Needle Cast of Spruce Trees
Needle Cast of Spruce Trees
Hello! I hope you are doing well!
The range in rainfall for the county in the past week was 0.32 inches to 1.0 inches with the average at 0.46 inches. The high temperature for the past week ranged from 45 to 69 degrees Fahrenheit with an average of 58 degrees Fahrenheit. That average is way below normal. The average was twelve degrees Fahrenheit below the normal average of 70 degrees Fahrenheit. The temperature forecast for the coming week will be below normal.
Backyard poultry producers please keep practicing biosecurity, the Highly Pathogenic Avian Influenza (HPAI) has now increased to 15 commercial or backyard flocks and to 212 wild birds this past week.
Needle cast disease of spruce trees is fairly common in Griggs County. Colorado blue spruce trees are the most susceptible. Black Hills spruce have some resistance and Norway spruce has the most resistance to the needle cast diseases, although it is possible for these to get them as well.
Normal spruce trees should retain four or more age (years) classes of needles. However shaded older needles can fall from the tree naturally. See figure 1 in the Extension publication entitled The Old and the New: Tow Needle Diseases of Spruce in North Dakota to learn about age classes of needles and other information about the diseases. The website to find the publication is as follows: https://www.ag.ndsu.edu/publications/lawns-gardens-trees/the-old-and-the-new-two-needle-diseases-of-spruce-in-north-dakota .
The two needle cast diseases that can affect spruce trees are Rhizosphaera needle cast and stigmina needle cast. At a distance from the tree what you will observe is the loss of needles starting at the lower canopy and moving upwards into the tree. When walking closer to the tree you will see older needles turning a dark yellow to brown to reddish brown to purple color. To determine if these diseases are present you will need a hand lens looking at individual needles. If you look at normal needles with a hand lens you will see rows of white spots on the needles. These pores are called stomata and are used for gas exchange. With diseased needles you will find a black area coming out of the pores. If the black spot is round, then it is most likely Rhizosphaera, but to be sure you need a microscope to look at the size of the spore. If the black spot goes out in an irregular fuzzy pattern, then it is most likely stigmina. It is somewhat important to correctly identify the disease because management is a little different between the two diseases. If you want to be confident, then send a sample of needles to the Plant and Pest Diagnostic Lab. The following website will get you to instructions on how to submit a sample: www.ag.ndsu.edu/pdl .
The pathogen causing Rhizosphaera needle cast has a one-year life cycle. In North Dakota, the fruiting bodies called pycnidia produce spores in late May through July. These spores are spread by splashing water and will affect all age classes of needles. The pathogen causing Stigmina needle cast has a two-year life cycle. The fruiting bodies called sporodochia develop by late spring the year after infection, mature that fall and produce spores the next spring.
If planting spruce trees consider planting Black Hills or Norway spruce. If you already have Colorado blue spruce trees, then observe them throughout the year for needle droppage and for the spores in the needles. Do not run a lawn sprinkler over the needles as this will encourage the diseases. If caught soon enough you can cut out single infected branches. If over half the tree has lost its needles then it needs to be cut down.
Chemical control is an option, but it is expensive and timing is very critical. Chlorothalonil can control these diseases. For Rhizosphaera the first spray must go on when this year’s needles have reached half their length and sprayed again this year depending upon the label and will need to be sprayed for two to three years. For Stigmina the first application goes on at bud break in the spring and needs sprayed again according to the label for at least four to five years.
