Field experiments were conducted in 1993 and 1994 to evaluate barnyardgrass control with fenoxaprop-ethyl applied alone or in a mixture with bentazon or bensulfuron. Bensulfuron at 52 g ai/ha did not reduce barnyardgrass control with fenoxaprop-ethyl applied at rates of 56, 75, or 94 g ai/ha. In contrast, mixing bentazon at 1.1 kg ae/ha with fenoxaprop-ethyl reduced barnyardgrass control and rice yield compared with fenoxaprop-ethyl applied alone or mixed with bensulfuron.

Sixteen sweet corn cultivars, representing a range of endosperm genotypes, were evaluated to determine cultivar tolerance to nicosulfuron plus rimsulfuron in greenhouse and field studies conducted over a two-year period. Response to nicosulfuron plus rimsulfuron varied widely, depending on cultivar and application rate. In the field, four cultivars were tolerant to applications of nicosulfuron plus rimsulfuron at rates of 50 g/ha. In the greenhouse, eight cultivars were tolerant to nicosulfuron plus rimsulfuron at 25 g/ha. ‘Merit’ and ‘Silver Extra Sweet’ were most sensitive, with applications of nicosulfuron plus rimsulfuron resulting in death of all plants. ‘Miracle,’ ‘Extra Early Super Sweet,’ ‘Bunker Hill,’ and ‘Sweet Belle’ were tolerant.

The allelopathic influence of sweet potato cultivar ‘Regal’ on purple nutsedge was compared to the influence on yellow nutsedge under controlled conditions. Purple nutsedge shoot dry weight, total shoot length and tuber numbers were significantly lower than the controls (47, 36, and 19% inhibition, respectively). The influence on the same parameters for yellow nutsedge (35, 21, and 43% inhibition, respectively) were not significantly different from purple nutsedge. Sweet potato shoot dry weight was inhibited by purple and yellow nutsedge by 42% and 45%, respectively. The major allelopathic substance from ‘Regal’ root periderm tissue was isolated and tested in vitro on the two sedges. The I50's for shoot growth, root number, and root length were 118, 62, and 44 μg/ml, respectively, for yellow nutsedge. The I50's for root number and root length were 91 and 85 μg/ml, respectively, for purple nutsedge and the I50 for shoot growth could not be calculated.

Yellow hawkweed infests permanent upland pastures and forest meadows in northern Idaho. Conventional surveys to determine infestations of this weed are not practical. A charge coupled device with spectral filters mounted in an airplane was used to obtain digital images (1 m resolution) of flowering yellow hawkweed. Supervised classification of the digital images predicted more area infested by yellow hawkweed than did unsupervised classification. Where yellow hawkweed was the dominant ground cover species, infestations were detectable with high accuracy from digital images. Moderate yellow hawkweed infestation detection was unreliable, and areas having less than 20% yellow hawkweed cover were not detected.

Corn (maize) genotypes which varied in days to maturity were evaluated for level of Striga hermonthica parasitism in western Kenya during three seasons. Fifteen genotypes, with a wide range in days to maturity, were grown in fields heavily infested with S. hermonthica. Early and late-season Striga numbers and corn grain yield were used to evaluate Striga parasitism. There was considerable variation in the timing and amount of Striga attachment among seasons. Days to silking and late-season Striga numbers were correlated (P ≤ 0.05) in all experiments although only weakly in one of the experiments. Grain yield was negatively correlated with days to silking in two of three experiments as were yield and early season Striga numbers. Although earlier-flowering genotypes consistently supported less Striga, they did not always yield more than the later-maturing genotypes due to confounding effects of yield potential and adaptation. There was considerable variation in Striga parasitism among genotypes within maturity groups, and the relative response of genotypes varied between seasons. These data suggest that in some seasons early maturing genotypes have potential to reduce Striga attack in heavily infested areas and yield more than later-maturing genotypes.

Greenhouse studies assessed the susceptibility of three common lambsquarters biotypes to foliar-applied bromoxynil, dicamba, and thifensulfuron. Field studies evaluated the effectiveness of the same herbicides in conjunction with atrazine and row cultivation for the control of common lambsquarters in corn. In the field, bromoxynil was applied at 140, 280, and 420 g/ha, dicamba at 140, 280, and 560 g/ha, and thifensulfuron at 2, 3, and 4 g/ha. In the greenhouse, bromoxynil and thifensulfuron reduced common lambsquarters growth by at least 55%, while dicamba reduced growth 45% or less. Two of the three biotypes were resistant to atrazine. In the field, weed control was up to 70% better in cultivated plots than in noncultivated plots. Cultivation sometimes promoted additional weed emergence, but later emerging weeds rarely reached reproductive maturity. Atrazine improved the level of weed control only if triazine-susceptible weeds were present. The lowest rates of bromoxynil and dicamba (140 g/ha) controlled common lambsquarters 85% or greater even without cultivation, whereas control with the low rate of thifensulfuron (2 g/ha) was acceptable (greater than 85%) 8 wk after planting only in combination with cultivation. Combinations of reduced herbicide rates and mechanical cultivation provided effective, alternative control strategies for both triazine-resistant and susceptible common lambsquarters.

Nicosulfuron and primisulfuron are sulfonylurea herbicides that may persist in the soil and injure sensitive rotational crops such as sugarbeet. Studies were initiated to measure sugarbeet response one and two years after application of 70 and 140 g/ha of nicosulfuron and 40 and 80 g/ha of primisulfuron to corn. Nicosulfuron did not injure sugarbeet one or two years after application. In contrast, sugarbeet yield was reduced one year after application of 40 and 80 g/ha of primisulfuron. Injury was visible two years after application of 80 g/ha primisulfuron but this did not cause a yield reduction. In greenhouse studies, the concentration of nicosulfuron and primisulfuron that reduced sugarbeet growth by 50% were determined for six soils. Primisulfuron reduced sugarbeet growth more than nicosulfuron on four of six soils indicating greater potential for sugarbeet injury from primisulfuron. Sugarbeet response was highly correlated with soil organic matter content (R2 = 0.88). The sorption coefficients, Kd values, for nicosulfuron were 0.30 to 2.58 and the Kd values for primisulfuron were 0.76 to 3.47. Primisulfuron Kd values were higher than those of nicosulfuron on four of five soils indicating stronger affinity of primisulfuron for soil sorptive sites. The Kd values for both herbicides indicate low overall sorption. The greater sugarbeet injury observed in the field from primisulfuron is not due to greater availability of primisulfuron compared to nicosulfuron.

Field and greenhouse studies were performed to examine the influence of various surfactants with glyphosate on whole plant efficacy. Relationships were examined between glyphosate phytotoxicity and surfactant properties, including ionic form, degree of ethoxylation, and hydrophobe composition. Cationic tertiary amine surfactants enhanced glyphosate performance in both field and greenhouse studies. Nonionic allinol and octoxynol surfactants were not effective in combination with glyphosate. In field studies, glyphosate efficacy increased with increasing surfactant ethylene oxide (EO) content. Soybean and velvetleaf responded similarly to glyphosate-surfactant spray applications, as both demonstrated significant linear and quadratic relationships between increasing surfactant ethoxylation and phytotoxicity, while common lambsquarters showed a significant linear relationship only. Cationic surfactants were evaluated in the greenhouse and a significant quadratic regression of glyphosate phytotoxicity to common lambsquarters on increasing surfactant ethoxylation indicated an optimum surfactant EO content of about 10 moles. Both tertiary and quaternary ethoxylated fatty amines were effective with glyphosate in decreasing common lambsquarters' fresh weight. Fatty amine hydrophobe composition did not correlate with glyphosate phytotoxicity to common lambsquarters.

Absorption, translocation, and metabolism of 14C-triclopyr were compared in the rice cultivars ‘Lemont’ and ‘Tebonnet’ under flooded and non-flooded conditions. Radioactivity washed from 14C-triclopyr-treated leaves was 26% at 6 h and decreased to about 11% of that applied at 96 h after treatment. Triclopyr was immobile with 98% of the recovered 14C remaining in the treated rice leaf. An average of 19% of triclopyr was metabolized at 6 h and was similar among flooded and nonflooded rice cultivars. Absorption, translocation, and metabolism of triclopyr did not differ among rice cultivars or flooding treatments.

With the increased development of new tall fescue cultivars used in turf, it is important to understand their individual response to herbicide treatment. The effect of prodiamine on tall fescue root dry weight and root length of selected tall fescue cultivars was studied in the greenhouse in 1.3-m-deep pots of calcined clay. Prodiamine at 0.8 kg ai/ha did not significantly affect either root dry weight or root length. However, the mean root dry weight and maximum root length averaged over all cultivars were significantly reduced at 4 wk after treatment with 1.7 kg/ha. When the prodiamine treatments were repeated in a second experiment, both rates caused a significant reduction in the mean root dry weight and maximum root length but there was no significant difference between prodiamine rates. Single degree of freedom contrasts between the untreated and treated turfs for each cultivar had some differential response in root dry weight. The reduction in root dry weight in the prodiamine treatments was more pronounced in the second study because the turf was less mature. ‘Olympic’ and ‘Rebel’ tall fescue had significantly reduced root dry weight at the 1.7 kg/ha rate in first study; whereas, ‘Amigo,’ Olympic, ‘Sundance,’ and ‘Taurus' tall fescue had significant reduction in root dry weight at both 0.8 and 1.7 kg/ha prodiamine rates. ‘Midnight’ Kentucky bluegrass had significantly reduced root length at both prodiamine rates in the second experiment but in general there was little difference among tall fescue cultivars treated with prodiamine.

Field studies were conducted to determine rhizomatous johnsongrass and barnyardgrass control with clethodim, quizalofop-P-ethyl, fluazifop-P, sethoxydim, fenoxaprop-ethyl, and quizalofop-P-tefuryl applied alone and with lactofen, imazaquin, chlorimuron, and fomesafen. Graminicides applied alone controlled johnsongrass and barnyardgrass 83 to 99%. Of the graminicides evaluated, clethodim was the most susceptible to decreased grass control in mixture with broadleaf herbicides. Imazaquin and chlorimuron were most antagonistic of the broadleaf herbicides toward the activity of graminicides. Clethodim mixed with imazaquin reduced johnsongrass control as much as 64% and mixed with chlorimuron reduced barnyardgrass control as much as 52%. Quizalofop-P-tefuryl was least affected by broadleaf herbicides and fomesafen was least antagonistic in mixture with graminicides.

Solution pH from 6.0 to 8.0 did not affect the germination of Italian ryegrass, ‘Pensacola bahiagrass,’ or common bermudagrass grown in petri dishes in growth chambers. Seeding intervals following metsulfuron methyl application varied from species to species and between soil types. Greenhouse studies indicated that in an Okolona silty clay, common bermudagrass should not be planted until 12 wk after metsulfuron methyl application. Italian ryegrass showed no metsulfuron methyl injury at the 6-wk sampling date when no lime was added, indicating reseeding was feasible at this time; however, a 12-wk time interval was not sufficient when lime was applied. Pensacola bahiagrass was injured when reseeded at 12 wk, regardless of liming rate. In a Prentiss fine sandy loam soil, common bermudagrass could be reseeded 12 wk after application when no lime was added, but not when lime was added. Italian ryegrass and Pensacola bahiagrass should not be reseeded for at least 12 wk, regardless of lime rate. Field experiments, where metsulfuron methyl was applied to the field and seeding was carried out in the greenhouse, indicated on the Okolona silty clay that common bermudagrass reseeding could occur at all liming rates after 3 wk, and Italian ryegrass and Pensacola bahiagrass after 6 wk. In the Prentiss fine sandy loam, common bermudagrass reseeding could occur at 3 wk, regardless of lime rate. Italian ryegrass emergence was not affected when reseeded immediately after metsulfuron methyl application, but height was reduced for longer periods, and increased lime rate lengthened this interval. Pensacola bahiagrass reseeding was feasible at 3 wk.

Field experiments were conducted to evaluate the hypothesis that johnsongrass control in corn causes increased maize dwarf mosaic virus (MDMV) and maize chlorotic dwarf virus (MCDV) disease severity because of increased movement of insect vectors from dying johnsongrass to the corn crop. Johnsongrass control treatments included 1) broadcast POST nicosulfuron, 2) directed POST imazethapyr, 3) mechanical control, and 4) no treatment. Disease severity in both a virus-susceptible and a virus-tolerant corn hybrid was evaluated. With the virus-susceptible hybrid, greater disease severity was observed where johnsongrass was controlled in the experimental area than where johnsongrass was not controlled. Increases in disease severity were independent of the method of johnsongrass control. Corollary studies conducted on the same site verified a double infection of corn with MDMV and MCDV and documented movement of blackfaced leafhoppers, the insect vector of MCDV, subsequent to treatment of johnsongrass.

Weed control with thiobencarb, molinate, or fertilizer granules coated with quinclorac or bensulfuron was evaluated in 1992 and 1993. With thiobencarb or fertilizer granules, less than 55% control of 4-leaf junglerice was obtained, regardless of additional herbicide coating. Coating thiobencarb or fertilizer granules with quinclorac at 550 g ai/ha increased junglerice control, but was not satisfactory. Molinate granules at 4.4 kg ai/ha controlled junglerice at least 81% and improved rice yields over fertilizer or thiobencarb granules. Fertilizer coated with bensulfuron at 111 g ai/ha controlled ducksalad 86 to 96%.

In commercial fields of creeping red fescue, spring applications of sethoxydim at 500 g/ha and fluazifop-P at 250 g/ha consistently reduced the heading, and consequently the seed production, of foxtail barley and volunteer bromegrass by ≥90% without affecting crop seed yield, 100-seed wt or germination. The effectiveness of sethoxydim at 500 g/ha and fluazifop-P at 250 g/ha to reduce heading of grass weeds was not affected by tank mixing with metsulfuron at 4.5 g/ha but was reduced when tank mixed with either dicamba plus 2,4-D at 280 plus 560 g/ha or 2,4-D alone at 560 g/ha. Metsulfuron alone, or in tank mixtures with sethoxydim (500 g/ha) or fluazifop-P (250 g/ha), effectively controlled dandelion and volunteer alsike clover (probability of ≥80% control was 0.94 or more). Dicamba plus 2,4-D provided a similar level of volunteer alsike clover control but was less effective on dandelion, while 2,4-D was ineffective on both weeds. Treatments containing dicamba plus 2,4-D reduced crop seed yield and germination, and increased seed weight.

Field experiments evaluated barnyardgrass, broadleaf signalgrass, and rhizomatous johnsongrass control with sethoxydim, clethodim, fluazifop-P, quizalofop-P, and fenoxaprop applied alone and with bentazon or chlorimuron when crop oil concentrate or BCH 815 was used. Bentazon strongly antagonized sethoxydim and clethodim. BCH 815 partially reduced the antagonism with sethoxydim and clethodim compared with crop oil concentrate. Chlorimuron was most antagonistic towards fluazifop-P, fenoxaprop, and quizalofop-P, and BCH 815 did not reduce antagonism. Additional experiments evaluated Italian ryegrass control with diclofop applied alone and with bromoxynil, metribuzin, 2,4-D amine, or tribenuron plus thifensulfuron with these adjuvants. The amine formulation of 2,4-D and tribenuron plus thifensulfuron reduced Italian ryegrass control with diclofop, irrespective of the adjuvant.

Sensitivity of 49 tomato cultivars and four weeds to DPX-E9636 was determined in greenhouse experiments. Cultivar tolerance varied from completely tolerant to intolerant. The most efficacious application method in greenhouse experiments was early POST for the weeds tested (yellow nutsedge, prostrate eclipta, and paraquat-resistant and -sensitive American black nightshade). Paraquat-resistant American black nightshade was 123 times more sensitive to DPX-E9636 than the paraquat-sensitive biotype. Under field conditions and at 0, 36, or 72 g ai/ha applied one week after transplanting, tomato cultivars showed no response to DPX-E9636 in visual vigor ratings 3 wk treatment, or in shoot fresh or dry weight 4 wk after treatment.

Applications of both terbufos and nicosulfuron can result in a synergistic interaction that injures corn. Field studies were conducted at two Illinois locations in 1991 to determine the effect of insecticide formulation and application method on the serverity of this interaction. Terbufos, applied to the soil at planting, interacted with nicosulfuron applied postemergence to injure corn and reduce grain yield. In-furrow-applied terbufos caused a more injurious interaction to corn than terbufos placed in a surface band; the 15G formulation was more injurious than the 20CR formulation. Simulated rainfall timing experiments were conducted in 1992 and 1993 by treating corn with terbufos 15G and terbufos 20CR and applying rainfall (3.8 cm) 1, 7, or 14 d before nicosulfuron application. No visual injury or yield reductions were noted in corn treated with nicosulfuron alone. Terbufos 15G caused greater corn injury than did terbufos 20CR at each rainfall timing when sprayed with nicosulfuron. Corn injury and subsequent grain yield that can result from the interaction between nicosulfuron and terbufos was greater when simulated rainfall occurred 1 and 7 d before nicosulfuron application than when rainfall occurred 14 d before application.

Field studies were conducted at Carbondale, IL from 1992 to 1994 to evaluate rhizome johnsongrass control in field corn with nicosulfuron and primisulfuron applied POST without or with EPTC applied PPL EPTC applied PPI at 4480 and 6720 g ai/ha plus dichlormid controlled johnsongrass 38 and 60% in 1992 and 29 and 41% in 1993, respectively, and 0% in 1994. EPTC did not decrease johnsongrass rhizome weight, length, or number of nodes in any year. Nicosulfuron at 35 g/ha and primisulfuron at 40 g/ha applied to 38-cm tall plants controlled 94 to 100% and 85 to 100%, respectively, from 1992 to 1994. Plots treated for three consecutive seasons with nicosulfuron or primisulfuron did not have any rhizomes. Corn yield was more than double in nicosulfuron and primisulfuron plots compared with control plots.

2,4-D has been reported to antagonize glyphosate activity on grass weed species. In addition, sodium bicarbonate antagonized 2,4-D activity on broadleaf species. Experiments were conducted using Nuclear Magnetic Resonance (NMR) technology to evaluate interactions of 2,4-D dimethylamine and 2,4-D butoxyethylester formulations with glyphosate in solution. The 2,4-D dimethylamine formulation associated with glyphosate to form the dimethylamine salt of glyphosate. NMR spectra also showed that the molecular orientation of the glyphosate molecule was affected by the 2,4-D butoxyethylester formulation. The antagonist was not the active 2,4-D butoxyethylester molecule itself, but appeared to be due to an association of glyphosate with organic components in the 2,4-D butoxyethylester formulation. The molecular influence of sodium bicarbonate on technical grade 2,4-D free acid, and dimethylamine and butoxyethylester formulations was also evaluated. Sodium bicarbonate was found to react with the 2,4-D free acid and 2,4-D dimethylamine to form the sodium salt of 2,4-D. The 2,4-D butoxyethylester formulation did not react with sodium bicarbonate.