Surfactant‐induced deposit structures in relation to the biological efficacy of glyphosate on easy‐ and difficult‐to‐wet weed species

BACKGROUND: Typical active ingredient (AI) residue patterns are formed during droplet drying on plant surfaces owing to the interaction of spray solution characteristics and leaf micromorphology. Currently, comparatively little is known about the influence of AI deposit patterns within a spray droplet residue area on the penetration and biological efficacy of glyphosate. A scanning electron microscope with energy dispersive X‐ray microanalysis has been used to characterise residue patterns and to quantify the area ultimately covered by glyphosate within the droplet spread area. RESULTS: The easy‐to‐wet weed species Stellaria media L. and Viola arvensis L., as well as the difficult‐to‐wet Chenopodium album L. and Setaria viridis L., differing in their surface micromorphology, have been used. Rapeseed oil ethoxylates (RSO 5 or RSO 60) were added to glyphosate solutions to provide different droplet spread areas. Addition of RSO 5 enhanced droplet spread area more than RSO 60, and both caused distinct glyphosate residue patterns. The biological efficacy of treatment solutions showed no significant correlation with the area ultimately covered by glyphosate. CONCLUSION: The results have implications on herbicide uptake models. This study shows that droplet spread area does not correspond to the area ultimately covered by glyphosate, and that the latter does not affect glyphosate phytotoxicity. Copyright © 2009 Society of Chemical Industry     

The use of digital image analysis and real‐time PCR fine‐tunes bioassays for quantification of Cercospora leaf spot disease in sugar beet breeding

Cercospora leaf spot, caused by the fungus Cercospora beticola, is a major fungal sugar beet disease worldwide and the cause of significant yield losses. The disease is most successfully countered by the introduction of genetic tolerance into elite sugar beet hybrids. To this end, breeding programmes require high quality biological assays allowing discrimination of minor differences between plants within a segregating population. This study describes the successful implementation of image analysis software in the bioassays for quantification of necrotic lesions at different stages of C. beticola infection, allowing selection on minor phenotypic differences during the sugar beet breeding process for C. beticola resistance. In addition, a real‐time PCR assay was developed for the quantification of C. beticola pathogen biomass in infected beet canopy. The use of both techniques, even in an early stage of infection, fine‐tunes current bioassays, allowing more accurate and efficient selection of resistant breeding material.     

Production of <Emphasis Type="Italic">Guignardia bidwellii</Emphasis> conidia on grape leaf lesions is influenced by repeated washing events and by alternation of dry and wet periods

The ascomycete Guignardia bidwellii is an economically important pathogen in many grapevine-growing areas. Primary infections are caused by ascospores and conidia produced in mummified berries and in cane lesions. Secondary infections are caused by the conidia produced by pycnidia formed in leaf lesions and, in later season, in rotted berries. Environment-controlled experiments were conducted to study the production dynamics of G. bidwellii conidia on grape leaf lesions as influenced by: i) repeated washing events, and ii) alternate dry and wet periods. Under optimal environmental conditions (25 °C, 100 % relative humidity), production of conidia declined over washings and was almost completely depleted after four washings. When pycnidia were kept in a low humidity environment (average of 54 % relative humidity) between two successive washings, the production of conidia progressively diminished as the time between washings increased, with few conidia being still produced after 87 days. This decline in conidial production was faster at 29 °C than at 20 °C. This information is relevant in that it determines the potential of black-rot lesions to produce conidia along the grape-growing season and, therefore, their contribution to epidemic development.