Vapors of 11 dinitroaniline herbicides from soil were trapped in a Florisil column under controlled laboratory conditions for a 3-hr period. No vapor losses of nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline] and oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) were detected at the highest temperature, 50 C, from moist Lakeland sand with an air flow of 50 ml/min; whereas, under the same conditions vapor losses approached 25% for benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine), profluralin [N-(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine] and trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine). Vapor losses for the remaining herbicides studied were moderate with values ranging between 2 and 13%. Volatility of all herbicides increased with increasing temperatures of 30, 40, and 50 C. Vapor losses for each herbicide from Hagerstown clay loam, Littleton silt loam and Lakeland sand were statistically different for five of the 11 herbicides.

The effects of several concentrations of glyphosate [N-(phosphonomethyl)glycine] and siduron [1-(2-methylcyclohexyl)-3-phenylurea] on germination and seedling growth of Kentucky bluegrass (Poa pratensis L. ‘Nugget,’ ‘Prato,’ ‘Fylking,’ ‘Park’), creeping bentgrass (Agrostis palustris Huds. Penncross,’ ‘Seaside’), and red fescue (Festuca rubra L. ‘Pennlawn,’ ‘Wintergreen’) were evaluated in petri dishes under controlled environmental conditions. A high concentration of glyphosate (10-4 M) reduced shoot growth in all but two cultivars. Siduron had no effect. Glyphosate or siduron applied to the soil and incorporated did not affect turfgrass germination or growth. When the glyphosate was sprayed over the soil and on the seed lying on the soil surface, red fescue germination was reduced and shoot growth of Kentucky bluegrass, creeping bentgrass, and red fescue was inhibited at the high rate of glyphosate application (17.9 kg/ha). Under field conditions, none of the glyphosate treatments reduced turfgrass germination or growth.

Freshly harvested seeds of Florida pusley (Richardia scabra L.) require light for germination. Gibberellic acid (GA3) successfully replaced the light requirement of both scarified and unscarified seeds, while cyclic 3′,5′-adenosine monophosphate (C-AMP) stimulated the dark germination of scarified seeds only. Cold-stratification reduced seed germinability. The germination inhibition by cold-stratification was reversed by both GA3 and KNO3 treatments. Indole-3-acetic acid (IAA), kinetin, thiourea, and acetylcholine (ACh), either had no effect or reduced the germination percentages of Florida pusley seeds under all conditions studied.

The effect of quackgrass [Agropyron repens (L.) Beauv.] rhizome length and foliage height on glyphosate [N-(phosphonomethyl)glycine] translocation was determined on the basis of bud kill and 14 C-accumulation in quackgrass rhizomes. Foliar glyphosate treatments of 0.28 kg/ha resulted in significantly reduced quackgrass rhizome bud survival, and rates of 0.56, 0.84, and 1.12 kg/ha gave nearly complete bud kill. Rhizome buds on glyphosate-treated quackgrass plants with 20 to 90 nodes had a higher survival rate than rhizome buds on plants with 10 nodes. Quackgrass bud kill was greatest when glyphosate was applied to taller foliage. When all rhizome buds were not killed, those closest to the mother shoot survived glyphosate treatments. The 14C accumulation following applications of 14C-glyphosate was greatest in nodes near the rhizome tip and least in nodes near the mother shoot. This suggests that greater bud kill near the rhizome tip was due to larger accumulation of glyphosate in this part of the rhizome.

Populations of the waterhyacinth mite (Orthogalumna terebrantis Wallwork) of ca 200,000 galleries/m2 (or 10,000 per plant) caused serious damage to waterhyacinth [Eichhornia crassipes (Mart.) Solms.] in the field, but such damage was sporadic and confined to small areas of plants in midsummer. Two or three generations a year occurred in the field. Adults emerged in late December, March, and May and adults were found on waterlettuce (Pistia stratiotes L.) throughout the winter. Development, appearance of the different stages, behavior of immatures and adults, and manner of attacking waterhyacinth is described. Only small differences were found between the biology of the mites studied in Argentina and of that reported in Uruguay and the United States.

Injury to navy bean (Phaseolus vulgaris L.) from EPTC (S-ethyl dipropylthiocarbamate) was investigated as a function of soil moisture, planting depth, soil compaction, temperature, available nitrogen, and seed quality. Experiments in the greenhouse and growth chamber showed that both high and low moisture stress increased injury. Deep planting increased the injury from high rates of EPTC. Soil compaction alone reduced plant growth. In combination with EPTC at 4.5 kg/ha, further growth reduction was observed. Ambient temperature did not alter susceptibility to EPTC. Stimulation of growth by nitrogen as measured by increased fresh weight was inhibited by EPTC. Field and greenhouse studies showed that EPTC injury was greater to mechanically damaged seed than non-damaged seed.

Over a 3-yr period the placement of weeds in relation to cotton (Gossypium hirsutum L.) plants greatly influenced the seed cotton yields. After 3-yr of competition the cotton with no weeds yielded about 2300 kg/ha. With weeds confined to between-the-rows placement, yields were about 850 kg/ha. When weeds were confined to in-the-row placement, the cotton was completely shaded and produced no yield. After 3-yr of intense competition throughout each entire growing season no statistical differences were demonstrated between the competitiveness of large crabgrass [Digitaria sanguinalis (L.) Scop.], spurred anoda [Anoda cristata (L.) Schlecht.], prickly sida (Sida spinosa L.) and velvetleaf (Abutilon theophrasti Medic.) to cotton.

In rolling topography, soil and water runoff losses can be greatly reduced by conservation production systems. Alfalfa (Medicago sativa L.) is an important crop in Nebraska and other states which is often followed in the crop sequence by corn (Zea mays L.) or sorghum [Sorghum bicolor (L.) Moench]. Three years of field experiments indicated that herbicides can substitute for erosive moldboard plowing to destroy alfalfa without loss in the subsequent corn yield. Herbicides applied just prior to corn planting in the spring gave more consistent alfalfa control than those applied the preceeding fall. The most consistent treatment used for alfalfa control and supplemental annual weed control while producing maximum corn yield was 2,4-D amine [(2,4-dichlorophenoxy) acetic acid] plus dicamba (3,6-dichloro-o-anisic acid) at 1.12 and 0.28 kg/ha, respectively. Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] plus propachlor (2-chloro-N-isopropylacetanilide) versus no preemergence herbicide was used for annual weed control in addition to the treatments to control alfalfa. This treatment was essential for maintaining corn yields where a non-residual or limited residual herbicide was used for alfalfa control.

Six herbicides including DNP (2,4-dinitrophenol) were tested for their effects upon nitrate metabolism in green leaves. It was found that these herbicides which are not classified as “photosynthetic inhibitors” permitted nitrite to accumulate within green leaves in darkness but not in light. It is postulated that these herbicides have an uncoupling effect, similar to that of DNP, which indirectly affects the process of nitrate reduction. A new technique which demonstrates this effect is presented and discussed.

Navy bean (Phaseolus vulgaris L.) treated with the combination of EPTC (S-ethyl dipropylthiocarbamate) and atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] developed more chlorosis of the leaves than beans treated with atrazine alone. Navy bean yields in field studies in 1972, were reduced 39% when grown in the presence of 0.55 kg/ha of atrazine and 3.4 kg/ha of EPTC, whereas the single application of either herbicide reduced yields 0 to 14%, respectively. In 1973, atrazine at 0.28 kg/ha did not significantly reduce yields, but combinations of 0.28 kg/ha of atrazine plus 2.2, 3.4, and 4.5 kg/ha of EPTC, reduced yields 40, 30, and 62% respectively. The combination of atrazine and EPTC also reduced plant weight and delayed flower and pod development. EPTC was found to increase wind blast damage under conditions of low relative humidity, high winds, and limited soil moisture. EPTC at 2.2, 3.4, and 4.5 kg/ha reduced the chloroform-soluble leaf extract from the surface of leaves and scanning electron micrographs confirmed that EPTC at 10-6 M altered leaf surface waxes. EPTC at 10-5 and 10-6 M increased the transpiration rate of plants. Increased uptake of 14C-atrazine from solution was associated with increased transpiration.

A rapid cotyledon disc bioassay developed for photosynthetic inhibitors was tested on several herbicides of different modes of action. In addition to being an excellent bioassay method for photosynthetic inhibitors it was found to be useful for the detection of diquat (6,7-dihydrodipyrido[1,2-α:2′,1′-c] pyrazine-diium ion), paraquat (1,1′-dimethyl-4,4′-dipyridinium ion), and dinoseb (2-sec-butyl-4,6-dinitrophenol). Herbicides representing several other modes of action could not be readily detected by this method.

Studies of the development and distribution of root systems of intraspecific and interspecific competition were conducted between soybean [Glycine max. (L.) Merr. ‘Lee 68′] and tall morningglory [Ipomoea purpurea (L.) Roth]. Tall morningglory at three plant densities and soybean were grown for 2 yr on a Taloka silt loam. The greatest density of soybean and tall morningglory roots grown under intraspecific competition was in the surface 12 cm and in the center of the row. Greater values of root length and density were during the dryer season. The largest fraction of total root length at a given date also was in the surface 12 cm and decreased with depth. The fraction at a given depth was a dynamic property of the root system during the growing season. When compared with the soybean root system, tall morningglory roots were found at deeper depths and had greater root densities. Little expansion of the soybean root system was found after initiation of the soybean reproductive phase. During this phase, the tall morningglory root system was increasing at a faster rate of growth than the soybean root system. The greatest density of roots grown under interspecific competition also was in the surface 12 cm and at the center of the row. These values were less than those found under intraspecific competition. Root distribution and development are dynamic functions of growth stage, planting density, and plant species.

Translocation of 14C-labeled and toxicity of nonradiolabeled bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-(4)3H-one 2,2-dioxide] was determined for common cocklebur (Xanthium pensylvanicum Wallr.) and soybeans [Glycine max (L.) Merr.]. Significantly greater 14C-movement and herbicide toxicity occurred in common cocklebur growing in wet soil at field capacity than in dry soil near the wilting point. In common cocklebur there was a trend toward greater bentazon toxicity and 14C-translocation at high temperature (35 C) and high relative humidity (RH) (96%) than at low temperature (25 C) and low RH (35%). ‘Lee 68’ soybeans were injured less than 10% by bentazon under any environmental condition of this study. Translocation of 14C was primarily acropetal in both common cocklebur and soybeans. Herbicide movement was affected by leaf maturity with the greatest movement of 14C resulting from 14C-bentazon applied to the most mature common cocklebur leaf near the base of the shoot and to soybeans at the youngest fully expanded leaf near the apex of the shoot. Bentazon was more toxic and 14C translocation was greater in the soybean cultivar ‘Hurrelbrink’ than ‘Hill’ or Hill X Hurrelbrink cross.

Field experiments were conducted to compare the effects of 0.07, 0.14, 0.28, and 0.56 kg/ha of 2,4-D [(2,4-dichlorophenoxy)acetic acid] amine on plant growth, seed production, and seed quality when applied at four growth stages of summer rape (Brassica napus L. ‘Zephyr’) and turnip rape (Brassica campestris L. ‘Span’). At all growth stages, seed yield of turnip rape, was significantly reduced by each additional increment of 2,4-D. The difference in response of the two species may relate in part to differences in spray droplet retention of the leaf surfaces. The herbicide did not affect the germination of harvested seed although treatment with the higher rates at the bolting and flowering stages resulted in the production of some shrivelled seed that was lost on cleaning. Some herbicide treatments caused a marked increase in size of harvested seed. There was a trend towards decreased seed oil content with increasing rate of 2,4-D at the bolting and flowering stages, but oil production losses were mainly reflected through losses in seed yield. The time required for both species to reach maturity increased with increasing rate of herbicide when applied at the vegetative stages. In additional field studies, 2,4-D significantly reduced seed yield in turnip rape when applied at the 3- to 4-leaf stage at 0.035 kg/ha, and 0.018 kg/ha sometimes produced visible effects without noticeable loss in yield.

Application of EPTC (S-ethyl dipropylthiocarbamate) at 3.4 and 4.5 kg/ha in 1972 increased root rot severity and reduced navy bean (Phaseolus vulgaris L.) yields in soil with an artificial root rot [Fusarium solani (Mart.) Appel and Wr. f. Phaseoli (Burk.) Snyd. and Hans.] inoculum level. EPTC at 3.4 kg/ha and chloroamben (3-amino-2,5-dichlorobenzoic acid) at 3.4 kg/ha in 1973 caused the greatest root rot severity and greatest decrease in yield. Dinoseb (2-sec-butyl-4,6-dinitrophenol) and fluorodifen (p-nitrophenyl α,α,α-trifluoro-2-nitro-p-tolyl ether) at 5 kg/ha interacted with root rot less than the other herbicides assayed. In the growth chamber at 23 C, EPTC at 3.4 kg/ha and alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl) acetanilide] at 2.8 kg/ha applied to navy bean grown in soil infested with F. solani reduced plant growth. Root rot injury was most severe in plants treated with EPTC at 20 C ambient temperature. Navy bean growth was reduced as the level of F. solani chlamydospore inoculum increased in the presence of EPTC.

In field studies, HOE 22870 [4-(4′-chlorophenoxy)-phenoxy-α-propionic-isobutylester] and HOE 23408 methyl 2-[4-(2,4-dichlorophenoxy)phenoxy] propanoate at 0.84 to 3.36 kg/ha were sprayed over the top of soybeans [Glycine max (L.) Merr.], corn (Zea mays L.), and giant foxtail (Setaria faberi Herrm.). Rates of 0.84 or 1.68 kg/ha of either herbicide controlled corn and giant foxtail. Soybeans tolerated 3.36 kg/ha (the highest rate used) of either herbicide. Both herbicides performed quite similarly, but HOE 22870 was generally more effective on giant foxtail and less effective on corn than was HOE 23408. The optimum time of application, in terms of soybean development, was the first trifoliolate stage. At this stage, corn had four to five leaves and giant foxtail had three to five leaves. HOE 23408 was applied to 32 inbred lines of corn in a greenhouse study. Several inbreds had considerable tolerance. When HOE 23408 at 0.56 kg/ha was applied to these 32 inbreds in a field study, control ranged from 100% for the most susceptible inbred to 22% for the most resistant inbred. At 1.12 kg/ha, control of corn ranged from 100% to 42%.

The adsorption, desorption, and mobility of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)one] in eight Ontario soils were investigated. The distribution coefficients varied from 0.56 for the least adsorptive Fox sandy loam soil to 31.67 for the most highly adsorptive Leamington muck soil. Most of the adsorbed metribuzin was desorbed from the mineral soils after six aqueous extractions, however substantial amounts of the herbicide remained adsorbed on the muck soils after 10 aqueous extractions. The herbicide was relatively mobile in mineral soils but was immobile in the muck soils. Mobility was inversely correlated with the amount of soil organic matter. Bioassay studies indicated that phytotoxicity of metribuzin also decreased with increasing organic matter content of the soil. Persistence of metribuzin was dependent on microbial degradation. In a field study with Guelph loam, the half-life of metribuzin was approximately 3 months.

The fate of 2,4-D [(2,4-dichlorophenoxy)acetic acid] in the soil under winter wheat (Triticum aestivum L. ‘Nugaines’) and fallow cropping schemes was studied under the field conditions of eastern Washington in 1973 and 1974 using formulated dimethylamine salt and isooctyl ester of 2,4-D. Soil samples taken 1 hour after herbicide application showed that amine-treated plots retained considerably more applied 2,4-D than ester-treated plots. The rapidity of 2,4-D breakdown decreased gradually with time, and at the end of 6 months, an average of 0.04 ppm of 2,4-D remained in the sampled soil profile regardless of formulation, application rate, or cropping scheme. Loss of 2,4-D from the soil surface in runoff occurred when the plots were irrigated heavily one day after the herbicide application. The herbicide was also leached into the soil profile by both irrigation and natural precipitation. Herbicide concentrations in the sampled portion of the upper soil profile decreased during the summer and then increased slightly in the fall.

Low pressure and reduced pressure fan and reduced pressure hollow cone nozzles were compared to conventional fan and hollow cone nozzles to determine their potential for reducing spray drift. Other comparisons included two different spray pressures for a low pressure fan nozzle, low and reduced pressure fan nozzles versus air-aspirating foam nozzles, low pressure versus reduced pressure fan nozzles, and reduced pressure hollow cone nozzles versus reduced pressure fan nozzles. Spray recoveries within 36 m downwind of the spray release point were significantly greater for the low pressure and reduced pressure fan and reduced pressure hollow cone nozzles than for the conventional fan and hollow cone nozzles. An air-aspirating nozzle producing spray without foaming adjuvant resulted in significantly greater spray recovery than a low pressure fan nozzle. The recovery from a reduced pressure fan nozzle having a rated flow of 12.6 cm3/s was significantly greater than that from a low pressure fan nozzle.