New fungicides and strategies for sustainable management of Sclerotinia and Rhizoctonia diseases on vegetable crops in A
Sclerotinia diseases are major threats to the sustainable production of many vegetable crops in Australia. They affect a wide range of vegetable crops. The availability of effective fungicides is critical for the management of Sclerotinia diseases. Green beans and lettuces are the two main vegetable crops that are highly susceptible to Sclerotinia diseases, where losses can range from 20% to 100%. In 2004, when procymidone was withdrawn from use on bean and lettuce crops in Australia, boscalid was identified as a suitable replacement fungicide. Boscalid is a new active ingredient that had not been registered for use in any vegetable crops in Australia. Currently, it is used under a temporary permit on the condition that the product will be registered for long term use in Australia. This project was aimed at facilitating trial studies to collate the necessary efficacy and residue data to expedite the registration of this product for long-term commercial use on vegetables in Australia. Efficacy trials in this project showed that boscalid was as effective as procymidone for Sclerotinia control under most conditions. However, similar to procymidone and other fungicides, its level of disease control can be influenced by crop variety, plant vigour and weather conditions. Boscalid was also shown to be highly effective on Botrytis. Trials in this project also established that Amistar (azoxystrobin, Syngenta Crop Protection Pty Ltd) has little or no effect in controlling Sclerotinia. Under relatively dry conditions, Du-Wett, a new spray adjuvant, was shown to enhance disease control by Filan. Twenty-three residue trials were conducted to provide the necessary data to support Filan (boscalid, Nufarm Australia Limited) registration in Australia for long term use in vegetables that are susceptible to Sclerotinia diseases: leafy vegetable groups, legume vegetables, brassica vegetables and root vegetables. The residue trials were conducted under Good Laboratory Practice (GLP) in Tasmania, Queensland, Victoria, South Australia and Western Australia. Applications to the Australian Pesticides and Veterinary Medicines Authority (APVMA) are in progress and its registration for use in leafy vegetable groups, legume vegetables, brassica vegetables and root vegetables is expected in 2011. Although Rhizoctonia solani is believed to be a limiting factor in crop productivity by many vegetable growers, there has been limited knowledge on the pathogen and its impact on vegetable crops. Not all Rhizoctonia can cause disease problems and it is important to find out which sub-groups are common in vegetable soils and whether they are pathogenic to vegetables. In this project, R. solani AG2.1 was the most common sub-group in vegetable soils, where it was found in 83% of the soil samples. AG2.1 was also shown to be the highly pathogenic to vegetables, causing severe damping off on peas, beans, cauliflowers and lettuces. In vegetables, there is also a lack of management options to control Rhizoctonia diseases. Trials were therefore conducted to evaluate novel non-chemical treatment methods as well as fungicides for their efficacy in controlling Rhizoctonia diseases. Seed treatments with azoxystrobin, fludioxonil or tolclofos-methyl were found to be more effective than Captan or Thiram in preventing early seedling damping off due to Rhizoctonia. Azoxystrobin and tolclofos-methyl applied as infurrow soil applications at sowing were found to be the highly effective in preventing Rhizoctonia infections in infected soil. Azoxystrobin, applied as seed or in-furrow soil treatments caused a delay in seedling emergence, whereas tolclofos-methyl had no phytotoxic effects. Other non-chemical soil treatments including gypsum, molasses and biocontrol agents have little or no effect in soils inoculated with high levels of Rhizoctonia AG2.1.