Apr 18, 2017Now is the time for scouting mummy berry in blueberries
Now is the time to scout under your blueberry bushes for mummy berry mummies. Michigan State University Extension advises scouting in “hot spots” first, especially wet areas and close to the woods with a history of the disease. Due to snow cover over the winter and a very wet spring, an early crop of apothecia is ready to shoot ascospores into the air and cause shoot strike infections (if green tissue is present).
Mummy berry mummies look like tiny, black pumpkins (about 0.375 inch in diameter) and may be partially embedded in the soil or located underneath leaf litter. Germinated mummies have small brown finger-like projections that develop into apothecia that look like small brown trumpets or goblets. There can be anywhere from one to six or seven apothecia on a mummy. Germination is heavily influenced by soil moisture.
During a wet spring, we have measured up to 40 percent germination in high pressure sites and 2017 may fall into that category. In dry fields or dry years, only about 5-10 percent of the mummies may germinate. Mummies can survive at least two years if they have not germinated, but once they germinate, they die.
Apothecia are now visible in fields and range from barely open to almost 0.125 inch in diameter in the most advanced sites. Remember that the larger the apothecial cup, the greater the number of ascospores released and the higher the infection risk. Apothecia can become dime-sized under the right conditions and can discharge millions of spores into the air per day. Also, the more apothecia occur per unit area, the greater the infection risk. Since most growers have done a good job of controlling mummy berry in past years, the number of apothecia in blueberry fields will generally be low, but it is good to keep an eye on the fungus to time fungicide sprays.
There are various options for managing mummy berry. First, is it important to ascertain that there are apothecia that are large enough to shoot ascospores (greater than 2 millimeters or roughly 0.0625 inch) in the field and that green leaf tissue is present. If you saw shoot strikes or mummified berries in the field last year, it is safe to assume there are apothecia present now. If there are neighboring fields with mummy berry, there is also a risk of infection since the ascospores are windborne and theoretically can travel at least a mile on the wind. However, in practice, most ascospores travel only about 30-100 feet from the source.
The wettest sites or areas in the field are at the highest risk unless they are completely flooded. In flooded fields, apothecial development will be somewhat delayed, but they will become visible when the field drains. Dormant sprays with lime sulfur suppress mummy germination, and a ground spray of urea can burn apothecia if they are present. Protective fungicide sprays can prevent shoot strikes, which are the primary infections.
Fungicides work best when applied preventatively (before infection). While the risk of fungicide resistance development appears to be low for this pathogen, it is nonetheless advisable to alternate fungicide chemical classes as indicated by different Fungicide Resistance Action Committee (FRAC) code numbers. If shoot strikes are controlled well (you can scout fields to confirm this) and no shoot strikes are present during the bloom period, the risk of fruit infection is minimal. Be careful with fungicide applications during bloom: avoid spraying after bee hives have been placed in the field or spray at night when bees are not active.
— Annemiek Schilder, Michigan State University
Source: Michigan State University Extension