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The first symptoms of the disease caused by O. neolycopersici consist of white patches of external sporulating mycelia on the upper surface of the leaves and stems. Occasionally, yellow chlorotic spots also appear on the leaves. The white fungal colonies gradually enlarge, merge together, and finally cover large surfaces of the leaf and stem tissues. White mycelial patches may appear on the lower leaf surfaces, petioles and also the calyx. The infected plant tissues finally wither and die. There are no symptoms on the fruit. Severe infections cause leaf chlorosis, premature senescence and a reduction in fruit size and quality (Mieslerova and Lebeda, 1999; Jones et al., 2001). The disease occurs in both greenhouse and field tomato production, but causes more economic damage under greenhouse conditions.
General agro-technical practices such as the removal of infected plant residues and adequate spacing between plants help to reduce both the risk of infection and the disease severity. High relative humidity (>90%) may reduce disease development (Whipps and Budge, 2000). Excessive nitrogen fertilization probably results in more severe infection.
Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:
Severe infections caused by O. neolycopersici lead to a reduction in fruit size and quality, especially if they start early in the growing season (Jones et al., 2001). Infections later in the growing season may not result in yield loss (Dik, 1999) but the inoculum present in the greenhouse could become a threat for the next harvest. There are no data on the impact of O. neolycopersici on plant species other than tomato, although it can infect a large variety of crops, ornamentals and wild plant species (Whipps et al., 1998; Jones et al., 2001).