The active concentration of a pesticide declines with time due to volatilization, absorption and translocation, microbial degradation, adsorption on soil particles and plant parts, chemical reactions, photodecomposition, and other reactions with the environment. However, slow-release formulations can provide a continuing input of pesticide. This leads to a rise and subsequent fall in the active concentration. Because diffusion is a factor in most controlled release methodologies, the concentration to be expected for release by diffusion of a substance, which then decays with time by a first order rate law, is examined theoretically. This provides guidance to the experimenter for separating the effects due to diffusion from these attributable to other and newer concepts such as water-degradable polymers. An approximate result of this exact solution is that the persistence of the substance can be increased. More precisely, the long-term behavior is like that of a more persistent pesticide with smaller first-order rate constant.

Application of 10-8 M 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) to the roots of 10-day old barley (Hordeum vulgare L. ‘Coho’) seedlings grown in nutrient cultures increased the water-soluble protein content when grown at 20 C day, 15 C night with 3 mM nitrate nitrogen. The water-soluble carbohydrate content decreased with increases in water-soluble protein. In a time-course study simazine increased 14C-leucine incorporation into protein prior to increasing nitrate uptake, indicating that simazine may have a direct influence on protein synthesis. The nonherbicidal metabolite of simazine, 2-hydroxy-4,6-bis(ethylamino)-s-triazine (hydroxysimazine), did not affect 14C-leucine incorporation into protein.

The absorption and translocation patterns of terbutryn [2-(tert-butylamino)-4-(ethylamino)-6-(methylthio)-s-triazine] and propazine [2-chloro-4,6-bis(isopropylamino)-s-triazine] were determined in wheat (Triticum vulgare Vill. ‘Kaw’) and sorghum (Sorghum bicolor L. ‘RS 612’). Bioassay studies showed sorghum to be tolerant and wheat susceptible to terbutryn. Absorption and translocation of uniform 14C-labeled terbutryn from 1 to 24 hr after initial treatment showed the roots of sorghum and the foliage of wheat to be the major sites of radioactivity accumulation. Foliage was the major site for propazine accumulation with both plant species. Thin-layer chromatography of extracts from terbutryn-treated plants showed that sorghum contained a higher percentage of metabolic breakdown products in the foliage than did the root systems, and wheat contained a high percentage of intact terbutryn in the foliage and roots. High temperature (32 C) enhanced translocation of terbutryn and propazine in both sorghum and wheat. The susceptibility of wheat and sorghum to terbutryn appears to be correlated with a combination of the factors of accumulation within the foliage of the plant and the ability to degrade the terbutryn molecule.

Greenhouse studies showed that common cocklebur (Xanthium pensylvanicum Wallr.), green foxtail (Setaria viridis (L.) Beauv.), sunflower (Helianthus annuus L.), and velvetleaf (Abutilon theophrasti Medic.) were selectively controlled with postemergence herbicides in soybeans (Glycine max (L.) Merr. ‘Ford’). In the field the control of velvetleaf in soybeans was obtained by applying a postemergence-directed herbicide when soybeans were 15 cm tall and had the second trifoliolate leaf present. Postemergence-directed herbicides did not adequately control grass weeds. It was necessary to use a preplant or preemergence herbicide for grass control. Mechanical removal of lower leaves of soybean plants grown in the greenhouse significantly decreased yield. However, with field-grown ‘Amsoy’ soybeans mechanical removal of cotyledons, unifoliolate, and the first trifoliolate leaves did not reduce yield.

Autoradiography and radioassay results indicated that 14C-picloram (14C-4-amino-3,5,6-trichloropicolinic acid) was absorbed and translocated rapidly in Canada thistle [Cirsium arvense (L.) Scop.], soybean [Glycine max (L.) Merr. ‘Harosoy 63’], and barley (Hordeum vulgare L. ‘Parkland’) following foliar or root application. Foliar absorption was much faster and more complete in soybean and Canada thistle than in barley. The radioactivity from 14C-picloram accumulated in shoot meristems in Canada thistle and soybean, whereas in barley it was distributed throughout the plant following uptake by foliage or roots. Decarboxylation of 14C-picloram by foliarly-treated Canada thistle, soybean, and barley plants did not occur in appreciable amounts. Chromatographic analysis of ethanol extracts of plants treated with 14C-picloram up to 20 days revealed no evidence of picloram metabolism by these plant species. It is concluded that differences in absorption and in distribution patterns of picloram after shoot or root uptake contribute greatly to the expression of its selective action in the species studied.

Seven cultivars of spring wheat (Triticum aestivum L.) and one hybrid (Triticale hexaploid Lart. ‘Rosner’) were evaluated in seven field experiments and one greenhouse test for tolerance to the postemergence application of the sodium salt of trichloroacetic acid (TCA) for the control of green foxtail (Setaria viridis (L.) Beauv.). The control of green foxtail and broadleaf weeds was also studied. Of the seven cultivars, ‘Pitic 62’ and ‘Stewart’ were most susceptible to injury from TCA. All other cultivars were tolerant to 0.56 kg/ha. ‘Selkirk’ appeared to be most resistant. With ‘Manitou’ 0.56 kg/ha of TCA gave about 50% control of green foxtail. Higher rates permitted increased growth of broadleaf weeds as a result of reduced competition from injured wheat and green foxtail. Control of all weeds was improved by 10 to 30% when TCA was applied with one of the phenoxy herbicides. Satisfactory crop tolerance and good weed control was achieved with 0.56 kg/ha TCA and 0.56 kg/ha of the amine salt of (2,4-dichlorophenoxy)acetic acid (2,4-D).

Tall morningglory [Ipomoea purpurea (L.) Roth] seeds were germinated at various temperatures and dry weight conversion measured at 24, 48, 72, 96, and 120 hr. Germination and dry weight conversion were slower at the lower temperatures although both occurred. Tall morningglory could germinate and become established over a wide range of temperatures. Some herbicides were effective in reducing germination, and dry weight conversion was reduced most with the dithiocarbamates followed in sequence by the amides, benzoic acids, uracils, dinitroanilines, phthalamic acids, triazines, and ureas.

Autoradiographic studies showed that regardless of whether 5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone (pyrazon) was applied to the leaves or to the roots of sugar beet (Beta vulgaris L.) plants, it moved in the apoplastic system. The pattern of pyrazon distribution from root absorption in sugar beet seedlings was identical at either 35 or 18.3 C. However, root absorption at 35 C was twice as great as at 18.3 C; and translocation of pyrazon into the shoot was more rapid at the high temperature. A major metabolite of pyrazon, a pyrazon-glucose conjugate, was produced in leaves and cotyledons but not in roots of sugar beets. A minor metabolite, less than 5%, was found in sugar beet leaves. Pyrazon was not metabolized by the susceptible species common lambsquarters (Chenopodium album L.). The rate of pyrazon-glucose conjugate formation in pyrazon-infiltrated sugar beet leaf discs was practically identical at 35 and 18.3 C. Therefore, it was concluded that the increased susceptibility of sugar beets to pyrazon at higher temperatures was due to an increase in absorption and translocation of the herbicide at higher temperatures which was not accompanied by a parallel increase in the conversion of pyrazon to its glucose conjugate.

Preplant or preemergence application of 2-chloro-2′, 6′-diethyl-N-(methoxymethyl) acetanilide (alachlor) at 3.36 or 4.48 kg/ha effectively controlled yellow nutsedge (Cyperus esculentus L.) in field and greenhouse studies. Depth of tubers in the soil did not affect response to alachlor. Alachlor at 3.36 kg/ha only controlled yellow nutsedge effectively in soils with less than 6% organic matter. Alachlor at 3.7 × 10-6 M and 1.8 × 10-4 M inhibited growth and killed newly emerging shoots in petri dish cultures. However, alachlor did not inhibit sprouting of yellow nutsedge tubers.

Placing hydrilla (Hydrilla verticillata Royle) in 2.7 and 5.4 μM solutions of carbon-14-labeled endothali [7-ox = abicyclo(2,2,1)heptane-2,3-dicarboxylic acid] under controlled conditions resulted in a sigmoid-shaped uptake curve for both herbicide concentrations. Apical sections of hydrilla, which included the apical bud, absorbed greater amounts of endothall-14C than sections excised from the center of the plant below the apical bud. Low concentrations of copper as copper sulfate pentahydrate solutions of 0.4 and 2.0 μM in combination with endothall-14C increased the amount of radioactivity found in hydrilla, but copper concentrations of 4.0, 8.0, and 16.0 μM inhibited endothall-14C uptake. The greatest uptake by hydrilla in 5.4 and 2.7 μM solutions of endothall-14C exposed to temperatures of 10, 20, and 30 C occurred in the 20 and 30 C solutions, respectively. Endothall-14C uptake was studied under light intensities of 0, 540, 5400, and 21,500 lux. Uptake of radioactivity from 2.7 and 5.4 μM solutions of endothall-14C was greatest at 540 and 21,500 lux, respectively.

The main site of uptake of soil-applied 2-chloro-2′, 6′-diethyl-N-(methoxymethyl) acetanilide (alachlor) by yellow nutsedge (Cyperus esculentus L.) plants is the portion of the plant above the tuber. Primarily acropetal and some basipetal 14C translocation occurred from 14C-alachlor applications to seedlings with shoots 2 to 4 cm in length. Alachlor is metabolized rapidly in yellow nutsedge to at least one water-soluble metabolite. Applications of 14C-alachlor to shoots 15 cm in length resulted in limited acropetal 14C translocation.

Twenty herbicides were tested for activity in a paper disc agar bioassay. The growth of Chlorella pyrenoidosa Chick was inhibited by dinoseb (2-sec-butyl-4,6-dinitrophenol), diquat [6,7-dihydropyrido(1,2-a:2′,1′-c)pyrazinediium ion], paraquat (1,1′-dimetnyl-4,4′-bipyridinium ion), 3′,4′-dichloro-2-methylvaleranilide, propachlor (2-chloro-N-isopropylacetanilide), and linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea]. The growth of Bacillus subtilis Cohn was inhibited by dinoseb, diquat, paraquat, and 3′,4′-dichloro-2-methylvaleranilide. This assay using C. pyrenoidosa or B. subtilis offers a convenient means for the testing of herbicides.

Investigations were undertaken to ascertain whether residues of soil-applied carbaryl (1-naphthyl N-methyl carbamate) and diazinon [O,O-diethyl-O-(2-isopropyl-4-methyl-6-pyrimidyl) phosphorothioate] insecticides may be absorbed from the soil and translocated to foliage of rice (Oryza sativa L. ‘Nahda’) and to determine the phytotoxic interaction between them and foliar-applied propanil (3′,4′-dichloropropionanilide). Results from greenhouse studies showed that carbaryl and diazinon were translocated and affected hydrolytic activity in rice shoots at all rates of application. Carbaryl was more inhibitory but diazinon persisted longer in the soil. When propanil was applied in the presence of diazinon, no additive phytotoxicity occurred on rice plants over that occurring from propanil alone. Synergistic effects in rice, resulting in dry weight loss, were marked when soil was treated with 5 mg of diazinon per kilogram of soil and subsequently sprayed with propanil. Synergistic phytotoxicity was apparent when propanil was applied 1 day after carbaryl treatment and most plants were killed. Slight injury was noticed on plants treated with propanil 2 weeks after carbaryl treatment at 1 and 5 mg/kg.