212-Botrytis Blight Control for Wild Blueberries
Fact Sheet No. 212, UMaine Extension No. 2027
Original text prepared by Rick Delbridge, Delbridge Disease Management Kentville, Nova Scotia, and Dr. Paul Hildebrand, Agriculture Canada, Kentville, Nova Scotia, and modified by David Yarborough, Extension Blueberry Specialist, and Seanna Annis, Associate Professor of Pathology, The University of Maine, Orono, ME 04469. February 2007.
Botrytis or Blossom Blight
Botrytis blight occurs during bloom and can be a problem in some fields or in seasons when extended wet periods occur during bloom or shortly after petal fall. See Wild Blueberry Fact Sheet 211, Blueberry Diseases 1 for identification and life cycle details. Blossoms with Botrytis blight have short black “hairs” that stick out from blighted tissue. Frost damage may look similar but occurs in low areas or throughout the field versus Botrytis which occurs more on individual clones.
Botrytis cinerea, is a fungus that survives as sclerotia, a resistant survival structure, and dormant mycelium on dead twigs of bushes and on infected weeds both within and outside the blueberry field. Weeds that have been found to be sources of this disease are blackberry, wild strawberry, pearly everlasting, Potentilla, goldenrods, and especially sheep sorrel. During periods of wet weather, the fungus produces spores on the overwintered diseased tissue and these spores are carried by wind to developing blueberry blossoms. Wet periods are necessary for infection and the length of time of the wet period required for infection decreases as the temperature increases (see Table below). The severity of the infection increases with longer wet periods at warmer temperatures. At a temperature of 68°F, only 8 hours of leaf wetness is required for some infection to occur. At 39°F, low levels of blossom infection may occur after a 36 hour wet period, but at 61°F high levels of blossom infection may occur after 13 hours of leaf wetness. Obviously, the greater the number of wet periods at favorable temperatures that occur prior to and during bloom, the more serious Botrytis blight will be.
| Severity Rating of Botrytis Infection Periods | |||||
| Mean Temperature (°F) during Infection Period | |||||
| Wetness Duration (Hours) |
39° | 46° | 54° | 61° | 68° |
| 4 | LOW | LOW | LOW | LOW | LOW |
| 6 | LOW | LOW | LOW | LOW | LOW |
| 8 | LOW | LOW | LOW | LOW | MED |
| 10 | LOW | LOW | LOW | LOW | HIGH |
| 13 | LOW | LOW | LOW | HIGH | HIGH |
| 24 | LOW | MED | HIGH | HIGH | HIGH |
| 36 | LOW | HIGH | HIGH | HIGH | HIGH |
| 48 | MED | HIGH | HIGH | HIGH | HIGH |
Early blooming clones may be the first to become infected because they come into bloom first. Flowers become susceptible just prior to opening. At full bloom, blossoms are very susceptible. Once the fungus becomes established on early flowering clones, the infected tissue can serve as a source of spores to infect later flowering clones. Growers should monitor both weeds, especially sheep sorrel, and early blooming blueberry clones for Botrytis infections. Weed infections can usually be observed in mid to late May. Shortly thereafter infections may be seen on blueberry blossoms. If the disease is evident at mid-bloom and favorable wet periods for infection are predicted, then a fungicide should be applied. Refer to the Table above for severity ratings of infection periods based on temperature and leaf wetness durations. If Botrytis is noted in a field or the field has a history of this problem, use one of the fungicides listed in Wild Blueberry Fact Sheet 219 Disease Control for Wild Blueberries at mid-bloom to late-bloom and thereafter as required. Fungicides must be applied prior to the wet period. Further sprays at seven- to ten-day intervals may be necessary, depending upon the weather.
Repeated use of some fungicides will lead to resistance in the Botrytis fungus to these fungicides. To slow this development of resistance, use the products at full rates and rotate with other fungicides from different chemical families or groups. See Wild Blueberry Fact Sheet 219, Disease Control for Wild Blueberries for more information on chemical families and fungicides available for Botrytis disease control. Avoid application of more than two consecutive sprays of the same fungicide or a fungicide from the same group. If additional protection or control is required, choose a product from another chemical family. Refer to the labels for more detailed information on resistance management.
Information in this publication is provided purely for educational purposes. No responsibility is assumed for any problems associated with the use of products or services mentioned. No endorsement of products or companies is intended, nor is criticism of unnamed products or companies implied.
© 1987, 2007
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