In field plantings, granular 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) were the most effective herbicides, but injured Spiraea media, S. trichocarpa, Syringa prestoniae and Physocarpus opulifolius. Diuron also injured newly planted evergreens. Granular 3-amino-2,5-dichlorobenzoic acid (amiben), isopropyl N-(3-chlorophenyl)carbamate (CIPC), 2-chloroallyl diethyldithiocarbamate (CDEC) and 4,6-dinitro-o-sec-butylphenol (DNBP) did not cause injury. Preplanting application of ethyl N,N-di-n-propylthiolcarbamate (EPTC) reduced the vigor of the deciduous shrubs. Chamaecyparis and Thuja species were tolerant to simazine under greenhouse conditions, while tolerance in Juniperus varied according to species.

Salinization is affecting many rice (Oryza sativa L.) areas worldwide and weed infestation, together with the occurrence of herbicide-resistant populations, is further limiting rice yield. This study aimed at evaluating the effect of water salinity on the emergence and seedling growth of five Italian barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.] populations (three sensitive and two resistant to acetolactate synthase–inhibiting herbicides), three Italian weedy rice (Oryza sativa L.) populations (all sensitive to imazamox), and two rice varieties (the conventional ‘Baldo’ variety and the imazamox-tolerant ‘CL80’ one). In 2017, seeds were sown in alveolar trays filled with sand, a nutrient solution, and water with the following salt concentrations: 0, 50, 100, 150, 200, and 250 mM NaCl. Plant emergence (after 15 d), plant height, shoot and root weight, chlorophyll a, chlorophyll b, and carotenoid content were measured at 40 d after sowing. Echinochloa crus-galli showed a higher tolerance to salinity than O. sativa and rice. All species were affected more at the seedling stage than at emergence. A variable behavior of the herbicide-resistant populations was shown; one resistant E. crus-galli population was affected more by salinity and showed a lower emergence rate (about 20% against 40% emergence of the other populations at the highest salt concentration) and reduced seedling growth, while the other resistant population’s response was similar to that of the sensitive populations. The chlorophyll content increased as the salt content increased in all E. crus-galli populations. The highest emergence and growth reduction in O. sativa were recorded in the imazamox-tolerant rice. Rice and O. sativa were able to grow only up to 50 mM. Echinochloa crus-galli populations are probably favored under saline conditions, while lower infestation by O. sativa can be expected.

The most successful herbicides for control of downy brome (Bromus tectorum L.) in grassland were: 3-amino-1,2,4-triazole (amitrole), 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine), 2-chloro-4,6-bis(isopropylamino)-s-triazine (propazine), and 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine). More consistent downy brome control was obtained with atrazine than the other s-triazines. Amitrole improved postemergence control of the s-triazines in the tillering stage. Intermediate wheatgrass (Agropyron intermedium (Host.) Beauv.), crested wheatgrass (Agropyron cristatum L. Gaertn.), western wheatgrass (Agropyron smithii Rydb.), blue grama (Bouteloua gracilis (H. B. K.) Lag.), and sedge (Carex spp.) appeared to be more sensitive to most s-triazines than needle-and-thread (Stipa comata Trin. & Rupr.) and sand dropseed (Sporobolus cryptandrus Torr.). Sand dropseed was extremely tolerant.

Given the importance of emergence level and timing to the competitiveness and success of annual crabgrass species in turfgrass, particularly in the context of increasing synthetic pesticide bans and the common cultural practice of fertilization, a study was conducted in a northern region of North America (Ontario, Canada) to determine the effect of fertilizer application on large and smooth crabgrass emergence in residential lawns. In petri dish experiments, we reconfirmed that KNO3 has a significant positive effect on large and smooth crabgrass seed germination but we showed that there is only an effect on fresh seed and no effect on aged seed, suggesting that the treatment affects dormancy level and not germination per se. In two other experiments using turf cores and commercial lawn fertilizer in growth room conditions and in field trials at three sites, we confirmed this result showing that neither fall nor spring fertilizer application had any effect on the emergence level of either smooth or large crabgrass. These results have practical relevance to homeowners and turf managers in this region because they are dealing with crabgrass emerging in the spring from seed shed the previous fall. The results also show that fertilizer can be used to aid turf quality and competitiveness without impacting true infestation level (density) of crabgrass in the spring.

Chloroplasts, isolated from fresh spinach (Spinacia oleracea L.) were treated with four concentrations of each 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) or 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) to determine the influence of these herbicides on the free fatty acid content in isolated chloroplasts. The treated chloroplast solutions were sampled at 0, 5, 15, 30, 60, and 120 min following treatment. Results indicated that most herbicide treatments increased free fatty acid content in isolated chloroplasts when compared with the zero concentration treatments. The increased fatty acid content was similar for most concentrations of simazine and atrazine. Results of individual fatty acid analyses indicated that the increase in total fatty acids was a result of increases in concentration of unsaturated rather than saturated fatty acids.

The prolificacy of honeyvine milkweed [Ampelamus albidus (Nutt.) Britt.] was investigated. Mature seeds stored at 0, 10, and 24 C and germinated at 32 C demonstrated high viability from harvest to 1 year old. Immature seeds were slightly less viable but followed the same trends in germination. Studies with rhizomes excavated at four different times throughout the year showed that segments 1 inch long with at least one live bud were capable of generating regrowth. These reproductive characteristics with the inherent tenacity of honeyvine milkweed indicate a potentially serious weed problem in many agricultural regions of the United States.

The hydrogen bonding of 2,2-dichloropropionic acid (dalapon) to N-methylacetamide (NMA) as a model protein was studied using infrared spectra. Changes in the spectra indicated that the dalapon carboxyl-OH, hydrogen bonds significantly to the model amide carbonyl.

Determining the mechanisms of herbicide resistance in weeds allows for the development and implementation of applied management practices aimed to control and to prevent further spread of herbicide-resistant populations in crop fields. This research was conducted to determine propanil resistance and cross-resistance to other photosystem II (PSII) inhibitors in ricefield bulrush biotypes and to elucidate the mechanism of propanil resistance. To this end, propanil-resistant (R) and propanil-susceptible (S) biotypes were selected from field-collected populations after propanil spraying at the field rate, and whole-plant, dose–response experiments were conducted to evaluate cross-resistance to PSII inhibitors and interactions between propanil and the insecticides malathion and carbaryl. In addition, the psbA gene from R and S biotypes was sequenced for amino acid alterations following polymerase chain reaction (PCR) amplification. Plant survival data indicated the R biotype displayed a 14-fold increase in propanil resistance relative to the susceptible (S) biotype. In addition, the propanil-R biotype also had increased resistance to the PSII-inhibitors bromoxynil, diuron, and metribuzin but was more susceptible to bentazon than were propanil-S plants. Synergism between propanil and the insecticides carbaryl and malathion was greater in the S biotype than it was in the R biotype, indicating that, unlike propanil resistance in weedy grasses, enhanced degradation of the herbicide molecule is not a mechanism of resistance for propanil in ricefield bulrush. A Val219 to Ile substitution in the propanil-R chloroplast D1 protein was identified following sequencing of the psbA gene. This research suggests a single-point mutation at the target site causes resistance to propanil, diuron, metribuzin, and bromoxynil but increasing susceptibility to bentazon in propanil-R ricefield bulrush, a novel Val219–Ile feature. To our knowledge, this is the first instance of propanil resistance in weeds because of a mechanism other than enhanced herbicide metabolism. Tank-mixing bentazon and propanil, where permitted, can control both propanil-R and propanil-S biotypes.

Field experiments were conducted to evaluate soybean interference on common cocklebur and entireleaf morningglory under irrigated and nonirrigated conditions. Interference from the mixture of soybean and entireleaf morningglory, and soybean alone reduced the total leaf area index (LAI), LAI within the common cocklebur canopy, and growth rate of common cocklebur more than did entireleaf morningglory; more reduction occurred without irrigation than with irrigation. Irrigated common cocklebur produced 687 burs per plant, while nonirrigated produced 359. Irrigated and nonirrigated soybeans and the mixture of soybeans and entireleaf morningglory reduced common cocklebur bur production 43 to 47%. Irrigated entireleaf morningglory reduced common cocklebur bur production 42%, while nonirrigated reduced bur production 28%. Interference from the mixture of irrigated soybeans and common cocklebur reduced the total leaf area index (LAI), LAI within the entireleaf morningglory canopy, and growth rate of entireleaf morningglory more than did soybean or common cocklebur alone. Irrigated entireleaf morningglory produced 542 and 1107 seeds per plant in 1982 and 1983, respectively. The mixture of irrigated soybeans and common cocklebur reduced entireleaf morningglory seed production 84 to 90%. Nonirrigated entireleaf morningglory was not competitive in any treatment combination either year due to lack of sufficient LAI.

Specially constructed runoff plots were used to study the effect of simulated rainfall intensity, antecedent soil moisture, and subsequent rainfall on prometryn [2,4-bis(isopropylamino)-6-methylthio-s-triazine] movement across and through a field soil with a 1% slope. The first cm (45.4 L) of runoff was collected and subdivided. The initial 3.8 L of runoff water generally contained a higher concentration of prometryn than did a composite from the next 41.6 L. The sediment contained a higher prometryn concentration than did the runoff water. However, due to the greater volume of water lost compared to sediment, over 90% of the prometryn lost was in the water fraction. When prometryn was applied to a dry soil and rainfall simulated, runoff losses of prometryn were 0.5% or less of the total amount initially applied. The first runoff producing simulated rainfall caused the largest prometryn losses, but prometryn could not be detected in the runoff 1 month subsequent to application. Prometryn was never detected at soil depths greater than 5 cm. Prometryn runoff was greater from plots in which the soil was wet at the time of application.

In preliminary greenhouse evaluations and then in field studies, common cocklebur (Xanthium pensylvanicum Wallr.) and wild common sunflower (Helianthus annuus L.) were controlled by early postemergence applications of 3,5-dibromo-4-hydroxybenzonitrile (bromoxynil). Bromoxynil on young soybeans [Glycine max (L.) Merr.] caused temporary necrosis, retarded growth, and delayed maturity but did not reduce the stand of soybeans. Subsequent recovery and final yields of treated soybeans were such that selective control of common cocklebur and wild common sunflower appeared feasible. Treatments were applied as aqueous sprays over the tops of both the weeds and the crop. Rates of 140 or 196 g/ha were sufficient to control common cocklebur or wild common sunflower that was in the six true-leaf stage or smaller. In terms of soybean development, the optimum time for treatment appeared to be about the first trifoliolate stage.

London rocket is a common winter annual weed in southern New Mexico that can host beet curly top virus and its insect vector, the beet leafhopper. Experiments were conducted in southern New Mexico to determine if London rocket could serve as a host for overwintering beet leafhopper. Field experiments were carried out from 2002 to 2003 and from 2003 to 2004 to compare the impact of three London rocket planting dates on plant emergence and life history and leafhopper survival. Emergence was highest in October-planted London rocket, low in January/February plantings, and did not occur for August plantings. The life cycle was 185 d and 125 d for October- and January-planted London rocket, respectively, and growth of the plant (including height and rosette base diameter) was greater for London rocket that was planted in October. October-planted London rocket survived from late October through mid to late April, the period of time needed to serve as an overwintering host for beet leafhoppers. Caging the plants to assess beet leafhopper survival did not affect rate of plant growth, but it reduced the time to flowering for October-planted London rocket and increased the height and weight of plants. Beet leafhoppers were able to survive for approximately 2 mo in early winter or spring on caged London rocket plants.

Hypocotyl callus cultures were established from six tomato (Lycopersicon esculentum L.) cultivars that exhibited differential tolerance to preemergence and postemergence metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] at 0.5 kg ai/ha in the greenhouse. Metribuzin in a low sucrose growth medium inhibited callus growth, but calli were not highly sensitive to the herbicide Differences between cultivars in the response of calli to 50 ppm metribuzin were observed. The degree of tolerance of tomato cultivars to postemergence metribuzin at 0.5 kg/ha was similar to the degree of tolerance of their hypocotyl calli to 50 ppm metribuzin in the growth medium.

One greenhouse and two field experiments were conducted to determine if crop protectants used in conjunction with herbicides would permit weed-free establishment of orchardgrass (Dactylis glomerata L. ‘Potomac’) with alfalfa (Medicago sativa L. ‘WL 307’). Herbicides used were EPTC (S-ethyl dipropylthiocarbamate) and butam [2,2-dimethyl-N-(1-methylethyl)-N-(phenylmethyl)propanamide] plus cyprazole {N-[5-(2-chloro-1,1-dimethylethyl)-1,3,4 thiadiazol-2-yl] cyclopropanecarboxamide}. These experiments revealed that banded activated charcoal allowed limited orchardgrass establishment with a herbicide but did not result in consistently better orchardgrass stands than the untreated control. Orchardgrass was not protected from herbicide injury by 1,8-naphthalic anhydride (NA) or R-25788 (N,N-diallyl-2,2-dichloroacetamide). The butam plus cyprazole mixture consistently controlled grass and broadleaf weeds as effectively as EPTC.

A 50:50 mixture of phenmedipham (methyl m-hydroxycarbanilate m-methylcarbanilate) and desmedipham [ethyl m-hydroxycarbanilate carbanilate (ester)] was applied at 1.1, 2.2, and 4.4 kg/ha to weed-free sugarbeets (Beta vulgaris L. ‘Mono-HyD2’) at three growth stages in the morning and afternoon to evaluate factors associated with phytotoxicity. Sugarbeet stand loss from herbicide application had a much greater effect on yield than temporary vigor loss. Increasing herbicide rate always increased stand loss. Spraying in the afternoon was much less injurious than spraying in the morning when maximum temperature during the day exceeded 22 C. Excessive stand loss occurred, even with the 1.1 kg/ha rate and 4 to 6 leaf sugarbeets, when sprayed on the morning of a day with maximum temperature of 30 C or greater. Yield loss was determined by percent stand loss and by sugarbeet stand density prior to herbicide application. Significant sucrose yield loss occurred with all rates when applied in the morning to a marginal sugarbeet stand.

Foliar applications of 14C-bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] with PPA (polymeric polyhydroxy acid) at 1 or 2% (v/v) or nonoxynol (9.5 POE) [α-(p-nonylpheny1)-ω-hydroxypoly(oxyethylene)] at 1% (v/v) or mixtures of PPA and nonoxynol did not increase absorption or translocation of 14C-bentazon in soybeans [Glycine max (L.) Merr. ‘Lee 74′] or common cocklebur (Xanthium strumarium L. # XANST). PPA alone at 1 to 2% (v/v) did not significantly affect absorption or translocation of 14C-bentazon in smooth pigweed (Amaranthus hybridus L. # AMACH), but PPA with nonoxynol significantly increased translocation out of the treated leaf. Both PPA and nonoxynol decreased absorption and movement of 14C-MSMA [monosodium salt of methylarsonic acid] out of the treated leaf of johnsongrass [Sorghum halepense (L.) Pers. # SORHA]. In greenhouse research, PPA at 0.25 and 0.5% (v/v) did not increase the level of control of common cocklebur obtained following postemergence applications of bentazon at 0.24 and 0.48 kg ai/ha. Similarly, PPA at 0.25 and 0.50% (v/v) did not increase the toxicity of MSMA at 0.3 and 0.6 kg ai/ha to either johnsongrass or common cocklebur.

Soil carryover of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] following annual applications to a sorghum [Sorghum bicolor (L.) Moench] monoculture was studied by assessing sorghum yield factors as well as yields of a subsequent bioassay crop of oats (Avena sativa L.). Atrazine applications of 3.4 kg/ha or more increased sorghum injury and rates of 4.5 kg/ha and more increased seed weight and decreased sorghum stand. Sorghum recovered from early atrazine injury and stand loss and generally maintained yields. Rates of 2.2 kg/ha did not reduce sorghum yields even with repeated annual usage. There appears to be little hazard of reducing sorghum yields due to atrazine carryover in the soil from annual atrazine applications at normal rates to a clay loam or silty clay loam soil in eastern Nebraska. However, atrazine carryover will have to be a consideration if the grower plans to rotate to a susceptible crop such as oats.

Cotyledons of 6-day old etiolated cucumber (Cucumis sativus L. ‘Alpha Green’) seedlings treated on the second day with EPTC (S-ethyl dipropylthiocarbamate) accumulated 35 to 45% more protochlorophyll and 30 to 40% more glycolipids than the controls. on illumination the treated cotyledons accumulated chlorophyll faster than the controls. Exposure of cucumber cotyledons to a variety of amide, carbamate, and other thiocarbamate herbicides did not produce a similar effect. EPTC, was found to cause an increase in chlorophyll accumulation.

The fate of 4-chloro-2-oxobenzothiazolin-3-ylacetic acid (benazolin) in wild mustard [Brassica kaber (DC.) L.C. Wheeler var. pinnatifida (Stokes) L.C. Wheeler], turnip rape (Brassica campestris L. ‘Echo’), and rape (Brassica napus L. ‘Target’) was investigated with the aid of 14C-benazolin. The label was more mobile in wild mustard than the rape species following leaf treatment and accumulated in young leaves, stem, and stem apex. The label was also found in foliage after root treatment. In both cases, the translocated label was primarily that of 14C-benazolin, implying phloem and xylem transport. The susceptibility of wild mustard and tolerance of the rape species to foliar-applied benazolin can be partly explained by different rates of transport to susceptible meristematic sites. Root exudation of the label following leaf treatment was greater in wild mustard than in the rape species and was not correlated with selectivity. Labeled benazolin was rapidly metabolized by the Brassica species to four derivatives which appear to be less toxic than benazolin. Specific differences in metabolism were not sufficient to explain selectivity. Negligible amounts of 14CO2 were released by the three species following treatment with 14C-benazolin.

Two wild oat (Avena fatua L.) biotypes and two barley (Hordeum vulgare L.) varieties known to have intraspecific differential response to foliarly-applied 4-chloro-2-butynyl m-chlorocarbanilate (barban) were studied. When barban was applied to the roots, the intraspecific differential response (measured by shoot retardation) was maintained in both species but to a much lesser extent than previously observed with foliar application. Wild oat maintained a greater differential response than barley. Therefore, the factors causing the differential response to foliarly-applied barban may reside primarily in the leaves of both species but to some extent elsewhere (perhaps at the plant apex) in the wild oat biotypes and to a lesser extent elsewhere in the barley varieties. Differential response to foliar applications was not caused by differential uptake, but may be caused primarily by the susceptible biotype or variety's reduced ability to degrade barban beyond 3-chloroaniline. This might cause the greater build-up of compound X (a water-soluble 3-chloroaniline-containing metabolite of barban) observed in the susceptible biotype or variety. Compound X appeared to be nonphytotoxic. The build-up of compound X in turn may reduce the rate of metabolism of barban resulting in the greater amount of free barban found in the treated leaf of the susceptible biotype or variety 12 to 24 hr after treatment. This greater amount of free barban in the leaf of the susceptible biotype or variety may be responsible for the differential response to foliar applications of barban. Evidence for this partial explanation of the differential response was better for barley than for wild oat.