Experiments conducted for two consecutive years indicated that barnyardgrass, large crabgrass, and giant foxtail interfered with the growth and development of container-grown ‘Gold Drop’ bush cinquefoil. Grass weed densities ranging from one to six weeds per container reduced Gold Drop bush cinquefoil growth. Bush cinquefoil shoot dry weight, averaged over all grass weeds, was decreased as much as 75% after 83 days of interference. The reduction of cinquefoil growth was independent of the number of grass weeds in the container.

The nonionic surfactants Tween 20 [oxysorbic (20 POE) polyoxyethylene sorbitan monolaurate] and Tween 80 [oxysorbic (20 POE) polyoxyethylene sorbitan monooleate] at concentrations of 0.05, 0.1, 0.2, and 0.4% v/v stimulated germination of barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG] seeds in petri dishes. Stimulation occurred under both 30/20 and 25/15 C diurnal temperature cycles whether or not light was supplied during the 8-h high-temperature portion of the cycle. Barnyardgrass responded most to treatment under environmental conditions in which untreated seeds germinated the least. A 0.1% surfactant concentration often stimulated germination of weed seeds as effectively as did higher concentrations. Germination of redroot pigweed [Amaranthus retroflexus L. # AMARE] seeds was inhibited by Tween 80 in the light under both the low- and high-temperature regimes and by Tween 20 at low temperature in the light. Germination of tumble pigweed (Amaranthus albus L. # AMAAL) seeds was inhibited by both surfactants in the high-temperature regime whether or not light was supplied. Common purslane (Portulaca oleracea L. # POROL) seeds were insensitive to treatment.

Field research was conducted in 1988 and 1989 to compare effects of clethodim, fenoxaprop, haloxyfop, and sethoxydim each applied singly and sequentially at full (1X) and reduced (0.5X) rates on barnyardgrass, bearded sprangletop, and rice. A tank-mixture of propanil plus thiobencarb (2.2 + 2.2 kg ha–1) applied sequentially was included as a standard treatment. Control of barnyardgrass and bearded sprangletop was equal to that of the standard treatment both years with 1X rates of clethodim and fenoxaprop, and with 0.5X rates of clethodim, fenoxaprop, and sethoxydim each applied after propanil; rice so treated produced high grain yields. In 1988, severe rice injury occurred after the second application of clethodim at the 0.5X rate, but rice recovered. Grass control costs were reduced 57% with a single application of fenoxaprop at the 1X rate compared with the standard treatment, but net returns were not different.

Manure applied to cropland may serve as a source of weed introduction and dispersal. In 36 manure samples from 20 farms, apparently-viable seeds from 13 grasses and 35 broadleaf plants were found. Common lambsquarters was on more than half the farms, yellow foxtail on 35%, common chickweed and dandelion on 30%, and wild mustard, redroot pigweed, and barnyardgrass on 25%. Four farms had manure with no seeds at all; the remainder averaged 75 100 per 1000 kg manure. Twelve milking-cow and heifer barns on six farms with large velvetleaf infestations also were sampled with an average of 133 000 seeds per 1000 kg manure. Only one barn contained velvetleaf seeds. When compared to soil seedbank numbers, manure is not an important seed source for New York farms. However, problems may arise with imported feeds heavily infested with weed seed or which contain even small numbers of noxious weeds.

Field experiments were conducted to compare efficacy of BAS 514, bromoxynil, fenoxaprop, sethoxydim, and triclopyr with standard herbicides for barnyardgrass and bearded sprangletop control in rice at four locations. Sequential applications of BAS 514 and fenoxaprop, or propanil and sethoxydim consistently controlled barnyardgrass and bearded sprangletop as well as or better than standard treatments of propanil, thiobencarb, or pendimethalin alone or combined; and rice so treated produced high yields. BAS 514 applied postemergence alone, BAS 514 applied sequentially with sethoxydim, or BAS 514 tank mixed with propanil controlled barnyardgrass but not bearded sprangletop. Bromoxynil or triclopyr tank mixed with fenoxaprop or sethoxydim antagonized activity on barnyardgrass and bearded sprangletop. Combinations of fenoxaprop with BAS 514 or propanil consistently provided barnyardgrass and bearded sprangletop control and high yields.

In laboratory experiments, we studied barnyardgrass, common lambsquarters, and redroot pigweed seed dormancy release by alternating temperatures under different soil water regimes, to determine whether that response serves as a mechanism for assuring seedling establishment. Alternating temperatures were important in breaking seed dormancy in the three weeds, but the species' response to alternating temperatures differed with soil water content. For redroot pigweed and newly dispersed seeds of barnyardgrass, dormancy breaking by alternating temperatures occurred only when soil water content was high enough for germination. Moreover, adverse incubation conditions (constant temperature and low water content) induced secondary dormancy in these seeds. Seventy percent of seeds incubated in open boxes emerged before the soil reached wilting point, when seeds were incubated at temperatures high enough for a high germination rate. A dormancy breaking mechanism that triggers a high rate of germination may be important in assuring success of seedling establishment where rainfall patterns result in wetting and drying cycles of the soil, especially in soil types that lose water rapidly from the surface layers.

The relative sensitivity of various crops and weeds to celery root residue incorporated into soil was determined in greenhouse experiments. A range of concentrations was used to determine the percentage of celery residue needed to cause a 50% reduction in plant growth (I50). The most sensitive weed was spiny amaranth and the least sensitive was common purslane. The most sensitive crop was radish and the least sensitive was celery. Selectivity was calculated as crop I50/weed I50 and varied from a maximum of 13 for celery and spiny amaranth to a low of 0.4 for radish and common purslane. Selective weed suppression might be obtained when celery residue is present.

Herbicide treatments of tank mixtures or sequential applications were applied at different growth stages and compared with standard treatments for control of barnyardgrass [Echinochloa crus-galli (L.) Beauv. ♯ ECHCM], bearded sprangletop [Leptochloa fascicularis (Lam.) Gray ♯ LEFFA], and aquatic weeds in rice (Oryza sativa L. ‘Starbonnet’). Some herbicides injured rice more than the propanil (3’,4’-dichloropropionanilide) or molinate (S-ethyl hexahydro-1H-azepine-1-carbothioate) standards, but injury for all treatments was inconsequential. Postemergence tank mixture treatments that controlled barnyardgrass (two- to four-leaf stages), bearded sprangletop (two-leaf to tillering stages), and aquatic weeds better than standard treatments were propanil plus butachlor [N-(butoxymethyl)-2-chloro-2’,6,-diethylacetanilide], oxadiazon [2-tert-butyl-4(2,4-dichloro-5-isopropoxyphenyl)-δ2-1,3,4-oxadiazolin-5-one] thiobencarb {S-[(4-chlorophenyl)methyl]diethylcarbamothioate}, or pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine].

Dinitroaniline herbicides are major herbicides used to control annual grass weeds in cool-season turfgrasses. At least three herbicides, benefin, pendimethalin, and trifluralin are labeled preemergence to control weeds in established turfgrass. Prodiamine could be a competitive product. Benefin at 2.2 to 3.4 kg ai/ha, pendimethalin at 1.7 to 3.4 kg ai/ha, prodiamine at 0.6 to 1.7 kg ai/ ha, and benefin plus trifluralin at 1.1 plus 0.6 to 2.3 plus 1.1 kg ai/ha effectively control many annual grass weeds, including large and smooth crabgrass, yellow and green foxtail, barnyardgrass, goosegrass, fall panicum, and annual bluegrass. Most dinitroaniline herbicides provide residual preemergence weed control for the entire growing season. In general, Kentucky bluegrass, perennial ryegrass, tall fescue, red fescue, and other cool-season turfgrasses tolerate most of these herbicides, although higher-than-normal rates of any dinitroaniline herbicide could restrict root growth and cause stand thinning in turfgrass species.

Six experiments were conducted in three rice fields near Harrisburg, AR in Poinsett County in 1991 and 1992 to confirm barnyardgrass resistance to propanil and to compare herbicide treatments for control of propanil-resistant barnyardgrass. In all experiments, standard treatments of thiobencarb applied delayed PRE or tank mixtures of propanil + thiobencarb applied POST controlled propanil-resistant barnyardgrass. In five of six experiments, propanil failed to control barnyardgrass at 6 to 8 kg ai/ha (three times use rates) and in three experiments it provided inconsistent control at 11 kg/ha. Emulsifiable propanil at 11 kg/ha frequently controlled resistant barnyardgrass better than the dry flowable formulation. Treatments that consistently controlled propanil-resistant barnyardgrass included propanil tank-mixed with pendimethalin or quinclorac applied POST to two-leaf grass; quinclorac applied alone delayed PRE or POST or applied POST tank-mixed with thiobencarb, pendimethalin, or a formulated mixture of molinate and propanil; a formulated mixture of propanil and molinate applied POST in tank mixtures with thiobencarb or pendimethalin; and fenoxaprop or fenoxaprop-P alone applied POST to four-leaf grass prior to flood establishment. Herbicide treatments that failed to control resistant barnyardgrass included POST applications of a formulated mixture of propanil and molinate alone and propanil in tank mixtures with bromoxynil or triclopyr. These studies confirm that barnyardgrass from several farms in Arkansas have resistance to propanil and identified treatments that control propanil-resistant barnyardgrass.

Experiments were conducted in 1982, 1983, and 1984 to determine whether herbicides can effectively control weeds in annual statice (Limonium sinuatum Mill.) without reducing the marketability of the crop. A greenhouse evaluation of chlorpropham (1-methylethyl 3-chlorophenylcarbamate), napropamide [N,N-diethyl-2-(1-naphthalenyloxy)propanamide], EPTC (S-ethyl dipropyl carbamothioate), oxadiazon {3-[2,4-dichloro-5-(1-methylethoxy)phenyl]-5-(1,1-dimethylethyi)-1,3,4-oxadiazol-2-(3H)-one}, and trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] indicated that preemergence applications of the latter three herbicides resulted in the most effective weed control and least statice injury. Oxadiazon was the most effective for broadleaf and grass ed control in field-grown statice. Yield and quality were greatest in oxadiazon-treated plots and exceeded those of the handweeded controls. Annual statice was most sensitive to trifluralin.

Greenhouse studies were conducted to determine host status of weed species for Rhizoctonia solani AG-1, which causes Rhizoctonia foliar blight of soybean. Weed species were barnyardgrass, broadleaf signalgrass, common cocklebur, entireleaf morningglory, hemp sesbania, itchgrass, johnsongrass, large crabgrass, northern jointvetch, prickly sida, purple nutsedge, redweed, sicklepod, and smooth pigweed. Seedling weeds were inoculated with suspensions containing intraspecific group IA and IB isolates of the fungus. In the first study, sclerotia of IA were recovered from tissue of all weeds except smooth pigweed, and mycelia of IA were recovered from all except smooth pigweed and redweed. In that study, neither microsclerotia nor mycelia of IB were recovered from sicklepod, barnyardgrass, or large crabgrass, and only microsclerotia were recovered from itchgrass and purple nutsedge. In the second study, sclerotia of IA, microsclerotia of IB, and mycelia of each isolate were recovered from all weed species. In other studies, R. solani spread from at least six of seven weed species to a noninfected soybean plant growing in close proximity. These studies emphasize the importance of weed control, not only for reducing plant competition and increasing yield, but also for the potential impact on development of RFB.

The practical application of yield loss prediction models using relative leaf area of weeds is limited due to the lack of a quick and accurate method of leaf area estimation. Leaf cover (the vertical projection of plant canopy on the ground) can be used to approximate leaf area at early stages of plant development. An automated digital image analysis system for measuring leaf cover has been developed. The system has an operator-assisted module aimed at validating the automated functions. The objective of this research was to demonstrate the accuracy of the operator-assisted module under different weed–crop conditions. A laboratory experiment was conducted using simulated weed–crop populations. Two additional field experiments were conducted using corn in competition with: (1) common lambsquarters, barnyardgrass, or a mixture of both species, and (2) a natural weed community. In the laboratory experiment, a narrow linear relation was observed between leaf cover estimated with the operator-assisted module and leaf area measured with an optical area meter (r 2 > 0.98). In field experiments, the regression between corn leaf cover estimated by the operator-assisted module and corn leaf area measured with the optical area meter was not as good (r 2 < 0.55). The poor performance of the module was probably due to the overlapping and the architecture of corn leaves (especially unexpanded leaves). Nevertheless, the system showed high precision in estimating leaf area of both grassy weeds and broadleaf weeds (r 2 > 0.89). Generally, the accuracy of the estimates decreased as the growth stage became more advanced. Apart from its initial purpose as a calibration tool for the automated system, the operator-assisted module can have several potential research applications. It can be used: (1) as an alternative to destructive leaf area measurement at early stages of plant development, (2) as a tool in the study of plant competitive ability, and (3) as an objective and quantitative support to visual observations.

Experiments were conducted to determine the influence of nitrogen (N) fertility and winter wheat cultivars on weed infestations in a winter wheat-ecofallow sorghum-fallow rotation near North Platte, NE. Centurk 78 and Lancota winter wheat suppressed density and growth of barnyardgrass and green foxtail significantly more than Eagle winter wheat before and after wheat harvest. Increasing N rates applied to winter wheat decreased annual grass weed population and weed yields. However, 67 and 101 kg N ha−1 reduced winter wheat grain yields compared to 34 kg N ha−1. Plots treated at 2.8 plus 0.3 kg ai ha−1 of atrazine plus paraquat 31 d after wheat harvest had more barnyardgrass before grain sorghum planting in 1983 than plots treated 17 d after wheat harvest but the reverse was true for green foxtail after grain sorghum emergence in 1984. Increasing N rates from 34 kg ha−1 to 67 and 101 kg ha−1 in the previous wheat crop decreased weed density before and after grain sorghum planting. There was no advantage in weed control in the grain sorghum from applying N to winter wheat in the fall vs. spring.

Experiments were conducted in 1991 and 1992 to evaluate annual grass and broadleaf weed control with bromoxynil applied alone and with graminicides. Bromoxynil controlled velvetleaf better than entireleaf morningglory and controlled both species better than sicklepod. Mixing bromoxynil with fluazifop-P, quizalofop-P, and sethoxydim reduced control of barnyardgrass, green foxtail, large crabgrass, and shattercane. Control of broadleaf signalgrass with quizalofop-P was reduced by bromoxynil. Annual grass control with clethodim was not affected by bromoxynil.

Barnyardgrass, large crabgrass, and Texas panicum were evaluated in field experiments over 3 yr to measure their duration of interference and density on grain sorghum yield. When grain yield data were converted to a percentage of the weed-free control, linear regression predicted a 3.6% yield loss for each week of weed interference regardless of year or grass species. Grain sorghum grown in a narrow (61-cm) row spacing was affected little by full-season interference; however, in wide (91-cm) rows, interference increased as grass density increased. Data from the wide-row spacing were described by linear regression following conversion of grain yield to percentages and weed density to log10. A separate nonlinear model also was derived which could predict the effect of weed density on grain sorghum yield.

Agrichemical interactions between propanil; the herbicides HOE 30374, pendimethalin, piperophos, quinclorac, and thiobencarb; and the insecticide carbaryl were evaluated under field conditions to find synergistic or additive interactions useful to control a barnyardgrass biotype resistant to propanil (R-BYG) without injuring rice. Propanil and each compound were evaluated at four rates for a total of 16 rate combinations for each additive. Averaged over all experiments, 2- to 3-leaf R-BYG control with propanil alone at 0.83, 1.65, 3.3, and 6.6 kg ai/ha was 33, 53, 62, and 81% at 7 d after treatment (DAT). Propanil-susceptible barnyardgrass (S-BYG) response to propanil alone at similar rates was 52, 73, 88, and 94% control. HOE 30374, carbaryl, piperophos, or pendimethalin in combination with propanil produced synergistic effects on R-BYG. For each compound tested, at least one rate combination with propanil controlled R-BYG > 80% with minimal rice injury (< 20%) at 7 DAT. Use of these combinations of compounds could provide more effective control of this resistant biotype and help prevent its spread.

The recent introduction of glufosinate-resistant and glyphosate-resistant crops provides growers with new options for weed management. Information is needed to compare the effectiveness of glufosinate and glyphosate on annual weeds. Greenhouse trials were conducted to determine the response of barnyardgrass (Echinochloa crus-galli), common lambsquarters (Chenopodium album), common ragweed (Ambrosia artemisiifolia), fall panicum (Panicum dichotomiflorum), giant foxtail (Setaria faberi), large crabgrass (Digitaria sanguinalis), and velvetleaf (Abutilon theophrasti) to glufosinate and glyphosate. The response of velvetleaf and common lambsquarters was investigated at multiple stages of growth. Glufosinate and glyphosate were applied to each weed species at logarithmically incremented rates. The glufosinate and glyphosate rates that provided a 50% reduction in aboveground weed biomass, commonly referred to as GR50 values, were compared using nonlinear regression techniques. Barnyardgrass, common ragweed, fall panicum, giant foxtail, and large crabgrass responded similarly to glufosinate and glyphosate. Common lambsquarters 4 to 8 cm in height was more sensitive to glufosinate than glyphosate. In contrast, 15- to 20-cm tall-velvetleaf was more sensitive to glyphosate than glufosinate.

Barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG] spikelets were collected from greenhouse-grown plants at various developmental stages. Caryopses contained in a single spikelet were dormant at maturity, but dormancy was overcome when the spikelets were dry afterripened at 23 C or were treated with high temperatures, acid scarification, or punctured with a scalpel. The season at which anthesis occurred affected the length of time for afterripening. Enhanced germination due to puncturing and scarification was not related to removal of a restriction to water entry. The effectiveness of puncturing in overcoming dormancy depended on moisture content of the spikelets at the time of puncturing. Above 18% moisture content germination percentage was low regardless of the dormancy-releasing treatment.

The weed control spectrum of clomazone, the influence of clomazone on the performance of other herbicides, and the performance of tank mixtures containing clomazone were evaluated from 1985 through 1987. Clomazone applied preemergence at 280 g ai/ha controlled 90 to 100% of barnyardgrass, giant foxtail, goosegrass, large crabgrass, seedling johnsongrass, prickly sida, and velvetleaf. Clomazone at reduced rates was more effective applied preemergence than preplant-incorporated for 10 of 23 weed species. Clomazone enhanced imazaquin activity on entireleaf morningglory and sicklepod in 1986. A tank mixture of clomazone, imazaquin, and metribuzin at half the labeled rates reduced soybean injury, increased soybean yield, and controlled weeds as well as the mixture at labeled rates.