Losses due to weeds in the United States and the cost of their control are now more than $20 billion annually (35). Of this total, $13 billion represents a 10% annual loss in agricultural production that includes not only the direct competition of weeds to reduce crop yields but also the reduced quality of produce, livestock losses, and increased cost of fertilizer, irrigation, harvesting, grain drying, transportation, and storage. In addition, farmers spend more than $7.2 billion to control weeds each year. About 43% of the expenditures to control weeds is the retail cost of herbicides, $3.1 billion, in 1980 (15). The value of herbicides sold in 1984 will probably be about 15% higher than in 1980. An additional $4.1 billion represents the cost of tillage and hand labor required for weed control (35). The total loss of over $20 billion represents an indirect annual weed tax of about $85 on each individual living in the United States.

Results from identical experiments conducted at Headland, AL, and Plains, GA, from 1980 through 1982 show insecticide treatment had little effect on soybean [Glycine max (L.) Merr. ‘Coker 237′] growth and morphology. Maximum insecticide applications increased soybean seed weight in two of five trials. Soybeans maintained free of sicklepod (Cassia obtusifolia L. ♯3 CASOB) for 4 weeks after emergence produced yields equal to those receiving season-long control in all trials, and 2-week control was equal to season-long maintenance in three trials. Length of weed interference-free maintenance did not affect soybean height. The number of pods per plant and seed weight were decreased when there was no control. Sicklepod shoot fresh weight and numbers decreased as the weed-free period increased from 0 weeks through the season. Row spacing had no effect on soybean height or seed size; however, the number of pods per plant was higher in 80- than in 40-cm rows. Row spacing influenced yield in only one trial where 20-cm rows outyielded 40-cm rows. A significant interaction occurred between the weed-free period and row spacing in two trials. Soybeans in 20-cm rows outyielded those in 40- and 80-cm rows when sicklepod was not controlled (i.e., 0 weeks interference-free maintenance).

Three wash techniques, each with 1, 10, or 95% (v/v) ethanol:water were used to measure foliar absorption of 14C-glyphosate [N-(phosphonomethyl)glycine], 14C-3,6-dichloropicolinic acid, and 14C-chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} in Tartary buckwheat [Fagopyrum tataricum (L.) Gaertn. ♯3 FAGTA], Canada thistle [Cirsium arvense (L.) Scop. ♯ CIRAR], and barley (Hordeum vulgare L. ‘Galt’). For the herbicides and species tested, the most suitable common procedure for determining absorption consisted of a double or triple rinse with or immersion in 10% ethanol. Wiping the treated leaves with cotton balls moistened with the solvent was much less effective. Efficiency of herbicide removal by a given solvent was not related consistently to solubility of the herbicide in the solvent.

Laboratory studies were conducted to evaluate the degradation of butylate (S-ethyl diisobutylthiocarbamate), EPTC (S-ethyl dipropylthiocarbamate), cycloate (S-ethyl N-ethylthiocyclohexanecarbamate), and vernolate (S-propyldipropylthiocarbamate) in soil with prior thiocarbamate herbicide exposure. EPTC degradation was accelerated in soil which had previously been treated with butylate, vernolate, or EPTC in 1979, 1980, and 1981. The evolution rate of 14CO2 from 14C-labeled vernolate was increased in soil which had previously been treated with vernolate or EPTC in 1979, 1980, and 1981. Cycloate degradation was not enhanced in soil with prior exposure to butylate, EPTC, or vernolate. Butylate breakdown was enhanced to the greatest extent in soil with previous exposure to butylate.

In velvetleaf (Abutilon theophrasti Medic. ♯3 ABUTH), accelerated leaf abscission was a conspicuous response following foliar chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} treatment at 35 g ai/ha. Leaf abscission of treated plants was decreased by AVG [L-2-amino-4-(2-aminoethoxy)-trans-3-butenoic acid], an inhibitor of endogenous ethylene production. Chlorsulfuron stimulated ethylene production in the abscission zone and leaves of treated plants and also increased cellulase activity in the abscission zone. Accelerated leaf abscission of velvetleaf following chlorsulfuron application appears to result from chlorsulfuron-induced increases in endogenous ethylene production and cellulase activity.

Field experiments to compare the loss of oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) from straw-mulched and nonmulched soils indicated that oryzalin disappeared more rapidly in soils covered by straw in 1980 and 1981 but not in 1982. It appeared that greater rainfall in 1982 was responsible for this difference. Straw mulch on the soil at the time of application reduced the amount of oryzalin reaching the soil surface after subsequent rains or irrigation. Straw levels of 2250 or 4500 kg/ha, when present at the time of treatment, reduced oryzalin concentration in the soil by approximately 15 or 43%, respectively, following 1.3 cm of water applied by sprinkle irrigation. Increasing the straw levels above 4500 kg/ha did not significantly affect the amount of oryzalin detected in the soil beneath the straw mulch.

Solar heating (SH) of wet soil by mulching it with transparent polyethylene (PE) during the hot season increased soil temperature in a typical daily course which varied with soil depth. Annual weed species responded to soil heating in the laboratory with the same pattern as under SH conditions in the field. Rhizomes of bermudagrass (Cynodon dactylon L. Pers. ♯3 CYNDA) and johnsongrass (Sorghum halepense L. Pers. ♯ SORHA) were very sensitive to heat treatment, but purple nutsedge (Cyperus rotundus L. ♯ CYPRO) tubers were able to survive temperatures as high as 80 C for 30 min. Species having big and heavy seeds or vegetative propagules were able to emerge from deep layers of soil, thus practically escaping the lethal temperature prevailing in the upper layer. Transparent and black PE mulching effectively prevented water loss from soil, as compared with perforated PE and nonmulched control. CO2 concentration in the soil atmosphere under transparent PE mulching increased rapidly during the first week and reached a maximal level which was 20-fold higher than that formed in nonmulched soil. Ethylene at 0.2 ppm was detected only in a mulched soil environment. No differences in levels of CH4 or CO were detected.

Adsorption and desorption of 14C-methazole [2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione] were characterized on two silt loam soils (Dundee and Palouse; 0.7 and 3.0% organic matter, respectively) using the batch equilibration technique. Freundlich adsorption isotherm coefficients (Kf and l/n) were calculated after equilibration of methazole solutions (initial concentrations = 0.11 to 4.10 nmol/ml) with soil for various times. After a rapid attainment of an apparent equilibrium, 14C- concentration in solution for the Palouse soil decreased at a low rate. The greater adsorption (Kf) on the Palouse soil, for a given equilibration period, was attributed to the greater organic matter content. The continued trend of increase in apparent Kf with time was due to degradation of methazole in solution to 3-(3,4-dichlorophenyl)-1-methylurea (DCPMU), which was highly adsorbed, rather than to increased adsorption of the parent compound. The calculated adsorption coefficients expressed in terms of soil organic carbon would classify methazole and DCPMU as immobile in Palouse soil and methazole as slightly mobile in Dundee soil. Calculated desorption isotherms, which exhibited a hysteretic effect, were also dependent on the rate of methazole degradation. The adsorption, desorption, and degradation data indicate that methazole would not leach readily in most soils.

Norflurazon [4-chloro-5-(methylamino)-2-(α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazinone] decreased the total chlorophyll content and the chlorophyll a/b ratio of nine plant species. Grain sorghum [Sorghum bicolor (L.) Moench.], wheat (Triticum aestivum L.), and sicklepod (Cassia obtusifolia L. ♯3 CASOB) were the most susceptible plants, and cotton (Gossypium hirsutum L.) was the most tolerant. The soil properties most closely correlated with norflurazon activity were organic matter content and clay component, not clay content. A high treatment rate was necessary for effective control of plant growth in soil high in organic matter content and high in montmorillonite or vermiculite. Approximately twice as much norflurazon was required to reduce chlorophyll content 50% when applied to the soil preplant incorporated as was required when applied preemergence.