Efficacy of fungicides on mycelial growth of diatrypaceous fungi associated with grapevine trunk disease

Several species of Diatrypaceae have been recently isolated from the wood of cankered grapevines in several regions of the world and shown to be pathogenic with varying degrees of virulence when inoculated in stems of potted vines. Existing management strategies have focussed on the evelopment of procedures and products to prevent or reduce Eutypa lata infection. The best method to prevent infection is by applying fungicides to wounds, but there are few registered chemicals for any of the diatrypaceous fungi in Australia. Six selected fungicides were evaluated in vitro for their efficacy in reducing mycelial growth of Eutypa lata, Cryptovalsa ampelina, Diatrypella vulgaris, Eutypa leptoplaca, Eutypella citricola and Eutypella microtheca. Carbendazim, fluazinam, tebuconazole, and prothioconazole + tebuconazole were effective at inhibiting mycelial growth of all Diatrypaceae spp. tested. Pyraclostrobin reduced colony diameter of most of the fungal species by 50% or more. Pyrimethanil was ineffective at reducing mycelial growth of these pathogens. Five of the six fungicides evaluated in this study have shown efficacy in vitro against Diatrypaceae spp. and require further evaluation in the field. This study represents the first approach for fungicide evaluation against mycelial growth of diatrypaceous fungi, other than Ea. lata. It contributes to the development of integrated management strategies for grapevine trunk diseases. © 2011 Australasian Plant Pathology Society Inc.Peer Reviewe

Soil solarization and sustainable agriculture

Pesticide treatments provide an effective control of soilborne pests in vegetable and fruit crops, but their toxicity to animals and people and residual toxicity in plants and soil, and high cost make their use hazardous and economically expensive. Moreover, actual environmental legislation is imposing severe restrictions on the use or the total withdrawal of most soil-applied pesticides. Therefore, an increasing emphasis has been placed on the use of nonchemical or pesticide-reduced control methods. Soil solarization is a nonpesticidal technique which kills a wide range of soil pathogens, nematodes, and weed seeds and seedlings through the high soil temperatures raised by placing plastic sheets on moist soil during periods of high ambient temperature. Direct thermal inactivation of target organisms was found to be the most important mechanism of solarization biocidal effect, contributed also by a heat-induced release of toxic volatile compounds and a shift of soil microflora to microorganisms antagonist of plant pathogens. Soil temperature and moisture are critical variables in solarization thermal effect, though the role of plastic film is also fundamental for the solarizing process, as it should increase soil temperature by allowing the passage of solar radiation while reducing energetic radiative and convective losses. Best solarizing properties were shown by low-density or vynilacetate- coextruded polyethylene formulations, but a wide range of plastic materials were documented as also suitable to soil solarization. Solar heating was normally reported to improve soil structure and increase soil content of soluble nutrients, particularly dissolved organic matter, inorganic nitrogen forms, and available cations, and shift composition and richness of soil microbial communities, with a marked increase of plant growth beneficial, plant pathogen antagonistic or root quick recolonizer microorganisms. As a consequence of these effects, soil solarization was largely documented to increase plant growth and crop yield and quality along more than two crop cycles. Most important fungal plant pathogenic species were found strongly suppressed by the solarizing treatment, as several studies documented an almost complete eradication of economically relevant pathogens, such as Fusarium spp., Phytophthora spp., Pythium spp., Sclerotium spp., Verticillium spp., and their related diseases in many vegetable and fruit crops and in different experimental conditions. Beneficial effects on fungal pathogens were stated to commonly last for about two growing seasons and also longer. Soil solarization demonstrated to be effective for the control of bacterial diseases caused by Agrobacterium spp., Clavibacter michiganensis and Erwinia amylovora, but failed to reduce incidence of tomato diseases caused by Pseudomonas solanacearum. Solarization was generally found less effective on phytoparasitic nematodes than on other organisms, due to their quicker soil recolonization compared to fungal pathogens and weeds, but field and greenhouse studies documented consistant reductions of root-knot severity and population densities of root-knot nematodes, Meloidogyne spp., as well as a satisfactory control of cyst-nematode species, such as Globodera rostochiensis and Heterodera carotae, and bulb nematode Ditylenchus dipsaci. Weeds were variously affected by solar heating, as annual species were generally found almost completely suppressed and perennial species more difficult to control, due to the occurrence deep propagules not exposed to lethal temperature. Residual effect of solarization on weeds was found much more pronounced than on nematodes and most fungal pathogens. Soil solarization may be perfect fit for all situations in which use of pesticides is restricted or completely banned, such as in organic production, or in farms located next to urban areas, or specialty crops with few labeled pesticides. Advantages of solarization also include economic convenience, as demonstrated by many comparative benefit/cost analyses, ease of use by growers, adaptability to many cropping systems, and a full integration with other control tools, which makes this technique perfectly compatible with principles of integrated pest management required by sustainable agriculture