Dose-response studies are an important tool in weed science. The use of such studies has become especially prevalent following the widespread development of herbicide resistant weeds. In the past, analyses of dose-response studies have utilized various types of transformations and equations which can be validated with several statistical techniques. Most dose-response analysis methods 1) do not accurately describe data at the extremes of doses and 2) do not provide a proper statistical test for the difference(s) between two or more dose-response curves. Consequently, results of dose-response studies are analyzed and reported in a great variety of ways, and comparison of results among various researchers is not possible. The objective of this paper is to review the principles involved in dose-response research and explain the log-logistic analysis of herbicide dose-response relationships. In this paper the log-logistic model is illustrated using a nonlinear computer analysis of experimental data. The log-logistic model is an appropriate method for analyzing most dose-response studies. This model has been used widely and successfully in weed science for many years in Europe. The log-logistic model possesses several clear advantages over other analysis methods and the authors suggest that it should be widely adopted as a standard herbicide dose-response analysis method.

The study of weed life cycles, reproductive strategies, and the soil seed bank is emphasized in the undergraduate weed science course at Ohio State University as central to an understanding of the survival of weeds in the environment. A laboratory exercise was conducted every spring and fall academic quarter from 1991 to 1993 to demonstrate the effects of long-term cropping and soil disturbance histories on weed seed banks and aboveground weed communities. Five sites with diverse histories of culture were sampled; these included a field cultivated in vegetables under continuous conventional tillage for 59 yr, a field cultivated in field corn under continuous no-tillage for 11 yr, a 24 yr-old turfgrass research farm, a 70 yr-old forest, and a section of the forest border. Students conducted a survey of the weeds growing at the sites and separated and identified seeds from soil samples over a 3-wk period in weekly 2-h laboratory periods. Students wrote reports interpreting the data based on their knowledge of the site histories, weed life cycles, and weed seed production and longevity characteristics. The data were consistent over academic quarters as well as with published research, indicating that the survey and soil sampling techniques provided a reasonably accurate representation of the weed flora and soil seed populations. Weeds found growing at the sites were primarily summer annuals at the vegetable site, and a mix of summer and winter annuals, biennials, and perennials at the remaining sites. Annual weeds dominated the seed banks of all sites with common lambsquarters, pigweed spp., and common purslane being the most commonly found seeds. The presence of most seeds in the soil could be explained by a combination of species seed production and seed longevity characteristics and species abundance in the standing community. Interpretation of the data required students to integrate and apply lecture material and provided an excellent thinking exercise.

Studies were conducted at two sites in South Dakota in 1992 and at one site in 1993 to measure the effect of velvetleaf on corn growth and yield. Velvetleaf was overseeded in corn rows and thinned to densities of 0, 1.3, 4, 12, and 24 plants/m2. Velvetleaf leaf area index and total biomass were positively correlated with velvetleaf density. Biomass per velvetleaf plant and corn biomass were correlated negatively with velvetleaf density. The percent corn yield reduction was similar for locations and years in spite of large yield differences. Maximum yield loss estimated by a hyperbolic yield reduction model was 37.2% with a loss of 4.4% per unit velvetleaf density.

The response of littleseed canarygrass biotypes to isoproturon, pendimethalin, and diclofop-methyl was evaluated in India, in pot studies and the field during the winters of 1991 to 1992 and 1992 to 1993. Some biotypes of littleseed canarygrass were resistant to isoproturon but cross-resistance to pendimethalin and diclofop-methyl was not confirmed. The resistant biotype required a higher dose of diclofop-methyl than the susceptible biotype. Variations in the response of littleseed canarygrass biotypes were not due to isoproturon formulation. Resistant biotypes required 2 to 8 times more isoproturon than a susceptible biotype for the same level of control. Diclofop-methyl at 1.0 kg ai/ha applied at the 2- to 3-leaf stage of littleseed canarygrass in pot experiments and PRE pendimethalin at 1.5 kg ai/ha in field trials controlled resistant biotypes. Field surveys of the affected areas revealed that resistance in littleseed canarygrass is more prevalent in rice-wheat rotations compared to other crop sequences. Control of littleseed canarygrass with isoproturon dropped from 78 to 21% from 1990 to 1993.

Few postemergence (POST) herbicides provide adequate control of broadleaf weeds in potato. Field experiments were conducted at Lethbridge and Vauxhall, Alberta in 1991 and 1992 to determine the suitability of rimsulfuron and HOE-075032 for selective POST control of weeds in potato. Rimsulfuron applied at 15 to 30 g ai/ha controlled flixweed, kochia, and redroot pigweed and suppressed the growth of redstem filaree. HOE-075032 at 50 to 60 g ai/ha provided comparable control. The potato cultivars, ‘Shepody,’ ‘Norchip,’ ‘Russet Burbank,’ ‘Niska,’ and ‘Ranger Russet,’ tolerated up to 80 g/ha rimsulfuron, but rimsulfuron at 120 g/ha caused fissures in some tubers and reduced marketable and total tuber yields. Tuber quality factors such as specific gravity and chipping ability were not affected by rimsulfuron. HOE-075032 at 15 to 30 g/ha caused fissures in tubers and reduced marketable and total tuber yield of all potato cultivars. Rimsulfuron, but not HOE-075032, provided excellent selective POST broadleaf weed control in potato.

Fall-planted rapeseed and sudangrass were evaluated for weed control in potato during a two-year study. Rapeseed incorporated in the spring in a loamy sand soil reduced weed density 85 and 73% in 1992 and 1993, respectively, and reduced weed biomass 96 and 50% in 1992 and 1993, respectively, in following potato crops compared to potato after fallow. Potato following rapeseed yielded 25% and 17% more total tuber weight than potato following sudangrass in 1992 and fallow in 1993, respectively. In greenhouse trials, rapeseed tissue added to a loamy sand soil at 20 g fresh weight per 400 g dry soil reduced biomass of hairy nightshade and longspine sandbur by 90 and 83%, respectively. Similarly, white mustard tissue added at 20 g fresh weight per 400 g dry soil reduced biomass of hairy nightshade and green foxtail by 83 and 70%, respectively.

A method was developed and tested for in vivo assay of acetolactate synthase (ALS). The method used foliar application of 1,1-cyclopropanedicarboxylic acid (CPCA) to inhibit ketol-acid reductoisomerase, the enzyme immediately following ALS in biosynthesis of branched-chain amino acids, thereby causing accumulation of acetolactate. Since the amount of acetolactate accumulation is a function of carbon flux through ALS, quantification of acetolactate accumulation determined ALS activity. Accumulation of acetolactate in soybean leaves resulted from CPCA rates as low as 15 g/ha and occurred within 1.5 h. Accumulation rates in soybean leaflets declined with leaf age from 84 μg/h/g tissue at 3 d to 17 μg/h/g tissue at 7 d. Foliar application of CPCA also caused acetolactate accumulation in corn, grain sorghum, velvetleaf, common cocklebur, and smooth pigweed. The ability of the in vivo assay to quantify the reduction in ALS activity following applications of ALS-inhibiting herbicides was validated by comparing ALS activity following thifensulfuron application to ‘Williams 82’ soybean, which has a sulfonylurea-sensitive ALS, and ‘Asgrow 3200’ soybean, which has a sulfonylurea-insensitive ALS. Thifensulfuron reduced ALS activity in Williams 82 soybean to 0, 0.8, 3.3, and 15.6% of the CPCA control at 6, 12, 24, and 48 HAT, but ALS activity in Asgrow 3200 soybean was reduced only to 34, 40, 57, and 88% of the CPCA control.

Bentazon efficacy was evaluated in early, normal, and late plantings of green pea with the addition of four adjuvants: crop oil concentrate (COC), LI-700, Sylgard 309, and X-77. Weed control was improved by all adjuvants in normal and late plantings of green pea, but only by Sylgard 309, X-77, and LI-700 in the early planting. In normal and late plantings, weed control with bentazon applied at 0.56 kg/ha with any adjuvant was equal to weed control with bentazon applied alone at 1.12 kg/ha. Bentazon injury on green pea plants varied from slight to severe, with the lowest injury resulting from bentazon applied with COC and LI-700 and highest injury from bentazon applied with Sylgard 309. Bentazon injury was greater in normal and late plantings than in the early planting.

Imazethapyr dose response curves were developed under laboratory and field conditions with the imazethapyr-resistant and -susceptible corn hybrids Pioneer 3180IR, IR denoting a hybrid homozygous for the XA17 gene conferring resistance to imazethapyr, and normal Pioneer 3180, respectively, and their F1 progeny to establish methods of measuring the presence of the XA17 gene and quantifying its impact. At two field locations, absorption of photosynthetically active radiation was a sensitive index of corn injury caused by imazethapyr. Imazethapyr, at 35 g/ha (one half the labeled rate), reduced absorption of photosynthetically active radiation in Pioneer 3180 by 8.3% at 1 wk after treatment. Plant height also was a sensitive index of injury. The minimum rate at which imazethapyr injury was detected in the Pioneer 3180IR/Pioneer 3180 F1 hybrid differed with location. Pioneer 3180IR was not injured by 280 g/ha of imazethapyr. The Pioneer 3180IR/3180 F1 hybrid was injured slightly by imazethapyr at 140 g/ha, but recovered within 5 wk after treatment, and grain yield was not reduced by 280 g/ha of imazethapyr. A seedling assay reliably detected differences between progeny of Pioneer 3180IR and Pioneer 3180IR/3180 F1.

Imazethapyr and bentazon were applied with petroleum oil adjuvant in a factorial arrangement to weed species in greenhouse and field research to determine if postemergence weed control by imazethapyr was antagonized when bentazon was tank-mixed. Tank-mixing 840 g/ha of bentazon with 13 or 27 g/ha of imazethapyr increased redroot pigweed and eastern black nightshade dry weight as compared to Colby's expected values in the greenhouse. However, weed control was not reduced in field studies. Subsequent greenhouse studies indicated that soil interception and resulting root uptake of imazethapyr increased redroot pigweed control. Bentazon decreased foliar absorption of 14C-imazethapyr by 15% and translocation of 14C from the treated leaf by more than 50% compared to l4C-imazethapyr applied alone.

The pH of deionized water, initially adjusted to a pH of 6 to 9, all decreased to near pH 5 upon pressurization with CO2 in a backpack spray system. When deionized water contained bicarbonate (NaHCO3 or KHCO3) at 0 to 800 mg/L to buffer against a pH decrease from CO2 pressurization the return to their initial pH was more rapid than deionized water alone regardless of bicarbonate source. Acidification of spray solution following CO2 pressurization of 138, 276, or 414 kPa was similar and bicarbonate had a greater effect than spray pressure. Addition of acidifying buffer and bicarbonate to the solution resulted in an initial and post-CO2 pressurization pH range of less than one pH unit. All spray solution pH levels returned to near their initial pH following depressurization, indicating that the pH decrease was not permanent. Rate of recovery from acidification with CO2 increased with initial pH and bicarbonate concentration.

The response of Persian darnel, green foxtail, wild oat, and volunteer cereals to clethodim applied at two growth stages, and the effect of these treatments on flax yield and quality were determined in a series of field experiments in which each weed species was evaluated separately. Clethodim applied at 45 g/ha provided excellent control of Persian darnel, green foxtail, wild oat, and volunteer wheat and barley. Sethoxydim applied at 150 g/ha provided excellent control of Persian darnel, green foxtail, wild oat, and volunteer barley. Rax was tolerant at five times the recommended rate of application and was unaffected by plant growth stage at time of application. When applied at an early (2- to 3-leaf) stage, control of Persian darnel, green foxtail, wild oat, and volunteer wheat and barley was excellent at 20 g/ha. Except for Persian darnel, weed control as determined by reduction in plant dry weight, was negatively affected by growth stage at time of application. Although visible control and reduction in plant dry weight were somewhat less when clethodim was applied at the 4-to 5-leaf stage, control of each weed species was acceptable. When weight of water in plant tissue (fresh weight – dry weight) was used as a measure of living plant tissue, wild oat and volunteer barley control were unaffected by growth stage at time of application.

Field and greenhouse studies were conducted to evaluate selected PRE-applied herbicides for sprangletop control. In greenhouse studies, oxadiazon and dithiopyr provided excellent (> 89%) red sprangletop (L. filiformis) control. Pendimethalin and metolachlor + atrazine provided good (80–89%) to excellent control for 6 mo and 2 mo during studies 1 and 2, respectively. Isoxaben and atrazine provided poor (< 70%) control during both greenhouse studies. In field studies, good to excellent bearded sprangletop (L. fascicularis) control followed dithiopyr, pendimethalin, metolachlor, and metolachlor + atrazine treatments. Dithiopyr at 0.8 kg ai/ha provided best (> 95%) sprangletop control throughout the 6-mo testing period. Under field conditions, control was inconsistent following oxadiazon with good to excellent control during one study and poor control in another study. Better or equal control than metolachlor + atrazine followed dithiopyr, pendimethalin, and metolachlor alone treatments. Oxadiazon also provided similar or better control than metolachlor+atrazine in three of four studies. Over all studies, dithiopyr provided best sprangletop control, followed by metolachlor, metolachlor + atrazine, pendimethalin, and oxadiazon. Isoxaben and atrazine treatments provided poorest or inconsistent sprangletop control.

With few exceptions, north temperate North American weeds are native species that have proliferated following site disturbance. Social pressures are rapidly eroding the availability of essential silvicultural tools such as chemical herbicides and prescribed burning. Biological control with microorganisms in forestry is at an early stage of development. An inoculation strategy involving a fungus pathogen (PFC-082: Nectria ditissima Tul./ALDERKILL™), its formulation for biological control of Alnus rubra Bong. in the form of the PFC-MYCOCHARGE™ and a newly devised instrument for bioherbicide delivery into woody stems (PFC-ALDERWAK™) are described. The overall strategy and implements are potentially useful for the delivery of any biological or translocatable material into amenity or orchard trees as well. PFC-082 was the single isolate of N. ditissima tested that produced 100% infection and incited the formation of red alder cankers longer than 0.5 m in 30 mo when inoculated by the method described herein. Natural infections by this pathogen occur on fewer than 1% of red alder stems in the forest.

Experiments were conducted to evaluate PRE and POST cotton herbicides for control of MSMA-resistant (R) and -susceptible (S) common cocklebur biotypes, and to determine potential cross-resistance of the R biotype to other arsenical and membrane disruptor herbicides. Cyanazine and clomazone applied PRE were the most effective herbicides for control of R populations. Lactofen or cyanazine in combination with MSMA controlled R and S biotypes better than fluometuron or pyrithiobac combined with MSMA. MSMA-resistant common cocklebur was not cross-resistant to other arsenical herbicides. Significant differences in cellular electrolyte leakage and chlorophyll content of the treated leaf between biotypes were not evident for paraquat, acifluorfen, and MSMA.

The efficacy of postemergence herbicide applications was evaluated in the greenhouse and the field in 1993 and 1994, using variables of carrier volume and diluent type. Ultra-low volume (ULV) applications of herbicides using an air-assisted sprayer calibrated at a volume of 9.4 L/ha were compared to 94 and 187 L/ha applications with a conventional hydraulic system. In greenhouse studies, reduced rates of sethoxydim, clethodim, fluazifop-P, and quizalofop were used to compare the effects of carrier types and volumes on their efficacy to yellow foxtail. All herbicides applied in oil diluents at 9.4 L/ha, with the exception of fluazifop-P and quizalofop applied in soybean oil, provided better yellow foxtail control than when applied in water at 94 and 187 L/ha. Sethoxydim and clethodim applied at 25 and 16% of the recommended rate, respectively, provided over 90% control in both petroleum oil and methylated seed oil. Reduced rates of glyphosate in petroleum oil or soybean oil were more effective at reducing bermudagrass growth than in water or methylated seed oil. Activity of glyphosate in methylated seed oil was no more effective than in water. Field experiments were conducted to study the efficacy of ULV applications of sethoxydim, clethodim, fluazifop-P, imazethapyr, and bentazon. Rates of the postemergence grass herbicides could be reduced by applying them at ULV in oil diluents while maintaining annual grass control equal to that achieved with higher herbicide rates in larger volumes of water. Control of annual grasses and annual broadleaf weeds with bentazon and imazethapyr applied at ULV were inconsistent and did not provide acceptable weed control. This may be partially due to the poor suspension of these herbicides in oil carriers.