Botrytis Fruit Rot Management

Thursday, May 19, 2011

Rain, rain go away! It has been a cool wet spring and I am very concerned about fruit rot as we come into bloom. The Kentville Research Station reported 139.8 ml (or 5.5 inches) of rainfall from May 1 to May 18 and many areas are reporting even higher levels. Fields are sodden, fertilizer and herbicide may have washed away, and growers are challenged to even get on their fields to put on new sprays. What a miserable spring!

The weather has to improve (doesn’t it?) but in the meantime conditions have been ideal for fruit rot infection. Bloom is the most significant period for infection and the time when we need to apply protectants, especially so in wet seasons like this. Typically three applications of fungicide are recommended, corresponding with early (10%), mid- (50%), and late (90%) bloom, and these are usually about 7 days apart. It is always best to apply fungicides before expected rainfall although some products have some level of systemic activity and may control new infections. Rick Delbridge of Delbridge Disease Management prepared an excellent review of the registered fungicides for fruit rot management in strawberries this spring and they are outlined below, along with their pre-harvest interval (in brackets), approximate application cost and chemical group. Many of these are a high risk for resistance development with repeated use so it is always best to rotate among chemical families.

Botrytis (grey mould) fruit rot fungicides registered for bloom time application in strawberries:

• Supra Captan 80WDG or Maestro 80DF(2 days) $44/A Group M
• Folpan 50WP (1 day) $43/A Group M
• Rovral 50WP (1 day) $79/A Group 2
• Elevate 50WDG (1 day) $125/A Group 17
• Lance 70WGD (0 days) $51/A Group 7
• Senator 70WP (1 day) $51/A Group 1
• Scala SC (1 day) $63/A Group 9
• Pristine WG (1 day) $86/A Group 7 & 11
• Switch 62.5 WG (1 day) $96/A Group 9 & 12
• Serenade Max/ASO – biofungicide for suppression only
• Actinovate SP – biofungicide for suppression only

Generally, the three bloom time applications are sufficient to control fruit rot for the season; however, if wet conditions persist up to harvest consider making an additional application of one of these fungicides just prior to harvest. Remember that it is easier to prevent a fruit rot problem than to clean one up after it has started!

Botrytis Fruit Rot