By Rachel Webber, College of Agricultural, Human & Natural Resource Sciences
SPOKANE, Wash. – What’s wrong with my ponderosa pine trees? Are they dying? Why are the needles turning brown and reddish? Forestry experts have received several inquiries about ponderosa pine tree health this spring, so if you’re asking these questions, you are not alone.
Many insects and pathogens (microscopic organisms) in northeast Washington can damage or kill ponderosa pine trees, and weather can take its toll as well.
The most evident problem this year is the abundance of ponderosa pine trees affected by foliar pathogens – microorganisms that infect tree needles.
The problem is widespread across the region because cool, moist conditions were prevalent across a broad geographic area. Numerous overly dense forest stands provide optimal conditions in which the pathogens can thrive.
The good news is:
1) The needle problems caused by this fungus rarely kill trees, although they do add stress that can weaken tree resistance. This can increase susceptibility to other insects and diseases that affect trees, especially in combination with other weather events such as low rainfall or exceptionally hot summers.
2) The area’s consecutive cool, moist springs that are affecting trees across a broad area are not typical for eastern Washington, so a return to normal weather – and greener needles – is likely in the near future.
Foliar pathogens cause older needles to die and turn brown or reddish-brown and make the tree look like it is dying. Foliar pathogens mainly affect lower and inner branches on ponderosa pine trees.
Needles on infected trees will have small brown or black splotches on them – the fungal body (or pathogen) that kills ponderosa pine needles. Some needles wither and turn white rather than fall off, looking like a goat’s beard; on these needles the fungal body will usually not still be visible.
Because foliar pathogens kill older needles, tree branches will sometimes look like a lion’s tail, with long skinny branches and a tuft of only green recent needles at the end.
The foliar pathogens causing problems to ponderosa pines this year can occur wherever ponderosa pine trees are present.
Most years, only a few trees are infected – usually those growing in cool, moist conditions such as near streams or lakes and in draws and valleys. Often infected trees are in dense stands that allow for little air movement; moisture can linger creating favorable conditions for the pathogen.
Ponderosa pine is a valuable tree for wood products, shade in city parks and neighborhoods, wildlife habitat – food and shelter even after it dies – and more.
Foliar pathogens affecting ponderosa pine trees are always present, as is changeable weather. So what do we do?
If you are concerned your ponderosa pine trees are unhealthy or dying, take a good look to see if the cause might be foliar pathogens.
If you see that the entire tree crown has brown or red needles, or the tree appears to be dying from the top down (needles towards the top of the tree are thinner and/or turning red), you may have a different problem. You may want to call your local state Department of Natural Resources stewardship or extension forester to get more information about what may be affecting your trees.
If the problem is a foliar pathogen and your stand is dense (lots of trees with little room for growth), you could consider thinning trees to open the stand to improve air circulation. Department of Natural Resources stewardship or extension foresters can provide information on thinning and cost-share programs that help landowners pay for thinning stands. For a list of contacts, see http://forestry.wsu.edu/staff/.
If you have foliar pathogens in your stand but have no issues with tree density or vigor, you can relax in knowing that the problem is unlikely to be serious or long-lasting; odds are good trees will be green again next year.
For more detailed information about foliar pathogens in eastern Washington, see http://www.spokane-county.wsu.edu/Forest%20&%20Wildlife%20Resources/Ponderosa_Pine_Needle_Cast.pdf .
Steve McConnell, WSU forestry extension regional specialist, SMCCONNELL@spokanecounty.org, 509-477-2175
Washington Department of Natural Resources in Colville, Wash., 509-684-7474