PRE herbicides are generally less effective in conservation farming systems because of high levels of crop residue. However, performance can be improved if the herbicides are applied with a high carrier volume. This research investigated the interaction of carrier volume and row spacing or height of crop residue on the control of rigid ryegrass with trifluralin, at Cunderdin and Wongan Hills Western Australia. To create plots with varying residue row spacing in 2011, wheat was seeded in 2010 using a narrow row spacing (25 or 22 cm at Cunderdin and Wongan Hills), wide spacing (50 or 44 cm), or not planted to wheat. Narrow or wide row spacing or no crop plots had an average residue biomass of 4480, 3560, and 2430 kg ha−1 at Cunderdin and 1690, 1910, and 1030 kg ha−1 at Wongan Hills. To vary residue height, the wheat was harvested to produce tall, medium, or short crop residue (22, 13, and 5 cm at Cunderdin and 27, 22, and 17 cm at Wongan Hills). Rigid ryegrass seeds were broadcast onto each site in 2011 and trifluralin was sprayed using 50, 75, or 100 L ha−1 carrier volume (directly prior to seeding). Increased carrier volume increased spray coverage at both sites (average cover of 9, 15, and 26% at 50, 75, and 100 L ha−1), leading to improved control of rigid ryegrass (68, 75, and 82% control at Cunderdin and 23, 41, and 68% control at Wongan Hills). Reduced crop residue height or increased row spacing led to reduced rigid ryegrass density at Cunderdin but had no impact at Wongan Hills. Therefore, carrier volume has a more consistent impact on the performance of trifluralin than crop residue row spacing or height.

Dicamba and 2,4-D, which are used prior to seeding in conservation tillage systems, were applied in late fall and early spring to determine their residual effect on subsequent spring-seeded crops. The herbicides 2,4-D ester and 2,4-D amine with dicamba or glyphosate, applied 0 or 15 d prior to spring seeding, damaged canola, peas, lentils, and alfalfa. The legumes were damaged by spring-applied dicamba. There was also a slight reduction in the total dry matter yield of wheat and barley by 2,4-D applied in spring prior to seeding. All crops tested, except lentils, were tolerant of recommended fall applications of 2,4-D for the control of winter annual flixweed and field pennycress.

Alternaria cassiae Jurair and Khan applied as conidia at 1 × 105 spores/ml controlled 100% of sicklepod, and 1 × 106 spores/ml controlled coffee senna in the greenhouse. In the field, sicklepod control did not differ between one or two fungal applications, but coffee senna control increased following two applications. Although showy crotalaria resisted A. cassiae infection more than the other two weeds, total biomass was reduced significantly in both greenhouse and field tests.

The GLEAMS model (Groundwater Loading Effects of Agricultural Management Systems) is used to illustrate model application in evaluating potential pesticide runoff of two similar pesticides from one soil. This limited application was chosen for simplicity in illustrating relationships between annual means and single events. When using annual totals of simulated pesticide runoff for comparing two pesticides or assessing risks, long-term 50-yr simulations are preferable to short 10-yr simulations. When short-term simulations are performed, care must be exercised in selecting representative climatic periods. For short half-life pesticides, as demonstrated in this study, initial rainfall events on or near the day of application will often contribute most to annual pesticide lost. In these cases, single event analysis may be required. Procedures are demonstrated for expressing annual total pesticide losses and single rainfall event losses probabilistically in terms of expected recurrence intervals.

The uptake, translocation, and metabolism of the ethyl ester of chlorimuron in three soybean cultivars and two morningglory species was investigated. Soybean used included the normal cultivars ‘Vance’ and ‘Essex,’ and the sulfonylurea-resistant cultivar ‘W-20.’ Entireleaf morningglory and pitted morningglory, both moderately tolerant to chlorimuron, were used. Twenty-day-old seedlings of all plant species were exposed to root-applied 14C-labeled chlorimuron for 6, 24, and 72 h. After 24 and 72 h, chlorimuron uptake was lowest in W-20 soybean and the two morningglory species. Translocation of root-absorbed chlorimuron to shoots and leaves of all species was limited and it did not differ among species. The moderate tolerance of pitted and entireleaf morningglories to chlorimuron may be due to reduced herbicide uptake. The response of Essex and Vance soybean to chlorimuron was related to herbicide metabolism. At 6 h after treatment with radiolabeled chlorimuron, Essex soybean metabolized the herbicide more rapidly than either W-20 or Vance soybean. At 24 h and 72 h, Essex and Vance soybean metabolized chlorimuron to the same extent. W-20 was not very efficient in metabolizing chlorimuron at any time after treatment and its resistance to chlorimuron is due to an altered target site.

Pathogenicity of four Colletotrichum coccodes isolates to potato, eastern black nightshade, and hairy nightshade was evaluated in greenhouse studies. Three Idaho isolates, AC-14, AC-28, and AC-44, and an isolate obtained from Mycogen Corporation, AC-Myc, produced lesions on potato foliage. Plants inoculated with AC-14, AC-28, and AC-44 also showed wilt symptoms similar to those produced by Verticillium dahliae as potatoes were beginning to senesce. Infection by AC-44 reduced tuber fresh weight and specific gravity. All isolates colonized eastern black and hairy nightshade, although some isolates caused little or no symptom development. Thus, both species may serve as sources of primary inoculum for C. coccodes isolates that are pathogenic to potatoes. Only AC-Myc substantially injured the leaves of both nightshade species. AC-Myc was more pathogenic to eastern black than to hairy nightshade, and to plants inoculated at the 3- to 4-leaf versus the 7- to 8-leaf stage.

Six, 9, and 12-mm diam dicalcium phosphate tablets were evaluated for their release of acetochlor, metolachlor, and metribuzin. Greenhouse bioassays with Italian ryegrass demonstrated that herbicides from the smaller tablets did not control grass as long as from the larger tablets. Italian ryegrass was controlled within a 5- to 7-cm diam circle around the 12-mm diam tablet and a 5-cm diam circle around the 6-mm diam tablet. All tested herbicides responded in a similar fashion. Six-mm diam tablets released metolachlor for 11 weeks, while the 12-mm tablet was active for 28 weeks.

Organic soil amendments are known to affect the composition and density of annual weed communities. The objective of this research was to measure the effect on emergence and growth of redroot pigweed seedlings when soil was amended with composted dairy manure at 18, 36, and 54 T/ha, or with raw dairy manure at 41, 82, and 123 T/ha. Data recorded (1) seedling emergence over 12 days, (2) number of leaves and total leaf area, (3) shoot and root dry weight, and (4) seed number. Maximum seedling emergence (32%) occurred in nonamended soil (the control). Emergence declined in a linear fashion when soil was amended with manure or with compost. Compost additions affected seedling emergence more severely than did manure additions. For every measure of redroot pigweed growth except seed production, amendment with manure at 123 T/ha retarded growth compared to soil alone or compost-amended mixes. Manure applied at 82 T/ha reduced leaf area and plant height relative to other treatments. Growth of redroot pigweed in soil amended with compost at 36 and 54 T/ha was always equal to or greater than growth in soil that was not amended. Seed production in one of two runs of the experiment was more than double in soils amended with compost at 36 and 54 T/ha compared to the nonamended soil. These results suggest that amending soils with raw dairy manure may decrease the competitiveness of redroot pigweed, whereas amending with composted manure is likely to increase competitiveness.

Field trials were conducted in New Jersey during 1991 and 1992 to evaluate the efficacy of nicosulfuron, primisulfuron, dicamba, and clopyralid on horsenettle control in field corn. Horsenettle biomass was reduced 74%, 68%, 64%, 61%, 48%, and 40% by primisulfuron + dicamba, primisulfuron, nicosulfuron + dicamba, dicamba, clopyralid, and nicosulfuron, respectively. No treatment was statistically more effective than dicamba. Corn yields were not influenced by the herbicide treatments. Horsenettle populations were not reduced by any treatment.

Dicamba-resistant crops are being rapidly embraced by growers in the United States to manage glyphosate-resistant and other difficult-to-control broadleaf weeds. However, dicamba resistance in kochia, one of the troublesome weeds of the North American Great Plains, is already widespread. Hence, POST application of dicamba may not adequately control kochia. In recent years in the High Plains Region of Colorado, Kansas, and Nebraska, dicamba has been widely applied, often in combination with atrazine or metribuzin, in early spring for PRE control of kochia. However, there is concern this use pattern may increase the selection for dicamba-resistant (DR) kochia. Hence, there is need to understand the efficacy of dicamba applied PRE versus POST for managing DR kochia. A greenhouse study was conducted to test the efficacy of PRE-applied dicamba compared with POST application using both DR and dicamba-susceptible (DS) kochia. Efficacies of PRE-applied dicamba were compared at seeding densities of 300, 600, 900 and 1200 viable seed m−2. At eight weeks after PRE and four weeks after POST treatment, control of DR kochia seeded at 300 viable seed m−2 was improved from 10% with 560 g ae ha−1 dicamba applied POST to 94 and 97% with 350 and 420 g ha−1 dicamba applied PRE, respectively. However, the efficacy of PRE-applied dicamba was negatively correlated with seed density. When kochia seeding density was increased from 300 to 1200 seed m−2, the ED50 of PRE-applied dicamba increased from 237 to 705 g ae ha−1 for DR kochia, and from 129 to 361 g ae ha−1 for DS kochia, respectively. Thus, PRE-applied dicamba was effective in controlling the population of DR kochia tested, suggesting that PRE-applied dicamba may still provide substantial control of some DR kochia populations. However, it is not advisable to apply dicamba alone for PRE kochia control.

Field experiments were conducted to evaluate the integration of cover crops and POST herbicides to control glyphosate-resistant Palmer amaranth in cotton. The winter-annual grasses accumulated the greatest amount of biomass and provided the most Palmer amaranth control. The estimates for the logistic regression would indicate that 1540 kg ha−1 would delay Palmer amaranth emerging and growing to 10 cm by an estimated 16.5 days. The Palmer amaranth that emerged in the cereal rye and wheat cover crop treatments took a longer time to reach 10 cm compared to the hairy vetch and crimson clover treatments. POST herbicides were needed for adequate control of Palmer amaranth. The glufosinate-based weed control system provided greater control (75% vs 31%) of Palmer amaranth than did the glyphosate system. These results indicate that a POST only herbicide weed management system did not provide sufficient control of Palmer amaranth, even when used in conjunction with cover crops that produced a moderate level of biomass. Therefore, future recommendations for GR Palmer amaranth control will include integrating cover crops with PRE herbicides, overlaying residual herbicides in-season, timely POST herbicide applications, and hand weeding in order to achieve season-long control of this pest.

Field studies were conducted to determine the effect of metam sodium and S-metolachlor applied through drip irrigation on yellow nutsedge, common purslane, bell pepper, and tomato (injury and yield) in plasticulture. Treatments consisted of weed-free, weedy, S-metolachlor alone at 0.85 kg ha-1, methyl bromide, metam sodium (43, 86, 176, and 358 kg ai ha–1) alone, and metam sodium (43, 86, 176, and 358 kg ai ha–1) followed by S-metolachlor at 0.85 kg ha–1. Metam sodium and S-metolachlor was applied preplant 2 wk before and 2 wk after transplanting (WAT) through drip irrigation, respectively. No injury was observed to bell pepper and tomato from metam sodium alone, or metam sodium fb S-metolachlor treatments. With the exception of yellow nutsedge density 15 WAT in bell pepper, herbicide program did not influence yellow nutsedge and common purslane density at 4 and 6 WAT and bell pepper and tomato yield. At 15 WAT, yellow nutsedge density was lower in treatments that received metam sodium fb S-metolachlor compared to those treatments that only received metam sodium. Drip-applied metam sodium at 176 and 358 kg ha–1 in both bell pepper and tomato provided similar control of common purslane, and yellow nutsedge, produced comparable yields, and failed to elicit any negative crop growth responses when compared to MeBr. In conclusion, metam sodium at 176 and 358 kg ha–1 fb S-metolachlor 0.85 kg ha–1 is an effective MeBr alternative for season long weed control in plasticulture bell pepper and tomato.

Rhizoma et Radix Notopterygii is often used as a traditional medicine in China. In our recent work, we found that the ethanol crude extract of Rhizoma et Radix Notopterygii could reduce phytotoxicity of acetochlor on rice. The crude extract of Rhizoma et Radix Notopterygii was isolated and purified by activity-guided fractionation. Two coumarins, isopimpinellin and 5-methoxypsoralen (5-MOP) were identified, and their bioactivity was tested in a growth chamber. The results showed that the two coumarins increased herbicide tolerance of rice shoots, and 5-MOP demonstrated better protection than isopimpinellin. The treatment of 5-MOP at 50 g ai ha−1 recovered the shoot height of rice from 42.6% (treated with acetochlor only) to 81.6% of the control treated without acetochlor, whereas the phytocidal activity of acetochlor on barnyardgrass was not impaired by 5-MOP. Further study suggested that 5-MOP increases herbicide tolerance of rice by enhancing the glutathione S-transferase level of activity in rice. Our findings suggest that isopimpinellin and 5-MOP have the potential to be applied as safeners for rice.

Six postemergence herbicides were applied two consecutive years in single and split applications to compare johnsongrass [Sorghum halepense (L.) Pers. # SORHA] control in soybeans [Glycine max (L.) Merr.] planted in 25- and 76-cm inter-row spacings. Significantly less johnsongrass existed at harvest in the 25-cm spacings than in the 76-cm spacings with split applications of fenoxaprop {(±)-2-[4-[(6-chloro-2-benzoxazolyl)oxy] phenoxy] propanoic acid} at 100 g ae/ha, fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} at 100 g ae/ha, sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} at 200 g ai/ha, and SC-1084 {3-hydroxy-4-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] pentanoic acid} at 250 g ae/ha. Quizalofop {(±)-2-[4-[(6-chloro-2-quinoxalinyl)oxy] phenoxy] propanoic acid} at 70 g ae/ha and haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} at 100 g ae/ha controlled johnsongrass so well that differences between the two row spacings were not significant.

Field experiments were conducted to identify herbicides for selectively controlling foxtail barley seedlings in spring wheat and flax. ICIA0604, fenoxaprop-P/safener, CGA184927/safener, metribuzin, and MON37500 in wheat and sethoxydim, clethodim, quizalofop, fluazifop-P, and the mixture of fluazifop-P/fenoxaprop-P in flax were applied at the three- to four-leaf and one- to three-tiller stages of foxtail barley. MON37500 was the only herbicide tested in wheat that provided excellent control of foxtail barley and a high degree of crop tolerance. MON37500 at 13 to 19 g/ha applied at the early growth stage controlled foxtail barley but rates of 25 to 30 g/ha were needed at the later growth stage. In flax, quizalofop was the most efficacious herbicide on foxtail barley. Sethoxydim and clethodim sometimes provided weed control similar to that of quizalofop when applied at the three- to four-leaf stage, but quizalofop was always more effective at the one- to three-tiller stage of foxtail barley. Wheat and flax yields were greater when effective herbicides were applied at the early than at the late stage, indicating the need for early control of foxtail barley to minimize weed competition. MON37500 in wheat and quizalofop in flax provide growers with highly efficacious herbicide options for in-crop control of foxtail barley in conservation tillage systems.

Experiments were conducted using oat in the greenhouse to determine phytotoxicity and spray deposit characteristics of sethoxydim on oat as influenced by adjuvants, ultraviolet (UV) light, and temperature at and shortly after application. Petroleum oil of low viscosity was equal or more effective with sethoxydim when applied at 10 than at 25 C, but high-viscosity petroleum oil was more effective at 25 than at 10 C. UV light reduced sethoxydim efficacy more for high- than low-viscosity petroleum oil adjuvant at 25 C, but not at 10 C. Commercial vegetable oil adjuvant was less effective with sethoxydim at 10 than at 25 C, and UV light reduced efficacy at both temperatures. Commercial methylated vegetable oil was the most effective adjuvant and efficacy was only slightly reduced by UV light at 25 C. A secondary alcohol surfactant that is considered hydrophilic enhanced sethoxydim efficacy even when exposed to UV light. Adjuvants that gave discernible uniform spray deposits with close contact to the epicuticular surface, including over anticlinal walls, resulted in the most effective treatments. The results indicated that temperature at application is important to adjuvant efficacy, partly because of the effect on spray deposit characteristics.

In field experiments, wheat row spacing, seeding rate, and herbicide treatment affected cheat seed content of harvested wheat, wheat yield, and net returns. No individual practice or combination of practices consistently increased net returns from cheat-infested wheat. Net returns frequently were increased and never decreased by applying metribuzin at 420 g ha−1 or chlorsulfuron + metsulfuron at 21.9 + 4.4 g ha−1 or by increasing the seeding rate compared to baseline inputs. The data indicate that herbicide rates should not be reduced when row spacing is decreased and/or seeding rates increased.

Jerusalem artichoke has been reported to colonize several ecological niches and agronomic crops in southern Europe. This plant is also of interest because of its high biomass production and its potential to produce ethanol for biofuel. Allelopathy may be an advantageous trait in Jerusalem artichoke under cultivation, as it potentially reduces weed interference with the crop, theoretically allowing a reduction of mechanical or chemical input required for weed management. However, this trait may also be unfavorable if other crops are cultivated in rotation with Jerusalem artichoke or in areas infested by this species. The aim of this study was to investigate the sensitivity of selected diverse crops (wheat, lettuce, corn, tomato, rice, and zucchini) and weeds (barnyardgrass, black nightshade, common lambsquarters, common purslane, large crabgrass, and pigweed) to the presence of Jerusalem artichoke dried leaf tissues in laboratory experiments performed under controlled conditions. The simulated soil incorporation of different Jerusalem artichoke residues (four cultivars and a weedy population) was carried out in a series of laboratory and greenhouse experiments. Jerusalem artichoke reduced the radicle growth of seedling lettuce (60%), tomato (30%), large crabgrass (70%), and barnyardgrass (30%), whereas total germination of these species was less affected. Sensitivity to Jerusalem artichoke residues was species dependent; germination and initial growth of corn were not affected, whereas winter wheat, lettuce, tomato, rice, and zucchini seedlings were more sensitive to residue presence. Our experiments show that both wild and cultivated decomposing Jerusalem artichoke residues, particularly leaves and stems, possess phytotoxic potential. Additional field experimentation remains to be conducted to determine if allelopathy in the field contributes to its invasibility.

The ability to accurately estimate herbicide efficacy is critical for any decision-support system used in weed management. Recent efforts by weed scientists in the North Central United States to adopt WeedSOFT across a broad region have resulted in a number of regional research projects designed to assess and improve the predictive capability of WeedSOFT. Field studies were conducted from 2000 to 2002 in Nebraska, Missouri, and Illinois to evaluate herbicide-efficacy predictions made by WeedSOFT in two corn-row spacings. Following crop and weed emergence, input variables, such as weed densities and heights, were entered into WeedSOFT to generate a list of treatments ranked by predicted crop yields. The five treatments evaluated included those predicting highest crop-yield potential (recommended control treatment 1), a 10% yield reduction, a 20% yield reduction, a 10% yield reduction plus cultivation, and cultivation alone. These treatments were applied to corn grown in 38- and 76-cm rows. Generally, treatments applied in 38-cm rows had more accurate herbicide-efficacy predictions compared with 76-cm rows. WeedSOFT provided better control predictions for broadleaf than grass species. WeedSOFT provided excellent herbicide-efficacy predictions for the highest crop-yield potential, which indicates a good potential for practical use of this software for herbicide recommendations.

Both alachlor at 3.6 kg ai/ha and metolachlor at 2.8 kg ai/ha applied preplant incorporated consistently controlled red rice 82% and 90%, respectively, over a 3-yr period. Averaged across years, only mefluidide at 0.14 kg ai/ha plus bentazon at 0.84 kg ai/ha, haloxyfop at 0.28 kg ai/ha, and quizalofop at 0.14 kg ai/ha applied postemergence controlled red rice comparable to the preplant herbicide treatments. High rates of sethoxydim and fluazifop (0.56 kg ai/ha), haloxyfop (0.28 kg ai/ha), and quizalofop (0.14 kg ai/ha) were needed to obtain soybean yields equivalent to alachlor and metolachlor.