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tomato powdery mildew

Pseudoidium neolycopersici


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Host plants / species affected

Main hosts

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Solanum lycopersicum (tomato)

List of symptoms / signs

Leaves - abnormal colours
Leaves - abnormal forms
Leaves - abnormal leaf fall
Leaves - fungal growth
Leaves - wilting
Leaves - yellowed or dead
Stems - mould growth on lesion
Stems - mycelium present
Stems - wilt


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.

Prevention and control

Cultural Control

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.

Chemical Control

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:

This information is part of a full datasheet available in the Crop Protection Compendium (CPC); For information on how to access the CPC, click here.


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).