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.

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.

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.

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.

The 14C-labelled insecticide, 2,3-dihydro-2,2-dimethyl-7-benzofuranyl methylcarbamate (carbofuran), supplied to the roots of barley (Hordeum vulgare L. ‘Larker’) and corn (Zea mays L. ‘Mich 400’) seedlings was readily taken up and transported to the shoots. Alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] did not inhibit carbofuran metabolism in barley or corn. Butylate (S-ethyl diisobutylthiocarbamate) slightly inhibited carbofuran metabolism in corn roots. Chlorbromuron [3-(4-bromo-3-chlorophenyl)-1-methoxy-1-methylurea] inhibited carbofuran metabolism by decreasing the concentration of 14C found in the acetone-insoluble residue and the methanol-soluble fraction in barley shoots. Chlorbromuron increased the carbofuran content and decreased the 2,3-dihydro-3-hydroxy-2,2-dimethyl-7-benzofuranyl methylcarbamate (3-hydroxycarbofuran) content of the chloroform-soluble fraction in both barley shoots and roots. Chlorbromuron did not affect carbofuran metabolism in corn.

Weed control trials were conducted on loblolly pine (Pinus taeda L.) or slash pine (Pinus elliottii Engelm.) seedbeds at 12 locations in the southeastern United States. Good weed control was obtained from 2,4-bis-(isopropylamino)-6-(methylthio)-s-triazine (prometryne) at 2.2 and 4.5 kg/ha; N,N-dimethyl-2,2-diphenylacetamide (diphenamid) at 4.5 and 9 kg/ha; α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) at 1.1 and 2.2 kg/ha; and 2-ethylthio-4,6-bis-isopropylamino-s-triazine (GS-16068) at 2.2 and 4.5 kg/ha as preemergence applications immediately followed by irrigation. Diphenamid and trifluralin treatments were not injurious to either pine species at either rate. GS-16068 was only slightly injurious at the high rate at one location. Prometryne was injurious at two locations at the high rate and at one location at the low rate.