Visual Injury Ratings Research Articles

Steam application with paraquat to control goat weed (Scoparia dulcis) in citrus orchards

Reducing herbicide use in horticultural crop production can ameliorate adverse environmental effects but may also impact weed control effectiveness, especially as it pertains to difficult-to-control weeds. This challenge can be addressed by integrating a non-chemical strategy such as steam application with herbicide application. In this study, steam, as a non-chemical approach, was combined with post-emergence herbicide (paraquat) application for goatweed (Scoparia dulcis) management in citrus orchards. Two field trials based on randomized complete block design were conducted in citrus orchards in Immokalee, FL, in 2018 and 2021. Steam was applied to goatweed at a flow rate of 53 L ha−1 for 5–6 s. Twenty-four hours after steam application, low and high paraquat rates (0.3366 and 1.010 kg ai ha−1) were applied. In addition, the same rates of paraquat were applied without steam for comparison. Untreated checks (UTC) of no herbicide or steam applications were also included in the experiment as a control. Based on visual injury ratings, a combination of steam + low dosage of paraquat was as effective as the high dosage of paraquat alone and steam + high dosage of paraquat at 1, 8, and 16 days after treatment application (DAT) in 2018 trial and 1, 8, 16 and 22 DAT in 2021 trial.However, based on one site-year of biomass data, the percentage of dead weed biomass out of total biomass was statistically similar among all the treatments. Results from this study demonstrate that combining a low rate of paraquat applied in tandem with the steam application has the potential to provide effective goatweed control in citrus orchards.

Responses of rice genotypes to foliar-applied metribuzin

AbstractThe increasing development of herbicide resistance in weeds found in rice cropping systems has encouraged researchers to evaluate alternate herbicides to prevent and manage herbicide-resistant weed biotypes. Metribuzin is a photosynthetic-inhibiting herbicide that controls various important grass and broadleaf weeds. Several crops, including soybean, wheat, peas, and potato, have shown differential varietal responses to metribuzin. To determine whether rice has differential varietal responses to metribuzin for potential utilization in a rice breeding program, greenhouse experiments were conducted to evaluate the responses of 142 long-, medium-, and short-grain rice genotypes to the herbicide. Metribuzin was applied at 0, 22, 44, 88, 176, and 352 g ai ha−1 when rice plants were in the 3- to 4-leaf stage. Crop response regarding phytotoxicity, height reduction, and biomass reduction was evaluated. Metribuzin caused significant injury to all rice genotypes tested, but short-grain rice genotypes were, on average, more susceptible than medium- and long-grain rice genotypes. Short-grain rice genotypes generally had greater height reduction and produced less biomass than long-grain or medium-grain rice genotypes. Crop visual injury ratings were correlated with plant height reductions and biomass reductions. The results indicate that the level of metribuzin tolerance in rice is inadequate for commercial use; however, further research is needed to develop higher levels of herbicide resistance by mutagenized rice cultivars.

Effects of early season soil moisture and nitrogen applications on tolerance of quizalofop‐resistant rice to quizalofop

AbstractQuizalofop‐resistant rice (Oryza sativa L.) allows for postemergence applications of quizalofop. Previous research reported that soil moisture availability strongly influences the response of grass species to aryloxyphenoxypropionate herbicides. Experiments were conducted at Stuttgart, AR, and at Colt, AR, in 2021 to investigate the influence of early season soil moisture and nitrogen (N) applications on the tolerance of quizalofop‐resistant cultivars to sequential quizalofop applications. The experiment was implemented as a two‐factor, randomized complete block design. The factors evaluated were cultivar (PVL02 and RTv7231 MA) and herbicide treatment (nontreated control; nontreated control fertilized with ammonium sulfate [AMS] at 100 lb acre−1 and surface irrigated at the two‐leaf stage; sequential quizalofop applications at 1× and 2× rates; sequential quizalofop at 1× and 2× rates surface irrigated at the two‐leaf stage; and sequential quizalofop applications at 1× and 2× rates fertilized with AMS at 100 lb acre−1 then surface irrigated at the two‐leaf stage). Sequential quizalofop applications were applied at the two‐leaf and five‐leaf stages, with 1× and 2× rates of quizalofop being 0.11 and 0.22 lb a.i. acre−1, respectively. RTv7231 MA injury was 2‐ to6‐percentage points higher than PVL02 at all visual injury ratings averaged across treatment and location. Sequential quizalofop applications caused 1–9% visible injury to quizalofop‐resistant cultivars pooled over locations and rating timings. Growers could consider environmental conditions before herbicide applications to mitigate the risk of injury to quizalofop‐resistant cultivars from quizalofop, and drier soil conditions could be used for quizalofop applications onto rice compared with saturated soil conditions.

LibertyLink®, WideStrike® and XtendFlex® Tolerance to Late Postemergence Applications of Glufosinate and S-Metolachlor

Glufosinate remains an important postemergence (POST) herbicide for controlling glyphosate-resistant Amaranthus palmeri (S. Wats) in auxin-tolerant trait systems. Although visual injury from glufosinate applications to WideStrike cultivars is expected, concerns have been raised on the visual injury noted in XtendFlex cultivars, particularly with sequential late-POST glufosinate applications or when S-metolachlor is tank-mixed with glufosinate. Field trials were established in Jackson, TN during 2015 and 2017 and in Huntersville, TN during 2016. Herbicide treatments included an untreated; one, two, and three sequential applications of glufosinate; and glufosinate + S-metolachlor followed by (FB) glufosinate FB glufosinate + S-metolachlor. Applications began 40 days after planting and sequential applications were made every 10 to 14 days. Cultivars included DP 1522 B2XF (DeltaPine, Bayer CropScience, St. Louis, MO), PHY 333 WRF (Phytogen, Corteva Agriscience, Indianapolis, IN), and ST 4946 GLB2 (Stoneville, BASF Corp., Florham Park, NJ). Visual injury ratings varied across timing, treatment, cultivar, and site-year. Three sequential applications of glufosinate with two applications of S-metolachlor caused 7 to 20%, 2 to 15%, and 1 to 8% injury 10 days after the last application in PHY 333 WRF, DP 1522 B2XF, and ST 4946 GLB2, respectively. Cultivar lint yield and fiber quality did not vary by herbicide treatment. Producers who apply glufosinate should expect increasing visual injury from LibertyLink to XtendFlex to WideStrike cultivars, with a sharp increase in visual injury from XtendFlex to WideStrike cultivars; however, sequential, labeled applications of glufosinate with or without two applications of S-metolachlor will likely not impact yields of LibertyLink, WideStrike, or XtendFlex cultivars.

Response of Glyphosate-Tolerant Soybean Yield Components to Dicamba Exposure

Exposure of soybean to dicamba can result in leaf malformation and sometimes yield loss, but it is unclear how yield components are affected by exposure to low quantities of this herbicide. The objectives were to characterize soybean injury and quantify changes in seed yield and yield components of soybean plants exposed to dicamba, and determine if seed yield loss can be estimated from visual injury ratings. Nine dicamba rates (0, 0.06, 0.23, 0.57, 1.1, 2.3, 4.5, 9.1, and 22.7 g ae ha−1) were applied at three growth stages (V2 – two trifoliates, V5-five trifoliates, or R2-full flowering soybean) to Beck's brand ‘342NRR’ soybean planted near Lafayette, IN, in 2009 and 2010 and near Fowler, IN, in 2009. Visually estimated soybean injury of 20% at the V2, V5, or R2 timing was 0.676 to 0.937 g ha−1dicamba at 14 d after treatment (DAT) and 0.359 to 1.37 g ha−1dicamba at 28 DAT. Seed yield was reduced by 5% from 0.042 to 0.528 g ha−1dicamba and a 10% reduction was caused by 0.169 to 1.1 g ha−1dicamba. The number of seeds m−2, pods m−2, reproductive nodes m−2, and nodes m−2were the most sensitive yield components. Path analysis indicated that dicamba reduced seeds m−2, pods m−2, reproductive nodes m−2, and nodes m−2which were the main causes of seed yield loss from dicamba exposure. The correlation of seed yield loss and visual soybean injury was significant (P < 0.0001) for both the V2 treatment timing (R2= 0.92) and the V5 and R2 treatment timings (R2= 0.91). Early-season injury rating of 8% at the V2 treatment and 2% at the V5 or R2 treatments caused 10% or more yield loss.

Soybean yield and yield components as influenced by the single and repeated flaming

Field experiments were conducted to study the impact of single and multiple flaming on crop injury, yield components, and yield of soybean. The goal of this experiment was to determine the number of the maximum flaming treatments which soybean could tolerate without any yield loss. The treatments consisted of a non-flamed control, and broadcast flaming conducted one time (at VC-unfolded cotyledon, V2-second trifoliate, and V5-fifth trifoliate), two times (each at VC and V2, VC and V5, and V2 and V5 stages), and three times (at VC, V2, and V5 stages) resulting in a total of eight treatments. All plots were kept weed-free for the entire growing season by hand hoeing. A propane dose of 50 kg ha−1 was applied with torches parallel to the crop row and at an operating speed of 4.8 km h−1 for all treatments. The response of soybean was measured as visual injury ratings (at 7 and 28 days after treatment – DAT) as well as effects on yield components and yield. Broadcast flaming conducted once (at VC or V5 stage), as well as twice (at VC and V5 stages) exhibited the lowest injury of about 8% at 28 DAT. Any treatment that contained flaming at V2 stage resulted in more than 70% injury at 28 DAT. The highest crop yields were obtained from the non-flamed control (3.45 t ha−1) and the plots flamed once at VC (3.35 t ha−1), V5 (3.32 t ha−1), and two times at VC and V5 (3.24 t ha−1), which were all statistically similar. Soybean flamed at V2 stage had lower yields (1.03 t ha−1 at V2, 0.46 t ha−1 at VC and V2, and 0.38 t ha−1 at V2 and V5). The lowest yields were in soybean flamed three times (VC, V2, and V5 stages), which yielded only 0.36 t ha−1. These results indicate that soybean could tolerate a maximum of two flaming treatments at VC and V5 growth stages per season without any yield reduction.

Tolerance of selected weed species to broadcast flaming at different growth stages

Organic producers rank weeds as the most important pests that limit their crop production. In order to optimize the use of propane flaming as a weed control tool, the objective of this study was to test tolerance of selected weed species to broadcast flaming performed at different growth stages. Six annual species, including one grass [barnyardgrass ( Echinochloa crus-galli)] and five broadleaves [field bindweed ( Convolvulus arvensis), kochia ( Kochia scoparia), ivyleaf morning glory ( Ipomoea hederacea), velvetleaf ( Abutilon theophrasti) and Venice mallow ( Hibiscus trionum)] were flamed at three growth stages with six doses of propane. The propane doses applied were 0, 12, 31, 50, 68 and 87 kg/ha. Flaming treatments were applied utilizing a custom built flamer mounted on a four-wheeler moving at a constant speed of 6.4 km/h. Species response to propane were described by log-logistic models based on visual injury ratings and dry matter (DM) for each weed species. Overall response to flaming varied among species, growth stage and propane dose. Broadleaf weeds were more susceptible to flaming than the grass regardless of the growth stage. A dose of 76 kg/ha of propane was needed to obtain 90% DM reduction for 7-leaf (L) barnyardgrass compared to much lower doses of 40, 49, 55, 56 and 51 kg/ha propane for 8-L bindweed, 6-L kochia, 10-L morning glory, 7-L velvetleaf and 5-L Venice mallow, respectively. Moreover, the tolerance of both grassy and broadleaf weed species to broadcast flaming increased with increase in plant size. A 90% DM reduction in velvetleaf was obtained with 42, 56 and 102 kg/ha of propane for 5-L, 7-L and 16-L stages, respectively. The tested broadleaf weed species were effectively controlled (90% DM reduction) with propane dose of 30–60 kg/ha when flamed at early growth stages (3-L to 14-L), while the same dose of propane provided only 80% DM reduction in barnyardgrass when flamed at vegetative stages (4-L to 7-L). It was not possible to obtain 90% DM reduction in barnyardgrass when flamed at flowering stage with the propane doses tested in this experiment.

Turfgrass species response exposed to increasing rates of glyphosate application

To investigate the response of nine turfgrass species exposed to increasing rates of glyphosate application, the dry matter production, visual leaf injury symptoms (e.g., chlorosis and necrosis) and the concentrations of shikimate and mineral nutrients were determined in shoots. The rates of foliar glyphosate application were 0%, 5% (1.58 mM), and 20% (6.32 mM) of the recommended application rate for weed control. In general, there was a negative and weak correlation between the intensity of visual injury and relative decreases in shoot dry matter production caused by glyphosate application. The decreases in shoot dry matter production and the severity of leaf damage pronounced by increasing glyphosate rate showed a substantial variation among the turfgrass species. Of the turfgrass species tested, Festuca arundinacea ‘Falcon’ and Buchloe dactyloides ‘Bowie’ were selected as the most tolerant and sensitive species to applied sublethal rates of glyphosate as judged from visual injury ratings, respectively. At the highest glyphosate rate, shoot dry weight was decreased by 4-fold in Bowie and only 1.6-fold in Falcon. When glyphosate was not applied, shoot shikimate concentration of all species was very low and below 2.8 μmol g −1 FW (fresh weight). Glyphosate applications resulted in increases in shoot shikimate concentration with substantial variations among species. At 6.32 mM glyphosate treatment, shikimate concentration ranged between 156.1 μmol g −1 ( F. rubra, Ambrose) and 16.5 μmol g −1 FW ( F. rubra, Cindy Lou). However, the highly sensitive and the tolerant genotypes were not different in shoot shikimate concentrations. Even, in the case of some genotypes, high glyphosate tolerance is accompanied by higher shoot concentrations of shikimate. Depending on the turfgrass species and mineral nutrients tested, increasing glyphosate application either did not affect or reduced mineral nutrient concentrations. In the case of decreases in shoot concentration of mineral nutrients, the decreases in Ca, Mg, Mn and Fe were most distinct. The results obtained indicate existence of a large genetic variation in tolerance to glyphosate toxicity among the turfgrass species. This differential variation in tolerance to glyphosate could not be explained by the changes in shoot concentrations of shikimate and mineral nutrients.

Cotton Injury and Yield as Affected by Simulated Drift of 2,4-D and Dicamba

Experiments were conducted at Manhattan, KS in 2005 and 2006 to evaluate cotton response to simulated 2,4-D and dicamba drift rates at different stages of growth and multiple applications of 2,4-D. Cotton was treated with 2,4-D and dicamba at 0, 1/200, and 1/400 of the use rate (561 g ae/ha) when plants were at the three- to four-leaf, 8-, 14-, or 18-node growth stages. Injury symptoms after 2,4-D and dicamba application were more severe at the three- to four-leaf stage compared with other stages with greatest injury from 2,4-D. In general, plants partially recovered from 2,4-D and dicamba injury symptoms, and only 2,4-D applied at the 1/200 rate reduced fiber yield. In a separate study, cotton was treated with 2,4-D at 0, 1/400, 1/800, and 1/1,200 of the use rate for one, two, or three applications. Yield reduction increased as herbicide rate increased from 1/1,200 to 1/400 and the number of applications increased from one to three. In both studies, plants partially or fully recovered from injury symptoms and recovery was greater with dicamba than 2,4-D. Correlation coefficient analysis showed that visual injury ratings later in the growing season are a good predictor of yield reduction (R2= 0.58).

Inheritance of resistance of common waterhemp (Amaranthus rudis) to protoporphyrinogen oxidase-inhibiting herbicide

Abstract Common waterhemp resistance to protoporphyrinogen oxidase (protox)-inhibiting herbicides was first reported in northeast Kansas in 2001. The objective of this research was to determine the inheritance characteristics of the protox-resistance trait. Resistant and susceptible common waterhemp were screened for resistance and inbred lines were developed using full-sib mating for three generations in the greenhouse. After the third generation, resistant and susceptible plants were crossed in a male and female reciprocal manner creating 57 F1 (first generation) lines. A proportion of the F1 progeny was screened for resistance and the remaining progeny were used to create F2 (second generation) and backcross (BC) lines. Approximately 500, 400, and 1400 F1, BC, and F2 progeny, respectively, were treated with 105 g ha−1 of lactofen when plants reached the 8-node growth stage. Visual injury ratings were determined at 14 days after treatment and based on a scale of 0 = no injury and 100 = mortality. A plan...

Effect of the foliar application of diquat herbicide on selected natural area and field crop species

Field experiments were conducted to determine the non‐target impact of foliar‐applied diquat on selected plant species. Diquat was applied to emerged bracken fern, chain fern, slash pine, soybean, sunflower, cotton, corn, and onion at rates varying from 0.02–4.5 kg ai ha−1 of diquat cation, which allowed for the determination of the no‐effect rate and the rate that caused 25, 50, and 100% injury, as measured by visual injury ratings, plant heights, and dry weights. Bracken fern, chain fern, and slash pine were more tolerant to diquat and exhibited regrowth potential at the higher rates. The other six species were not only more susceptible to diquat, but they did not exhibit regrowth potential at high rates. However, these species were able to recover from slight injury caused by the lower rates of diquat.

Impact of Corn Gluten Meal Applications on Spring-Transplanted Onion Injury and Yields

Research to determine the relative benefits among alternative herbicides for weed control in onions (Allium cepa L.) should focus on weed control efficacy, and the impact of herbicides on crop injury, and the resulting weed competition on crop yields. Herbicide injury and weed competition can produce disproportionate reductions in onion yields as a result of onion's slow growth rate, short height, non-branching plant structure, low leaf area, and shallow root system. Field research was conducted in 2002 and 2003 in southeast Oklahoma (Lane, OK) to determine crop safety and yield response of selected pre-emergent synthetic herbicides and corn gluten meal (CGM) on spring-transplanted onion, cv. Hybrid Yellow Granex PRR, production. There were 21 treatments [12 synthetic herbicide treatments, five CGM applications, a full-season weed-free (hand-weeded) treatment, a full-season weedy-check, a partial-season weed-free (weed-free for the first half of the growing season by handweeding, then the weeds were allowed to grow), and a weedy-check without onions]. Synthetic herbicide treatments included pendimethalin applications at 0.5, 1.0, and 1.5 kg·ha−1 ai, oxyfluorfen at 0.1, 0.2, and 0.3 kg·ha−1 ai, and also tank-mixed at these three levels. In addition, the highest rate of each herbi-cide-pendimethalin (1.5 kg·ha−1 ai), oxyfluorfen (0.3 kg·ha−1 ai), and the tank mix of pendimethalin (1.5 kg·ha−1 ai) plus oxyfluorfen (0.3 kg·ha−1 ai)-were applied and kept weed-free by hand to determine the crop safety of these herbicides. CGM was applied at 1,000,2,000,3,000, and 4,000 kg·ha−1. A weed-free (hand-weeded) treatment was also combined with the highest CGM rate (4,000 kg·ha−1) to determine the effect of the CGM on crop injury and growth. Visual crop injury ratings were collected at 3, 5, 10, 20, and 30 days after planting, along with yields of marketable bulbs segregated by size. No phytotoxic symptoms or yield reductions were observed due to the synthetic herbicides or CGM applications. These compounds provided sufficient crop safety when applied at the rates studied. Increased weed competition caused a shift in bulb size distribution across the four bulb categories (colossal, large, medium, and small), resulting in a decreased number of colossal and large bulbs and an increase in small bulbs. Although the synthetic herbicides and CGM provided crop safety, and to some extent early weed control, reductions in crop yields as a result of weed competition demonstrated the need to include supplemental weed control with post-emergence herbicides or other weed control methods to produce maximum onion yields.

Cotton Response to Simulated Drift of Seven Hormonal-Type Herbicides

Field experiments were conducted at Manhattan and Hesston, KS, in 2004, and at Manhattan, KS, in 2005, to evaluate cotton response to seven hormonal-type herbicides. Herbicides 2,4-D amine, 2,4-D ester, clopyralid, picloram, fluroxypyr, triclopyr, and dicamba were each applied at 0, 1/100, 1/200, 1/300, and 1/400 of the herbicide use rates on cotton in the six- to eight-leaf stage. Herbicide use rates were 210 and 280 g ae/ha for fluroxypyr and clopyralid and 561 g ae/ha, for 2,4-D amine, 2,4-D ester, dicamba, picloram, and triclopyr. At 14 d after treatment (DAT), all herbicides caused leaf cupping and epinasty, except triclopyr and clopyralid, which caused severe bleaching and chlorosis. The order of visual injury ratings was 2,4-D ester > 2,4-D amine > picloram > dicamba > fluroxypyr > triclopyr > clopyralid. By 56 DAT, slight injury symptoms were observed on plants treated with all herbicides, except all rates of 2,4-D, from which symptoms were severe. All rates of 2,4-D and the highest rate of picloram caused more than 60% flower abortion. Ranking of fiber yield reduction after herbicide treatment was 2,4-D ester > 2,4-D amine > picloram > fluroxypyr > dicamba > clopyralid > triclopyr. This research demonstrated that cotton is extremely susceptible to simulated drift rates of 2,4-D and picloram, whereas clopyralid and triclopyr caused early injury, with minimal effect on cotton yield.

Shikimic Acid Accumulation in Field-Grown Corn (Zea mays) Following Simulated Glyphosate Drift

Field studies were conducted in 2001 through 2003 to determine if shikimic acid accumulation could be used to accurately predict yield reductions in field corn exposed to sublethal rates of glyphosate. Glyphosate (0-0.32 kg ae/ha) was applied to corn at the V6 to V8 growth stage. Corn whorls were randomly collected up to 14 days after application (DAA), and shikimic acid accumulation in the whorls was determined using HPLC-UV. Maximum shikimic acid accumulation occurred 3-7 DAA in corn receiving 0.16 and 0.32 kg/ha. Shikimic acid accumulation 3, 5, and 7 DAA did correlate (r = 0.80-0.86) to yield losses from a sublethal application of glyphosate. Shikimic acid accumulation 3, 5, and 7 DAA was better correlated to visual injury at 14 DAA than to yield reductions. Visual injury ratings 14 DAA were a slightly better indicator of potential yield losses (r = 0.93) than shikimic acid accumulation in field-grown corn whorls (r = 0.8-0.86).

Phytotoxic response and yield of chickpea (Cicer arietinum) genotypes with pre-emergence application of isoxaflutole

Balance® (75% a.i. isoxaflutole) at 100 g/ha is registered in Australia for the control of several broadleaf weeds in chickpea. Polyhouse and field experiments were carried out to examine the tolerance of chickpea genotypes to isoxaflutole. Seven rates of isoxaflutole [0, 18.75, 37.5, 75 (recommended rate), 150, 300 and 600 g a.i./ha] were applied to 20 genotypes in the first polyhouse experiment while in the second experiment, 16 genotypes were tested. In the field, six genotypes were treated with five herbicide rates (0, 37.5, 75, 150 and 300 g a.i./ha). There was a strong dose response in the polyhouse experiments in visual injury ratings, plant height, and shoot and root dry weight. In general, there was less herbicide injury to the kabuli genotypes than in the desi chickpea genotypes. Chickpea genotypes Yorker, Howzat, Amethyst, Gully, 91025-3021, Jimbour, S 95425 and FLIP 94-92C exhibited higher overall mean injury rating in experiment 1. Among these genotypes, shoot dry matter was reduced significantly in Amethyst, Jimbour, 91025-3021 and S 95425. Root dry matter in Amethyst, Jimbour, Yorker, 91025-3021 and S 95425 was also reduced significantly. Height was reduced significantly in all of the above eight genotypes. Although there was less overall injury level in the second polyhouse experiment, which was at lower temperatures, Howzat, Yorker, 91025-3021, FLIP 94-92C and S 95425 again recorded high overall mean injury ratings and should be regarded as more susceptible to isoxaflutole than the other strains. In comparison, 97039-1275 and Kyabra recorded very minor injury symptoms in all the experiments and can be regarded as the most tolerant. The herbicide injury to the genotypes in the field was less than in the polyhouse although Yorker and 91025-3021 showed injury symptoms at early stages of growth. The injury symptoms were temporary and did not produce significant effects on the overall crop growth and yield. It is suggested that plant breeding programs take into account the relative susceptibility of new chickpea genotypes to isoxaflutole.

Fungicide–herbicide interaction in soybean ( Glycine max)

Fungicide seed treatments are becoming increasingly popular for use with glyphosate-tolerant soybean ( Glycine max (L.) Merr.). This research was initiated in response to preliminary data indicating possible negative interaction(s) between certain agrochemicals. A 2-year field study was conducted to determine whether certain combinations of fungicide seed treatments and post-emergence herbicides affect soybean yield. The experiment involved six seed treatments (thiabendazole (TBZ), pentachloronitrobenzene (PCNB), captan, TBZ+PCNB+captan, fludioxonil and a fungicide-free control) and six weed control treatments (imazethapyr, imazamox, glyphosate, glyphosate+imazethapyr, glyphosate+cloransulam-methyl and a hand-weeded control). All 36 combinations were evaluated in four different environments in Illinois, USA. All fields had minimal disease pressure and were kept free of weeds (mechanically), allowing for the evaluation of chemical interactions independent of the confounding factors of herbicide and fungicide efficacy. The fungicide treatments did not significantly affect the crop's response to the herbicide treatments, as measured by visual injury ratings. In addition, neither fungicide, herbicide, nor fungicide–herbicide combination significantly affected crop yield. No significant chemical interactions were found to exist between any of the examined fungicidal seed treatments and post-emergence herbicides.

Sweet Corn Cultivar Sensitivity to Bentazon

Five sweet corn cultivars were evaluated for tolerance to bentazon in five field experiments conducted during 2 yr in Ontario. Bentazon was applied postemergence (POST) at 1.08 and 2.16 kg ai/ha, the highest registered rate and twice the highest registered rate, respectively, used in sweet corn in Ontario. When bentazon was applied POST at 1.08 and 2.16 kg/ha to sweet corn cultivar ‘DelMonte 2038’, injury included plant stunting and leaf damage ranging from 6 to 69% and 15 to 90%, respectively. Plant height was reduced to 48 and 100% of the untreated check when treated with bentazon at 1.08 and 2.16 kg/ha, respectively. The visual injury and height reductions were reflected in the marketable yields, which were reduced to 94% when treated with bentazon. Significant reductions in height and marketable yield were not observed in the other four cultivars tested. No correlation was observed between bentazon sensitivity and endosperm genotype. Based on visual injury ratings, sweet corn height, and marketable yield, it was concluded that ‘Calico Belle’, ‘GH 2684’, ‘Reveille’, and ‘Rival’ are tolerant to POST application of bentazon.

Responses of black and cranberry beans (Phaseolus vulgaris) to post-emergence herbicides

There is a limited number of post-emergence (POST) herbicides available for weed management in black and cranberry beans in Ontario. The tolerance of two cultivars of black beans (AC Harblack and Midnight Black Turtle) and two cultivars of cranberry beans (Hooter and SVM Taylor) to POST applications of bentazon, bentazon plus fomesafen and imazamox plus fomesafen was evaluated at the maximum-use dose (1×) and twice the maximum-use dose for soybeans (2×) at two Ontario locations in 2001 and 2002. There were no differences between AC Harblack and Midnight Black Turtle or Hooter and SVM Taylor cultivars in their responses to the POST herbicides tested. The POST application of bentazon, bentazon plus fomesafen and imazamox plus fomesafen at 7 DAT caused only minor crop effects in dry beans. At 14 DAT visual injury ratings were higher in black beans (1.4–3.0%) compared to cranberry beans (0.4–1.6%). Visual injury was minimal at 28 DAT and was below 1% for all cultivars and market classes. The POST application of bentazon, bentazon plus fomesafen and imazamox plus fomesafen at the single or double-use rate caused no significant effect on plant height, shoot dry weight, seed moisture content and yield of black or cranberry beans compared to the untreated. Black and cranberry beans were more sensitive to bentazon and bentazon plus fomesafen than imazamox plus fomesafen. Based on these results, there is sufficient tolerance for use of these herbicides post-emergence in black bean and cranberry bean production in Ontario.

Turf Herbicide Injury to Landscape Trees as Influenced by Mulch

Abstract A two year field study was conducted in 1991 and 1992 to evaluate the sensitivity of landscape trees to certain turf herbicides as affected by mulch. The study included four tree species (‘Bradford’ callery pear, crape myrtle, Eastern redbud, red maple), four mulch treatments (shredded hardwood bark, pine bark, pine needles, no mulch), and six herbicide treatments [Banvel (dicamba), BAS 514 OOH (quinclorac), Image (imazaquin), Redeem (triclopyr), Stinger (clopyralid)]. Herbicides were applied as directed sprays at the labeled rates for use on turf. Visual injury (%) ratings were measured at 30, 60, 90, 120, and 150 days after treatment. Trunk diameters and total plant fresh weights were measured at the conclusion of the study. In most cases, applying the herbicide over mulch decreased tree injury compared to applications to bare soil (Fig. 3). Red maples were most severely injured by Stinger (clopyralid) (27%) (60 DAT) and BAS 514 OOH (quinclorac) (33%) (60 DAT). Redbuds were most severely injured by the same two herbicides, but at 89% (120 DAT) and 73% (120 DAT), respectively. ‘Bradford’ pears were injured by Banvel (dicamba) (32%) (120 DAT), and crape myrtles by Image (imazaquin) (10%) (120 DAT).

Glyphosate tolerance in maize (Zea mays L.). 1. Differential response among inbred lines

Variation in susceptibility to the safe broad-spectrum herbicide glyphosate was investigated in maize. Eleven inbred lines, grown in a growth chamber, were evaluated for their tolerance to the herbicide at 2.4 mM (0.2 kg a.i. in 400 I ha-1 of water). Following treatment with glyphosate at the three-leaf stage, significant variation in damage, expressed as visual injury ratings scored 7, 14 and 21 days after the application of the herbicide, was found. Effects on dry weight and shoot height were consistent with visual scores and the carbon-exchange rate was found to be a sensitive index of differential injury. Biochemical characterization of 5-enol-pyruvyl-shikimate-3-phosphate (EPSP) synthase, the main target of the herbicide, ruled out the possibility that this differential susceptibility was due to variations in the sensitivity of the enzyme. On the contrary, a positive correlation was found between in vivo tolerance and EPSP synthase levels, measured at different stages during seedling growth. This result suggests that a naturally occurring difference in EPSP synthase levels in the tissues may contribute to the differential response observed in vivo in maize inbreds.