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White Mould in Drybean: How It Can Affect Your Rotation

By: Harold Brown, Senior Market Development Specialist, Bayer CropScience

What is White Mould?

Growers of all crops know the dangers of unpredictable weather for their fields. For farmers of dry and edible beans specifically, moist and humid conditions during vegetative development and flowering can mean disaster, as these conditions promote the growth of white mould. Ideal environments for the development of the disease are extended periods of moist conditions resulting in high relative humidity. Germination of the sclerotia, which eventually give rise to the spores responsible for initial infection is favoured in these damp soil conditions. White mould infections that are not managed eventually produce more of these sclerotia that can then survive in the soil for up to five years, affecting future susceptible crops.

When it comes to white mould, the stakes are high for dry bean growers. Twenty per cent yield losses are not uncommon, and yield losses up to 65 per cent have been confirmed in severely infected fields.

What can growers do about white mould?

Unfortunately, no dry bean variety is completely resistant to infection, and management once infection has occurred is difficult. That’s why the best management option Canadian growers have is prevention.

Here are four tips all dry bean growers should consider to help combat white mould:

Crop Rotation
Since sclerotia can live within soil for several years, it is important to avoid growing susceptible broad-leaf crops back-to-back in rotation. Instead, take advantage of a rotation that includes non-host crops like cereals and other grasses, with a minimum of one year and preferably three years between susceptible crops. Rotations that include susceptible crops with a high capability to return viable sclerotia to the soil (e.g. canola, sunflowers and borage) will limit the effectiveness of crop rotation on sclerotia reduction.

Variety Selection and Row Spacing
Although no dry bean variety is resistant to white mould, there are certain types that are less prone to developing infections. These tend to be shorter, less viny and with stronger stalks (leading to less lodging). Also, to help the soil dry out after rain, thereby reducing local RH levels and soil moisture, rows can be planted further apart to allow more sunlight to reach the surface. Keep in mind though that planting in wider rows could lead to decreased yield, and may not be as cost effective as preventatively applying a fungicide.

Weed Control
Weed control is often overlooked when it comes to white mould management. Unwanted plants can block sunlight and contribute to the shady and moist conditions favoured by white mould. Many broadleaf weeds that are common within dry bean growing areas, such as stinkweed and wild mustard, are also hosts to the pathogen responsible for white mould infections. This means that even if a long-term crop rotation is established, inconsistent weed management can contribute to sclerotia development, potentially leading to future infections.

Fungicide Application
For any grower, one of the most powerful tools against white mould is a fungicide treatment plan. An effective plan for dry and edible beans is to apply a fungicide just prior to when the first pin bean is formed, and if prevailing weather conditions are conducive to disease development, again 10-14 days later. An ideal fungicide application provides good coverage of the entire plant, particularly the flowers, which are where white mould spores often begin their infection. Luckily, dry bean growers now have more fungicide options than ever before. Earlier this year, Bayer CropScience introduced Propulse, which is a multi-mode of action fungicide (Groups 3 and 7) that has proven to be an effective means of white mould prevention. Field trials with heavy white mould infection have shown an average of a 35 per cent yield increase over untreated fields.

White mould is a challenging reality facing dry and edible bean growers across the country. A prevention plan that integrates multiple strategies, such as those listed above, provides the best chance of limiting the damage this disease can have on your crop on an annual basis. Through these methods, we can help ensure that in the future, both yield and dry bean quality are at a level Canadian growers can continue to be proud of.

Source: Bayer CropScience Released