Hypocotyl callus cultures were established from six tomato (Lycopersicon esculentum L.) cultivars that exhibited differential tolerance to preemergence and postemergence metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] at 0.5 kg ai/ha in the greenhouse. Metribuzin in a low sucrose growth medium inhibited callus growth, but calli were not highly sensitive to the herbicide Differences between cultivars in the response of calli to 50 ppm metribuzin were observed. The degree of tolerance of tomato cultivars to postemergence metribuzin at 0.5 kg/ha was similar to the degree of tolerance of their hypocotyl calli to 50 ppm metribuzin in the growth medium.

A modified analytical procedure involving gas-liquid chromatography was used to investigate the relative amounts of 2,4-D [(2,4-dichlorophenoxy)acetic acid] and two of its amino acid conjugate metabolites, 2,4-D-Asp [(2,4-dichlorophenoxy)acetylaspartic acid] and 2,4-D-Glu [(2,4-dichlorophenoxy)acetylglutamic acid], in soybean [Glycine max (L.) Merr. var. Amsoy] plants, soybean callus tissue and red oak (Quercus rubra L.) plants at 2, 4, and 10 days after application of either 2,4-D, its ester, or its salts. 2,4-D-Asp and 2,4-D-Glu were found as major metabolites in all soybean tissues analyzed and their amounts varied depending upon the days following treatment, the formulation of treatment, and the plant substrate (0.03 to 57 ppm for 2,4-D-Asp and 0.05 to 75 ppm for 2,4-D-Glu). The amount of amino acid conjugates peaked at 2 days after treatment of callus tissue and 4 days after treatment of soybean plants. Much higher amounts of these amino acid conjugates were obtained from soybean plants treated with the propylene glycol butyl ether ester of 2,4-D than plants treated with amine salts of 2,4-D. No amino acid conjugates were observed with red oak plants.

Four forest watersheds (1 ha each) in the upper piedmont of Georgia were treated with hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H, 3H)-dione] pellets3 at a rate of 1.68 kg ai/ha. From the end of April, 1979, until May, 1980, 26 storms were monitored to determine movement of hexazinone and two of its metabolites [A: 3-(4-hydroxycyclohexyl)-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H, 3H)-dione, and B: 3-cyclohexyl-6-(methylamino)-1-methyl-1,3,5-triazine-2,4(1H, 3H)-dione] in runoff water. Residues in runoff peaked in the first storm after application (mean concentration of 442 ± 53 ppbw), and declined with subsequent storms in a power curve function: Conc. (ppbw) = 405 × rate × (1 + 0.44 × days)-1.1. Loss of hexazinone in storm runoff averaged 0.53% of the applied herbicide, with Storms 1 and 17 accounting for 59.3% of the chemical exported. Storm 1 had high residue concentrations and low runoff volume, while Storm 17 contained only low residue levels but a very large stormflow. Hexazinone was the predominant compound in the runoff of all 26 storms. Metabolites A and B occurred in runoff in low-to-trace concentrations (<23 ppbw) for up to 7 months after application. Subsurface movement of hexazinone appeared in streamflow 3 to 4 months after application and produced an additional loss of 0.05%. A second-order perennial stream below the treated watersheds periodically contained hexazinone residues of <44 ppbw.

Increasing plant density of grain sorghum [Sorghum bicolor (L.) Moench.] from 57100 to 114300 plants/ha had no significant effect on grain yields, but significantly increased Striga hermonthica (Del.) ‘Benth’ # STRHE shoot yields by 49% in S. hermonthica infested soil of the Sudan. Addition of urea at 43, 86, and 172 kg N/ha increased grain yields by 14, 25, and 45%, respectively, above the control and S. hermonthica shoot yields were reduced by 14, 21, and 35%, respectively, below the control. Although average grain yields in 1981 were 77% less than in 1980, S. hermonthica shoot yields were significantly increased by about sixfold. Grain sorghum yields of pure stands were not consistent over both years. In 1980, the cultivar ‘Ariana’ outyielded ‘Tetron’, but in 1981 the reverse occurred. However, in both years, the 50:50 mixture of both cultivars gave intermediate grain yields. While pure stands of Tetron’ sustained the lowest infestations of S. hermonthica and ‘Ariana’ had the greatest, the mixture had intermediate infestations which were on average 31% less than those of ‘Ariana’. Thus, the results suggest that the cultivation of equiproportional mixtures of relatively resistant and susceptible grain sorghum varieties, coupled with the use of high rates of nitrogenous fertilizer and wider inter- and intra-row spacing, may be a better cultural practice under dense striga infestations.

The effects of herbicide concentration, adjuvants, and temperature on the phytotoxicity of CGA-82725 {2-propynyl 2-[4-[3,5-dichloro-2-pyridinyl)oxy] phenoxy] propionate}, RO 13-8895 {acetone-O-[D-2-[p-(α,α,α-trifluoro-p-tolyl)-oxy] phenoxy] propionyl] oxime}, and BAS 9052 OH {2-[1-(ethoxyimino)-butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexene-1-one} to large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA] were evaluated. The addition of adjuvants increased the toxicity of BAS 9052 OH at herbicide rates below 0.14 kg ai/ha, whereas the adjuvants had little effect on the activity of CGA-82725 or RO 13-8895. There were no differences among the adjuvants in enhancing grass control with any of the herbicides. Control of large crabgrass with CGA-82725 or BAS 9052 OH was not affected by temperature at the time of spraying; RO 13-8895 was slightly more toxic at 16 C than at 32 C. Soybean [Glycine max (L.) Merr.] had good tolerance to the three herbicides at rates 3 to 10 times those recommended; no differences in tolerance were observed among seven soybean cultivars. Stage of growth and the addition of an emulsifiable oil adjuvant did not affect soybean tolerance to BAS 9052 OH.

Experiments were conducted to determine the influence of water depth, fall flooding, and burial depth on the development of common waterplantain (Alisma triviale Pursh. # ALSPA) in wild rice (Zizania palustris L.). The optimum water depths for common waterplantain from corms were 20 cm when grown outside in submerged pots at St. Paul and 2 and 15 cm when grown in a sloping field at Grand Rapids. Growth of common waterplantain from seeds was maximum at the lowest water depths (2 to 7 cm) at both locations. Wild rice dry weight and seed yield in the same experiments were maximum at the 20- and 30-cm water depths at St. Paul and the 15- and 28-cm depths at Grand Rapids. The increased wild rice seed yield and dry weight at these depths was related to increased tiller production. Wild rice yield was similar at all water depths at Grand Rapids when grown with common waterplantain from corms at a density of 11 plants/m2. Water depths that decreased the effect of common waterplantain interference with wild rice, reduced wild rice yield. Establishment of common waterplantain from corms was maximum at the 5- and 15-cm depths and was severely reduced at the 0- and 30-cm soil depths in soils not flooded in the fall but flooded in the spring. Fall flooding killed all corms regardless of burial depth. Corm mortality under fall-flooded conditions may be due to the effects of ice-encasement.

Alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] at 3.4 and 6.7 kg/ha controlled weeds present in sweet potatoes (Ipomoea batatas L. ‘Jewel’, ‘Centennial’, ‘Caromex’) at two locations in North Carolina. Yield was not reduced from slight early season injury observed with the herbicide treatments. Most sweet potato root samples contained less than the detectable limit of 0.05 ppmw of alachlor. At one location, samples of the cultivars Jewel and Centennial that received 6.7 kg/ha contained 0.06 and 0.05 ppmw, respectively. Averaged over locations, residue levels in soil samples from plots treated at 6.7 kg/ha decreased from 1.55 ppmw initially to less than 0.05 ppmw by 16 weeks after application.

Major differences in above- ground biomass and tuber production of yellow nutsedge (Cyperus esculentus L. # CYPES) were not observed when corn (Zea mays L. “CO-OP S265”) was seeded on different dates (1st, 2nd, 3rd and 4th week of May; and 1st week of June). The final seedbed was prepared just prior to each seeding date and this cultivation stimulated dormant tubers to sprout. As a result, a large population of yellow nutsedge emerged with the corn at all seeding dates. Because fertilizer was banded near the corn row, yellow nutsedge biomass, tuber dry weight and number of tubers were higher within corn rows than between rows. Tuber size was affected by seeding date and shifted toward smaller tubers within corn rows and larger tubers between the rows as the corn was sown late. The optimum seeding date of corn was in the 3rd week of May when the highest corn yield was obtained and yellow nutsedge growth was generally reduced.