Rhizosphaera Needlecast

Rhizosphaera Needlecast

What is it?

Rhizosphaera Needlecast, or Rhizosphaera kalkhoffii, is a fungus that affects spruce trees, most commonly Colorado blue spruce. It usually doesn't kill tree, however it does make them look sick. This is particularly devastating to tree nurseries or Christmas tree farms.

What does it do?

A spruce tree that has no issues will normally keep its needles for around 6 years. When one becomes infected with Rhizosphaera Needlecast, however, it may only hold the infected needles for one year. As with other diseases of conifers, the fungus starts at the bottom of the tree and works its way up. The reason this happens is because the ground under the tree is more susceptible to growing and sheltering diseases than the tree itself. 

It starts off by infecting the new needles in May or June, however it usually will not be noticeable until spring the following year. This is when the needles on the lower branches get a somewhat purplish hue to them (see above picture), then die off and start dropping. The spring rain then splashes the infection onto healthy needles, which restarts the cycle. This can sometimes kill the lower branches of the tree.

Do you have it?

Your first hint at a Rhizosphaera Needlecast infection will be when you see needles that appear to be purple when the sun hits them. The best way to find out for sure if your trees have it is to look at the infected needles under a magnifying glass. If they have hairy looking black spots on them, then there's a pretty good chance you found your disease. These black spots are actually the breeding grounds of the fungus, waiting for the rain to take them somewhere else on the tree. Here's what it will look like:

Photo credit: ohioline.osu.edu/hyg-fact/3000/3059.html

How to manage it:

As always, the best form of control is to know the disease before you buy a tree that might have it. If it's already in your yard, you're going to have to do a little more than that.

• If you have several spruce in your yard and only one of them is infected, make sure that you trim that tree last. The disease can be transmitted to the healthy trees just from the clippers. If you must trim your infected tree, be sure to trim that one last. Afterwards, sterilize your tools in a bucket of denatured alcohol for about 5 minutes.
• Try to keep the tree as healthy as possible. This includes vertical mulching, irrigation and aeration.
• Chemical: Since  Rhizosphaera Needlecast is a fungus, an applied fungicide could do wonders for your tree. Brands such as Daconil 2787 and Bravo might just do the trick for you. If you are goping to do it yourself, make sure to read all of the warnings and instructions. 
• Or you could always call your local tree care specialists.