Studies on the development of leafy spurge (Euphorbia esula L.) were conducted in the field and growth room. Sixteen months after planting in field plots, leafy spurge plants arising from underground bud-producing root segments, transplanted seedlings, or seeds averaged 96, 83, and 136 shoots per plant, respectively, when grown free of interference from other vegetation. A number of plants arising from each source flowered the first year, and all plants flowered and produced seed the second year after planting. When grown in a perennial grass sod consisting of crested wheatgrass [Agropyron desertorum (Fisch. ex Link) Schult.] and smooth brome (Bromus inermis Leyss.), no plant flowered or produced additional shoots. Soil moisture was less where a dense sod was present. In the growth room, total dry matter of tops and roots was greatest at a soil temperature of 18.3 C or higher, and plant height was greatest at 33.3 C. An early emerging crop might suppress leafy spurge by utilizing the available soil moisture early in the growing season.

Field experiments were conducted to study the effect of fall and spring pre-plant incorporated applications of trifluralin (α,α,α-tri-fluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) and metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)-one] alone and in combinations on crop tolerance, seed yield, and weed control in fababeans (Vicia faba L. ‘Diana’). Trifluralin applied either in the fall or the spring resulted in acceptable control of green foxtail [Setaria viridis (L.) Beauv.] and wild oat (Avena fatua L.) while metribuzin resulted in excellent control of wild mustard [Brassica kaber (DC.) L.C. Wheeler var. pinnatifida (Stokes) L.C. Wheeler]. In 2 out of 3 yr, a tank-mixture of trifluralin plus metribuzin applied in the fall at 1.4 and 0.4 kg/ha, respectively, resulted in significantly larger seed yield than the same combination applied at 1.1 and 0.3 kg/ha in the spring. Although the fall treatments generally resulted in higher seed yields, there was no consistent difference in weed densities between fall and spring applications. In both field and growth room studies, trifluralin reduced the injury to fababeans from metribuzin. A postemergence application of metribuzin in the spring at 0.3 kg/ha following a fall-application of trifluralin resulted in good wild mustard control but caused considerable crop damage. Dinoseb (2-sec-butyl-4,6-dinitrophenol) and bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2dioxide] controlled wild mustard effectively with no injury to the crop.

The effect of temperatures below 0 C and plant maturity on the phytotoxicity of glyphosate [N-(phosphonomethyl)glycine] on rapidly growing alfalfa (Medicago sativa L. ‘Vernal’) and quackgrass [Agropyron repens (L.) Beauv.] plants was studied in a controlled environment. Pretreatment at −4 C partially protected alfalfa from injury by 0.8 kg/ha of glyphosate at six alfalfa maturities. This same treatment had no significant effect on glyphosate phytotoxicity to quackgrass. Pretreatment at −4 C increased translocation of glyphosate in quackgrass but reduced its translocation in alfalfa. A greater reduction in translocation occurred in the smaller alfalfa plants.

Numerous cations were evaluated as possible substitutes for copper in mixtures with diquat (6,7-dihydrodipyrido[1,2-α:2′,1′-c] pyrazinediium ion) for control of hydrilla [Hydrilla verticillata (L.f.) Royle]. Several cations, including ferrous and ferric iron, when substituted for equal weights of copper in the mixtures, were as effective as copper in enhancing the phytotoxicity of diquat to hydrilla. In most instances, death of the test plants occurred more rapidly when the substitutes were used. Ferric chloride, because of its apparent innocuous behavior in the aquatic environment, is a desirable substitute for the more toxic copper. Bluegill sunfish (Lepomis macrochirus RAf.) were unaffected by week-long exposure to ferric chloride at concentrations as high as 100 ppmw. Since ferric chloride alone exhibited no toxicity to hydrilla in the range of concentrations tested, the greater phytotoxicity of the mixtures probably was due to the increased toxicity of diquat. In evaluations using other species of aquatic weeds, neither the addition of copper nor the addition of other cations increased the phytotoxicity of diquat. In most tests, the mixtures of diquat with other cations reduced the level of activity of diquat on weeds other than hydrilla.

Dalapon (2,2-dichloropropionic acid), TCA ester [ethyleneglycol bis(trichloroacetate)], MSMA (monosodium methanearsonate), and glyphosate [N-(phosphonomethyl)glycine] were evaluated for their effectiveness as spot spray treatments to johnsongrass [Sorghum halepense (L.) Pers.] 30, 75, or 100 cm tall from rhizomes. Glyphosate was also applied as a spot spray to soybeans [Glycine max (L.) Merr. ‘Pickett 71′] to determine its effect on stand losses and subsequent soybean yields. Glyphosate at a concentration of 6 or 12 g/L of water was the most effective treatment regardless of johnsongrass height. A single application provided excellent-to-complete seasonal control within 2 weeks after application. Repeated applications of dalapon, MSMA, and TCA ester would be needed for season-long control. Glyphosate at a concentration of 6 g/L of water applied to 0.5 m long spots of soybeans in late August reduced soybean yields 9, 17, and 28% while the stand was reduced 5,10, and 20%, respectively.

Hydroponic treatment with EPTC (S-ethyl dipropylthiocarbamate) inhibited leaf growth and stimulated stem growth of hybrid corn (Zea mays L. ‘Wisconsin 473′). Root treatment with GA3 (gibberellic acid) prevented leaf stunting from EPTC. Most abnormalities in foliar display and height from treatment with 50 μM EPTC were prevented by increasing GA3 levels from 0.5 μM to 10 μM over a week. The effect of EPTC on endogenous gibberellin activity was measured by bioassay of shoot extracts. EPTC (6.7 kg/ha) reduced the levels of total endogenous gibberellin-like substances in eight-day-old seedlings grown in treated soil. Under the environmental condtions of the experiment, this corresponded to the first discernable signs of injury. In addition EPTC induced an abnormal distribution of endogenous gibberellins in the shoots of older corn plants. Leaves of two-week-old EPTC-treated plants contained less gibberellin activity than the leaves of controls. Stems of herbicide-treated plants contained the same levels of gibberellin-like substances as the controls.