Plant Pathogens

Conservation biological control of plant pathogens is in the early stages of development but the technology shows great potential. The most recent work has been done on the grapevine/Botrytis cinerea system where the pathogen's life cycle was disturbed and levels of primary inoculum were reduced through the use of organic mulches or of cover crops, mulched in situ. Levels of primary inoculum from vine debris were reduced under mulch, through an increase in the activity of soil biota, both through competition with the pathogen for resources and through increasing rates of vine debris degradation. The changes in soil biota were linked to soil moisture and possibly soil nutrient levels. The vines under the organic mulches used in this work sustained half the rates of botrytis bunch rot at harvest, compared with nonmulch con trols, averaged over 2 years (Figure 1), and brought the disease below the economic threshold of the region. Progressive grape growers are now using organic mulches for this purpose in their vineyards. This adoption sets a precedent for other growers and large scale adoption of the technique is possible. Other advantages of the mulches that may help adoption are that they are easy to apply/manage and the materials they use are either cheap or waste stream products from the vineyard itself. This biological system is potentially applicable to other plant pathogen systems (e.g., downy mildew (Plasmopara viticola)) which over winter on plant debris. The technology could also be integrated into other understorey manipulation tech niques, such as the provision of flowering plants

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Economic threshold

Control Mown grass Anaerobic Aerobic marc Paper marc

Mulch treatments

Figure 1 Severity of botrytis bunch rot in grape vines at harvest, under different mulch treatments over two consecutive seasons in Seresin Estate Vineyard, Marlborough, New Zealand. Three of the mulch treatments bring botrytis bunch rot below the economic threshold in the second year.

(discussed above), where plants could be mulched after flowering.

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