The persistence of alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl) acetanilide], metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], and propachlor (2-chloro-N-isopropylacetanilide) in soil was examined under laboratory and field conditions using sorghum (Sorghum vulgare Pers. ‘NB280S′) or annual ryegrass (Lolium multiflorum Lam.) as bioassay species. In laboratory studies, degradation rate of alachlor and propachlor was greater at 50 and 80% than at 20% field capacity at 20 C. Degradation of metolachlor was greater at 80 than at 20% field capacity. Degradation rate of alachlor and metolachlor at 50% field capacity was greater at higher temperatures. Propachlor degradation rate varied with temperature. Under irrigated, cropped field conditions, the order of persistence was metolachlor > alachlor > > propachlor.

DCPA (dimethyl tetrachloroterephthalate), bensulide [O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide], and oxadiazon [2-tert-butyl-4(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4-oxadiazolin-5-one] were applied to bermudagrass [Cynodon dactylon (L.) Pers. ‘Common′] as consecutive repeated annual treatments or in all possible sequence combinations for 3 yr to determine the effects on species composition of winter and summer annual weeds. Regardless of the rotation of treatments on winter weeds, oxadiazon increased the cover of common chickweed [Stellaria media (L.) Cyrillo], spur weed (Soliva spp.), and thymeleaf sandwort (Arenaria serpyllifolia L.); bensulide increased the cover of corn speedwell (Veronica arvensis L.); and DCPA in most instances increased the cover of hop clover (Trifolium agrarium L.) and spur weed. When a herbicide controlled large crabgrass [Digitaria sanguinalis (L.) Scop.] or goosegrass (Eleusine indica L. Gaertn.), the cover of weeds not controlled increased rapidly, with the exception of oxadiazon applied for 3 consecutive yr.

To determine the competitiveness of common cocklebur (Xanthium pensylvanicum Wallr.) with cotton (Gossypium hirsutum L. 'Stoneville 213′), experiments were conducted on a Lucedale fine sandy loam from 1978 through 1980. Common cocklebur dry weight increased with increasing density up to 16 plants/15 m of row. No further increase in dry matter occurred beyond this density. Regression analysis showed that common cocklebur produced an average of 342 kg/ha of dry weight for each plant per 15-m row. Seed-cotton yields decreased as weed density increased up to 16 common cocklebur plants/15 m of row. Regression equations revealed yield losses ranging from 72 to 115 kg/ha for hand-harvested seed cotton and 57 to 90 kg/ha for machine-harvested seed cotton for each common cocklebur plant/15 m of row. Cotton stem diameter and height were reduced by weed competition in the same manner as seed cotton yields, but reductions were not as pronounced, indicating that these parameters were not good indicators of common cocklebur competition.

Paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) killed nearly 100% of the wild garlic (Allium vineale L.) plants when applied in spring, but was less effective when applied in the fall. Treatment in the spring with paraquat consistently killed more wild garlic plants than treatments at any other date. Eradication of a wild garlic infestation was achieved after applications for three successive springs. Near eradication was achieved with two annual applications of 2,4-D [(2,4-dichlorophenoxy)acetic acid]. Among herbicides evaluated postemergence on wild garlic, mefluidide (N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl] amino] phenyl] acetamide}, oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene], bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide], asulam (methyl sulfanilylcarbamate), and picloram (4-amino-3,5,6-trichloropicolinic acid) were not effective for controlling wild garlic. Glyphosate [N-(phosphonomethyl)glycine] and a mixture of cyperquat (1-methyl-4-phenylpyridinium) and 2,4-D ester reduced wild garlic populations by over 60%.

Thirty compounds that are precursors, analogs, derivatives, or fragments of strigol were prepared and tested for their activity as witchweed [Striga asiatica (L.) Kuntze] seed-germination stimulators. Five compounds showed significant stimulatory activity. Among these were 5-ethoxy-3-methyl-2(5H)-furanone, 3-hydroxy-2,6,6-trimethylcyclohex-1-ene-1-carboxaldehyde, a two-ring analog of strigol, and two isomers of a three-ring analog. Several of the other 25 compounds showed slight and/or non-reproducible activity when dimethylsulfoxide was used as the carrier at 0.1% (v/v) in aqueous solutions. Compounds with such diverse structures as trimethylcyclohexenes, furanones, and bicycloheptenones were among those that possessed some stimulatory activity.