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Home, landscape, and structural pest news from the UC Statewide Integrated Pest Management Program
Suburban Neighborhood
by Steve M Sanguinetti
on September 13, 2023 at 8:47 AM
Since this is an Urban Tree Blog I'm a bit surprised that more information on overwatering and poor drainage isn't included. Or is that no longer considered critical for all phytophthora problems.
Reply by Lauren Fordyce
on September 13, 2023 at 11:42 AM
Thanks for your comment. This article was focused more on SOD in natural areas/wildlands rather than the home landscape, which is why some of these cultural control practices are not mentioned. Overwatering and poor drainage are still important factors for Phytophthora development.
by Steven Swain
on November 29, 2023 at 10:29 AM
Hi Steve,  
It's important to understand the differences between different types of Phytophthora. The majority of Phytophthora species, such as P. cinnamomi and P. lateralus, are soil borne. Control of these diseases almost always requires careful consideration of irrigation practices to control their reproduction and spread, especially in landscape and nursery settings. Drainage, perhaps unsurprisingly, is also a critical consideration, and must be managed as well.  
However, some Phytopthora species, such as P. infestans (a major contributor to the Irish potato famine), and P. ramorum (the primary factor in sudden oak death and the topic of the article in question) are aerial Phytopthoras. Since these diseases don't frequently infect or spread in the soil, irrigation management and drainage considerations are largely moot, at least in landscape settings, and that's why this article doesn't explore those topics.  
In nursery settings, irrigation management IS an issue, as nurseries can ship the disease in infected plants, and the disease is federally quarantined. This means nurseries have to be free of P. ramorum to ship plants. Because P. ramorum can spread from one plant to another in the potting soil, even if it doesn't infect the plant (though some Rhodies can be infected this way), the pathogen has to be contained.  
Again, this article was aimed at the landscape and wildland urban interface audiences, not the nursery trade, so that information was not included. However, if you'd like to explore further, there's plenty of information available at .
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