swiss needlecast fungus on my douglas fir

Asked March 26, 2019, 6:27 PM EDT

I have a very large douglas fir in my yard that was diagnosed by someone at Ronnys Garden World with Swiss needlecast. They said to wait until the new candles are half grown and spray with Infuse, then again several weeks later, around July. They stressed that timing is important and I would have to spray for at least 2 years. The tree is out in the open in a large yard, and I don't have any close neighbors. Ronny's suggested that I contact your office for further information. Any help you can give would be appreciated. Linda Robinson. Thank you.

Kent County Delaware plant disease douglas fir needlecast

1 Response

Hello, Linda,

Swiss needlecast is a common disease of Douglas fir in our region. It is caused by a fungus that produces spores in the spring which infect the new developing needles. Spores are produced on needles that were infected last year. Those needles will then drop in the summer.

Infuse is a more expensive product containing the fungicide propiconazole. Although Infuse will work, a better choice of fungicide might be chlorothalonil, available as Bravo Weather Stik or Daconil. Chlorothalonil is cheaper and very effective if applied correctly. Remember, fungicides act by preventing infection, they do not cure infections.

Trees should be sprayed with chlorothalonil (Daconil 2787 WP) at 2 1/2pounds WP per 100 gallons of water in hydraulic spray equipment or 51/2pounds per 100 gallons in high-pressure mist blower. Use 1 1/2 to 2 3/4lbs/acre for aerial application. Make first application in the spring as soon as new shoots are 1/2 to 3/4 inches long, usually mid-May in our area. Make the second application 2 weeks later. A third application may be necessary two to three weeks after that. Coverage and timing are very important. Two years of fungicide protection will restore moderately infected trees to full foliage, as needles are able to grow out healthy.

Thank you for contacting Cooperative Extension,

Nancy