Common bean and azuki bean are poor competitors with weeds and demonstrate sensitivity to herbicides used for weed control in soybean. S-metolachlor, flufenacet, and acetochlor are categorized as Group 15 herbicides and provide control of multiple annual grass and select small-seeded broadleaf weeds. By way of field trials near Exeter and Ridgetown, Ontario, in 2019, 2020, and 2021, four dry bean market classes (azuki, kidney, small red, and white bean) were evaluated for their tolerance to 1× established label rates and 2× rates of S-metolachlor (1,600 and 3,200 g ai ha−1), flufenacet (750 and 1,500 g ai ha−1) and acetochlor (1,700 and 3,400 g ai ha−1) applied preplant incorporated (PPI). Injury was evaluated by assessing visible injury symptoms, density, shoot biomass, height, seed moisture content, and seed yield. Azuki bean was more sensitive to the Group 15 herbicides than other dry bean market classes; the Group 15 herbicides caused a 12% reduction in azuki bean growth at 2 wk after emergence; growth reduction was ≤2% in the other bean classes. Flufenacet (2× rate) was the most injurious treatment, causing a 27% reduction in azuki bean yield. This study concludes that kidney, small red, and white bean have a sufficient margin of crop safety to flufenacet, acetochlor, and S-metolachlor applied PPI. Azuki bean was sensitive to flufenacet; additional research is needed to investigate azuki bean tolerance to acetochlor and S-metolachlor applied PPI.

Numerous perennial horticultural crops are grown across the southeastern United States. Blueberry and blackberry (also known as caneberry) are commonly found in roadside stands, promote agritourism via pick-your-own markets, are important for fresh market commercial production in the region, and when processed, provide desirable value added products. Season-long weed control using residual herbicides is crucial for these perennial fruit crops to maximize berry quality and yield. Studies performed from 2012 to 2014 in Lanier and Clinch counties in Georgia evaluated the effects of repeated applications of indaziflam at 35, 75, or 145 g ai ha−1 applied biannually in March and September (five total applications) on growth of ‘Alapaha’ rabbiteye and ‘Palmetto’ highbush blueberry, and ‘Apache’ thornless blackberry. All indaziflam treatments were mixed with glufosinate, and a glufosinate-only treatment was included as a check. Minor leaf chlorosis (<10%) was noted within 30 d after application for all blueberries for all treatments, but this was always transient. Blueberry stem diameter was not different for any treatment, even when indaziflam was applied up to 725 g ai ha−1 over 3 yr as compared to glufosinate alone. There was no chlorosis or stem diameter differences for blackberry noted for any treatment. Indaziflam applied in blueberry and blackberry production provides season-long control of numerous troublesome weed species, without causing injury or negatively impacting crop growth.

Drift of sulfonylurea and phenoxy herbicides from spring cereal fields to nearby spring pea and lentil crops was simulated by spraying pea and lentil with 2,4-D or the 2:1 commercial mixture of thifensulfuron and tribenuron at rates of 0, 0.33, 1, 3.3, or 10% of the use rates (X) for spring cereal crops approximately 3 and 5 wk after planting pea and lentil. 2,4-D had minimal inhibitory effects on both crops at all rates tested. Lentil was slightly more sensitive than pea to 10% X 2,4-D. Thifensulfuron:tribenuron had no effect on either crop at rates less than 3.3% X. Two weeks after application of thifensulfuron:tribenuron, 10% X, and to a lesser degree 3.3% X rates, caused newly emerged leaves to become chlorotic, reducing chlorophyll content 25 to 50%. These treatments also reduced net photosynthesis by 37% and reduced or halted growth of the main stem. Early formation of leaves was reduced, thus tripling light penetration through the canopy. Five to six weeks after application, 10% X thifensulfuron:tribenuron had, in some treatments, more than tripled branching in pea, more than quadrupled branching in lentil, and reduced biomass as much as 42%. Flowering and maturity were delayed. Plants recovered from stunting by thifensulfuron:tribenuron to varying degrees depending on environmental conditions, and final seed yield generally was reduced less than 25%. In controlled greenhouse experiments, rate response to thifensulfuron generally was similar to that observed in field experiments. Pea was stunted less at 30 C than at 10 C, whereas lentil was affected similarly at these temperatures. Overall, visual symptoms from thifensulfuron:tribenuron exposure were more pronounced in pea than in lentil and were detectable at levels substantially lower than those that affected final seed yields.

Chlorophyll content of wheat (Triticum aestivum L. ‘Mericopa’) and corn (Zea mays L. ‘Merit’) treated with the herbicide fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)-phenyl]-4(1H)-pyridinone} and grown under high light intensity (10.8 klux), was markedly reduced. Corn and wheat germinated from seeds treated with 10 uM fluridone and grown for 6 days were almost completely bleached. Under low light intensity (108 lux) the influence of fluridone on chlorophyll production was greatly reduced. Under very low light intensity (21.5 lux) this influence was almost completely lost. The effect of light on the activity of fluridone suggests that the inhibition of carotenoid production may represent the mode of action of this herbicide. This study shows that the carotenoid content of wheat or corn drops dramatically when these plants are treated with fluridone.

Glyphosate [N-(phosphonomethyl)glycine] significantly decreased the chlorophyll content of field-grown soybeans (Glycine max L. Merr. ‘Williams’) within 48 h after a 2.24-kg/ha treatment. In laboratory studies, 0.0001, 0.001, 0.01, 0.1, and 1 mM glyphosate reduced chlorophyll content of 7-day-old etiolated barley (Hordeum vulgare L. ‘Barsoy’) shoots 8, 12, 25, 49, and 77%, respectively, following 8 h dark incubation and 24 h illumination. Reduction of chlorophyll accumulation ranged from 6% with 0.001 mM glyphosate to 82% with 1.0 mM glyphosate. In studies with 8-day-old etiolated corn (Zea mays L. ‘Pioneer Brand 3535’) shoots, 0.1, 1.0, and 10.0 mM glyphosate decreased chlorophyll content of corn shoots 24, 42, and 50%, respectively, after 12 h of illumination. The rate of chlorophyll accumulation in corn shoots was significantly reduced 64% by 1.0 mM glyphosate over a 15-h illumination period. These rapid and substantial effects on chlorophyll accumulation suggest that interference with greening may be important in the mechanism of action of glyphosate.

Fifty-day-old jimsonweeds (Datura stramonium L.) were susceptible and tomatoes (Lycopersicon esculentum Mill.) tolerant to soil-applied metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] at 0.25 and 0.50 kg/ha. Spray applications of 0.50 kg/ha metribuzin to jimsonweed foliage, or to both foliage and soil, reduced jimsonweed height growth 39 and 66%, respectively; whereas, tomato height was reduced 57 and 50% by the two placement methods, respectively. Metribuzin applied to a basal leaf appeared to move both basipetally and acropetally in jimsonweed, but only basipetally in tomato. Metribuzin applied to tomato leaves reduced growth 28% more when leaves had been abraded than when not abraded. Differential translocation appeared to be a major factor in selectivity. Directed sprays of metribuzin at 0.3 and 0.6 kg/ha on the lower 75% of jimsonweed leaves provided control in the field without injury to tomatoes.

The effect of 1.0 ppmw fluridone {1-methyl-3-phenyl-5-[3-trifluoromethyl)phenyl]-4(1H)-pyridinone} on growth of American pondweed (Potamogeton nodosus Poir.) and sago pondweed (Potamogeton pectinatus L.) was examined in plants kept in darkness or under various numbers of 12-h photoperiods. When plants were exposed to 1.0 ppmw fluridone for 1 to 10 12-h days, no stunting of American pondweed occurred until 21 days after treatment. Thirtythree days after treatment, plants that had received 4 to 10 days' exposure were most stunted. Sago pondweed was slightly more susceptible than American pondweed (87% and 50% reduction in length, respectively) 37 days after a 10-day exposure. Chlorophylls a and b were significantly lower in both species 14 days after all fluridone treatments. American pondweed plants exposed to fluridone continuously (1.0 ppmw) for 15 days, but given 0, 3, 6, 9, 12, or 15 12-h days were stunted only after having received at least six photoperiods. Stunting in sago pondweed was only slightly light-dependent. Neither species absorbed significantly more 14C-labeled fluridone after 2, 4, or 14 photoperiods compared to plants kept in darkness for the same time.

Bispyribac-sodium selectively controls annual bluegrass in cool-season turf but efficacy may be influenced by management practices, such as plant growth regulator use. Experiments were conducted in New Jersey to investigate efficacy and absorption of bispyribac-sodium applied with trinexapac-ethyl for annual bluegrass control and turfgrass tolerance. In laboratory experiments with annual bluegrass, creeping bentgrass, and perennial ryegrass, tank-mixing trinexapac-ethyl with 14C-bispyribac-sodium increased presumed foliar absorption of 14C-bispyribac-sodium compared with nontrinexapac-ethyl treated; absorption increased with trinexapac-ethyl rate. Differences in 14C-bispyribac-sodium absorption were not detected among emulsifiable concentration, microencapsulated concentration, and wettable powder trinexapac-ethyl formulations. In field experiments, sequential bispyribac-sodium applications controlled annual bluegrass 93%, but trinexapac-ethyl did not affect efficacy. Tank-mixing all trinexapac-ethyl formulations with bispyribac-sodium provided similar annual bluegrass control and creeping bentgrass quality compared with bispyribac-sodium alone. Applications of bispyribac-sodium reduced dollar spot cover in both years, whereas trinexapac-ethyl reduced dollar spot cover only in 2005.

Annual bluegrass is a troublesome weed of Kentucky bluegrass because of a lack of selective POST herbicides for control. Field experiments were conducted in New Jersey to investigate the potential of bispyribac-sodium, primisulfuron, and sulfosulfuron for selective annual bluegrass control in Kentucky bluegrass. Primisulfuron provided the best combination of Kentucky bluegrass safety and annual bluegrass control with greater efficacy in summer than fall. Bispyribac-sodium also provided substantial annual bluegrass control, especially in the summer, but caused unacceptable (> 20%) Kentucky bluegrass injury, whereas annual bluegrass control with sulfosulfuron was inconsistent. Growth chamber experiments confirmed that greater primisulfuron efficacy in summer than fall may be attributed to higher temperatures. Overall, primisulfuron has promising implications for future use in Kentucky bluegrass for annual bluegrass control whereas bispyribac-sodium will likely be more applicable in other cool-season turfgrasses.

Black medic is a troublesome weed in commercial strawberry fields in Florida. It emerges during crop establishment from the planting holes punched in plastic mulches that are installed on raised beds. Clopyralid is registered for posttransplant applications at 140 to 280 g ae ha−1 but growers typically report suppression, not control. An outdoor potted experiment was designed to model the black medic dose-response curve and determine the effect of plant size at application on control. Two plant sizes were selected: designated small (0.5- to 1-cm stem length) and large (3- to 6-cm stem length). Dose-response curves were generated using a log-logistic four-parameter model. At 22 d after treatment (DAT), there was a significant interaction between clopyralid rate and black medic growth stage on both epinasty (P = 0.0022) and chlorosis (P = 0.0055). The effective dosage to induce 90% (ED90) epinasty were 249.5 and 398.3 g ha−1 for the small and large growth stages, respectively. The ED90 for chlorosis was 748.2 for the small growth stage, whereas the estimated value for the large was outside the measured range. For necrosis there was no significant effect of growth stage, and the ED90 was 1,856.3 g ha−1. The aboveground dry biomass ED90 for the small growth stage was 197.3 g ha−1, and the estimated ED90 value for the large was not within the measured range. Results indicate that clopyralid adequately controls black medic when applied at maximum label rates when stems were 0.5 to 1 cm long but not when plants were larger. Poor efficacy typically observed in commercial fields is likely due to black medic plant size or lack of herbicide coverage via shielding by strawberry plants.

Field and laboratory experiments were conducted in New Jersey to investigate the influence of spray adjuvants on foliar absorption and efficacy of bispyribac–sodium on annual bluegrass, creeping bentgrass, and perennial ryegrass. In laboratory experiments on annual bluegrass, 14C–bispyribac–sodium without an adjuvant had 25% foliar absorption by 8 h after treatment, whereas absorption increased to 45, 46, and 75% when applied with crop oil concentrate, nonionic surfactant, and methylated seed oil, respectively. In creeping bentgrass fairways, sequential bispyribac–sodium applications at 37 g ai/ha with spray adjuvants controlled annual bluegrass similarly to 74 g ai/ha applied sequentially without adjuvants. In perennial ryegrass, treatments with methylated seed oil and nonionic surfactant required 25 and 41% lower bispyribac–sodium rates, respectively, to obtain annual bluegrass control levels comparable to bispyribac–sodium rates without adjuvants. Spray adjuvants did not exacerbate turf-grass discoloration from bispyribac–sodium. Overall, spray-adjuvant use with bispyribac–sodium may allow practitioners to reduce application rates and enhance efficacy for annual bluegrass control.

Several field observations and limited research have confirmed that sulfonylurea herbicides commonly used in warm-season turf can laterally relocate via turf equipment and injure neighboring cool-season grasses. This phenomenon is referred to as ‘tracking’ among turf managers and often occurs when mowers traverse treated areas and adjacent creeping bentgrass putting greens, fairways, and tee boxes while foliage is wet with dew. Tracked flazasulfuron and metsulfuron at 9 and 42 g/ha, respectively, caused little injury to creeping bentgrass. Flazasulfuron at 26 and 53 g/ha, and foramsulfuron at 28 g ai/ha tracked while dew was present 20 h after treatment (HAT) resulted in the most noticeable creeping bentgrass injury when tracked. Flazasulfuron at higher rates and foramsulfuron tracked 20 HAT on dew-covered turf reduced turf color compared to nontracked turf. When the mower traversed dry turf at 6 HAT and wet turf at 68 HAT, turf color was reduced less than wet turf tracked 20 HAT. Length of track and creeping bentgrass injury decreased with flazasulfuron rate. When using flazasulfuron at rates between 9 and 53 g/ha, a 1.5- and 4.5-m border, respectively, around creeping bentgrass would eliminate most injury from tracked herbicide.

Effects of soil pH and cation exchange capacity (CEC) on sunflower tolerance to sulfentrazone were investigated in a greenhouse study. Variables were soil pH (7.0, 7.3, 7.5, and 7.8), soil CEC (8.2, 13.7, 18.4, and 23.3 cmol/kg), and sulfentrazone rate (0, 105, 158, and 184 g ai/ha). Sulfentrazone-induced leaf chlorosis was affected by soil pH at 12 d after planting (DAP), but plants recovered, and earlier differences were not visible 9 d later. At 12 DAP, leaf chlorosis was 3 or 4% more severe in soils with pH 7.3 or higher compared with soils with pH 7.0 when averaged over both sulfentrazone rate and soil CEC. Leaf chlorosis resulting from sulfentrazone rates of 105, 158, and 184 g/ha was 17, 25, and 35% less at 23 cmol/kg than at 8.2 cmol/kg, respectively. Differences in chlorosis among sulfentrazone rates were greatest in soil with low CEC and lessened as soil CEC increased. Plants regained normal color over time, and newly emerging leaves were not affected. However, plant dry weights were reduced when sulfentrazone rate was ≥158 g/ha. Averaged over sulfentrazone rate and soil pH, sunflower dry weights were less when soil CEC was 8.2 compared with a CEC of 13.7 cmol/kg or higher, indicating a greater response at low CEC. Sunflower plant dry matter was not different in sulfentrazone-treated soil with a CEC above 13.7 cmol/kg. At the ranges tested, soil CEC had a considerably greater effect than did pH on sunflower tolerance to sulfentrazone.

Amicarbazone is a photosystem II (PSII) inhibiting herbicide of the triazolinone herbicide family. Greenhouse experiments were conducted to compare the effects of amicarbazone and atrazine on annual bluegrass control and quantum yield (ΦPSII) when applied at three treatment placements (soil-only, foliage-only, and foliage + soil). Herbicide rates for amicarbazone and atrazine were 0.53 and 2.25 kg ha−1, respectively. Amicarbazone applied soil-only and foliage + soil controlled annual bluegrass 57 and 59%, respectively, 1 wk after treatment (WAT). Atrazine applied to foliage + soil controlled annual bluegrass 48% at 1 WAT. All soil-only and foliage + soil treatments were similar 2 WAT. Foliage-only application of amicarbazone provided significantly less control than other amicarbazone treatments throughout the study. Amicarbazone applied soil-only and foliage + soil controlled annual bluegrass 100% at 3 WAT. Soil-only and foliage + soil applications of atrazine and amicarbazone had similar reductions in quantum yield (ΦPSII) at 1 to 3 WAT. Foliar-applied amicarbazone reduced ΦPSII 78, 84, and 86% at 1, 2, and 3 WAT, respectively. The rapid reduction in annual bluegrass ΦPSII and the increase in control resulting from soil contact of amicarbazone indicate root exposure of amicarbazone is beneficial for annual bluegrass control.

Sulfosulfuron was recently registered for grassy weed control in creeping bentgrass, but turf sensitivity is a concern for intensively managed golf courses. Field and growth chamber experiments in New Jersey investigated creeping bentgrass growth responses and tolerance to sulfosulfuron. Creeping bentgrass chlorosis increased with sulfosulfuron rate but turf had less chlorosis from sequential sulfosulfuron applications compared to bispyribac–sodium. Herbicide-treated turf had similar root weight compared to untreated turf on six sampling dates. In growth-chamber experiments, creeping bentgrass treated with sulfosulfuron had chlorosis and clipping weight reductions exacerbated by reductions in temperature from 25 to 15 C. Overall, creeping bentgrass appears to tolerate sequential sulfosulfuron applications better than or comparable to bispyribac-sodium in early summer, whereas creeping bentgrass sensitivity to sulfosulfuron increases at cooler temperatures.

Bispyribac-sodium is a POST herbicide that selectively controls annual bluegrass in creeping bentgrass, but inconsistent results with seasonal applications are believed to occur from temperature influences on bispyribac-sodium efficacy. Growth chamber experiments at the New Jersey Experimental Greenhouse Research Complex, New Brunswick, NJ, investigated three temperature regimes on ‘L-93’ creeping bentgrass and annual bluegrass responses to bispyribac-sodium. Annual bluegrass and creeping bentgrass exhibited contrasting responses to bispyribac-sodium as temperature increased from 10 to 30 C. Regressions of 4 week after treatment (WAT) data revealed as temperature increased from 10 to 30 C, required bispyribac-sodium rates for 50% clipping reduction (CR50) of annual bluegrass decreased from 85 to 31 g ai/ha and required rates for 50% leaf chlorosis decreased from greater than 296 to 98, indicating increased herbicidal efficacy at higher temperatures. In contrast, required bispyribac-sodium rates for creeping bentgrass CR50 increased from 200 to greater than 296 as temperature increased from 10 to 30 C. Bispyribac-sodium discolored creeping bentgrass 0 to 20% at 20 and 30 C and discoloration increased 10 to 50% at 10 C. Thus, warmer temperatures (20 and 30 C) increase bispyribac-sodium efficacy for annual bluegrass control with minimal bentgrass discoloration; however, cooler temperatures (10 C) have minimal efficacy on annual bluegrass and increase bentgrass chlorosis.

Bispyribac-sodium effectively controls annual bluegrass in creeping bentgrass fairways but efficacy on putting greens may be affected by management differences and thus, application regimes may need to be modified for effective annual bluegrass control. To test this hypothesis, field experiments investigated various bispyribac-sodium application regimens for annual bluegrass control on creeping bentgrass putting greens. Bispyribac-sodium regimes totaling 148, 222, and 296 g ha−1 controlled annual bluegrass 81, 83, and 91%, respectively, over 2 yr. Pooled over herbicide rates, bispyribac-sodium applied two, three, and six times controlled annual bluegrass 78, 83, and 94%, respectively. The most effective bispyribac-sodium regime was 24.6 g ha−1 applied weekly, which controlled annual bluegrass 90% after 8 wk with acceptable levels of creeping bentgrass discoloration. After 8 wk, all regimes reduced turf quality as a result of voids in turf following annual bluegrass control; regimes with six applications reduced turf quality the most.

Aphid–plant interactions depend on genotypes of both organisms, which determine the two-way molecular exchange that leads to compatible or incompatible outcomes. The underlying genes are mostly unknown, making it difficult to predict likelihood of aphid success or host resistance, and hampering crop genetic improvement. Here we screened eight pea aphid clonal genotypes collected from diverse legume hosts, on a species-wide panel of Medicago truncatula (Mt) genotypes. Aphid virulence was measured by survival, fecundity and growth rate, together with scores for chlorosis and necrosis as host response indicators. Outcomes were highly dependent on the specific aphid–host genotype combinations. Only one Mt line was fully resistant against all clones. Aphid-induced host chlorosis and necrosis varied greatly, but correlated with resistance only in a few combinations. Bi-clustering analysis indicated that all aphid clones could be distinguished by their performance profiles across the host genotypes tested, with each clone being genetically differentiated and potentially representing a distinct biotype. Clones originating from Medicago sativa ranged from highly virulent to almost completely avirulent on both Medicago species, indicating that some were well adapted, whereas others were most likely migrants. Comparisons of closely related pairs of Australian Mt genotypes differing in aphid resistance revealed no enhanced resistance to European pea aphid clones. Based on the extensive variation in pea aphid adaptation even on unfamiliar hosts, most likely reflecting multiple biotype-specific gene-for-gene interactions, we conclude that robust defences require an arsenal of appropriate resistance genes.