This study evaluated the response of sweet cherry to different herbicides applied at rates simulating drift. Chlorsulfuron, thifensulfuron, bromoxynil, 2,4-D, glyphosate, and a combination of 2,4-D and glyphosate were applied on one side of one- and two-year-old established cherry trees at 1/3, 1/10, 1/33, and 1/100 of the maximum rate for small grain production. The order of herbicide phytotoxicity was chlorsulfuron > 2,4-D > glyphosate > 2,4-D + glyphosate > thifensulfuron > bromoxynil. Trees recovered from injury caused by all treatments except higher rates of chlorsulfuron, 2,4-D, and glyphosate. The herbicides caused characteristic symptoms, but some resembled disease, mineral deficiency, and environmental stress symptoms. Therefore, any allegations about herbicide drift based on chronic symptoms should be supported by analysis of plant tissue.

Broomrapes (Orobanche spp.) are root holoparasitic plants that cause severe damage to economically important crops, especially in Mediterranean countries. Egyptian broomrape is the most troublesome weed on tomatoes grown for processing in Israel. In the present study, we tested the efficacy and selectivity of four sulfonylurea herbicides in controlling Egyptian broomrape on tomatoes grown in pots under greenhouse conditions. MON 37500, rimsulfuron, HOE 404 and SL-160 were applied postemergence (POST) and preplant incorporated (PPI) followed by POST applications. MON 37500 and rimsulfuron were more selective to tomato and controlled the parasite more effectively than HOE 404 and SL-160. MON 37500 and rimsulfuron at 50 and 100 g ai/ha and at 100, 150, and 200 g ai/ha, respectively, applied on tomato foliage 14, 28, and 42 d after planting (DAP) and followed by sprinkler irrigation to field capacity, resulted in complete control of the parasite. However, a significant reduction in control efficacy was observed when the experiment was repeated with charcoal-topped pots, suggesting that the herbicides act mainly through the soil. Except for rimsulfuron, the PPI followed by two POST treatments was more phytotoxic to tomato plants than the POST treatments. The PPI plus POST applications controlled Egyptian broomrape effectively, but tomato plants were injured by HOE 404 at all PPI application rates and by MON 37500 at the high rate at 150 g/ha. The present study determined that three POST applications or a PPI application followed by two POST applications of MON 37500 at 50 or 100 g/ha, or rimsulfuron at 100, 150, or 200 g/ha were effective and selective in controlling Egyptian broomrape on tomato, under greenhouse conditions.

Field studies were conducted in the spring of 1997 and 1998 to quantify the effect of season-long yellow nutsedge interference on watermelon yield. The competitive ability of watermelon with yellow nutsedge was compared in two establishment methods (watermelon transplanted and direct seeded). Critical yellow nutsedge densities and the biological threshold (BT) were used to characterize the competitive ability of watermelon. The critical density in both direct-seeded and transplanted watermelons was 2 yellow nutsedge plants/m2. The BT of yellow nutsedge in seeded watermelons was 37 yellow nutsedge plants/m2, whereas the BT in transplanted watermelons was 25 plants/m2. Transplanting watermelons did not improve their competitive ability with yellow nutsedge. Percent yield loss was similar for both establishment methods at the respective yellow nutsedge densities. Over 40% yield loss was incurred with 12 yellow nutsedge plants/m2 for both establishment methods. Furthermore, it was concluded that watermelons are poor competitors with yellow nutsedge.

Resistance to agricultural fungicides has increaséd dramatically in the past twenty years, following the introduction of systemic fungicides. Disease control failures associated with fungicide resistance have occurred with many classes of fungicides and in many genera of plant-pathogenic fungi. In some cases, resistance evolved extremely rapidly making the chemicals ineffective for disease control only a few years after they were introduced.

The rapid development of resistance to systemic fungicides has led to efforts to develop strategies to avoid or delay the evolution of fungicide resistance in plant pathogen populations. Despite a widespread interest in managing fungicide resistance, very few experimental studies have been performed to elucidate the important factors controlling resistance development. Most fungicide resistance studies have consisted of anecdotal field observations which have rarely been followed up with experimentation. In order to understand what factors affect the evolution of resistance, and to use this information to design effective resistance management strategies, more experimental studies are required.

An experiment was conducted at five locations in North Carolina during 2000 and 2001 to evaluate weed control, crop injury, and cotton yield. Weed management systems included different combinations of pyrithiobac preemergence (PRE), fluometuron PRE, CGA-362622 postemergence (POST), pyrithiobac POST, and monosodium salt of methylarsonic acid (MSMA) plus prometryn applied late POST-directed (LAYBY). At Goldsboro in 2000, cotton was injured 74 to 78% by CGA-362622 POST when evaluated 4 to 7 d after treatment (DAT). Injury at Clayton, Goldsboro, and Lewiston in 2001 and Rocky Mount in 2000 was less than 16% 4 to 7 DAT with the same treatment and was not apparent by 62 DAT. CGA-362622 controlled common lambsquarters, common ragweed, Palmer amaranth, sicklepod, smooth pigweed, and Ipomoea species including entireleaf, ivyleaf, and pitted morningglory, and the addition of pyrithiobac to the herbicide system, either PRE or POST, increased control of Amaranthus species, jimsonweed, and prickly sida. CGA-362622 did not control jimsonweed or prickly sida. Fluometuron PRE, pyrithiobac PRE, and MSMA plus prometryn LAYBY were beneficial for increasing weed control and cotton lint yields. Prometryn plus MSMA LAYBY increased control of common ragweed, entireleaf morningglory, jimsonweed, pitted morningglory, and smooth pigweed and provided higher cotton yields than similar systems without a LAYBY. The greatest weed control and greatest cotton lint yields required complete weed management systems that included a combination of PRE, POST, and LAYBY treatments.

A survey questionnaire was sent to cotton consultants of Arkansas and Mississippi through direct mail and Louisiana and Tennessee consultants through on-farm visits in fall of 2011. The survey was returned by a total of 22 Arkansas, 17 Louisiana, 10 Mississippi, and 11 Tennessee cotton consultants, representing 26, 53, 13, and 38% of total cotton planted in these states in 2011, respectively. Collectively, the area planted to glyphosate-resistant (Roundup Ready®, RR) cotton was 97%, glyphosate plus glufosinate-resistant (Widestrike® Flex, WRF) cotton was 30%, and glufosinate-resistant (Liberty Link, LL) cotton was 2.6% of the total cotton surveyed in 2011. Seventy percent of area in all states is still under continuous RR/WRF cotton. Average cost of herbicides in RR systems was $114 ha−1 and in LL systems was $137 ha−1. Across the states, cotton planted under no-tillage, conservation tillage, and conventional tillage was 31, 36, and 33%, respectively, of total scouted cotton. Area under conventional tillage increased and conservation tillage decreased in Arkansas compared with a previous survey conducted in 2006. Palmer amaranth, morningglories, and horseweed in the order of listing were the most problematic weeds of cotton across Arkansas, Mississippi, and Tennessee. In Louisiana, however, morningglories were the most problematic weed followed by Palmer amaranth and common waterhemp. Glyphosate-resistant (GR) Palmer amaranth infested only 13% of scouted cotton area in Louisiana compared with 75% in the remaining three states, and consequently, hand-weeding to control GR Palmer amaranth is practiced on only 2.5% of total scouted area of Louisiana and 49% of the scouted area of the remaining three states. Hand-weeding added an additional $12 to 371 ha−1 to weed-management costs. One-half (50%) of the cotton consultants emphasized the need for more research on residual herbicides that can control GR Palmer amaranth effectively.

Field and greenhouse experiments were conducted during 2005 and 2006 at Stoneville, MS, to determine control of ragweed parthenium with several preemergence (PRE) and postemergence (POST) herbicides registered for use in corn, cotton, peanut, rice, and soybean. Norflurazon, pendimethalin, clomazone, diuron, fluometuron, pyrithiobac, dimethenamid, flumetsulam, imazaquin, s-metolachlor, metribuzin, chlorimuron, atrazine, simazine, flumioxazin, and quinclorac were applied PRE. Ragweed parthenium control was highest with norflurazon (100%) and clomazone (100%) followed by fluometuron (96%), metribuzin (90%), diuron (87%), flumioxazin (84%), chlorimuron (77%), and quinclorac (67%) at 6 wk after treatment (WAT) under greenhouse conditions. Control of ragweed parthenium was less than 58% with all other herbicides. Ragweed parthenium appears to be highly sensitive to pigment and photosynthetic inhibitors compared to herbicides with other modes of action. Glyphosate, glufosinate, paraquat, bentazon, acifluorfen, chlorimuron, halosulfuron, MSMA, bromoxynil, atrazine, 2,4-D, flumioxazin, trifloxysulfuron, and clomazone were applied POST to field-grown rosette and bolted plants. Glyphosate, glufosinate, chlorimuron, and trifloxysulfuron applied at rosette stage provided greater than 93% control of ragweed parthenium at 3 WAT. Halosulfuron, MSMA, bromoxynil, 2,4-D, and flumioxazin controlled 58 to 90% rosette ragweed parthenium at 3 WAT. Ragweed parthenium control with all other POST herbicides was less than 38%. At bolted stage, glyphosate, glufosinate, and trifloxysulfuron controlled 86 to 95% ragweed parthenium and control was 61 to 70% with chlorimuron, halosulfuron, and 2,4-D 3 WAT. Overall, efficacy of POST herbicides was better on rosette plants than on bolted plants. Amino acid synthesis and glutamine synthase inhibitors were more active than herbicides with other modes of action. These results indicate that norflurazon, clomazone, fluometuron, flumioxazin, halosulfuron, chlorimuron, and trifloxysulfuron could provide effective control of ragweed parthenium.

Natural products might provide an organic means of weed control. Our objective was to evaluate the potential use of vinegar and a clove-oil product with regard to how volume, concentration, and application timing affect weed control and crop response. Treatments included broadcast applications of 200- and 300-grain vinegar at 318 liters per hectare (L/ha), 150- and 200-grain vinegar at 636 L/ha, a 3.4% v/v clove oil mixture in water (318 L/ha), and a 1.7% clove oil mixture in 200-grain vinegar (318 L/ha). Field trials were conducted in sweet corn, onion, and potato. Weed control, weed biomass, crop injury, and yield data were collected. Corn treated at 15 and at 30 to 45 cm was initially burned and stunted by these products. By 4 wk after application much of the initial injury was outgrown. Late applications significantly reduced yields of early-maturing sweet corn ‘Trinity’. With the exception of the 200-grain vinegar (318 L/ha) treatment, early applications to sweet corn ‘Avalon’ did not reduce marketable yield. Two hundred-grain vinegar (636 L/ha) applied to pre-emergence–flag stage onion reduced the duration of the first handweeding by 59 to 67%. All treatments reduced onion yields when treated at the 2-leaf stage. Potato treated early (2 to 10 cm) and late (30 cm) were injured by all vinegar treatments 59 to 83%, 1 d after treatment (DAT). Potato yield losses were insignificant with applications of 3.4% clove oil and with some low-volume (318 L/ha) vinegar treatments. Product efficacy was dependent on the weed species and their size at the time of application. Weed control was greatest (83%, 1 DAT) with 200-grain vinegar (636 L/ha). Broadcast applications of vinegar and clove oil have potential for use on young, actively growing sweet corn, onion, and potato.

Bioassay experiments were conducted to determine the phytotoxicity of methanol and ethyl acetate extracts of hairy vetch and cowpea residues on the germination and radicle elongation of three vegetable crops and three weed species. The species tested included common chickweed, redroot pigweed, wild carrot, tomato, corn, and cucumber. The extracts of both species were dissolved in methanol to yield seven concentrations ranging from 0 to 8 g/L. Germination was significantly reduced by methanol and ethyl acetate extracts of hairy vetch extracts except for corn and tomato. Common chickweed and wild carrot were the only species that showed consistent reduction in germination with the methanol and ethyl acetate cowpea extracts. The radicle growth of most species, with the exception of corn and cucumber, was reduced by the extracts of both cover crops. Corn and cucumber radicle elongation was stimulated at low concentrations of the extracts; however, these observations were not significantly different among treatments. This study demonstrated that methanol and ethyl acetate extracts of hairy vetch and cowpea contained allelopathic compounds and that their phytotoxicity is likely species specific. Future studies should focus on the identification and isolation of the allelochemical(s) found in the methanol and ethyl acetate extracts of the hairy vetch and cowpea residues.

Winter rape (Brassica napus L.) green manures have shown potential for erosion control and suppression of weeds and other pests in potato cropping systems. However, little information on residue cover, biomass production, glucosinolate concentration, and glucosinolate production with winter rape grown as a green manure is available. In field trials in southern Idaho, ‘Aspen,’ ‘Bridger,’ ‘Cascade,’ ‘Dwarf Essex,’ and ‘Humus’ winter rape were planted in mid-August and incorporated the following spring in late April or early May. All five cultivars provided > 80% fall, winter, and early spring residue cover. Winter rape dry weight just before incorporation was 2,880 to 4,462 kg/ha in 1994 and 5,438 to 7,837 kg/ha in 1995. The major glucosinolate in roots of all five cultivars was phenylethyl glucosinolate; the major glucosinolates in shoots were 4-pentenyl, 2-hydroxybutenyl, 3-butenyl, and 2-hydroxypentenyl glucosinolate. Glucosinolate concentrations varied between years, but concentrations were higher in Dwarf Essex and Humus than in Aspen both years. Glucosinolate production per hectare also was highest in Dwarf Essex and Humus and lowest in Aspen. Dwarf Essex and Humus produced higher amounts of isothiocyanate (ITC) and oxazolidinethione (OZT)-producing glucosinolates than Aspen, Bridger, or Cascade, and therefore may be better biofumigants.

Triazine-resistant common lambsquarters (TR-CHEAL) is a widespread weed problem in the northcentral United States. Field studies were conducted from 1995 to 1997 to determine the efficacy and consistency of metolachlor, pendimethalin, and acetochlor applied preemergence (PRE) for control of TR-CHEAL in corn. Pendimethalin provided greater (98%) and more consistent control of TR-CHEAL than metolachlor (66%) or acetochlor (86%). Studies were conducted from 1998 to 2000 to examine the potential of isoxaflutole, flumetsulam, and rimsulfuron plus thifensulfuron for control of TR-CHEAL in corn. In 1999 and 2000, isoxaflutole (35 g ai/ha), flumetsulam (35 g ai/ ha), and rimsulfuron plus thifensulfuron (26 g ai/ha) provided 98% or greater control of TR-CHEAL. In 1998 when rainfall was limited after application, isoxaflutole (70 g ai/ha) and flumetsulam (70 g ai/ha) provided 65 and 55% control, respectively, and rimsulfuron plus thifensulfuron (26 g ai/ha) provided 55% control. Results indicate that control of TR-CHEAL with currently labeled PRE herbicides is possible.

Italian ryegrass resistance to diclofop has been documented in several countries, including the United States. The purpose of this research was to screen selected putative resistant populations of Italian ryegrass for resistance to the acetyl-CoA carboxylase (ACCase)–inhibiting herbicides diclofop and pinoxaden and the acetolactate synthase (ALS)–inhibiting herbicides imazamox, pyroxsulam, and mesosulfuron in the greenhouse and to use field experiments to develop herbicide programs for Italian ryegrass control. Resistance to diclofop was confirmed in eight populations from Tennessee. These eight populations did not show cross-resistance to pinoxaden. One additional population (R1) from Union County, North Carolina, was found to be resistant to both diclofop and pinoxaden. The level of resistance to pinoxaden of the R1 population was 15 times that of the susceptible population. No resistance was confirmed to any of the ALS-inhibiting herbicides examined in this research. Field experiments demonstrated PRE Italian ryegrass control with chlorsulfuron (71 to 94%) and flufenacet + metribuzin (84 to 96%). Italian ryegrass control with pendimethalin applied PRE or delayed preemergence (DPRE) was variable (0 to 85%). POST control of Italian ryegrass was acceptable with pinoxaden, mesosulfuron, flufenacet + metribuzin, and chlorsulfuron + flucarbazone (> 80%). Application timing and herbicide treatment had no effect on wheat yield, except for diclofop and pendimethalin treatments, in which uncontrolled Italian ryegrass reduced wheat yield.

Field and growth chamber experiments determined the efficacy of temporal glyphosate applications on velvetleaf. Glyphosate was applied postemergence to velvetleaf periodically before and during light and after dark. In 1999, glyphosate at 840 g ae/ha applied before sunrise and after midday provided 54 and 100% velvetleaf control, respectively. In 2000, glyphosate at 840 g/ha applied before sunrise, midday, and after sunset provided 69, 100, and 37% velvetleaf control, respectively. In the growth chamber, glyphosate at 840 g/ha applied before or after light reduced velvetleaf biomass 15 to 20% or 32 to 47%, respectively, and reduced velvetleaf height 24% or 45 to 54%, respectively. Velvetleaf control was consistently greater with glyphosate applications during light compared with dark, regardless of constant air temperature and relative humidity (growth chamber), dew absence or presence (field and growth chamber), or leaf blade orientation (growth chamber) with natural light–dark movements or a fixed horizontal position.

Low-spatial resolution satellite imagery from the NOAA-10 polar-orbiting meteorological satellite was analyzed to determine if central New Mexico grasslands infested by broom snakeweed could be discriminated from unaffected areas. Distinctive phenological characteristics of broom snakeweed, including an early season growth flush and late season flowering, enable moderate to heavily infested areas to be separated from grasslands having few or no weeds present. The procedure used shows promise as a tool for locating and monitoring brown snakeweed and other weeds growing on shortgrass prairie.

Field experiments were conducted to determine the effect of shattercane interference on corn grain yield and nitrogen uptake in central Missouri. A glyphosate-resistant corn variety was planted, and atrazine was used to control all weeds except shattercane. Glyphosate was applied when shattercane was 8, 15, 23, 31, 38, or 46 cm tall, and plots were hand weeded weekly thereafter. Season-long shattercane interference resulted in an 85% yield loss in 1999 and a 43% yield loss in 2000. Yield reductions occurred when shattercane was allowed to remain with corn until it was 31 cm tall. In both years, late-season corn biomass N content was highly correlated (r = 0.95 and 0.84, respectively) with corn yield. When shattercane was allowed to reach the maximum recommended height for nicosulfuron or primisulfuron application (31 cm), significant yield losses occurred, and shattercane accumulated 10 and 20 kg N/ha, whereas corn accumulated 10 and 16 kg N/ha, respectively, in 1999 and 2000. Corn grain yield was reduced 0.66% (r 2 = 0.71) for each day of interference before a postemergence (POST) application of glyphosate.

Producers in the central Great Plains are seeking alternative strategies to manage weeds because of herbicide resistance, narrow profit margins, and a lack of registered herbicides in some crops. Thus, we evaluated the impact of cultural systems in winter wheat and tillage on weed dynamics in corn, sunflower, and proso millet planted the year following wheat harvest. Weed seedling densities were 25 to 30% lower in a no-till system compared with minimum-till with a sweep plow. With no-till, cultural systems that produced more crop residue reduced weed densities an additional 15 to 30%, compared with the conventional system. Cultural system effect was eliminated in dry years and by tillage. Weed biomass was 10-fold less in proso millet than in corn. Crop residue management, critical for successful cropping in semiarid regions, also will help weed management by reducing weed density in summer annual crops, especially in no-till systems.

Field studies were conducted near Clayton, Goldsboro, Kinston, and Rocky Mount, NC in 2003 to evaluate weed control and cotton response to postemergence (POST) treatments of glufosinate applied alone or in tank mixtures with s-metolachlor, pyrithiobac, or trifloxysulfuron. Late-season control of common lambsquarters, common ragweed, entireleaf morningglory, ivyleaf morningglory, jimsonweed, pitted morningglory, purple nutsedge, and sicklepod with glufosinate early postemergence (EPOST) was ≥90%. The addition of S-metolachlor to glufosinate EPOST improved control of all weeds except sicklepod, ivyleaf morningglory, and entireleaf morningglory. When applied POST, glufosinate provided ≥90% late season control of common lambsquarters, common ragweed, entireleaf morningglory, ivyleaf morningglory, jimsonweed, large crabgrass, pitted morningglory, purple nutsedge, and sicklepod. Control of goosegrass and Palmer amaranth was 81 and 84%, respectively. When pyrithiobac or trifloxysulfuron were added in POST tank mixtures, control of Palmer amaranth improved 6 and 9 percentage points, respectively. Control of goosegrass remained near 80% regardless of herbicide treatment used. The addition of a late post-directed (LAYBY) tank-mixture of glufosinate plus prometryn provided ≥88% late season control of all weeds. Reduced control of goosegrass and Palmer amaranth was observed with the LAYBY tank mixture of glufosinate plus MSMA when compared to other LAYBY tank mixtures. Cotton lint yields in plots receiving any herbicide application were significantly higher than plots receiving no herbicide application for all application timings. Cotton lint yields were ≥ 740 kg/ha where an EPOST was applied and ≥ 680 kg/ha when a POST herbicide was applied. Cotton lint yields were at least 200 kg/ha greater on plots receiving a LAYBY application when compared to plots where no LAYBY treatment was applied.

Field experiments were conducted in 1999 at Stoneville, MS, to determine the potential of multispectral imagery for late-season discrimination of weed-infested and weed-free soybean. Plant canopy composition for soybean and weeds was estimated after soybean or weed canopy closure. Weed canopy estimates ranged from 30 to 36% for all weed-infested soybean plots, and weeds present were browntop millet, barnyardgrass, and large crabgrass. In each experiment, data were collected for the green, red, and near-infrared (NIR) spectrums four times after canopy closure. The red and NIR bands were used to develop a normalized difference vegetation index (NDVI) for each plot, and all spectral bands and NDVI were used as classification features to discriminate between weed-infested and weed-free soybean. Spectral response for all bands and NDVI were often higher in weed-infested soybean than in weed-free soybean. Weed infestations were discriminated from weed-free soybean with at least 90% accuracy. Discriminant analysis models formed from one image were 78 to 90% accurate in discriminating weed infestations for other images obtained from the same and other experiments. Multispectral imagery has the potential for discriminating late-season weed infestations across a range of crop growth stages by using discriminant models developed from other imagery data sets.

Potential herbicide loadings to groundwater are determined by soil, chemical, management, and climatic factors. Several simple assessment procedures to rank pesticides according to their potential impact on groundwater are available. Most of these procedures are not specific to any climatic region, cropping practice, or soil. Using a continuous simulation model, GLEAMS (Groundwater Loading Effects of Agricultural Management Systems), to assess potential herbicide leaching allows more condition-specific assessment. Simple relationships for relative comparisons in a specific soil/climatic setting were developed by relating simulated 50-yr mean leaching losses to the herbicide half-life/Koc ratio. Other criteria of herbicide leaching potential such as 50-yr maxima or other values based on probability distributions could be used. Although differences in soils were demonstrated in this exercise, the same procedures could be applied to different management systems.

Common tansy [Tanacetum vulgare (L.) Bernh. ♯CHYVU], a native of Europe and Asia, is a perennial herbaceous composite growing erect to 1 m. It bears finely divided leaves and, in summer, umbels of small, button-shaped yellow flowers. It has had many traditional uses as medicine, preservative, and repellent from Medieval times to modern—uses which have been validated by contemporary research.