Mummy berry nurseries facilitate scouting for apothecia
Research is showing the nurseries may be a convenient way to identify when apothecia are peaking and ending development.
In 2010, we established mummy berry “nurseries” on seven blueberry farms in west Michigan. We pushed metal duct connectors about three-quarters down into the soil to provide a barrier to keep mummies from being washed or blown away. However, a barrier can be made of any suitable material, provided that water can flow freely through the soil and the rim is not so high as to cause shading or modify environmental conditions within the nursery. It may not even be necessary to provide a barrier if the mummies are not at risk of being disturbed. The location should be marked with a flag or flagging tape.
Mummy berry mummies were collected after harvest when they were still pale purple to pink in color and easy to see on the ground. They were placed in the enclosure in a part of the field with convenient access and known mummy berry pressure. Mummies were lightly pushed into the soil to ensure good contact with the soil. In some cases, we sprinkled a thin layer of soil on top of the mummies which proved to be less effective, as the mummies may get buried too deeply over the winter and early spring. In those cases, the mummies were struggling to produce apothecia, some of which had stalks more than an inch long to get to the soil surface. Two nurseries were established with a total of 100 mummies per farm. So far, the nurseries have proved to be very convenient as they preclude the need to search for mummies that are scattered on the ground under the bushes. Due to their dark color, small size and tendency to develop under leaf litter, they are often difficult to see. Searching for them can take an excessive amount of time, especially in fields with low numbers of mummies.
Mummies germinate in the spring by producing small trumpet-shaped mushrooms (apothecia) that release airborne ascospores. Soil moisture usually determines how many mummies germinate and how many apothecia are produced, and temperature influences the rate of growth and size of the apothecia. Mummies usually germinate in groups (cohorts) over a four- to six-week period in the spring. The ascospores infect young shoots, resulting in “shoot strikes.” Due to sufficient snow cover, which moderated moisture and temperature around the mummies during the winter and wet spring conditions, we are observing relatively high germination rates this year. This may also mean that the apothecia are going to be spent sooner this year. The nurseries will help us observe the peak as well as the end of apothecial development. Generally, apothecia collapse after they have released all or most of their ascospores, but they can also desiccate under warm and dry conditions such as happened in 2010. A hard freeze may injure apothecia but they tend to partially recover afterwards.
At this time, mummies are still germinating, but germination is slowing down in most locations, at least for the first cohort (Figure A). Time will tell if more cohorts are going to be producing apothecia this year. The number of apothecia is either slowly increasing in some sites or decreasing as older apothecia have started to collapse or flooding is interfering with production or observation of apothecia (Figure B). Apothecium size is generally still increasing, except in Benton Harbor, where a few “monster” apothecia were produced, which have now collapsed (Figure C). Remember, the bigger the size of the apothecial cup, the more spores are released, which can amount to more than 1 million per day per apothecium.
Cool, wet conditions will result in greater longevity of apothecia, some of which may persist for two to three weeks in the field. Since weather conditions continue to be cool and wet, systemic fungicides, such as Indar (fenbuconazole) and Orbit (propiconazole) will be most effective. Add Captan (captan) or Bravo (chlorothalonil) to simultaneously knock down the sporulating ability of other fungi, such as Colletotrichum and Phomopsis. Organic growers’ best bet is Serenade (Bacillus subtilis bacteria) + Nu-Film P (spreader-sticker) for control of mummy berry.