The effect of 3,6-dichloro-o-anisic acid (dicamba) was studied on wild buckwheat (Polygonum convolvulus L.) and wheat (Triticum aestivum L.) at two growth stages. Wild buckwheat, treated when 5 to 8 cm tall, was very susceptible to dicamba which caused rapid dehydration of the leaves and growth of callus tissue at stem internodes. Wild buckwheat, treated when flowering, increased in growth 2 days after treatment and then decreased after 4 days. Wheat growth tended to increase in all plant parts after treatment with dicamba at both the 2 to 3-leaf and the boot stages. Dicamba increased the RNA and protein content in wild buckwheat at both growth stages and in wheat at the boot stage. Dicamba affected the transition temperature and precipitation of reconstituted nucleohistone but not the uncombined nucleic acid or histone in vitro, indicating that a DNA-histone-dicamba complex had occurred. The binding of dicamba to protein varied with different proteins and reduced the UV absorbance of the bound proteins.

Analysis of 3-tert-butyl-5-chloro-6-methyluracil (terbacil) in treated and untreated pairs of purple nutsedge (Cyperus rotundus L.), connected by rhizomes, indicated translocation of the herbicide. The tops and tubers of connected, untreated plants contained approximately 10% as much terbacil as did plants treated directly.

Greenhouse studies indicated that 3,6-dichloro-o-anisic acid (dicamba) or its metabolic derivative was strongly accumulated in meristematic tissues of Tartary buckwheat (Fagopyrum tataricum (L.) Gaertn.) and wild mustard (Sinapis arvensis L.) following both foliar and root uptake. In barley (Hordeum vulgare L.) and wheat (Triticum vulgare L.), it was distributed throughout the plants. Detoxification of dicamba occurred in all four species though not at equal rates, and a common major metabolite was identified chromatographically as 5-hydroxy-3,6-dichloro-o-anisic acid. A minor metabolite, 3,6-dichlorosalicylic acid, was found in barley and wheat but not in Tartary buckwheat or wild mustard. The four species tolerated dicamba treatment in the order of wheat, barley, wild mustard, and Tartary buckwheat. This ranking corresponds with the ability of the plants to detoxify dicamba and is inversely related to the extent of dicamba absorption and translocation in them.

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.

A simple, inexpensive, and versatile tractor-mounted spray system will allow spray application to be made to approximately six 6.1-m plots per minute under continuous operation.

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 existing method for the analysis of 3-tert-butyl-5-chloro-6-methyluracil (terbacil) has been modified so that electron capture gas chromatography may be used for quantitation. The crop extract was applied to a powdered cellulose column, the interferences were eluted with hexane, and the terbacil was subsequently eluted with ethyl acetate. The ethyl acetate fraction may be used for analysis directly.

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.