Cacodylic acid (hydroxydimethylarsine oxide) was more phytotoxic than monsodium methanearsonate (MSMA), sodium arsenate, or sodium arsenite when foliarly-applied. MSMA was much more effective on dicotyledonous than on monocotyledonous species. Sodium arsenite and arsenate had little effect on grasses. A comparative study of absorption, transport, and metabolism in beans (Phaseolus vulgaris L. ‘Black Valentine’) revealed that cacodylic acid and MSMA were transported about equally from the leaves to the terminal bud and expanding leaves whereas negligible amounts of sodium arsenite and arsenate were translocated. The latter two compounds caused more rapid contact injury to the treated leaves than either organic arsenical. There was no indication that cacodylic acid or MSMA was demethylated to form inorganic arsenicals or reduced to trivalent arsenic compounds. Studies with 14C-MSMA indicated that about 40% of the 14C and arsenic recovered was bound rapidly to another molecule to form a ninhydrin-positive complex. In small amounts, arsenate combined with some component of plant tissues. Also, arsenite probably was oxidized to arsenate. In beans, root-applied sodium arsenite was more phytotoxic than sodium arsenate and both were much more phytotoxic than cacodylic acid and MSMA. Most differences in phytotoxicity could not be explained by differences in rates of absorption by bean roots. Arsenite caused considerable contact injury to the root system, probably accounting for its relatively great phytotoxicity. Both cacodylic acid and MSMA were more phytotoxic per mole of tissue arsenic when foliarly-applied than when root-applied.

The use of 1,8-naphthalic anhydride, at 0.5% by corn (Zea mays L. ‘501D’) seed weight, eliminated most of the corn yield loss caused by S-ethyl dipropylthiocarbamate (EPTC) at 3.4, 6.7, or 10.0 kg/ha. The seed protectant partially reduced the moderate corn yield loss from S-ethyl diisobutylthiocarbamate (butylate) at 9.0 kg/ha. This seed protectant provides a new approach to increased weed control while maintaining selectivity in the production of corn.

Representative species of six genera of marine unicellular algae (Chlorococcum sp., Dicrateria inornata Parke, Dunaliella tertiolecta Butcher, Nannochloris sp., Isochrysis galbana Parke, and Monochrysis lutheri Droop) were treated in unialgal culture with 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), 1-butyl-3-(3,4-dichlorophenyl)-1-methylurea (neburon), 3-(p-chlorophenyl)-1,1-dimethylurea (monuron), and 1,1-dimethyl-3-phenylurea (fenuron). Tests were conducted at salinities of 5, 10, 20, and 30 parts per thousand (ppt). The herbicides depressed concentration of carbohydrate in all species. Dunaliella tertiolecta was most resistant; its carbohydrate content decreased 9.2% at 5 ppt salinity and 17.9% at 30 ppt. Chlorococcum was most susceptible; its carbohydrate content decreased 49.1% at 5 ppt and 65.6% at 30 ppt salinity.

The phytotoxicity of 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron) to corn (Zea mays L.) and soybean (Glycine max (L.) Merr.) seedlings and 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) to soybean seedlings increased with increasing temperature from 20 to 30 C. The phytotoxicity of α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) did not change significantly between 20 and 30 C. Corn and soybean plants grown at 30 C translocated more 14C from 14C-atrazine and soybeans more 14C from 14C-linuron to the shoots during the 4-hr root uptake treatment period than plants grown at 20 C. There was less accumulation of 14C from 14C-atrazine in soybean roots and 14C-linuron and 14C-trifluralin in the roots of corn and soybean plants grown at 30 C compared to those grown at 20 C. Comparison of data at 30 C and 20 C during the 4-hr root uptake treatment period showed enhanced root to shoot movement of 14C from 14C-atrazine in corn and from 14C-linuron in soybean at the higher uptake treatment temperature indicating a possible relationship between increased herbicide transport to the shoot at high temperature and increased phytotoxicity.

Cotton (Gossypium hirsutum L.) was grown at two locations in Alabama during 1966 to 1969 with specific densities of sicklepod (Cassia obtusifolia L.) and tall morningglory (Ipomoea purpurea L. Roth). Competition from sicklepod and tall morningglory caused cotton yield reductions at densities as low as eight weeds per 7.31 m of row. Tall morningglory was usually more competitive than sicklepod in cotton. Both species were more competitive on Lucedale sandy clay loam than on Norfolk sandy loam. Sicklepod at eight weeds per 7.31 m of row reduced yields from 10 to 23% on the Norfolk soil and approximately 40% on the Lucedale soil. At the highest density, 48 sicklepod plants per 7.31 m of row, yields were reduced 45 to 65% on the Norfolk soil and approximately 80% on the Lucedale soil. Tall morningglory at a density of eight weeds per 7.31 m of row reduced cotton yields 10 to 40% on the Norfolk soil and 50 to 75% on the Lucedale soil. Vegetative growth, boll, and seed size were not affected as much as cotton yields by competition. Percentage lint and lint fiber properties were unaffected by competition.

Competitive effects of cocklebur (Xanthium pensylvanicum Wallr.) and redroot pigweed (Amaranthus retroflexus L.) on cotton (Gossypium hirsutum L.) were evaluated in four experiments at two locations in Alabama during the period 1966 to 1968. Cocklebur was more competitive with cotton than was pigweed on Norfolk sandy loam soil. A density of eight cocklebur plants per 7.31 m of row reduced cotton yields 20 to 40%. Higher densities of cocklebur resulted in greater yield reductions. Forty-eight cocklebur plants per 7.31 m of row caused cotton yields to be reduced more than 80%. Pigweed at a density of 48 weeds per 7.31 m of row reduced cotton yields less than 50% on the Norfolk soil. On Lucedale sandy clay loam, cocklebur and pigweed were equally competitive and both species were more competitive than on Norfolk soil. A density of eight cocklebur or pigweed plants per 7.31 m of row resulted in 60 to 70% cotton yield reductions. The highest density of pigweed studied, 48 plants per 7.31 m of row, reduced cotton yields 90% on the Lucedale soil. Vegetative growth, boll, and seed size were not affected as much as cotton yields by either weed species. Percentage lint and fiber properties were unaffected by plant competition.

A soil sampler was constructed for moisture and pesticide residue determinations that will retrieve soils with rocky and heavy clay layers. The sampler consisted of a commercially constructed worm-gear driven auger mounted in a 3.7-m-tall vertical frame. Depth, speed, accuracy, and ease of sample retrieval were substantially increased, compared to manual sampling.

Night applications of phenoxy herbicides on plains pricklypear (Opuntia polyacantha Haw.) resulted in more plants being killed than comparable day applications. Night applications gave rapid herbicidal responses that were negated by the second year if chemical concentrations were too high. With low herbicide concentrations (½ and 1 lb aehg) effectiveness increased with proportion of diesel oil in carrier. The ester forms of 2-(2,4,5-trichlorophenoxy)propionic acid (silvex) killed more plants than did the ester or amine forms of (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) in diesel oil:water (1:4, v/v) carriers.

The effect of temperature and soil moisture content on the toxicity of soil-applied 5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone (pyrazon) to sugar beets (Beta vulgaris L. ‘U.S. H-8’) was studied under controlled environmental conditions. High temperatures during or after germination increased the susceptibility of sugar beets to pyrazon while variations in soil moisture content did not have a significant effect. Sugar beet seeds absorbed three times more pyrazon at 35 C than at 18.3 C. During imbibition more than 90% of the pyrazon taken up by sugar beet fruits was concentrated in the pericarps surrounding the seeds. Furthermore, the herbicide which had been accumulated in the pericarp during imbibition did not move into the tissues of the developing seedling during or after germination. Comparative studies showed that there was a lag period in absorption of pyrazon by sugar beet seeds enclosed within their pericarps. This lag period did not occur in sugar beet seeds from which the pericarps had been removed, or in seeds of common lambsquarters (Chenopodium album L.). It is concluded, therefore, that the pericarp contributes to a physical mechanism of selectivity which enables sugar beets to avoid great accumulation of pyrazon when the mechanism of biochemical inactivation of the herbicide is not yet operative.

The phytotoxicity of 1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea (fluometuron) and three of its analogs was studied on cotton (Gossypium hirsutum L.), foxtail (Setaria sp.), and redroot pigweed (Amaranthus retroflexus L.). Fluometuron was the most active compound, and the demethylated derivative and aniline analog were the least phytotoxic. The activity of the monomethyl analog of fluometuron, when applied via nutrient solution and to clay soil, was about 50% and 70% of the parent compound, respectively. Photosynthesis in cotton and redroot pigweed was inhibited by fluometuron, to a lesser degree by the monomethyl analog, and not at all by the demethyl and aniline analogs. Cotton was most tolerant, and only slight differences were found between the susceptibility of foxtail and redroot pigweed. These differences in response to fluometuron and its metabolites may contribute to the differential response between cotton and weeds.

The activity of α-amylase in barley (Hordeum vulgare L. ‘Wong’) half-seeds, induced by exogenous gibberellic acid (GA), was almost completely inhibited by 5 × 10−4M commercial formulations of (2,3,6-trichlorophenyl)acetic acid (fenac), 3,5-dibromo-4-hydroxybenzonitrile (bromoxynil), and 7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylic acid (endothall). At the same concentration, 1,1′-dimethyl-4,4′-bipyridinium ion (paraquat) caused severe inhibition (72%); 2,2-dichloropropionic acid (dalapon) was intermediate (42%); and α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin), 2-(4-chloro-6-ethylamino-s-triazin-2-ylamino)-2-methylpropionitrile (SD 15418), and 2% solvent dimethylsulfoxide (DMSO) were only slightly inhibitory to GA-induced α-amylase production.

The uptake, translocation, and fate of 14C-labeled 3,6-dichloro-o-anisic acid (14C-dicamba) were studied in wheat (Triticum aestivum L., 'Selkirk’) and wild buckwheat (Polygonum convolvulus L.) as resistant and susceptible species, respectively. Selectivity could not be explained by interspecific differences in uptake of 14C-dicamba by leaf sections submerged in exogenous solutions. 14C-dicamba accumulated in meristems of wild buckwheat but not in the youngest tillers of wheat. Moreover, wheat main culms conjugated or metabolized 14C-dicamba more quickly than did wild buckwheat meristems. Therefore, selectivity of dicamba apparently was related to interspecific differences in translocation and metabolism.

Nonradioactive and 14C-labeled arsenical herbicides were applied to foliage of purple nutsedge (Cyperus rotundus L.) and yellow nutsedge (Cyperus esculentus L.) grown under greenhouse and growth chamber conditions. Disodium methanearsonate (DSMA) controlled purple nutsedge better at 20 and 29 C than at 13 C. Monosodium methanearsonate (MSMA) was as effective in controlling this weed at 13 C as at 20 and 29 C. DSMA and MSMA provided 80% or greater control of yellow nutsedge grown at the three temperatures. When plants were treated with 14C-DSMA and 14C-MSMA, greater radioactivity was detected in yellow nutsedge than in purple nutsedge. The apparent differential herbicide penetration of purple and yellow nutsedge leaves is believed to have contributed substantially to the control of nutsedge observed in this study.