Field plot experiments were conducted to examine the interactions between tall fescue grass (Festuca arundinacea Schreb.), musk thistle (Carduus nutans L. = thoermeri Weinmann # CRUNU), and two thistle weevils Trichosirocalus horridus (Panzer) and Rhinocyllus conicus Froelich. Restriction of musk thistle growth was greatest when the weevils were allowed to feed on the musk thistles competing with tall fescue. Significant reductions were found in total musk thistle seeds per plant, root weight, flower buds per plant, stem dry weight, seeds per head, root crown diameter, stem height, rosette diameter, and head diameter. Seed weight and viability were not reduced. Of the three stress factors (tall fescue and the two Carduus thistle weevils), tall fescue had the greatest impact. When musk thistle seeds were planted in 1-yr-old tall fescue, germination was low. Seeds that germinated did not grow more than four Leaves and none of the thistles developed to the reproductive stage. A 1-year-old tall fescue stand effectively prevented musk thistle reproduction. Thus, tall fescue helped suppress musk thistle growth more quickly than the use of Carduus thistle weevils alone without competitive vegetation. Dry weight of tall fescue grass was lower in musk thistle-infested plots than in the thistle-free plots.

Metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one], when applied pretransplant at 0.28 kg ai/ha, killed peppers (Capsicum annuum L.) that were transplanted bare root or in plugs. Activated carbon applied at 1 g/plant effectively reduced injury of such peppers in soils treated with up to 0.56 kg ai/ha metribuzin. The increase in crop tolerance to metribuzin was dependent on the amount of activated carbon added. The level of crop protection for plug transplants depended on the amount of activated carbon per plant rather than on the percentage in the greenhouse mix by dry weight. One gram was required to protect plug transplants grown in cells that held 10 or 20 g of greenhouse mix.

Benzyl isothiocyanate (BITC) was formulated in dry granules with tung oil and calcareous loess to facilitate safe handling of the water-sensitive lachrymator. Crop and weed seeds were exposed to granular BITC at 40 mg ai/kg (w/w) substrate on moist sand for 2 days. When the pretreated seeds were washed with water and placed on BITC-free sand in a germination chamber for 15 days, germination in comparison to untreated seeds was 0 to 8% for pitted morningglory (Ipomoea lacunosa L. # IPOLA), sicklepod (Cassia obtusifolia L. # CASOB), milo [Sorghum bicolor (L.) Moench. ‘Funks G-522DR’], and red rice (Oryza sativa L. # ORYSA) seeds; 15 or 16% for velvetleaf (Abutilon theophrasti Medic. # ABUTH) and johnsongrass [Sorghum halepense (L.) Pers. # SORHA]; and 39% for barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG]. Subjecting milo seeds to moist sand medium that contained BITC granules at 10, 20, and 40 mg ai/kg substrate reduced germination of milo by 78, 97, and 100%, respectively. However, BITC granules applied to the growth medium 2 to 4 days prior to sowing seeds had little effect on germination and growth of milo or sicklepod. Thus, BITC-treated soil soon became safe for newly sown seeds, but seeds present in soil when the toxin granules were applied failed to recover from exposure to BITC and deteriorated within 15 days.

Sugarcane (Saccharum officinarum L.) was planted in the fall; the seed cane was healthy or infected either with sugarcane mosaic virus (strain H) or with ratoon stunting disease (RSD) (Clavibacter xyli). Herbicide treatments were applied the following spring and each subsequent spring during the 3-yr crop cycle. Hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione] at 1.1 kg ai/ha was applied as a soil foliage treatment when sugarcane was about 30 cm tall. The methyl ester of diclofop {(±)-2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} at 1.1 kg ai/ha and the sodium salt of asulam {methyl [(4-aminophenyl)sulfonyl] carbamate} at 3.4 or 3.8 kg ai/ha were applied as foliage treatments when sugarcane was about 90 cm tall. Both mosaic and RSD reduced yield of sugar/ha by 16% for the 3-yr crop, primarily by causing a decrease in stalk population. Hexazinone reduced yield of sugar/ha by 24% primarily by causing a decrease in both stalk population and sugar content of stalks. Diclofop reduced yield by 7% and asulam caused no significant yield loss. Combinations of disease and herbicide treatment reduced yields in an additive manner, with the combination of hexazinone and either mosaic or RSD causing a 38% reduction.

Grass and broadleaf weed densities and seed numbers, weed control practices, and grain yields were included in a bioeconomic model that evaluates alternative weed management strategies for continuous corn (Zea mays L.). Weed seed numbers in soil and herbicide carry-over provided intertemporal links. Four weed management strategies – two fixed, one mixed, and one flexible – were evaluated with annualized net returns as the performance indicator. The flexible strategy (weed control based on observed conditions) had the largest annualized net return for high and low initial weed seed numbers. The fixed weed management strategy (weed control predetermined) of an annual application of only a preemergence herbicide ranked second in terms of annualized net returns for high weed seed numbers. The mixed weed management strategy of alternative year applications of preemergence herbicide and “as needed” applications of postemergence herbicide ranked second for low initial weed seed numbers. The fixed weed management strategy of alternate year application of preemergence herbicide only generated the lowest annualized net return, regardless of initial weed seed numbers.

The effects of twelve soil metabolites of trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] on soybean [Glycine max (L.) Merr.] growth, yield, and seed oil and protein content were determined. The metabolites included oxidative dealkylated, reduced nitro group, benzimidazole, azoxy, azo, oxidized, and hydroxylated derivatives of trifluralin. When applied at 0.22 kg ai/ha and incorporated 7.5 cm deep, no individual metabolite had a significant adverse effect on growth or yield. Three of the metabolites significantly decreased seed oil content and two of the metabolites significantly increased seed protein content. These effects are not considered important in that the differences, while statistically significant, are very small. Also, the amounts of metabolites applied greatly exceeded those expected to be found after many years of continuous use of trifluralin. Potential accumulation of individual metabolites from long-term use of trifluralin does not appear to adversely affect soybean growth, yield, or quality.

Field experiments were conducted during 1980, 1981, and 1982 to evaluate the effect of tillage and sicklepod density on sicklepod (Cassia obtusifolia L. # CASOB) interference with soybeans [Glycine max (L.) Merr.] and soil water use. In the absence of sicklepod, soybean yields were similar in nontilled plots covered with a straw mulch and in conventionally tilled plots with no mulch in all years. In the presence of sicklepod, higher soybean yields were obtained with the non-tilled-mulched plots than with the tilled plots at corresponding sicklepod densities and sicklepod fresh weights. Early soil water loss was greater in the tilled plots with increasing sicklepod density causing lower soil water content in both tillage treatments. Soil water depletion was greater in the no-till treatments during the soybean pod-filling stage.

Field experiments were conducted in 1982 and 1983 in cotton (Gossypium hirsutum L.) to evaluate alternatives in grass weed management programs with the use of postemergence herbicides and to assess the economic potential for incorporating the new over-the-top grass weed herbicides into total cotton production practices. Twelve weed management systems using the grass herbicides sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} and fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy]propanoic acid} were compared to six standard systems. Differences in cotton production costs among the 18 systems were due to cost differences in total weed management. Equal or greater net return values were obtained when over-the-top herbicides followed fluometuron {N,N-dimethyl-N′-[3-(trifluoromethyl)phenyl)urea} preemergence or when these materials were applied twice compared to the over-the-top materials used in conjunction with trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] preplant incorporated or with directed postemergence materials. High net returns were the result of both high seed cotton yields and low total production costs.

The influence of soil pH on the uptake, degradation, and movement of chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} in soil was examined. Phytotoxicity decreased as pH increased in a silty clay loam with an adjusted pH range of 5.9 to 7.5. Fresh weights of sorghum [Sorghum bicolor (L.) Moench. ‘Funks G-499 GBR’] shoots grown in soil at pH 7.5 and containing 0.8 or 1.6 ppbw chlorsulfuron were not different from the controls while large differences occurred at pH 5.9. Uptake of 14C-chlorsulfuron by wheat (Triticum aestivum L. ‘Centurk’) in a silty clay loam with a pH of 5.9 was 67 to 100% greater than at pH 7.5. Soil pH strongly influenced the degradation rate of chlorsulfuron in a laboratory incubation study. Chlorsulfuron half-life in a silty clay loam was 1.9 weeks at pH 5.6 and 10 weeks at pH 7.5. Soil thin-layer chromatography indicated a high leaching potential for chlorsulfuron, and mobility increased as soil pH was increased.

The dissociation constant for chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} in aqueous solution measured by spectrophotometric titration is 3.58 ± 0.05. Chlorsulfuron was more strongly adsorbed on IRA-400-Cl strong anion exchange resin than on IR-4B-OH weak anion exchange resin or Al2O3 anionotropic adsorbent. Hydrogen bonding was probably responsible for the adsorption observed on IR-120-Na(H) cation exchange resin. No chlorsulfuron was adsorbed on Al2O3 cationotropic absorbent, technical montmorillonite, illite, or kaolinite. Adsorption did occur on organic matter derived from a histosol. Chlorsulfuron was strongly adsorbed on activated charcoal but had little affinity for α-cellulose. Adsorption onto hydrophobic polymeric XAD-2 adsorbent at pH 5.2 was not significant for chlorsulfuron concentrations below 30 μM. No significant adsorption occurred on a variety of mineral soils low in organic matter. Adsorption on a Sharpsburg silty clay loam was inversely related to solution pH. Hydrogen bonding and charge transfer bonds were postulated as the major mechanisms responsible for chlorsulfuron adsorption in soil.

Forage quality was determined at vegetative, flowering, and fruiting stages for nine cool-season weed species and four cultivated forages. When compared at the vegetative stage of maturity, Carolina geranium (Geranium carolinianum L. # GERCA), Virginia pepperweed (Lepidium virginicum L. # LEPVI), Virginia wildrye (Elymus virginicus L. # ELYVI), wild oats (Avena fatua L. # AVEFA), cheat (Bromus secalinus L. # BROSE), and little barley (Hordeum pusillum Nutt. # HORPU) had high nutritive quality as indicated by in vitro dry-matter digestibility (IVDMD) values equal or superior to rye (Secale cereale L.), tall fescue (Festuca arundinacea Schreb.), and ladino clover (Trifolium repens L.). Cutleaf evening primrose (Oenothera laciniata Hill # OEOLA) and curly dock (Rumex crispus L. # RUMCR) had lower IVDMD values than the cultivated forages and all weed species except wild oats. However, the rate of decline in IVDMD as plants matured was generally greater for the weed species compared to cultivated forage plants. All weed and cultivated forage species had adequate levels of Ca and K for livestock. Nearly all weed and cultivated forage species had suboptimum levels of P for high-producing ruminant animals; Carolina geranium and cutleaf evening primrose had high Ca:P ratios, which can cause metabolic disorders. Carolina geranium, Virginia wildrye, wild oats, cheat, little barley, and all the cultivated forage species had inadequate levels of Mg and could be considered “tetany prone”. Most of the forbs had high Mg concentrations.

All of us expect good food in adequate quantities. The question is how to reach this aim in the near future with an increasing world population (Table 1). A comparison of past figures with those forecast for the coming years tells us that in the near future the rate of population growth will greatly outpace the available arable land. Dietary energy requirements will increase. Consumption of grain crops will increase although on a smaller scale than in the past. The need for protein products will also continue to soar.

In bioassays, rice (Oryza sativa L.) recovery from metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] injury tended to be slower in flooded rice, but was not significantly different from the recovery rate in a nonflooded rice. In soils treated with 1 ppm (w/w) metolachlor and incubated in constant-temperature chambers, the half-life of metolachlor was shorter at 40 C than at 30 C. The degradation rate of metolachlor was not significantly correlated with declining moisture potentials in the range of −30 to −80 kPa. The CO2 evolution from metolachlor-treated soil was negatively correlated with incubation time and positively correlated to declining moisture levels. In a field study, metolachlor, as determined by bioassay, was mobile in a Taloka silt loam soil profile. After being incorporated to 7.5 cm, it became evenly distributed in the top 15 cm of the soil profile within 18 days. Metolachlor adsorption was positively correlated with clay and organic carbon content.