Plots planted to corn (Zea mays L. var. Mo. 880) were treated with 0, 2.5, 5, and 10 lb/A of 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) or 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) plus 0, 100, or 200 lb/A of nitrogen fertilizer. Yields of corn forage harvested 5 weeks after planting were significantly reduced by herbicidal treatments. Reductions were more pronounced on corn treated with simazine than with atrazine. In a given year, yields of corn forage from each successive harvest were reduced less, percentagewise, than the previous ones. Yields of corn grain generally were unaffected by herbicidal treatments, except when 10 lb/A of simazine were applied. Herbicides caused an increase in percent nitrate in forage approximately 5 weeks after treatment. Percent of nitrogen in corn forage rose sharply, approximately 5 weeks after planting, due to herbicidal treatments, especially on plots not treated with nitrogen fertilizer.

Both carrot (Daucus carota L.) and common ragweed (Ambrosia artemisiifolia L.) plants metabolized 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron). Traces of all of the following derivatives of linuron were detected in both plants: 3-(3,4-dichlorophenyl)-1-methoxyurea, 3-(3,4-dichlorophenyl)-1-methylurea, 3-(3,4-dichlorohenyl)urea, and 3,4-dichloroaniline. Differences in absorption and concentration of these derivatives were observed between carrot and ragweed plants. All of the above derivatives were phytotoxic to common ragweed plants except for 3-(3,4-dichlorophenyl)urea and 3,4-dichloroaniline, while none of the derivatives were phytotoxic to carrot. In carrot, 87% of the applied linuron was metabolized to nonphytotoxic derivatives compared to only 13% in common ragweed plants. It appears that a combination of differences in absorption, metabolism, and phytotoxicity of several of the metabolite derivatives of linuron to carrot and common ragweed plants may be the primary reason for differences in sensitivity of these two plants to linuron.

Recovery of (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T), as the acid and ester, was significantly greater in live oak (Quercus virginiana Mill.) tissues treated with mixtures of the 2-ethylhexyl ester of 2,4,5-T (2 lb/A)-.potassium salt or isooctyl ester of 4-amino-3,5,6-trichloropicolinic acid (picloram) (1/2, 1 and 2 lb/A) than in tissues treated with 2 lb/A 2,4,5-T ester alone. Recovery of 2,4,5-T as the ester was noted in the middle and lower-stem tissues. Between 90 and 99% of the herbicide recovered 1 month after treatment was gone 6 months after treatment. Evaluation of brush reduction 2 years after treatment indicated that mixtures of picloram salt and 2,4,5-T resulted in greater reduction of brush than mixtures of picloram ester and 2,4,5-T or 2,4,5-T alone.

The phytotoxic monoterpenes, camphor, pulegone, and borneol, exhibit a marked synergistic action when used in combination. On a molar basis, these phytotoxic concentrations are enhanced from 40 to 100 times by using two compounds simultaneously. The toxicity of these compounds is about the same for radish (Raphanus sativus L.) and wheat (Triticum vulgare Vill.) but is less by an average of tenfold for oats (Avena sativa L.). When the compounds are used singly, they are from 3 to 12 times as effective in inhibiting root elongation as they are in inhibition of germination.

Resistance to the thiocarbamates has been selected in early watergrass populations within the rice-growing region of California. To elucidate the processes contributing to the spread of resistance among rice fields, we characterized the genetic diversity and differentiation of thiobencarb-resistant (R) and thiobencarb-susceptible (S) populations across the Central Valley using microsatellite markers. A total of 406 individuals from 22 populations were genotyped using seven nuclear microsatellite primer pairs. Three analytical approaches (unshared allele, Shannon–Weaver, and allelic-phenotype statistics) were used to assess genetic diversity and differentiation in the allohexaploid species. Low levels of genetic variation were detected within populations, consistent with other highly selfing species, with S populations tending to be more diverse than R populations. FST values indicated that populations were genetically differentiated and that genetic differentiation was greater among S populations than R populations. Principal coordinate analysis generated two orthogonal axes that explained 88% of the genetic variance among early watergrass populations and differentiated populations by geographical region, which was associated with resistance phenotype. A Mantel test revealed that genetic distances between R populations were positively correlated with the geographical distances separating populations. Taken together, our results suggest that both short- and long-distance seed dispersal, and multiple local and independent evolutionary events, are involved in the spread of thiobencarb-resistant early watergrass across rice fields in the Sacramento Valley. In contrast, resistance was not detected in early watergrass populations in the San Joaquin Valley.

Bioeconomic weed management models help growers achieve appropriate weed management with less herbicide by matching management to the weed population in a field. Growers, however, will not use bioeconomic models unless cost-effective methods to sample their weed populations are identified. Counting and identifying seeds and seedlings is the most time-consuming and costly part of sampling weed populations. The time required for this process was investigated and modeled as a first step in developing sampling plans for growers using WEEDCAM, a bioeconomic model for weed management in Zea mays L. in Colorado. The time required to count and identify seeds or seedlings was recorded for 9,405 soil cores (5 cm in diameter and 10 cm deep) and 9,726 quadrats (18-cm band over 1.52 m of crop row) collected or examined in eight corn fields in eastern Colorado. The time required to count and identify seeds was best described using a log-linear regression with time increasing with the number of seeds and species and the amount of sand in the core. The average cost of determining there are no seeds in a core is $1.07 for a core from a field with 37% sand and $4.32 if the field has 88% sand. The average cost of counting and identifying 36 seeds of four species is $2.70 and $10.88 for cores with 37 and 88% sand, respectively. The time required to count and identify seedlings was best described using a log-linear regression with time increasing with the number of seedlings and species. Classifying seedlings as grass or broadleaf did not improve the model. The average cost of determining that a quadrat is weed-free is $0.02. The average cost of counting and identifying 37 seedlings is $0.05, $0.07, $0.19, and $0.26 per quadrat for 1, 2, 4, and 6 species, respectively. The cost of identifying seeds and seedlings in eastern Colorado Z. mays fields to use WEEDCAM is estimated as $2.71 per core for the seed bank and $0.08 per quadrat for seedlings.

Agricultural production systems that reduce the use of in-crop herbicides could greatly reduce risks of environmental damage and the development of herbicide-resistant weeds. Few studies have investigated the long-term effects of in-crop herbicide omissions on weed seedbank community size and structure. A crop-rotation study was sampled 10 yr after a strictly annual rotation and an annual/perennial rotation were exposed to different in-crop herbicide omission treatments. In-crop herbicides were applied either in all annual crops (control), omitted from oats only, or omitted from both flax and oats. Seedbank densities were greatest when in-crop herbicides were omitted from flax and oats, and this treatment also reduced crop yield. Shannon-Wiener diversity differed among crops in the annual crop rotation and among herbicide omission treatments in the perennial rotation. Herbicide omissions changed the weed-community structure in flax and in wheat and canola crops in the annual rotation enough to warrant alternate control methods in some treatments. The magnitude of the effects on the seedbank parameters depended largely on the competitive ability of the crop in which herbicides were omitted. No yield response to omitting herbicides in oats indicated that standard weed management practices have reduced weed populations below yield-loss thresholds.

Greenhouse studies were conducted using bentgrass (Agrostis tenuis Sibth. ‘Highland′) as a bioassay species to measure herbicidal activity of 3.4 kg/ha of the isopropylamine salt of glyphosate [N-(phosphonomethyl)glycine] when applied directly to the soil surface prior to bentgrass emergence. Activity of glyphosate also was examined by applying glyphosate to a moist soil surface and placing alfalfa (Medicago sativa L. ‘Vernal′) and red clover (Trifolium pratense L. ‘Kenstar′) seeds on the sprayed surface 3, 6, 9, and 24 h later. In two high-organic soils, glyphosate reduced bentgrass growth in each of four experiments, even when applied up to 5 days before bentgrass emergence. Significant glyphosate activity was measured in one of the experiments in another organic soil and in three of the experiments in a Chehalis sandy loam soil. Germination and growth of alfalfa and red clover were reduced when seeds were distributed on a sprayed soil surface up to 24 h after glyphosate application. These results show that glyphosate, at least under certain conditions, can cause significant crop injury when used prior to planting or emergence of some species.

Seed survival of jointed goatgrass over 2 yr was related to cyclical seasonal changes in ability to germinate, field emergence, and seasonal precipitation and air temperature. The ability of seed to germinate was studied by incubating spikelets under constant, defined incubation conditions after retrieving samples from the field every 2 weeks over 2 yr. Less than 8% of jointed goatgrass seed that were initially set outdoors survived beyond 2 yr when left undisturbed on the soil surface or buried 5 cm deep. Periods of greatest seed loss coincided with periods of peak emergence in fall (late September and October). The ability of seed to germinate also peaked in fall and preceded the period of greatest field emergence and greatest decreases in seed survival.

Degradation of trifluralin in four soils, each represented at four sites, under field conditions was determined quantitatively and described mathematically. A biexponential equation that resulted from integration of first-order and second-order differential rate equations described degradation data better than the first-order kinetic model for 15 of 25 soil-site combinations. Biexponential model regression coefficients indicated extent of degradation and that degradation is rapid at initially high trifluralin concentrations but slows as concentration decreases. The first-order kinetic model initially underestimated but ultimately overestimated degradation of trifluralin, thereby inferring that a first-order half-life is inadequate for predicting trifluralin persistence.

The efficacy of glyphosate as affected by rate, time of application, and addition of surfactant3 was evaluated on blackberry, Japanese honeysuckle, poison ivy, sericea lespedeza, and trumpetcreeper. The addition of surfactant (0.5% v/v) to glyphosate had no effect on the control of the weeds studied. Glyphosate applied in mid-June to September at 1.1 or 2.2 kg/ha controlled blackberry. Mid-August glyphosate applications of 2.2 kg/ha controlled 83% of actively growing Japanese honeysuckle; there was less than 75% at one site due to moisture stress. Use of 2.2 kg/ha of glyphosate from mid-June through mid-August controlled 87% of poison ivy. Consistent commercially acceptable control of sericea lespedeza was obtained when glyphosate was applied at 1.1 or 2.2 kg/ha at the time of flowering. Applying glyphosate at 1.1 or 2.2 kg/ha from late July through early October controlled 50% or more of the trumpetcreeper.

Research was conducted to formulate a temperature-dependent population level model for johnsongrass seed germination and rhizome bud break. A nonlinear poikilotherm rate equation was used to describe development rate as a function of temperature, and a temperature-independent Weibull function was used to distribute development times for the population. Seed germination and initiation of rhizome bud break of johnsongrass were collected under constant temperature conditions to parameterize the model. Seed germination rate increased with temperature up to 36 C, then declined at 40 C. Rate of rhizome bud break increased with temperature up to 32 C, then rapidly decreased with further temperature increases. Rate of rhizome bud break was higher than for seed germination at temperatures of 32 C or below, but lower at higher temperatures. Time to first germination or bud break event was longer for seed than for rhizomes, but subsequent progression of development was higher for seed. A population level temperature-dependent model was developed by coupling the poikilotherm equation with the Weibull function. The model was validated against two independent seed germination and three independent rhizome bud germination data sets.

The herbicide 3,6-dichloro-o-anisic acid (dicamba) is very mobile in Tartary buckwheat (Fagopyrum tataricum (L.) Gaertn.), a susceptible weedy species. After foliar or root application, the compound was translocated rapidly to meristematic tissues at the shoot apex and in leaf axils. Redistribution of dicamba in the shoot, to young tissues, continued for at least 20 days. Metabolism of dicamba occurred very slowly, both in intact plants and in detached leaves, and the only metabolite detected was conjugated with sugars. The nonphytotoxic metabolite was identified by paper and thin-layer chromatography as 5-hydroxy-3,6-dichloro-o-anisic acid. Decarboxylation of dicamba also occurred in the plants but extremely slowly. The rapid entry and translocation of dicamba, its continued mobility in treated plants, and its very low rate of detoxification are major contributing factors to the effectiveness of dicamba for controlling Tartary buckwheat.

The influence of chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} on control of wild oat (Avena fatua L. ♯3 AVEFA) when mixed in the spray tank with three herbicides was tested in greenhouse and in field trials at Lacombe and Scott, Canada, during 1981 and 1982. In field experiments, chlorsulfuron mixed with diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy]propanoic acid} caused a 4 to 35% reduction in control of wild oat. Mixtures of chlorsulfuron with difenzoquat (1,2-dimethyl-3,5-diphenyl-1H-pyrazolium) caused a 0 to 19% reduction and mixtures with flamprop {N-benzoyl-N-(3-chloro-4-fluorophenyl)-DL-alanine} a 2 to 30% reduction in control of wild oat. Addition of chlorsulfuron to the wild oat herbicides under greenhouse conditions also resulted in losses in control of wild oat. Increasing the rate of the wild oat herbicide in the mixture tended to overcome these losses.

The organophosphate insecticides, malathion [S-1,2-di (ethoxycarbonyl)ethyl O, O-dimethyl phosphorodithioate], parathion (O, O-diethyl O-4-nitrophenyl phosphorothioate) and diazinon (O,O-diethyl O-2-isopropyl-6-methylpyrimidin-4-yl phosphorothioate) combined with bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide], caused severe injury to soybean [Glycine max (L.) Merr. ‘Corsoy′] and navy bean (Phaseolus vulgaris L. 'Seafarer′). Postemergence tank – mixture applications of bentazon with organophosphate or carbamate insecticides, or soil-applied organophosphate insecticides prior to bentazon treatments, did not interact with bentazon to injure corn (Zea mays L. ‘Great Lakes Hybrid 4122′). Technical grade malathion interacted with bentazon to the same extent as formulated malathion. Combination treatments of malathion with bentazon resulted in the same degree of injury whether they were applied as tank mixtures or split applications 48 h apart.

Field and greenhouse studies were conducted to evaluate annual bluegrass (Poa annua L. # POAAN) control and phytotoxicity of ethofumesate [(±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate] to selected warm- and cool-season turfgrass species. Annual bluegrass control in non-overseeded dormant hybrid bermudagrass [Cynodon dactylon (L.) Pers. X C. tranvaalensis Burtt-Davy Tifgreen’ # CYNDA] was 75% or greater with at least two ethofumesate applications at monthly intervals starting in December. Tifgreen bermudagrass spring growth was delayed with more than two applications of ethofumesate at 1.1 kg ai/ha, or when the second application was made after January. Under greenhouse conditions the growth of both Tifgreen and Tifdwarf bermudagrass was less when treated with ethofumesate. Stand and shoot growth of 29 cultivars of ryegrass (Lolium spp.), bluegrass (Poa spp.), bentgrass (Agrostis spp.), and red fescue (Festuca rubra L. # FESRU) were reduced by ethofumesate at 1.1 kg/ha as a preemergence or split (0.5 kg/ha preemergence + 0.5 kg/ha postemergence) application. Postemergence applications were less phytotoxic to cool-season turfgrasses than preemergence applications. Perennial ryegrass stands were generally not reduced by postemergence application of ethofumesate at 1.1 kg/ha. However, shoot growth of perennial ryegrass was reduced.

Seeds from natural populations of fierce thornapple and velvetleaf collected in a corn-growing area in central Spain were incubated at a range of constant temperatures and water potentials to model the progress of germination on the basis of the accumulation of hydrothermal time. Previous to the germination tests, the seeds were treated in two different ways: (1) dark storage under dry conditions (nonchilled seeds), and (2) burying in the original soil at 10-cm depth during 2 mo in winter (naturally chilled seeds). The results indicated different mechanisms inhibiting germination in both weed species. Whereas fierce thornapple displayed some type of embryo dormancy, the lack of germination in velvetleaf appeared to be entirely due to the seed coat. On the other hand, significant differences between nonchilled and naturally chilled seeds in fierce thornapple were observed, mainly due to the decrease in the mean base water potential of the 50th percentile in the latter, which indicated a loss of dormancy by exposure of the seeds to natural conditions. Hydrothermal time appears to be a good description of the germination patterns in both weed species, but in the case of fierce thornapple, only for naturally chilled seeds. Thus, the development of the hydrothermal model in fierce thornapple raises some questions for consideration concerning the influence of the type of seeds (conditions of storage, pretreatments of the seeds before germination tests) on its germination capacity.

Bacterial production of CO2 from sucrose substrate increased growth of seven species of algae in CO2-limited laboratory cultures. Decomposition of organic matter in pond water also supplied enough CO2 to support good algal growth in cultures deprived of other sources of CO2. Estimates of CO2 production from decay of dissolved organic matter in six pond waters ranged from 0.32 to 3.53 mg/L per 24 hr. The carbonate-bicarbonate equilibrium system is a major source of CO2 for algal photosynthesis. However, in waters of low or extremely high alkalinity, this system will not support high rates of photosynthesis. In such waters CO2 from decomposition will stimulate photosynthesis. Decomposable organic compounds must be considered with nitrogen and phosphorus as factors responsible for accelerated eutrophication and nuisance algal blooms.

The influence of depth (0 to 30 cm) and duration (1 to 24 months) of burial on the deterioration, germination, and viability of ripgut brome seed was studied in the field. Both surface-sown and buried ripgut brome seed were depleted within 15 months. Persistence of surface-sown seed declined relatively slowly during the first year, falling from 83 to 62 to 23% after 1, 9, and 12 months, respectively. Seed covered by soil, however, germinated more rapidly, with less than 10% of the initial population ungerminated after 1 month at all depths. The mode of seed disappearance was closely related to whether or not the seed was covered with soil. Seed loss at depths of 1 to 30 cm was primarily due to germination in situ, with little effect from viability loss or enforced or induced dormancy. In contrast, the persistence of surface-sown seed was due primarily to induced dormancy for up to 12 months, with viability loss and enforced dormancy becoming important thereafter. Tillage practices aimed at providing favorable germination conditions may reduce ripgut brome seed survival in the soil. Because seed is relatively short lived, seed supply in soil may be reduced by short-term rotation to a crop that allows for effective control of ripgut brome.

Different Saskatchewan soils were studied to determine their populations of 2,4-D [(2,4-dichlorophenoxy) acetic acid] degraders and gross aerobic bacteria. Soil from Indian Head field plots receiving relatively high field rates (1.12 or 1.68 kg/ha) of 2,4-D amine or ester applied annually over the previous 32 yr contained the highest population of degraders, ranging from 103 to 104 degraders/g soil. Control plots recorded lower populations of degraders (2.5 ± 0.5 × 103 degraders/g soil). Five soils from around the province were also studied, and a relationship was found between the rate of breakdown of 14C-2,4-D in the soil and the number of degraders. Another soil from a different site at Indian Head, but of a similar type to that in the field plots, displayed a much slower rate of 2,4-D degradation and also a much lower degrader population (7 ± 2 degraders/g soil) when compared to the other four soils (4 × 102 to 9 × 102 degraders/g soil). The ratio of degraders to the total bacterial flora varied in all studies between 1:6.5 × 102 and 1:3 × 105. When 1030 soil isolates were screened for their ability to degrade 2,4-D using an agar-block extraction technique, none possessed this feature. This would support the hypothesis that the ratio of 2,4-D degraders to the total microbial flora was indeed large (at least 1:103).