Agronomic outcomes of IPM control of citrus thrips in Riverland soils


Abstract: SARDI has undertaken trials with compost mulch, grape mark and animal manureat sites on three citrus orchards in South Australia for a number of years. The trials wereestablished to evaluate the potential of soil amendments as part of an integrated managementprogram for Kelly’s citrus thrips. Experimental sites were designed to obtain best possibledata for pest management within budget limitations, subsequently, the agronomic andenvironmental data was in some cases restricted to one site and selected representativetreatments. A range of data was collected, increasing fruit yields, fruit, soil, leaf, and waterquality measures and biological changes, and the potential for water savings assessed. Thefield trials involved application of various rates of compost to crops, ranging from 40-200m3ha-1 for compost mulch, 100-200m3 ha-1 for grape mark, and 10-40m3 ha-1 for animal manure.The recycled green waste and composted animal manure have provided significant pestmanagement and agronomic benefits through suppression of KCT and improved yield andfruit size. There were considerable economic net benefits from every type of trial applicationto citrus at both sites over the three year period assessed. For example, for every dollarinvested in an application of 40m3 ha-1 compost mulch at Loxton North, a return of about $5dollars was realised. Returns ranged from $1.90 to $5.38. There also is the benefit ofimproved water and nutrient efficiencies that could provide significant cost savings. Thelongevity of these benefits remains unknown and needs to be further evaluated, but is likelyto be greater than the three year duration of these trials, and five years used in estimatingreturns for high rate applications. Whilst the grape mark treatments improved yields, and arecheaper than the composted green waste, the level of suppression of KCT was not as good asthat provided by the compost, and the increased acidity that resulted from the high phosphatelevels associated with the grape mark treatments could result in reduced quality. It seems thathigher levels of application for compost mulch create more sustainable outcomes; howeverthis does not apply for grape mark or animal manure.

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