Effect of Chemicals on Hyphal Growth, Sporangia Production and Zoospore Germination of Phytophthora ramorum

Tamar Y. Harnik and Matteo Garbelotto, Department of Environmental Science Policy and Management, University of California, Berkeley, CA 94720; (510) 6434282; tami@nature.berkeley.edu

Phytophthora ramorum, causal agent of the Sudden Oak Death, has 23 regulated hosts. Some of these, such as coast live oak, tanoak and bay laurel, play a key role in the Californian forest ecology. There is one commercially available preventative treatment for two hosts, coast live oak and tanoak. New treatments that employ easier and cheaper application methods and protect both foliar and trunk/twig hosts are needed. Other products in the market registered to control other Phytophthora pathogens may be effective for controlling P. ramorum.

The ability of three chemicals to inhibit different stages in the life cycle of P. ramorum (hyphal growth, sporangia production and zoospore germination) was tested in vitro. The chemicals Subdue® (Metalaxyl), Agrifos400® (Phosphorus acid) and Champ® (Copper Hydroxide) were tested at different concentrations against 12 North American P. ramorum isolates. Additionally, we conducted in planta experiments on controlling the pathogen using foliar spray on bay laurel. Isolates varied in response to the treatment, but no isolates were tolerant to any of the chemicals. All the chemicals were effective in inhibiting all life cycle stages tested. In planta, copper hydroxide was very effective in controlling infection on bay laurel leaves up to 6 weeks after treatment.

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