The susceptibility of sweet pepper (Capsicum annuum L. ‘Keystone Resistant Giant’) and tolerance of hot pepper (Capsicum chinense L. ‘Bohemian Chili’) to bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] was demonstrated under greenhouse and field conditions. Sweet pepper growth and fruit production were inhibited by foliar applications of bentazon at rates of 0.6 to 6.7 kg ai/ha. Severity of injury increased with application rate. Injury symptoms in sweet pepper were leaf chlorosis, with necrosis and death of shoot apices. Foliar applications of bentazon to hot pepper resulted in little or no injury. Bentazon inhibited Hill reaction activity of isolated chloroplasts from both species to a similar extent, suggesting that selectivity of this compound in hot pepper is not due to resistance at the chloroplast level.

The influence of metribuzin [4-ammo-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] on net photosynthesis of goosegrass [Eleusine indica (L.) Gaertn. ♯3 ELEIN] and six cultivars of bermudagrass [Cynodon dactylon (L.) Pers. ♯ CYNDA cvs. ‘Common’, ‘Tufcote’, ‘Vamont’, and ‘Midiron’, Cynodon transvaalensis Davy., and Cynodon dactylon X Cynodon transvaalensis ‘Tifway’] was evaluated. Metribuzin rapidly inhibited carbon dioxide (CO2) uptake within 1 h after application in both goosegeass and bermudagrasses. Very often, net photosynthesis was completely inhibited. Net photosynthesis in goosegrass was inhibited by lower rates of metribuzin than those required for similar reduction in bermudagrasses. Common, Tufcote, Tifway, and C. transvaalensis bermudagrasses were less sensitive to metribuzin than Midiron and Vamont based upon the degree of inhibition of net photosynthesis, the rate of its recovery, and the level of foliar injury. Recovery from inhibition of net photosynthesis was observed in both species 24 h after treatment with low metribuzin rates. High rates caused several days lag period before net photosynthesis resumed. After 10 days, 95% of the goosegrass foliage was injured (either chlorosis or necrosis) from 2 kg ai/ha metribuzin treatment. The threshold concentration for inducing leaf injury in bermudagrasses was 1 kg ai/ha. Inhibition of photosynthesis was initially rapid in both grasses; however, recovery was evident earlier and there was less foliar injury in bermudagrasses than in goosegrass. Selective control of goosegrass in bermudagrass may therefore be partially dependent upon rapid metabolism and/or inactivation of metribuzin in the bermudagrass.

The effect of exposing tame oat (Avena sativa L. ‘Hudson’) to trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) and triallate [S-(2,3,3-trichloroallyl) diisopropylthiocarbamate] during seed imbibition was investigated in a growth cabinet at 21 C in the absence of light. Caryopses were imbibed in 0.0, 1.5, and 3.0 ppmv aqueous dilutions of trifluralin and triallate for up to 10 h, after which germination was continued in distilled water. Germination was not affected following imbibition in either herbicide. Both herbicides produced distinct visual symptoms of herbicide injury during subsequent seedling growth. Coleoptile length of 5-day-old seedlings was reduced following imbibition in a 1.5-ppmv dilution of either herbicide. Triallate at 1.5 ppmv resulted in a reduction in shoot dry weight. Both herbicides were largely excluded from embryos of imbibing caryopses. Seedlings were unaffected when cultured from embryos excised from caryopses imbibed in trifluralin and triallate dilutions. Seedling phytotoxic effects resulted from residual activity of trifluralin and triallate retained by the pericarp and testa of imbibed caryopses. Presence of the hull during imbibition decreased the phytotoxic effect of both herbicides on shoot growth. These findings suggest that germinating seedlings of Avena spp. may be affected by trifluralin and triallate at an earlier stage than previously realized.

Similar uptake and translocation patterns were observed in sweet pepper (Capsicum annuum L. ‘Keystone Resistant Giant’) and hot pepper (Capsicum chinense L. ‘Bohemian Chili’) following foliar applications of 14C-bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide]. In both species, most of the 14C absorbed remained in the treated leaves, with minimal acropetal and basipetal translocation from the application site. A significantly faster rate of herbicide metabolism occurred in hot pepper at 1 and 4 days after application compared to sweet pepper. Two unidentified metabolites of bentazon were isolated from methanol extracts of the two species.

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.

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.

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.