New Rot Products

Determining effective methods for bitter rot and black rot (Botryosphaeria obtuse) control is a priority for the apple industry. These rots are becoming bigger problems in Ontario apple orchards, and management options are limited. With the registration of new products in the past 2 years, growers now have a wider selection of products to choose from and can develop an effective rot management program.

Bitter rot (Figure 1) and black rot (Figure 2) have recently become serious pests in Ontario apple orchards. With an increase in occurrence and severity, growers are looking for more control options. Three new products are now available for either bitter rot or black rot, or both. Pristine offers control of both rots, while Allegro will control bitter rot and provide suppression of black rot. The third new product available for growers is Regalia Maxx, a biofungicide providing suppression of bitter rot.

Figure 1: Bitter Rot

Figure 1: Bitter Rot

Figure 2: Black Rot

Figure 2: Black Rot

This past season Ontario experienced perfect conditions for bitter rot development, with warm, hot weather early in the season followed by rainy periods extending into the summer. With the increased presence of bitter rot and ideal conditions for further disease development, proper management is critical. See the July 8th Hort Matters article, Bitter rot symptoms and management in apples during 2015, for more information on the disease and it's occurrence in Ontario.

There are a number of methods for bitter rot management, including cultural and chemical control. Until recently there have been limited options of fungicides for bitter rot. With the registration of new products growers now have more alternatives to use to develop a bitter rot management program.

Bitter rot:

  • New registrations include Pristine WG (Group 7 + 11), Allegro 500 (Group 29), and Regalia Maxx, a biofungicide registered for suppression of bitter rot.
  • Allegro added bitter rot to its label, along with cedar apple rust and Alternaria blotch, at a rate of 0.75 -1.0 L/ha. Do not mix Allegro with oil.
  • Pristine also added new diseases to the label, including both bitter rot and black rot, at a rate of 1.0-1.2 kg/ha. Pristine should be applied preventatively before disease development.
  • Regalia Maxx is a new product providing suppression of bitter rot at 0.125% v/v in 1000L water/ha. Continue applications on a 10-14 day interval depending on crop growth and disease pressure.

Apply these products at petal fall, before disease development. Continue on a 7-14 day interval.

Black rot:

  • Pristine WG and Allegro 500 F are also options for black rot management. Allegro 500 F is registered for suppression only.

Apply Pristine and Allegro beginning at pink, before disease occurrence.

If possible, time fungicide applications prior to a rain event to protect the fruit from splashing spores. Always rotate products to reduce the potential for resistance developing.


For more information:
Toll Free: 1-877-424-1300
E-mail: ag.info.omafra@ontario.ca