Location: Horticultural Crops Research UnitTitle: Diagnosis and management of new and re-emerging diseases of highbush blueberries in Michigan
|SCHILDER, A - Michigan State University|
|GILLETT, J - Michigan State University|
|MILES, T - California State University|
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 2/2/2016
Publication Date: 4/10/2016
Citation: Schilder, A., Martin, R.R., Gillett, J., Miles, T. 2016. Diagnosis and management of new and re-emerging diseases of highbush blueberries in Michigan. Abstract for: XI International Vaccinium Symposium, April 10-14, 2016, Orlando, Florida.
Technical Abstract: Blueberries are an important commodity in Michigan and disease management is crucial for production of high-quality fruit. Over the past 6 years, a number of new and re-emerging diseases have been diagnosed in the state. In 2009, Blueberry scorch virus (BlScV) and Blueberry shock virus (BlShV) were detected in several fields, leading to a statewide survey and eradication effort to safeguard the blueberry industry. Around the same time, a new syndrome characterized by brownish, cupped leaves and plant decline (“bronze leaf curl”) was observed in multiple older blueberry fields. While initially attributed to herbicide injury, a closterovirus similar to Blueberry virus A was found in affected bushes. The role of this virus in the disease is currently being investigated. Blueberry leaf rust is a sporadic problem that became prevalent in 2010 and 2011 after several particularly rainy summers. The pathogen was identified as Thekopsora minima whose alternate host is eastern hemlock (Tsuga canadensis). Fungicide efficacy trials showed that Pristine (pyraclostrobin + boscalid) was the most effective, followed by Indar (fenbuconazole) and Quash (metconazole). The organic fungicide Serenade (Bacillus subtilis) was moderately effective. The recent expansion of blueberry cultivation into previously wooded areas has led to localized outbreaks of Armillaria root rot, caused by Armillaria mellea. This soilborne fungus continues to kill many relatively young bushes in affected fields. There are currently no management tools available other than to remove infected plants. While root rots are relatively uncommon in Michigan blueberry fields, declining ‘Jersey’ plants were observed in a poorly drained field in 2009. A pathogenic oomycete, Pythium sterilum, was identified as the causal organism. Changes in cultivars, production practices or climatic conditions may lead to new disease outbreaks. Regular disease monitoring and use of virus-tested planting stock are recommended as well as a rapid response when exotic pathogens are detected.