Crop protection without copper-based fungicides

4 Crop protection without copper-based fungicides 

Disease-resistant varieties are attractive because they should pose little or no risk to the environment and enable growers to reduce and in some cases eliminate the need for pesticides. In some host-pathogen systems, resistance may persist for many years, but in others it may be short-lived (Koike et al., 2000). Unfortunately, resistance is not available to counter every disease and for some of the most damaging ones, such as tomato late blight (P. infestans) and white rot (Sclerotium cepivorum) of alliums, no acceptable resistant varieties are currently available. 

Crop rotation using a range of contrasting crops (including cover crops or a period of fallow) can decrease soilborne pathogen inocula, increase diversity in soil microflora over time and be unfavourable for the of spread foliar diseases in the shorter term. This reduces the need for pesticides. 

Crop rotation is the keystone of organic cropping systems and its importance is emphasized by all organic crop production standards, not only for its role in crop protection, but also for its contribution to soil fertility. Soil fertility may influence the severity of disease infection or offset its effects by accelerating the build-up of yield before the disease takes its toll. This aspect is considered further in Section 18.4.4. 

In many cases, the incorporation of organic matter in the soil may be a beneficial alternative to chemicals for plant disease control. Lor example, Viana et al. (2000) reported that matured cattle manure and sugarcane husks are efficient alternatives for control of bean damping-off (Sclerotinia sclerotiorum). Larmyard manure applied at 5 t/ha once every three years reduced dry root rot (Macrophominaphaseolina) to 32% in groundnut (Arachis 

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