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Issue No. 8, Article 4/May 25, 2012

Plant Clinic Report: Dying Pine and Spruce Windbreaks

Dead branches, falling or discolored needles, and sap coagulating in branch and trunk cankers can signal two of the most common fungal diseases that affect pine and spruce in our windbreaks, but many other factors can damage these pines and spruce. Though damage can result from wind, winter, salt, insects, other diseases, and chemical, environmental, and cultural issues, the past several springs have been particularly conducive in Illinois to infection by several endemic fungal diseases on spruce and pine.

Spruce: Windbreak spruce have had a hard go of it in recent years. The most common disease by far we have seen this season is Rhizosphaera needle cast. Spruce trees with purple-brown one- and two-year-old needles are suspect; newly emerged growth appears green, while needles from last year's growth appear brown or purplish brown. Since evergreens do not refoliate along the branches, the disease causes bare areas scattered throughout a tree if untreated. Norway spruces are considered fairly resistant to this needle cast, while Colorado blue spruce is a very common and susceptible host.

Rhizosphaera needle cast is diagnosed by the tiny black fruiting fruiting bodies of the Rhizosphaera fungus. You may be able to see these lined up in rows along the bottom of the needle. Typically microscopic evaluation is necessary because, unfortunately, a fairly new fungus affecting spruce in Illinois, Stigmina spp., also looks, without the aid of a microscope, like black dots lined up on the needles.

Random branch defoliation on blue spruce by Rhizosphaera needle cast.

Rhizosphaera needle drop can be managed with fungicide applications of chlorothanonil, but there is currently no treatment for Stigmina needle cast. Treatment for Rhizosphaera needle drop usually needs to be followed for 2 years. Foliar fungicide should be applied just after bud cap drop and again after needle elongation. We would be happy to help with diagnosis of your windbreak or other plant issues. Find our Plant Clinic sample submission forms on our website (plantclinic.cropsci.illinois.edu).

Pines: The most common disease we see on windbreak pines is Sphaeropsis blight of pine (aka Diplodia tip blight). We are seeing a lot of samples with this disease at the Plant Clinic because it thrives in cool and wet weather. Most pines are susceptible to Sphaeropsis blight. In Illinois this fungal pathogen most often infects Scotch, Austrian, and Mugho pines; white pine is rarely affected.

The tip and needle blight symptoms of Sphaeropsis that you may be seeing on your windbreak trees are often from last year's infections. The buds and new needles emerging at this time are very susceptible to infection. The Sphaeropsis pathogen infects healthy, unwounded needles as well as trees that are stressed by factors such as drought, compacted soil, root injury, hail, and winter injury.

Tip die-back on pine from Sphaeropsis (Diplodia) infection.

A characteristic symptom is the blighting of branch tips. Nearly all of the needles in the terminal six inches of growth will turn brown, dry out, and remain attached throughout the season. Frequently the tree will develop new growth below this dead area, causing the branch to grow in a zigzag pattern. Sphaeropsis can also cause cankers to develop on twigs that will noticeably ooze with sap. If the canker girdles the stem, the tissue beyond the canker will die. This disease is not known to cause tree death, but it can cause some very unsightly damage.

It takes some commitment to control Sphaeropsis blight, with cultural control being an important management tool. To reduce disease inoculum, prune and remove the dead wood or needles from the pine. To reduce the spread of the disease, remove dead tissue in the early spring before buds open, when the foliage is dry, or during the dormant season. Removing all of the infected cones will help deter the disease from overwintering and providing disease inoculum the following spring. If possible, it is a good practice to alleviate any stress to your pines by providing fertilizing or by watering during times of drought.

There are fungicides available to manage Sphaeropsis blight, including propiconazole and thiophanate-methyl, but they should be used in conjunction with the cultural controls described. Be sure to read and follow label directions. Fungicides should be applied at three different times: just as buds are expanding, just before new needles emerge from the sheath, and then 10 to 14 days later. For more details about this disease, read the Report on Plant Disease no. 625, Sphaeropsis Blight or Diplodia Tip Blight of Pines (Adobe PDF).--Suzanne Bissonnette

Suzanne Bissonnette

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