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Powdery mildew in tomatoes

brown discolored leaf
A leaf displaying the Leveillula taurica strain of powdery mildew

By Scott Mathew, Solutions Development at Syngenta

Heading from the summer season into the autumn period, it’s important that you keep an eye on powdery mildew infections in your tomato crops.

Different strains of powdery mildew can infect tomato crops, namely Leveillula taurica and Oidium lycopersici.

Leveillula taurica appears on lower leaves as bright yellow spots ranging from 3 mm to 12 mm in diameter. The spots enlarge and eventually turn brown. As the infection progresses, the entire leaf withers and dies but remains attached to the stem. There are no symptoms on the stems or fruit. However, with extensive loss of foliage, many exposed fruit will become sunburnt or fail to develop.

Oidium lycopersici is extremely common in glasshouse tomatoes and increasing in significance in field tomatoes. The first symptoms occur as powdery white lesions on all aerial parts of the plants except the fruit. Severe infections lead to leaf chlorosis, premature senesces and a marked reduction in fruit size and quality.

AMISTAR TOP® is a broad-spectrum fungicide that combines the two active ingredients found in Syngenta’s proven fungicides, AMISTAR® and SCORE®. This unique combination offers growers flexibility, compatibility and proven protection against a number of tomato diseases including target spot / early blight (Alternaria solani), late blight (Phytophthora infestans), sclerotinia (Sclerotinia minor), powdery mildew (Leveillula taurica and Oidium lycopersici).


Controlling powdery mildew with AMISTAR TOP

As powdery mildew develops on the lower leaves and inner canopy, the best opportunity to protect plants and developing fruit is before disease establishes. AMISTAR TOP is ideal for two consecutive applications at flowering/fruit set.

The below table displays the results of a number of Australian trials conducted by Syngenta. 

These Australian trials specifically highlighted that:

AMISTAR TOP (500 mL/ha or 750 mL/ha) provides significantly better control of powdery mildew compared to a high application rate of AMISTAR 250SC when applied on a 14 day spray interval.
The application of AMISTAR TOP at the highest rate (750 mL/ha) and shortest spray interval (7 days) provided the best control of all treatments, rates and spray intervals investigated.