Humid Air: Tough for Plants and People


Summer in central Ohio brings good times outside but also often brings hot humid air. Heat and humidity can aggravate some foliar fungal disease on trees and shrubs. One of the most common diseases we see is rhizosphaera needle cast on Blue Spruce trees.

This disease manifests itself in needles causing them to turn brown and even purplish before they fall off of the tree. Blue Spruce will often show the first signs of infection on the interior and lower needles where moisture persists, looking thinner and sickly in the middle during the early years of an infestation. Left to run wild without a managment plan, rhizosphaera needle cast will eventually kill its host tree.

Blue Spruce without (left) and with (right) rhizosphaera needle cast

Blue Spruce without (left) and with (right) rhizosphaera needle cast

If you have a mature Blue Spruce that has lost less than approx. 25-35% of its needles from needle cast, a treatment plan may include:

  1. Raking up and disposing of all of the old fallen needles under the tree that can still host the fungal spores.

  2. Pruning out dead branches.

  3. Adjust irrigation equipment to make sure that water is not directly sprayed onto the needles of the tree, this spreads the spores and accelerates the advancement of needle cast.

  4. Three rounds of fungicides applied in the spring, shortly after bud break can protect new growth from becoming infected.


Joe Russell | Member & Co-Owner, Russell Tree Experts

Joe Russell has been an ISA Certified Arborist® since 2003. He graduated from Ohio State University with his bachelors in Landscape Horticulture with a minor in Ag Business and started Russell Tree Experts with his wife Shari in 2005. Joe grew up in the Ohio Valley near Wellsville, Ohio and is a resident of Galena, Ohio.