Posted by: HortAlaska | May 9, 2019

Strategies to address emerging fungal diseases in peony (Paeonia lactiflora) in the US

A.R. Garfinkel1,a and G.A. Chastagner2

Acta Horticulturae 123: 199- 206. ISHS 2019 DOI 10.17660

 

Abstract

The most important step in any effective disease management strategy is proper diagnosis. Therefore, in an effort to assist growers with disease management, herbaceous peony (Paeonia lactiflora) samples were collected and submitted to our lab from 12 states in the United States to determine the range of diseases present in both landscape and commercial settings. Both morphological and molecular techniques were used in the identification of pathogens isolated from peony flowers, leaves, stems, and roots. Trials were conducted to confirm the ability of all pathogens to cause disease on healthy peony tissue. This survey revealed new species-host-state combinations in several states as well as five different fungal genera that had not previously been identified on peonies in the country: a Botryosphaeria sp., up to 3Colletotrichum spp., Mycocentrospora acerina, a Phoma sp., and Pilidium concavum. Each of these pathogens have only been reported a few times worldwide and there is correspondingly little to no information available on their management. Given the need for growers to address these emerging disease issues, we outline potential management strategies for fungal peony pathogens. Our recommendations take into account general fungal disease management tools, published information on the specific biology of these organisms, observations of peony diseases over our years of fieldwork, and examples from other pathosystems that have been successful in managing diseases caused by the pathogens we have found on peonies.

 

This article is one of several to come out of Andrea Garfinkel’s PhD thesis where she collected samples from Alaska grower’s fields as well as other locations. It is a practical summary of methods that can be used to manage the variety of fungal diseases that show up in peony fields. Below is a summary of recommended management steps:

  1. Reduce leaf wetness: many fungi need moisture on the leaves to grow and spread. Avoid overhead irrigation or water early in the morning so leaves can dry during the day.
  2. Try to minimize the spread of disease by spores. Remove diseased tissue throughout the growing season, Some fungi are spread via air currents and are difficult to contain. Others such as anthracnose, tan spot and licorice spot can also be moved via water splashes. Again avoid overhead irrigation.
  3. Petal tissue is extremely susceptible to Botrytis growth. Petals that fall during the season and land onto leaves or even the soil can be food for the growth of Botrytis disease. Remove all petals from the fields and do not allow petals to fall anywhere in the garden. They will quickly become infected.
  4. Prevent overwintering. Remove diseased tissues at the end of the growing season and cut as close to the soil level as possible to remove all foliage from the field.
  5. If the disease is found in the soil, it might require removal of the entire plant plus soil as well as adjacent plants. Avoid overwatering and make sure soils are well drained
  6. Apply appropriate fungicides. The full article lists some possible chemicals for management.
  7. Choose resistant or tolerant cultivars. ‘Kansas’ is extremely susceptible to Cladosporium leaf blotch, whereas ‘Sarah Bernhardt is quite resistant.
  8. Remove weeds from fields that can be hosts for diseases. Mycocentrospora red spot (licorice spot) also grows well on weeds growing near the stems of peonies.
  9. Avoid wounding of plant to prevent entry of disease. This is especially true for Phomopsis disease.

 

 

 

 


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