A 2-year field study was conducted to determine the effects of fertilization on elodea (Elodea canadensis Michx.), eurasian watermilfoil (Myriophyllum spicatum L.), and heartleaf pondweed (Potamogeton pulcher Tuckerm.). Plants, water, and sediment were sampled and inorganic mineral contents determined. Water concentrations of NO3, NH4, P, and K increased sharply following fertilization and generally reached maximum values within 7 days after treatment. Concentrations of these nutrients decreased rapidly after reaching maximum values. In the first year, plant growth was not increased due to fertilization while in the second year only heartleaf pondweed produced significantly greater yields. Elodea and eurasian watermilfoil grew better in the control environment, presumably due to less competition from algae, whose growth was increased by the addition of fertilizer. At the end of the study the top 1.3 cm of bottom sediment had increased in cation exchange capacity (C. E. C.), organic matter, total N, and available P for all treatments while the underlying sediment remained relatively unchanged. Available P was greater in the surface of the fertilized sediment than in the surface of the control sediment.

Clodionafop, an acetyl-coenzyme A carboxylase (ACCase) inhibitor, changed the shape of the chlorophyll fluorescence induction curve (Kautsky curve) in barley and oat in greenhouse experiments. Biomass ED50, based on log-logistic dose–response curves, for barley was considerably higher than that for oat in all experiments. Biomass ED50 and relative potency (ED50 [barley]/ED50 [oat]) were consistent among experiments when sprayed at the same phenological stage of plant development. Especially at high doses, clodinafop changed the shape of the Kautsky curve more for oat than for barley. From the numerous parameters that can be derived from the OJIP steps of the Kautsky curve, we found that (1) F vj, the relative changes at the J step [F vj = (F m − F j)/F m], (2) area between Kautsky curve and maximum fluorescence (F m), and (3) F v/F m, maximum quantum efficiency of Photosystem II [F v/F m = (F m − F 0)/F m], were closely linked to the biomass dose–response relationships for both species. The linkage between biomass and the fluorescence parameters may be used to shorten the screening period for ACCase inhibitors.

The seasonal emergence characteristics and seedbank ecology of annual bluegrass were evaluated in a vegetable field in the central coast of California. The emergence and germinability of annual bluegrass were monitored continuously for over 3 yr to detect seasonal variation in weed emergence. Weed emergence and seedbank densities were measured every 45 d for 41 mo. Weed emergence was monitored simultaneously in the field and in a growth chamber that was adjusted seasonally for day length and temperature. Samples were incubated in the growth chamber for 45 d and then elutriated to measure remaining viable ungerminated caryopses and relative germination potential. Seedbank densities ranged from 2,000 to 20,000 caryopses m−2 during the study period. Weed emergence and germinability were highest from October to November and lowest from March to July. Emergence from soils collected in the spring and fall and incubated under both spring and fall conditions in the growth chamber indicated that seed dormancy state determines germinability rather than environmental conditions during incubation. Soil samples collected in the spring had no emergence (<1%) when incubated under spring or fall conditions, whereas samples collected in the fall had high emergence (>95%) under both spring and fall conditions. A waveform regression fit the repeated emergence pattern with a cycle length of 364 d (365 d for the growth chamber). This model predicted that weed emergence would peak on November 5 and be lowest on June 20. A survey of organic vegetable fields found that caryopses were more common in soils with higher clay content than in lighter soils (R 2 = 0.77, P = 0.02). Our data suggest that annual bluegrass is more likely to emerge when the soil is wet during winter. The timing and location of annual bluegrass emergence may increase the probability of reproductive success during periods when seasonal rains and wet conditions limit tillage, weeding activities, and competition with other weeds.

The influence of mineral nutrition on the parasite-host relationship of witchweed (Striga lutea Lour.) and sorghum (Sorghum vulgare Pers. ‘Texas Bighead’) was investigated in greenhouse and growth chamber studies. Sorghum was grown in Eustis loamy sand, either infested or not infested with witchweed, and treated with one of three levels of mineral nutrients. Witchweed reduced host-shoot yields by about 70% at the low nutrient levels and by about 45% at the highest nutrient level. Witchweed produced seed at all nutrient levels, whereas the host produced seed at the highest level only. Increased nutrition also increased witchweed yields. Regardless of nutrient level, an early attack by witchweed was more destructive to the host than a late attack. Growth of witchweed in soil also was studied after the parasite was detached from the host or the host shoot was removed. When only the host shoot was removed, (a) witchweed growth was inhibited; (b) feeding of sucrose to witchweed did not restore parasite growth; (c) mineral nutrients were toxic to the parasite; and (d) high relative humidity around witchweed protected it from the nutrient toxicity. High relative humidity enhanced survival of the detached parasite but markedly inhibited growth of witchweed in the intact parasite-host relationship.

Inhibition of growth and photosynthesis in sugarbeet (Beta vulgaris L. var. ‘USH10’) treated with desmedipham [ethyl m-hydroxycarbanilate carbanilate (ester)] was most severe between 25 and 30 C and decreased with higher or lower temperatures. Transfer of sugarbeet plants grown at temperatures from 10 to 35 C to higher temperatures after treatment increased injury and photosynthetic inhibition. Higher temperatures prior to treatment reduced injury at all posttreatment temperatures. When the temperature was changed from 25 to 40 C, inhibition was most severe immediately after treatment. Two days after treatment this 15 C temperature change did not cause additional injury. High posttreatment light intensities caused greater inhibition of photosynthesis than low light intensities.

Enzymatically isolated leaf cells from cotton (Gossypium hirsutum L. ‘Stoneville’) and soybean (Glycine max (L) Merr. ‘Kino’) were used to study the effect of SAN 6706 [4-chloro-5-(dimethylamino)-2-(α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazinone] on photosynthesis, protein, RNA, and lipid synthesis during the first 19 hr of herbicidal treatment. Cotton plants are tolerant to SAN 6706, whereas soybean plants are susceptible. SAN 6706 inhibited the incorporation of 14C-bi-carbonate, uridine, and acetate into cotton leaf cells but stimulated incorporation of leucine. Incorporation of all of these precursors into soybean cells was inhibited. Cotton and soybean cells each took up equivalent amounts of labeled SAN 6706. The incorporation activity of the cotton and soybean cells appeared to regulate the entrance of the precursors into the cells by depleting the intracellular precursor pools. It is suggested that the inhibition of RNA and lipid synthesis in cotton and soybean cells is an indirect result of inhibited photosynthesis. Isolated cotton cells were not tolerant of the herbicide.

There was no antagonism between dalapon (2,2-dichloropropionic acid) or TCA (trichloroacetic acid) and BAS 9052 {2 - [1 -(ethoxyimino)butyl] - 5 - [2 -(ethylthio) -propyl] -3-hydroxy-2-cyclohexen-1-one} at 0.3 kg/ha for control of volunteer barley (Hordeum vulgare L. ‘Bonanza’) and wheat (Triticum aestivum L. ‘Neepawa’) in flax (Linum usitatissimum L. ‘Dufferin’). However, MCPA {[(4-chloro-o - tolyl)oxy] acetic acid} amine at 0.2 to 0.6 kg/ha had an antagonistic effect on BAS 9052, especially at 0.1 kg/ha, for control of wild oat (Avena fatua L.). BAS 9052 at 0.3 kg/ha overcame this antagonistic effect of MCPA. Field results confirmed that wild oat control with BAS 9052 at 0.3 kg/ha was not reduced by the mixtures with each of four broadleaf weed herbicides at 0.6 kg/ha. The mixtures gave excellent control of grass and broadleaf weeds. Flax seed yields were five times that of the unsprayed check and were equal to the yield of the handweeded treatment.

Reduced effectiveness of carbamothioate (thiocarbamate) herbicides in certain soils has been attributed to rapid herbicide degradation by soil microorganisms. Studies were conducted to determine if greater populations of EPTC (S-ethyl dipropyl carbamothioate)-degrading microorganisms were responsible for increased rates of degradation observed following repeated applications of EPTC to a Grenada silt loam soil. EPTC-degrading microorganism populations, measured with a 14C-MPN (most-probable-number) technique, were not larger in soils with accelerated rates of EPTC degradation, and degrader populations did not increase after application of 6 mg EPTC/kg of soil. Degrader populations increased after application of 60 mg EPTC/kg of soil only in soil previously treated for 6 yr with EPTC. Increased rates of metabolism of EPTC were apparently responsible for the increased rates of degradation, rather than increased populations of degraders.

Freshly harvested Florida pusley (Richardia scabra L.) seeds do not germinate in continuous dark, but do germinate if exposed to more than 2 hr of light each day. Increasing periods of illumination up to 16 hr per day increases the germination percentages. Scarification increases the rate of germination in the presence of light. Scarification also causes germination of seeds stored for 8 months or longer in total darkness. The seeds fail to germinate at constant temperatures of 15 C or less and at 40 C. Almost complete germination occurs at a constant temperature of 30 C, or at alternating temperatures of 20 and 30 C. The seeds germinate equally well in the pH range of 3 to 8. Increasing depths of planting reduces percent emergence, and none of the seedlings emerge from a depth of 1.5 cm or more. Air-dried seeds can be stored either at 5 or at 25 C without losing viability, at least up to a period of 1 year after harvest. Moist storage of seeds at 5 C reduces germinability.

The relative competitiveness of triazine-resistant (TR) and -susceptible (TS) common waterhemp, as a component of fitness, was assessed using TR and TS biotypes collected from the same field in Fillmore County, Nebraska. Competition between biotypes was evaluated under greenhouse conditions using a set of replacement series experiments with five ratios of TR:TS (1:0, 3:1, 1:1, 1:3, and 0:4) and four plant densities (50, 100, 150, and 300 plants m−2). No difference in final individual plant weight between TR and TS plants was observed in the absence of interbiotypic competition at all plant densities examined. Interbiotypic competition was indicated by ANOVA of plant weight and modified relative crowding coefficients (RCC) for plant weight, height, and volume. Replacement series diagrams showed TS plants were more competitive than TR plants, as measured by plant weight at densities of 50, 100, and 150 plants m−2. TS and TR plants were equally competitive at 300 plants m−2. Individual TS plant weight for 50, 100, and 150 plants m−2 was greatest at the 3:1 ratio (TR:TS) and decreased as the proportion of susceptible plants increased. Individual TR plant weight for 50, 100, and 150 plants m−2 was greatest at the 1:0 ratio and decreased as the TR proportion decreased. Lack of interbiotypic competition at 300 plants m−2 and decreasing TS plant weight with increasing ratios suggest intrabiotypic competition. RCC values for volume and height were calculated weekly during the experiment and indicated the competitive advantage of TS plants was constant from transplanting through harvest.

To simulate the effect of MSMA (monosodium methanearsonate) drift onto rice (Oryza sativa L. 'Starbonnet’ or ‘Labelle′), foliar applications at 0.20 to 0.78 kg/ha were made on rice at stages of maturity ranging from early tillering to panicle emergence. Foliage, sampled 1 to 2 weeks after application, and grain and grain parts harvested at maturity were analyzed by arsine generation atomic absorption spectrophotometry. Washed foliage contained 0.7 to 1.5 ppm background As, and 1 to 21 ppm As after MSMA application. The As content depended on application rate, stage of maturity at application, and the formulation of MSMA. Arsenic concentrations in grain increased exponentially as the time of application approached harvest, ranging from 0.25 to 7 ppm. There was little correlation between grain residues and rates, principally because dependence on the time of application was overriding. This study confirms previous observations that there is a specific stage in rice plant development, probably meiosis, during which rice is susceptible to sterilization by arsenic, and also indicates that significant yield reduction can occur from MSMA drift even when visual injury symptoms are not obvious.

Field studies were conducted in 1979 and 1980 to determine yield losses caused by perennial sowthistle (Sonchus arvensis L. # SONAR) in rapeseed (Brassica napus L., B. campestris L.) fields in Saskatchewan and Manitoba. The relationship between percentage yield loss and density of perennial sowthistle was expressed by the linear regression equation y = −3.81 + 13.76 rdx. Weed survey data indicated that perennial sowthistle occurred in 39% of the rapeseed fields but infested only 7% of the hectares surveyed. Using both the survey data and the yield loss equation, the average annual loss in rapeseed yield was estimated to be 9.4 million kg in Saskatchewan and 6.1 million kg in Manitoba, with a value of 2.6 million and 1.7 million dollars (Cdn.), respectively. Perennial sowthistle occurs with a similar frequency and density in other crops so that the total loss from this weed would be much greater.

The effect of herbicides applied to V3 soybeans on race 3 soybean cyst nematode (SCN) reproduction and glyceollin production in roots was measured. Soybeans were treated postemergence with 1 × and 2 × rates of herbicides plus adjuvants or with adjuvants alone, and SCN development was measured. Acifluorfen, bentazon, lactofen, crop oil concentrate (COC), and nonionic surfactant (NIS) applications reduced SCN egg population densities 50 to 60% compared with the untreated control 4 and 8 wk after application. The SCN reproduction on plants treated with fluazifop-P, sethoxydim, and imazethapyr was similar to the untreated control. Crop oil concentrate or NIS applications alone were as effective as acifluorfen, bentazon, or lactofen applications for reducing SCN reproduction. However, no additive effect of adjuvant-herbicide combinations was observed, nor did herbicide rate affect SCN reproduction. Treatments reduced SCN reproduction only when applied to soybeans and had no effect on SCN reproduction when applied directly to the soil. No treatment stimulated SCN reproduction relative to the untreated control. Soybeans treated with COC, NIS, acifluorfen, and bentazon also had more glyceollin detected than the untreated control. Herbicide-induced glyceollin production may have increased the resistance of soybean to SCN.

Growth of perennial sowthistle was examined under different levels of soil pH, soil moisture content, light intensity, and temperature. Soil pH ranging from 5.2 to 7.2 had little effect on the number of leaves, rosette diameter, plant height, and number of capitula. However, total dry weight was 30% less in plants grown in soil of pH 5.2 compared to those grown at higher soil pH levels. Perennial sowthistle demonstrated a consistent positive growth response to increasing soil water including saturation. Severe reduction in vegetative and reproductive growth occurred in plants grown in soil below field capacity. Plants grown under full light (1015 μE m−2 s−1 photosynthetic photon flux density) developed a fourfold increase in the number of capitula per plant and a 50% increase in total dry weight compared to plants grown at 285 μE m−2 s−1. Initiation of reproduction was delayed 4 weeks for plants grown at 580 μE m−2 s−1 and 285 μE m−2 s−1. Plants grown under less than full light developed fewer but larger leaves. Plants grown under a day/night temperature of 20/15 C grew more rapidly than those under 30/25 C or 10/5 C. Plants at 30/25 C began to senesce 7 to 8 weeks after planting. Net carbon assimilation, leaf conductance, transpiration, and water use efficiency decreased as soil moisture and light intensity decreased. Plants at 30/25 C had the highest rate of transpiration and the lowest water use efficiency. The observed optimum for perennial sowthistle growth occurred at a soil pH of 6.2 or 7.2, water-saturated soil, high light intensity, and a temperature of 20/15 C, day/night.

The phenolic content of purple nutsedge (Cyperus rotundus L.) and yellow nutsedge (Cyperus esculentus L.) was determined. The major phenolic components were p-coumaric, ferulic, p-hydroxybenzoic, syringic, vanillic, salicylic, proto-catechuic, and caffeic acids, and eugenol. High concentrations of eugenol and salicylic acid inhibited the sprouting of nutsedge tubers. The lack of activity at lower concentrations argues against a major role for these compounds in maintaining nutsedge tuber dormancy. Exogenous abscisic acid inhibited nutsedge tuber sprouting and may be a natural dormancy factor in nutsedge.

Laboratory studies were conducted in 2006 and 2007 to evaluate the effects of temperature and propanil on alligatorweed control with penoxsulam. Biomass reduction of alligatorweed at 42 d after treatment (DAT) compared to nontreated was greatest at 21/11 C (day/night) compared to 26/18 C or 30/25 C for all treatments. Propanil plus penoxsulam reduced biomass less than penoxsulam applied alone, independent of temperature. At 21 and 27 C, delaying propanil application 3 d after penoxsulam provided similar biomass reduction to penoxsulam applied alone. At 27 C and 30 C, delaying propanil application 10 d after treatment was required to achieve biomass reduction greater or equal to penoxsulam applied alone. Absorption and translocation of 14C penoxsulam indicated that propanil reduced absorption of penoxsulam into the treated leaf of alligatorweed 48 h after treatment. This research demonstrates the potential for propanil to antagonize penoxsulam when applied to alligatorweed. Under the most severe antagonistic conditions (30 C) propanil applications following penoxsulam needed to be delayed 10 d to avoid antagonism.

Experiments were conducted in 2002 and 2003 to determine the influence of soil thermal amplitude on common cocklebur emergence. Additionally, common cocklebur achenes were collected in fall of 2003 and of 2004 to assess changes in light and temperature requirements for germination over a 12-mo period under field conditions. Common cocklebur germination in response to the light environment and to constant and fluctuating temperatures were evaluated under controlled conditions following achene retrieval from the field. There was a linear inverse relationship between shade intensity and soil thermal amplitude, which explained 77% of the variability in emergence in the field over 2 yr. Emergence decreased as soil thermal amplitude declined, with 95% shading resulting in a 72 to 88% reduction in emergence. Neither red nor far-red light had much effect on germination, and burial did not induce a light requirement. Germination of achenes retrieved from the soil surface or buried in soil generally was not affected by red or far-red light, and the achenes did not acquire a red-light requirement following burial. Daily exposure to natural greenhouse light at 24 to 30 C was essential for germination immediately following achene maturation, whereas no germination occurred in darkness. A thermal fluctuation of 15 C increased germination percentages over those at constant temperatures regardless of time after maturation or retrieval-depth of achenes. The mean fluctuating temperature over all sample dates that was generally optimal for germination was 25 C (17.5/32.5 C low/high temperatures; 15 C daily fluctuation) in April or May and July or August in both years. Germination was generally optimum at constant temperatures of 35 or 40 C. The higher mean temperature requirement for germination at constant temperatures than at fluctuating temperatures likely contributes to reduced emergence in spring and summer months, when earlier emerging weed species or crops have already become established, and the thermal fluctuation requirement for germination reduces the likelihood of emergence in an environment where light availability is diminished.

Weed species or genera previously and currently targeted for biological control with phytophagous insects or phytopathogens in the United States (including Hawaii) and Canada are listed. The current status of and natural enemies involved in national, federal, state, and university biological control projects are reported.

Redroot pigweed (Amaranthus retroflexus L.) is a troublesome dicot weed species widely distributed across China. A population of A. retroflexus that survived the recommended label rate of thifensulfuron-methyl was collected from the main soybean [Glycine max (L.) Merr.] production area in China. Whole-plant dose–response assays indicated that the resistant (R) population was highly resistant (61.80-fold) to thifensulfuron-methyl compared with the susceptible (S1 and S2) populations. In vitro acetolactate synthase (ALS) activity experiments showed that the thifensulfuron-methyl I50 value for the R population was 40.17 times higher than that for the S1 population. A preliminary malathion treatment study indicated that the R population might have cytochrome P450–mediated metabolic resistance. The R population exhibited a high level of cross-resistance to representative ALS herbicides (imazethapyr, flumetsulam, and bispyribac-sodium) and multiple resistance to the commonly used protoporphyrinogen oxidase (PPO)-inhibiting herbicides lactofen and fomesafen. Two common mutations, Trp-574-Leu in ALS and Arg-128-Gly in PPO2, were identified within the R population. This study identified possible enhanced metabolism of thifensulfuron-methyl coexisting with target-site mutations in both ALS and PPO2 in a multiple-resistant A. retroflexus population.

Picloram uptake, translocation, and efficacy were studied using greenhouse-grown Russian knapweed plants. Uptake of 14C-picloram, applied as discrete droplets to adaxial leaf surfaces of well-watered plants, averaged less than 10% of that applied. Most uptake occurred within 30 min of application. Uptake increased linearly with external picloram concentrations from 6.2 to 74.5 mM and was proportional to picloram concentration. Only about 10% of absorbed picloram was translocated out of the treated leaf of well-watered plants within 96 h, with approximately equal acropetal and basipetal translocation. Water stress before, at the time of, and after picloram application did not affect picloram uptake, but reduced total translocation and increased the relative amount translocated basipetally. Water stress also reduced picloram efficacy. Although Silwett L-77 increased picloram uptake into Russian knapweed leaves, it did not increase efficacy under water stress conditions.