CYNDA]. Control from benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine) at 5 kg/ha, DCPA at 11 kg/ha, simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] at 5 kg/ha, and terbutol at 11 kg/ha was 90 to 99%. Bandane and bensulide persisted in soil to control large crabgrass a year after treatment.

In field experiments, preemergence applications of bensulide {O,O-bis(1-methylethyl)S-[2-[(phenylsulfonyl)amino] ethyl] phosphorodithioate} or DCPA (dimethyl-2,3,5,6-tetrachloro-1,4-benzenedicarboxylate) at 11.2 kg ai/ha controlled smooth crabgrass [Digitaria ischaemum (Schreb. ex Schweig.)Schreb. ex Muhl. #3 DIGIS] selectively in turf. Granular and liquid formulations of bensulide performed similarly. Napropamide [N,N-diethyl-2-(1-naphthalenyloxy)propanamide] granules when applied alone at 1.1 to 3.4 kg ai/ha were partially effective, but when combined with 5.6 kg ai/ha bensulide, controlled smooth crabgrass for the entire season. Oxadiazon {3-[2,4-dichloro-5-(1-methylethoxy)phenyl]-5-(1,1-dimethylethyl)-1,3,4-oxadiazol-2-(3H)-one} controlled crabgrass but temporarily injured the turf. Residual control of crabgrass the year after treatment was unacceptable for all treatments.

Eurasian watermilfoil, an aquatic flowering plant, was found to be a suitable bioassay plant for the detection of photosynthetic inhibitor herbicides in water and aqueous extracts of soil. Stock cultures of Eurasian watermilfoil were maintained in an algal-free medium under constant environmental conditions. Oxygen evolution from three lateral shoots 3 to 5 cm in length was measured before and after herbicide treatment. Inhibition of photosynthesis was detected within 10 min of treatment. Concentrations as low as 5.9 × 10–8M terbacil and 6.4 × 10–8M diuron were detected in water. Simazine, atrazine, and metribuzin were detected in water at a concentration of 10–7M. Eurasian watermilfoil bioassays in lake water spiked with various concentrations of terbacil, metribuzin, atrazine, and simazine indicated that the bioresidual activity of these chemicals can be estimated in samples of natural water without extraction or purification. Using aqueous extracts taken from herbicide-treated soil, the Eurasian watermilfoil bioassay detected minimum levels of 0.047 and 0.07 kg/ha terbacil and atrazine, respectively. Neither soybean nor oat showed visible injury symptoms at these concentrations. The Eurasian watermilfoil bioassay has the advantage of being more rapid and/or more sensitive than methods using algae, oat seedlings, or leaf discs.

Metazachlor degradation in soil was studied in fields of spring barley, turnips, brussels sprouts, and leeks. Metazachlor in soil was transformed into 2-hydroxy-N-(2,6-dimethylphenyl)-N-(1H-pyrazol-1-yl methyl)-acetamide (compound 2), 2-chloro-N-(2,6-dimethylphenyl)-acetamide (compound 3), and 4,4′-methylenebis-(2,6-dimethylbenzenamine) (compound 4). Soil concentrations of compound 4 were always lower than 0.1 ppm. The half-life of metazachlor in the 0- to 10-cm soil layer was 1 to 3 mo. Metazachlor and compounds 2, 3, and 4 were not detected in the 10- to 20- and 20- to 30-cm soil layers. Metazachlor and metabolites (compounds) 2, 3, and 4 were not detected in barley grain or in the edible part of the vegetables. The sensitivity limit for these compounds was 0.02 ppm.

Chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carboxyl]benzenesulfonamide} has recently been registered for the control of several broadleaf weeds in spring wheat (Triticum aestivum L.), durum wheat (Triticum durum Desf.), and barley (Hordeum vulgare L.) in western Canada. Residue carryover of this herbicide can cause injury to subsequent sensitive crops. A bioassay technique based on growth of pregerminated corn roots was used to detect levels of chlorsulfuron as low as 0.125 ppb in three Saskatchewan soils. Confidence levels of 95% were established. These confidence bands allowed the detection of chlorsulfuron levels within a minimum and maximum variation of 3.1 and 11.5% of root development.

Field experiments were conducted to determine the effect of different rates and application times of MON 37500 on downy brome control in winter wheat and on rotational crop injury. In southeastern Washington, MON 37500 applied postemergence at 36 to 72 g ai/ha in the fall and spring controlled downy brome 90 to 97% and 45 to 71%, respectively. MON 37500 was applied postemergence to winter wheat at 18, 36, and 72 g/ha during fall 1995 and spring 1996 near Moscow, ID; Pendleton, OR; and Endicott, WA, to determine its effect on rotational crops planted during spring 1997. At Pendleton, OR, fall applications of MON 37500 at 18, 36, and 72 g/ha applied to actively growing wheat reduced seed yield of spring barley and pea 13 to 59% and 26 to 29%, respectively, when these crops followed winter wheat in the rotation. At this site, spring applications of 36 and 72 g/ha reduced seed yield of spring barley 17 to 34%; when applied in the fall or spring, MON 37500 reduced canola yield 31 to 73%. MON 37500 at 18 g/ha in the spring reduced pea biomass 32% at Endicott. Aboveground biomass and seed yield of barley, pea, lentil, and mustard at Moscow were not affected by MON 37500 carryover. However, using a grain sorghum bioassay, predicted final concentrations of MON 37500 in soil at all three locations 360 d after treatment (DAT) was similar, ranging from 0.5 to 2 ng ai/g. In growth chamber herbicide dose–response studies, grain sorghum shoot height was reduced more at lower doses (0.025 to 5 ng/g) of MON 37500 in Pendleton soil than in soils from the other field locations. Perhaps the greater rotational crop injury observed at the Pendleton location was partly related to greater soil activity of the herbicide.

Sulfentrazone is commonly used for weed control in soybeans and tobacco, and vegetable crops and cotton are often rotated with soybeans and tobacco. Studies were conducted to evaluate the potential for sulfentrazone to carryover and injure several vegetable crops and cotton. Sulfentrazone was applied PRE to soybean at 0, 210, 420, and 840 g ai/ha before planting bell pepper, cabbage, cotton, cucumber, onion, snap bean, squash, sweet potato, tomato, and watermelon. Cotton, known to be susceptible to sulfentrazone carryover, was included as an indicator species. Cotton injury ranged from 14 to 18% with a 32% loss of yield in 1 of 2 yr when the labeled use rate of sulfentrazone (210 g/ha) was applied to the preceding crop. High use rates of sulfentrazone caused at least 50% injury with yield loss ranging from 36 to 100%. Bell pepper, snap bean, onion, tomato, and watermelon were injured < 18% by sulfentrazone at 840 g/ha. Squash was injured < 3% and < 36% by sulfentrazone at 210 and 840 g/ha, respectively. Yield of these crops was not affected regardless of sulfentrazone rate. Cabbage and cucumber were injured < 13% by sulfentrazone at 210 and 420 g/ha, and yields were not affected. Sulfentrazone at 840 g/ha injured cabbage up to 46% and reduced yield in 1 of 2 yr. Sulfentrazone injured cucumber up to 63% and reduced yield of No. 2 grade fruits. Sulfentrazone at 210 and 420 g/ha injured sweet potato < 6% and did not affect yield. Sulfentrazone at 840 g/ha injured sweet potato 14% and reduced total yield 26%. Our results suggest little to no adverse effect on bell pepper, cabbage, cucumber, onion, snap bean, squash, sweet potato, tomato, or watermelon from sulfentrazone applied at registered use rates during the preceding year.

BAY MKH 6561, a sulfonylaminocarbonyl-triazolinone herbicide for postemergence control of annual grasses and selected broadleaf weeds in wheat, was evaluated for weed control and rotational crop (barley, pea, lentil, and mustard) injury in the Pacific Northwest. BAY MKH 6561 was applied postemergence in winter wheat at 22, 45, and 90 g ai/ha during fall 1997 and spring 1998 near Moscow, ID, Pendleton, OR, and Wilcox, WA, to determine its effect on barley, pea, lentil, and mustard planted during spring 1999. At Pendleton, BAY MKH 6561 reduced barley height 6% and grain yield 11%, when applied in the spring at 90 g/ha, and visibly injured mustard 4 to 19% when applied at 45 or 90 g/ha. All BAY MKH 6561 treatments reduced mustard seed yield 47 to 54% at Moscow and 38 to 48% at Wilcox. Pea and lentil seed yields were not affected by herbicide treatments at all locations, whereas barley was not affected at Moscow and Wilcox. In growth chamber soil bioassay experiments, fall-applied BAY MKH 6561 dissipated 10 to 48% faster at Moscow compared to Pendleton, and the predicted half-life ranged from about 68 (Moscow) to 79 d (Pendleton). Dissipation of spring-applied BAY MKH 6561 at 45 and 90 g/ha was 17 to 21% slower at Moscow than Wilcox, and the predicted half-life ranged from 60 (Wilcox) to 69 d (Moscow).

Field studies were conducted from 2009 to 2011 in Oregon and from 2006 to 2008 in California to evaluate the response of various crops to imazosulfuron soil residues 91 to 731 d after application (DAA). Imazosulfuron rates applied in Oregon were 224 or 450 g ai ha−1 PRE, sequential 224 g ha−1 PRE and POST, or 450 g ha−1 as a tank mixture with PRE applied S-metolachlor at 1,060 g ai ha−1 followed by 224 g ha−1 POST to potato. Imazosulfuron was applied on bare ground PRE at 224, 336, and 450 g ha−1 and applied sequentially at 450 g ha−1 in California. Sugar beet planted 91 to 364 and 458 to 731 DAA were injured 83 to 94% and 54 to 78% among imazosulfuron rates and application timing in 2007 and 2008, respectively. Alfalfa planted 701 DAA at rates greater than 224 g ha−1 was injured, and the forage yield was reduced. Onion, spinach, carrot, and broccoli were also injured by imazosulfuron residues when planted 91 to 731 DAA, regardless of the rate or interval before planting. Imazosulfuron applied at 224 to 450 g ha−1 458 to 731 d before planting head lettuce resulted in moderate injury that did not reduce fresh-weight yield. The results indicated that imazosulfuron residues in the soil have the potential to injure many rotational specialty crops for 2 yr or more in soils with pH > 6.9.