Failure to control common groundsel (Senecio vulgaris L.) was observed in 1968 in a nursery where 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) or 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) had been used once or twice annually since 1958. Seedlings from seed collected at that location were not controlled by pre-emergence applications of simazine or atrazine at rates up to 17.92 kg/ha. Seedlings from a seed source where triazine herbicides had not been in continuous use were completely controlled by 1.12 or 2.24 kg/ha of either chemical, and partially controlled by 0.28 to 0.56 kg/ha. Postemergence applications of atrazine at 1.12, 2.24, or 4.48 kg/ha did not affect common groundsel from the nursery source, but killed small seedlings from the other source. Preemergence applications of four other herbicides were equally effective against seedlings from both sources.

Nitralin (4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline) controlled grasses and 3-[p-(p-chlorophenoxy)phenyl]-1,1-dimethylurea (chloroxuron) controlled broadleaf weeds in soybeans (Glycine max (L.) Merr.) as well singly as when combined. In 1 year out of 2, nitralin and chloroxuron in combination caused more plant injury than either herbicide alone. The combination of nitralin (0.56 or 0.84 kg/ha) with chloroxuron (1.68 kg/ha) reduced seed yields 37% from the value obtained with chloroxuron alone (1.68 kg/ha).

The influence of soil-applied phosphorus on the phytotoxicity of soil-applied 3-amino-s-triazole (amitrole) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) for corn (Zea mays L.), ryegrass (Lolium multiflorum L.), rye (Secale cereale L.), snapbeans (Phaseolus vulgaris L.), soybeans (Glycine max (L.) Mers.), sorghum (Sorghum vulgare Pers.), wheat (Triticum aestivum L.), cotton (Gossypium hirsutum L.), peanuts (Arachis hypogaea L.), and peas (Pisum sativum L.) was studied under greenhouse conditions. All species except cotton and peanuts indicated an amitrole-phosphorus interaction. Greater phytotoxicity was found for a given rate of amitrole as the soil phosphorus level was increased. A diuron-phosphorus interaction was observed for cotton and soybeans only.

Several herbicides were evaluated for control of spring parsley [Cymopterus watsonii (Coult. & Rose) Jones]. The propylene glycol butyl ether esters and dimethylamine salt of (2,4-dichlorophenoxy)acetic acid (2,4-D) applied at 2 lb/A were 99% effective. Ninety-nine percent control was achieved also with 0.5 lb/A of 4-amino-3,5,6-trichloropicolinic acid (picloram) and 2,4-D amine + picloram at 0.4 + 0.1 lb/A, 2,4-D amine + picloram at 0.33 + 0.17 lb/A, and (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) + picloram at 0.25 + 0.25 lb/A.

Nine field trials were carried out during 1968 and 1969 to study selective weed control in sugarbeets (Beta vulgaris L.) by preemergence and postemergence applications. The trials were conducted at various regions of Israel, under a wide range of climatic and edaphic conditions. Among the preemergence treatments, the herbicide 1-methyl-3-(2-benzothiazolyl)-urea (hereinafter referred to as benzthiazuron) gave adequate weed control and selectivity to sugarbeets. However, when heavy infestation with grasses was present, an addition of isopropyl carbanilate (propham) was needed to increase the spectrum of weed control. A preemergence application of 1-butyl-3-(3,4-dichlorophenyl)-1-methylurea (neburon) on each side of the drill-row of sugarbeets together with an over-band application of benzthiazuron or 5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone (pyrazon) improved weed control. Among postemergence treatments, a mixture of pyrazon and propham gave excellent broad-spectrum weed control. Applying this combination in an emulsion with a non-phytotoxic oil considerably improved weed control.

The preemergence herbicidal activities of 10 4-(methylsulfonyl)-2,6-dinitro-N,N-variously substituted anilines were determined on four plant species at four equimolar concentrations in nutrient solution. Several analogs were as active or slightly more active than 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline [nitralin]. Most amino groups on these compounds were of a mixed nature. Preemergence toxicity decreased when the N-substituents contained more than six carbons or less than five.

Purple nutsedge (Cyperus rotundus L.) develops as a series of shoots connected by bulbs, rhizomes, and tubers. The leaves contain parallel, collateral vascular bundles with the majority of the photosynthetic cells concentrated in the sheathing girdle around each bundle. The upper leaf surface consists of a single layer of large epidermal cells covered by a thick cuticle. Stomates occur only in the lower surface. The vascular bundles vary from collateral to amphivasal as they pass from the leaves through the bulb into the rhizomes and tubers. Newly developing rhizomes and tubers appear white and fleshy with a parenchymatous epidermis and cortex. Mature rhizomes appear brown and wiry with a deteriorated outer cortex and a lignified inner cortext and endodermis. Tubers and bulbs form similarly at the rhizome apices with each accumulating starch. The interconnecting vascular system appears to remain intact throughout the growing season.

Effects of three diphenylether herbicides [2,4-dichlorophenyl-p-nitrophenyl ether (nitrofen); 2,4,6-trichlorophenyl-4′-nitrophenyl ether (hereinafter referred to as MC-1478); and 2,4′-dinitro-4-trifluoromethyl-diphenylether (hereinafter referred to as C-6989)] were measured on phosphorylation and electron transport in spinach (Spinacia oleracea L.) chloroplasts, and mung bean (Phaseolus aureus L., var. Jumbo) and white potato tuber (Solarium tuberosum L.) mitochondria. All of the diphenylethers acted primarily as inhibitors of chloroplast noncyclic electron transport, and the coupled photophosphorylation. The compounds ranked in the following decreasing order of inhibitory effectiveness: MC-1478 ≥ C-6989 >> nitrofen. A site of action close to light reaction II was suggested. At high molar concentrations, marginal interference with cyclic electron transport or phosphorylation was obtained. In mitochondria, MC-1478 and nitrofen acted primarily as electron transport inhibitors with malate, NADH, and succinate as substrates. MC-1478 was a slightly stronger inhibitor than nitrofen. Only slight stimulation of ADP-limited oxygen uptake was obtained during the oxidation of NADH and succinate; whereas, strong inhibition of oxygen uptake was obtained with malate. C-6989 also weakly stimulated ADP-limited oxygen uptake with NADH and succinate but differed from the two chlorinated diphenylethers in that electron transport was not inhibited when ADP was present in excess. Interference with ATP generation could be one of the mechanisms through which the phytotoxicity of diphenylether herbicides is expressed.

Uptake of herbicides by excised roots of soybean (Glycine max (L.) Merr.) plants was studied over periods of 30 min, 8 hr, and 48 hr. In the 48-hr experiment, initial rate of herbicide uptake was rapid and was greater at higher temperatures and external herbicide concentrations. Rates of initial uptake varied among herbicides. Over 30-min periods, rapid herbicide uptake by excised roots for 2.5 to 5 min was followed by much slower uptake. Total uptake for 30 min and 1 hr was in the order of 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea(linuron) > isopropyl-m-chlorocarbanilate (chlorpropham) > S-ethyl dipropylthiocarbamate (EPTC) > 3-amino-2,5-dichlorobenzoic acid (amiben) > 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine). However, total uptake after 48 hr was in the order of chloropropham > linuron > EPTC > atrazine > amiben, indicating that rates of uptake for the herbicides changed over 48 hr. Values of Q10 for herbicide uptake were always less than 1.85, indicating that physical processes were important in uptake of herbicides by excised soybean roots. Uptake of herbicides over 8 hr by roots of intact plants was similar at 5, 10, and 20 C to uptake by excised roots, but uptake at 30 C was less for roots of intact plants than for excised roots. Transpiration increased as temperature increased, but herbicide uptake and transpiration were unrelated.

Weed control performance of several herbicides, their effects on tobacco (Nicotiana tabacum L.), and two methods of soil incorporation were studied in North Carolina in 1967 and 1968. Herbicides which gave acceptable weed control without injuring tobacco or lowering its quality were 4-(methylsulfonyl)-2,6-dinitro-N,Ndipropylaniline (nitralin),1,1,4-trimethyl-6-isopropyl-5-indanyl ethyl ketone (D-497), methyl ester of 3-amino-2,5-dichlorobenzoic acid (amiben), N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine (benefin), S-propyl butylethylthiocarbamate (pebulate), S-propyl dipropylthiiocarbamate (vernolate), N,N-dimethyl-2,2-diphenylacetamide (diphenamid), dimethyl tetrachloroterephthalate (DCPA), 2,3,5-trichloro-4-pyridinol (pyriclor), and 2-(α-naphthoxy)-N,N-diethylpropionamide (R-7465). Soil incorporation of benefin, pebulate, and benefin + vernolate with a power-driven rotary cultivator gave superior weed control compared to incorporation by discing four times. Significant early-season stunting of tobacco plants was observed both years in plots where benefin (1.12 or 2.25 lb/A), benefin + vernolate (0.75 + 1.5 lb/A), or benefin + pebulate (1.12 + 4.0 lb/A) was incorporated by discing. No stunting was observed where incorporation was with the rotary cultivator except for benefin at 2.25 lb/A. Neither yield nor quality of the crop was reduced.

Absorption of (2,4-dichlorophenoxy)acetic acid (2,4-D) by honeyvine milkweed [Ampelamus albidus (Nutt.) Britt.] was 7.2, 9.3, and 10.9% of the applied herbicide at 1, 4, and 8 days after treatment, respectively. Addition of 1.0% v/v Tween 80 to the treatments increased absorption to 55.8, 71.3, and 78.7% at the same sampling dates. Metabolic alteration of the herbicide occurred only in the aerial portions of the plant, and this was not great enough to be considered as a means of resistance. Translocation of 2,4-D into the roots was more closely related to new root growth than to the amount of top growth. Plants with six leaves and no new root growth did not translocate 2,4-D into the root zone. Plants with the same number of leaves but with an average of five and 20 new roots translocated 2.5 and 7.7%, respectively, of the applied herbicide to the roots.