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Keep an eye out for white mould in Ontario’s dry bean crops


July 16, 2020
By OMAFRA Field Crop Team

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Dry beans are either approaching flowering or have already started flowering across Ontario. White mould is an important disease of dry beans in Ontario, and in-crop management of white mould occurs during flowering. White mould spores can land on stems, leaves or pods, but deteriorating flower petals are very susceptible to infection.

Spores colonize flower tissue, and the disease enters otherwise healthy plant tissues when infected flower petals land on leaves or stems. Infection can then rapidly spread across neighbouring plants in the field. Risk factors for white mould include a field history of white mould, short crop rotations with susceptible crops, a dense canopy and warm (20-25 C), moist weather conditions.

Fungicide applications that coat flowers can help prevent the disease from infecting healthy plant tissue. Timing fungicide applications when there are one to three pin beans present on plants promotes good coverage of flower petals. If white mould risk is very high because of wet conditions, a two-pass program with applications at early bloom and again seven to 10 days later may be warranted.

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In dry bean trials conducted by Chris Gillard with the University of Guelph, Ridgetown campus, the top performing white mould fungicides in terms of disease severity, yield and return on investment have been Senator, Allegro, Propulse and Lance.

Temperatures above 28 C generally keep white mould at bay, and dry conditions do not favour mould development. However, risk of white mould in dry beans continues throughout the summer with continued flowering. Varieties or dry bean classes with longer flowering windows may have late season onset of mould, so producers should continue to monitor conditions and consider risks beyond the first pin bean.

Manitoba Pulse & Soybean Growers have a fungicide decision worksheet for managing white mould in dry bean that assists in evaluation of risk based on rainfall, temperature, humidity and other dry bean management factors. It can be found in the production resources section on the Manitoba Pulse and Soybean Growers website.

There is also an app called Sporecaster, developed by the University of Wisconsin-Madison, designed to assist soybean producers in making management decisions for white mould in soybeans. It uses local weather data based on the location of your mobile device. It can be found in the app store on your mobile phone.

Dry bean and soybean producers are also encouraged to continue monitoring for insect pests. Spider mites proliferate under hot, dry conditions. Scout field edges first and look for plants that are yellow or bronze in colour, look drought-stressed or sand-blasted. Dry bean producers should also monitor for potato leafhopper and tarnished plant bug. Western bean cutworm moths are just starting to fly, with very low numbers being caught in traps to date.