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Getting downy mildew under control | Ask the Industry

Preventative fungicides can be a useful tool to help avoid scenes like this in your crop.

With wet, cool weather upon us and shorter days, plants are growing more slowly. These conditions are conducive to the development of downy mildew, which can affect many vegetable crops, including lettuce, leafy vegetables, brassicas and cucurbits.

Downy mildew is an oomycete fungus, meaning it is water-loving and needs moisture to infect. Prolonged periods of leaf wetness and high humidity combined with low light intensity promotes disease development in the cooler months.

Plants are susceptible at all stages, from transplanting to harvest, both in greenhouses and field grown situations. Disease symptoms include premature yellowing and interveinal lesions on the upper leaf surface, and white fluffy fungal growth on the underside. Brassica crops may have a speckling appearance on the leaves which can turn brown and papery.

Poor air circulation in closed greenhouses during winter creates a perfect habitat for a rapid downy mildew outbreak. Cucumber crops can be particularly susceptible. It’s important to minimise leaf wetness and watch out for morning dew that leads to moisture for downy mildew to infect leaves.

Not all downy mildew is caused by the same fungal species. For example, downy mildew on lettuce (Bremia lactucae) cannot infect a brassica crop. A brassica crop is affected by the downy mildew fungus Peronospora spp. For this reason, it is important to select a fungicide that targets the downy mildew for your crop.

Preventative fungicide programs protect the crop from infection, particularly when wet weather is forecast. When we apply such products before disease symptoms appear, it is easier to get on top of the problem before the infection spreads.

ORONDIS® FLEXI is ideal for preventative protection against downy mildew and other common diseases, with dual modes of action for strong resistance management. For example, when used preventively on a brassica crop it will provide excellent protection against downy mildew, alternaria, white blister and sclerotinia. With an optimised formulation of azoxystrobin (Group 11) and oxathiapiprolin (Group 49), there is no need to tank mix with another fungicide when targeting downy mildew.

Copper fungicides are regularly used to control downy mildew, but do not enter the plant tissue. Fungicides, like ORONDIS FLEXI and REVUS® have translaminar movement into leaves to protect both the upper and lower leaf surfaces. Rapid movement into the plant also results in outstanding rainfastness within one hour, giving you the flexibility to apply the fungicide before a rain event or timed irrigation.

As downy mildew is considered high-risk for developing resistance to fungicides, CropLife provides resources to help you review your resistance management strategy, while providing information on fungicides with alternative modes of action.

By understanding when downy mildew can occur it becomes easier to implement an effective, preventative fungicide program to minimise the risk of downy mildew this season and help manage your resistance risk moving forward.

Dr Belinda (Brandy) Rawnsley

Syngenta Technical Services Lead - Horticulture and Viticulture




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