Q: I have a row of Austrian pines growing along my
property line. Over the
past few years, the needles have been turning brown, and I’m not sure if the cause is Diplodia Tip Blight or Dothistroma Needle Cast. Is the same control suggested for both of these diseases or do I need to determine the exact cause before applying something on the trees? — S.N.
A: Diplodia Tip Blight (also called Diplodia Shoot Blight) and Dothistroma Needle Cast are both fungal diseases. As its name implies, Diplodia Tip Blight kills needles at the tips of the branches, usually beginning on the lower branches and moving upward.
New growth (or candles) become distorted then turn yellow to tan as the new candles attempt to grow. Tiny black fungal fruiting bodies (pycnidia) can be seen at the base of infected needles, scales of seed cones and on the bark.
Dead shoots release a resin, and cankers may form causing branch death. Austrian pine is the most susceptible host, yet other pines are also susceptible, including red pine, Mugo pine and Scots pine.
And it just so happens that in the state of Wisconsin, Austrian pine is severely affected by Dothistroma Needle Cast, too. Being so susceptible to these two fungal diseases has decreased the acceptance of planting Austrian pine in our area.
Dothistroma is caused by a fungus that produces dark green water-soaked spots on the needles. Eventually, the spots turn yellow to tan to red-brown forming bands that encircle the needle. Pycnidia form and release spores resulting in infection of the needles, especially during wet weather. Infected needles usually stay attached to the branches and then fall normally.
To get an exact diagnosis of which disease may be affecting your trees, a sample can be sent to the Plant Diagnostics Clinic at the University of Wisconsin in Madison. The website for the clinic is http://pddc.wisc.edu" target="_blank">http://pddc.wisc.edu.
For both diseases, control measures include removing fallen needles and pine cones from the base of infected trees to remove sources of spores. For Diplodia, remove and destroy diseased tips by pruning 6-8 inches below the point of infection during dry weather. Stressed trees are more likely to be attacked by Diplodia, therefore try to keep trees healthy to help combat the problem. Fungicides containing chlorothalonil or thiophanate-methyl or a combination of the two products can be applied at 14-day intervals between bud break and shoot elongation.
For Dothistroma, a single application of a copper-containing fungicide in early June should provide sufficient protection of newly emerged needles. For more complete control, a second application can be applied three to four weeks after the first application. As with any fungicide, read and follow all label instructions.
Additional information on these two diseases can be found in publications XHT 1010 and XHT 1078 available on the University of WI Plant Diagnostics Clinic website, http://pddc.wisc.edu.