Over the past 2 weeks, the Plant Clinic has received numerous spruce samples from trees that are growing poorly. Spruces with branch death, internal needle drop, or areas of dead stems are the usual complaints. We have found Rhizosphaera needle cast on a few of these samples and addressed that problem in issue 2 of this newsletter. Spruce spider mites have also been confirmed on a few. The bulk of the samples, however, have not yielded a biotic cause of decline. Stress from overcrowding, deep planting, poorly drained soil, water stress over the past 2 years, and even salt injury have contributed, depending on the site. Keep an open mind and check into these possibilities when determining the cause of your tree’s decline.
If you would like some diagnostic help with struggling spruces or other evergreens, the Plant Clinic can help. Our quality of help, however, is directly related to the type of information provided. If you send a sample, use the guidelines provided on the clinic Web site, http://plantclinic.cropsci.uiuc.edu/. The sample should contain one or more branch tips, including about 12 inches of growth, with needles attached. Pick an affected area that is not completely denuded. Use the clinic data form if possible. Describe the symptoms in the entire planting, as well as on one tree; and include digital images when possible. We prefer only three images: a picture of the area, a close up of the trunk at the soil line, and a picture of an affected branch. Make sure they are in focus. You may include prints or a disc, or send them in an e-mail to firstname.lastname@example.org. Indicate that the sample is being sent in the mail. Don’t forget to send your payment with the sample.
The infectious spruce problems may be treated now, to help protect new growth. For this reason, you want to get to the bottom of the problem soon. The noninfectious problems are managed throughout the year. If you think the problem is abiotic (noninfectious), you have more time to spare.
Cytospora canker is another possible cause of spruce decline. It causes a canker at the base of the affected stem where it connects to the trunk. A canker is a dead area of wood. Cankers on spruce produce a white, crusty or sappy exudate. Cytospora cankers eventually girdle (surround) stems, killing tissue beyond the canker and causing newest needles to brown and die first. Eventually the entire branch dies. Check for cankers at the base of affected branches. Report on Plant Disease (RPD), no. 604, “Cytospora or Leucostoma Canker of Spruce,” shows you what to look for in your tree. This report is available on the Internet at http://www.ag.uiuc.edu/~vista/abstracts/a604.html. Cytospora canker is an infectious disease, but it is a disease that is known to affect stressed trees. In this case both the infectious and noninfectious factors need to be managed.