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Mummy Berry Apothecial Development and Potential for Disease Development in 2014

The following information applies to our major commercial blueberry production region in the southern part of the state, but other parts of the state will soon progress into a timeframe in which mummy berry disease could be an issue. Based on the best information we can derive from the literature at large, cold-damaged, exposed tissue (leaf and early bloom development) is more susceptible to mummy berry blighting, such as we observed in 2013 in many locations (90% losses in some cases). The blighting aspect of the disease basically wipes out whole bloom clusters, and this is not to be confused with the more controlled formation of mummies which occurs much later. Based on current weather predictions, I am hopeful that freezes will be at a minimum over the next few weeks, but we will likely have moisture and temperatures which will be ideal for mummy berry development. Botrytis can also occur on damaged tissue, especially if wet, warming conditions follow.

Early application of fungicidal materials that have both Botrytis and mummy berry activity are required (i.e. Pristine or DMIs (Orbit, Tilt, Quash, Indar, and generics) + Captan or CaptEvate). Pristine is generally my product of choice for the first application, since it would have activity on mummy berry/Botrytis, and it would have the potential to reduce potential Botrytosphaeria canker infections (also a potential on freeze-damaged stem tissue) as well. However, the advent of putative Exobasidium leaf and fruit spot resistance to Pristine has made me rethink this. If Exobasidium has been observed in your blueberries, I would not utilize Pristine, meaning that DMIs + Captan would be your choice for application during bloom. By label, you can’t mix Pristine with other fungicides or products, so that takes it out of the equation if Exobasidium is a concern.

Harald Scherm has generated current mummy berry information from a model he previously developed and tested. Based on his assessment, assuming that moisture is not limiting in south Georgia, we should be in the advanced stages of apothecium (mummy berry) development and initial infections of exposed green tissue or early bloom tissue as these emerge – especially rabbiteyes. If rain has recently occurred or will be occurring, mummy generation may coincide pretty well with the initial bud germination and push (again, minimally exposed leaf [green tip] or flower tissue can be initially infected). Please see below for Harald’s explanation of the information he generated. Also, please let your producers know that there is a current danger of mummy berry infection, especially if moisture is sufficient.  Furthermore, the below-freezing temperatures during the past few days may also have rendered earlier flower bud stages susceptible to infection.

Harald Scherm writes:

Please see attached for the output of the mummy berry model for three locations, Alma, Homerville, and Alapaha. The model is based on the balance of chilling and heating, assuming that moisture is sufficient for germination of mummies (which likely was the case this year). On the figure, the solid line and symbols indicate mummy germination in response to different experimental chill-hour and degree-day treatments, in conditions of optimal soil moisture. The red letters indicate the current predictions for Alma, Homerville, and Alapaha based on weather station data. Since these data points are well above the line, conditions for mummy germination and apothecium emergence are likely met, especially since conditions have been very moist. As such, the risk should be considered high for mummy berry infections as we head into green tip and bloom.

Potential Mummy Germination 3-4-2014

 

 

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About Phil Brannen

Phil Brannen is a Professor in the Plant Pathology Department at the University of Georgia. He attended the University of Georgia for his undergraduate degree in Plant Protection and Pest Management, where he also received an M.S. in Plant Pathology, followed by a Ph.D. in Plant Pathology from Auburn University. He has extensive experience with disease management programs in numerous cropping systems. He serves as the extension fruit pathologist for Georgia – conducting research and technology transfer for multiple fruit commodities. His blueberry efforts are directed towards developing IPM practices to solve disease issues and technology transfer of disease-management methods to commercial blueberry producers. He also teaches the graduate level Field Pathology Course, team-teaches the IPM Course, coordinates the Viticulture and Enology in the Mediterranean Region Course (Cortona, Italy), and guest lectures in numerous other courses throughout the year.