Weed-control evaluations in ratoon-cropped grain sorghum [Sorghum bicolor (L.) Moench.] indicated that acceptable broadleaf weed control (>80%) in the second crop could be achieved by the use of a contact herbicide plus a residual herbicide applied after first harvest. Annual grasses, especially volunteer grain sorghum, were controlled in the second crop with metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] plus propazine [2-chloro-4,6-bis(isopropylamino)-s-triazine] applied preemergence at planting and followed by metolachlor, cyanazine {2-[[4-chloro-6-(ethylamino)-s-triazin-2-yl] amino]-2-methylpropionitrile}, or pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] applied after first harvest. Second-crop grain yields were not adversely affected by any treatments, and it appeared that satisfactory weed control in the first crop lessened the need for a residual herbicide in the second crop.

SN 533 [1-(N-ethyl-N-propylcarbamoyl)-3-propylsulphonoyl-1,2,4-triazole] toxicity, uptake, translocation, and degradation were studied in soybeans [Glycine max (L.) Merr. ‘Williams’] and peanuts (Arachis hypogaea L. ‘GK 19′). Soybeans were more sensitive than peanuts to SN 533 applied in the nutrient solution. 14C-SN 533 was absorbed by the roots of both species, and the 14C was translocated into the shoot acropetally. Although differences in the uptake and translocation of 14C-SN 533 by soybeans and peanuts were observed, these were not large enough to account for its differential toxicity. Root-absorbed 14C-SN 533 was rapidly degraded in both species, with less than 2% of the radiolabel present in either species occurring as unaltered SN 533 8 days after treatment. Excised leaflets of both species also rapidly degraded 14C-SN 533. The data indicate that the herbicide is more rapidly degraded in peanuts than in soybeans, and thin-layer chromatography of leaflet extracts showed that different polar products were formed from 14C-SN 533 in soybeans and peanuts.

Seeds of 20 weed species buried at depths of 8, 23, and 38 cm in 1972 and 1973 were exhumed at regular intervals and tested for viability and germination. Burial depth had little to no significant influence on longevity. After 5.5 yr 48% of johnsongrass [Sorghum halepense (L.) Pers.], 36% of velvetleaf (Abutilon theophrasti Medic.), 33% of purple moonflower (Ipomoea turbinata Lag.), 30% of spurred anoda [Anoda cristata (L.) Schlecht], 18% of hemp sesbania [Sesbania exaltata (Raf.) Cory], and 13% of pitted morningglory (Ipomoea lacunosa L.) seeds were still viable. No more than 6% of the original population for any other species was viable at 5.5 yr. Hard seeds comprised a high percentage of the longer-lived seeds. Seeds of longest-lived species were losing viability at an average of 26% of the existing population each year from 3.5 to 5.5 yr.

Absorption of 2,4-D [(2,4-dichlorophenoxy) acetic acid], dicamba [3,6-dichloro-o-anisic acid], and the isopropylamine salt of glyphosate [N-(phosphonomethyl) glycine] by excised honeyvine milkweed [Cynanchum laeve (Michx.) Pers.] leaves was determined. Experimental variables included leaf position (terminal vs. basal), a surfactant, 4-isopropenyl-1-methylcyclohexane plus unspecified emulsifiers (SA-77), and leaf collection dates. Absorption of the three herbicides by terminal and basal leaves was increased by the addition of the surfactant. However, the surfactant increased absorption into basal leaves more than into terminal leaves. The surfactant reduced surface tension and increased drying time of water droplets on adaxial leaf surfaces by 50%. The pH of the herbicide solutions was reduced from about 5.8 to about 3.9 by SA-77. Absorption of all three herbicides was greater into terminal than into basal leaves when the surfactant was not present, but the difference disappeared when the surfactant was added. Generally, no differences were observed in the absorption of 2,4-D and dicamba. Glyphosate absorption was greater in terminal leaves collected after a period of adequate moisture than after a period of dry soil conditions.

The control of greasewood [Sarcobatus vermiculatus (Hook.) Torr.] and salt rabbitbrush [Chrysothamnus nauseosus ssp. consimilis (Greene) Hall and Clem.] was investigated with application of 2,4-D [(2,4-dichlorophenoxy)acetic acid] and a mixture of 2,4-D and picloram (4-amino-3,5,6-trichloropicolinic acid). The herbicides were applied at 2-week intervals from May 1 to August 1. Greasewood had accelerated shoot growth and was most susceptible to application of 2,4-D during June. Accelerated shoot growth and maximum susceptibility to 2,4-D of salt rabbitbrush began in June and extended into July. Mortality of greasewood and salt rabbitbrush from 2,4-D at 2.2 kg/ha applied at optimum dates averaged 72 and 87%, respectively. The picloram/2,4-D mixture was more effective for greasewood control than 2,4-D alone in 1 yr at very early and late application dates on a xeric site and only at the last date of application on a mesic site. Reapplication of 2,4-D at 2.2 and 3.3 kg/ha in June to partially controlled stands gave excellent control of both greasewood and rabbitbrush.

In greenhouse studies, the potential interactive effects of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] treatments combined with the air pollutant ozone (O3) or the antioxidants, piperonyl butoxide {α-[2-butoxyethyl) ethoxy]-4,5-dimethylenedioxy-2-propyltoluene} and n-propyl gallate, on the growth of sorghum [Sorghum bicolor (L.) Moench ‘Funk G522DR’] seedlings that were protected or unprotected with the antidote, CGA-43089 [α-(cyanomethoximino)-benzacetonitrile], were examined. Metolachlor was applied preplant incorporated at rates of 2.2, 3.9, and 5.6 kg/ha, and it was evaluated against fumigation with O3 at 0.2 and 0.3 ppmv or against 4.9, 6.7, and 9.0 kg/ha of each antioxidant applied preplant incorporated. In combination treatments, shoot dry weight at 30 days after planting was reduced more than expected by metolachlor in the presence of the protectant CGA-43089 and ozone or some rates of the two antioxidants, suggesting synergism. In the absence of the protectant, CGA-43089, growth responses of sorghum to combination treatments of metolachlor with ozone or propyl gallate suggested an additive effect, although some treatments of metolachlor combined with piperonyl butoxide interacted synergistically.