Ann L. Hayes

EFFECTS OF SOME AGRICULTURAL TANK-MIX ADJUVANTS ON THE DEPOSITION EFFICIENCY OF AQUEOUS SPRAYS ON FOLIAGE

Abstract The effects of 10 commercially available tank-mix adjuvants on the retention and coverage of aqueous sprays on foliage were examined quantitatively under track sprayer conditions, following application at their maximum recommended rates. Substantial enhancement of fluorescein retention was observed only on water-repellent barley and peas, but the differences in performance between the additives were considerable. Addition of the water-soluble tallow amine and nonylphenol surfactants gave the largest increases in retention, whereas there was little improvement in efficiency compared with water alone after inclusion of either the latex- or pinolene-based products or ammonium sulphate. Retention enhancement was also achieved using the mineral oil, vegetable oil, methylated vegetable oil and phospholipid ECs and the organosilicone surfactant, but this was often much less than that obtained for the water-soluble surfactants; the best EC was the methylated vegetable oil which also had the highest emulsifier content. Although spray quality was altered significantly in the presence of many of the adjuvants, modifications to this parameter alone could not account for changes observed in deposition efficiency, because retention enhancement was recorded in sprays with volume median diameters both smaller and larger than water. There was a better correlation between retention efficiency and the dynamic surface tension of the corresponding spray liquids, with the exception of the organosilicone, which, as expected from its high surface activity, gave essentially complete spray coverage on leaves. Nevertheless, good coverage could still be achieved by adding the two water-soluble surfactants, as well as the methylated vegetable oil and phospholipid ECs. Coverage performance of the other adjuvants tested was poor in comparison, reflecting, in part, their inferior retention enhancing properties.

Sterols of the plant pathogenic fungi Botrytis cinerea and Pyrenophora teres

Abstract Botrytis cinerea and Pyrenophora teres , grown in liquid culture, contained only C 28 -sterols, principally ergosterol and ergosta-5,8,22-trienol.

Studies of mechanisms of metalaxyl fungitoxicity and resistance to metalaxyl

Abstract The mode of action of the systemic fungicide metalaxyl and possible changes in Phytophthora spp. leading to resistance to metalaxyl were investigated. Uptake of labelled uridine and thymidine into RNA and DNA were reduced by sub-lethal amounts of metalaxyl. There was no evidence that metalaxyl caused a build-up of nucleotides or blocked the DNA template. Metalaxyl metabolites were absent from the fungus and the medium; the unchanged fungicide is probably the primary toxic agent. Washing metalaxyl-treated mycelium with water removed about 80% of the fungicide but the rest was firmly bound. Metalaxyl-resistant and sensitive strains of Phytophthora had similar growth rates in vitro, took up similar amounts of fungicide and incorporated uridine into RNA at similar rates. The mechanism of resistance remains obscure: subtle alterations to nucleic acid synthesis may be involved but other possibilities remain.

A comparison of the biochemical and physiological effects of the systemic fungicide cyprofuram with those of the related compounds metalaxyl and metolachlor

Abstract Strains of Phytophthora megasperma insensitive to the fungicide metalaxyl showed limited cross-resistance to the structurally related fungicide cyprofuram and to metolachlor, a herbicide with antifungal properties. The three compounds each inhibited nucleic acid synthesis, but the wide variation in resistance factors and in the degree of nucleic acid inhibition at the concentrations inhibiting mycelial growth by 50% indicated that cyprofuram and metolachlor possess alternative mechanisms of toxicity. Studies with protoplasts suggested that cyprofuram has a direct effect on the plasma membrane which may be important against those resistant strains where nucleic acid synthesis is least affected. Metolachlor also was extremely effective in causing protoplast lysis. Sporangia production by P. palmivora was stimulated by low concentrations of cyprofuram, and germination was delayed. As with other ‘acylalanine-type’ fungicides, inhibition of nucleic acid synthesis is considered to be the main mode of action. Some degree of cross-resistance between cyprofuram and other acylalanines is likely to occur in the field but the dual mode of action of cyprofuram might delay its onset. The effect of increased sporogenesis on the development of resistance is more difficult to assess.

Relationships between the herbicidal activity and foliar uptake of surfactant-containing solutions of glyphosate applied to foliage of oats and field beans

Abstract The enhancement effects of a C 13 /C 14 series of aliphatic alcohol (A) surfactants on the herbicidal activity of glyphosate-(monoisopropylammonium) were examined using a model formulation system that enabled relative performance to be assessed at equivalent spray deposition rates. Surfactants with mean molar ethylene oxide (E) contents of 11, 15 and 20 were more effective in increasing glyphosate activity against oats ( Avena sativa L.) than AE6, when the herbicide was sprayed at 54 or 108 g acid equivalent (a.e.) ha −1 . At the lower herbicide dose, these surfactants, when added at 1 and 5 g I −1 caused ∼70% more reduction in foliage weight than the herbicide alone, compared with a ∼50% greater reduction at 0.2 g l −1 . However, there was no significant concentration effect on enhancement with the same three surfactants at the higher herbicide dose. On field bean ( Vicia faba L.), surfactant E content had little influence on herbicide enhancement compared with surfactant concentration. This effect was noticeable only with glyphosate at 54 g a.e. ha −1 , with the highest surfactant concentration (5 g l −1 ) inducing a ∼35% greater reduction in foliage weight than herbicide without surfactant. At the higher glyphosate rate there were only modest improvements in efficacy on this species after surfactant addition. Results obtained from experiments using 0.2 μl droplet applications of formulations containing [ 14 C]glyphosate at herbicide (0.35 and 0.7 g l −1 ) and surfactant concentrations equivalent to those of the spray solutions, showed that the corresponding enhancements in uptake and translocation of the radiolabel correlated well with the observed improvements of herbicidal activity on oats but not on field bean. On both species, AE6 was antagonistic to uptake of radiolabelled herbicide. Increased herbicide absorption or biological activity did not appear to be related to the spreading properties of the surfactant-containing formulations on the two target surfaces. The implications of these findings are discussed with reference to the problems of predicting and optimizing the performance of agrochemical formulations with surfactant adjuvants.