kresoxim-methyl and fenpropimorph

The behaviour of (semi-)volatile organic compounds at the interface between the leaf surface and the atmosphere was investigated by finite-element numerical simulation. Three model systems with increasing complexity and closeness to the real situation were studied. The three-dimensional model systems were translated into appropriate grid structures and diffusive and convective transport in the leaf/atmosphere interface was simulated. Fenpropimorph (cis-4-[3-(4-tert-butylphenyl)-2-methylpropyl]-2,6-dimethylmorpholine) and Kresoxim-methyl ((E)-methyl-2-methoxyimino-2-[2-(o-tolyloxy-methyl)phenyl] acetate) were used as model compounds. The simulation showed that under still and convective conditions the vapours emitted by a point source rapidly form stationary envelopes around the leaves. Vapour concentrations within these unstirred layers depend on the vapour pressure of the compound in question and on its affinity to the lipoid surface layers of the leaf (cuticular waxes, cutin). The rules deduced from the numerical simulation of organic vapour behaviour in the leaf/atmosphere interface are expected to help in assessing how (semi-)volatile plant products (e.g. hormones, pheromones, secondary metabolites) and xenobiotics (e.g. pesticides, pollutants) perform on plant surfaces.

Topics: Algorithms; Atmosphere; Chemical Phenomena; Chemistry, Physical; Computer Simulation; Convection; Diffusion; Fungicides, Industrial; Methacrylates; Models, Biological; Morpholines; Phenylacetates; Plant Epidermis; Plant Leaves; Strobilurins; Volatilization; Waxes

Strobilurin fungicides have a broad spectrum activity against all major foliar pathogens of wheat. In addition to this extraordinary fungicidal activity side-effects have been reported which result in higher yields of cereals, e.g. the reduction of respiration, delayed leaf senescence, activation of nitrogen metabolism as well as increased tolerance against abiotic stress factors. In the vegetation period 2000/2001 field trials were carried out at three sites in North Rhine-Westphalia to study the effects of three strobilurin fungicides on the yield formation of six winter wheat varieties. The strobilurins were applied two times as the commercial products Stratego (trifloxystrobin + propiconazole), Amistar/Pronto Plus (azoxystrobin/spiroxamine + tebuconazole) and Juwel Top (kresoxim-methyl + epoxiconazole + fenpropimorph. Fungicide-treated plants were kept disease-free by an initial azole-application in GS 31 in order to exclude disease effects on physiological parameters relevant to yield formation. Photosynthetic electron transport of strobilurin-treated wheat, was improved as early as at GS 65 compared to azole-treated plants. Differences often increased with growth stage and were closely related to a delay in leaf senescence. A higher photosynthetic activity of strobilurin-treated plants was confirmed by gas exchange and chlorophyll fluorescence measurements under field conditions. The yield benefit of wheat from strobilurin treatments varied from 2% to 9% depending on an improved photosynthetic capacity due to a higher and/or prolonged activity. Neither yield potential nor disease susceptibility of the cultivar had an effect on the height of the extra yield which, in contrast was modified by location and wheat genotype.

Topics: Acetates; Acrylates; Azoles; Chlorophyll; Epoxy Compounds; Fungicides, Industrial; Germany; Imines; Methacrylates; Morpholines; Phenylacetates; Photosynthesis; Pyrimidines; Strobilurins; Triazoles; Triticum