Spring Fungal Diseases: Have You Seen These on Your Trees?
Tree diseases are rampant in the springtime, as the weather becomes rainy and new growth appears.
Diplodia shoot blight, Dothistroma needle blight, and Rhizosphaera needle cast are all fungal diseases that spread in the spring. This post will cover these spring fungal diseases and how to prevent, identify and treat each in the event of infection.
Diplodia Shoot Blight
Diplodia shoot blight (Diplodia Pinea, D. Scrobiculata) is a fungal disease that affects Austrian Pine, Ponderosa Pine, Scots Pine, Red Pine, and Jack Pine trees. It can look like or co-occur with Dothistroma needle blight, pine needle scale or salt damage.
How it spreads
In the spring, as shoots are expanding, fungal spores can spread from previous infections to the new growth. If trees are healthy, the infection only kills new shoots and trees recover quickly. Stressed trees can’t prevent infection, causing fungus to spread into the mature tissue. This causes cankers and whole branch death, resulting in a slow decline of the tree. Infections can remain dormant for years and flare up when trees become stressed.
How to prevent diplodia shoot blight
The best way to prevent a fungal infection, or any infection for that matter, is to reduce the amount of stress on your trees. Trees become stressed due to improper planting or watering, soil compaction, storm damage or extreme temperatures. While there are many stressors that are out of your control, you can make sure to not over-fertilize trees, not prune trees too early and use caution when using lawn irrigation systems.
When spring arrives, ensure that no irrigation is spraying the foliage. That will only create an ideal environment for disease to spread.
During dry conditions, water your trees and add mulch to conserve soil moisture. This is also a good time to prune any infected tissue. If you were to do this in wet conditions, those new wounds could become infected.
Also, don’t fertilize infected trees, as an increase in soil nitrogen can increase the disease severity.
How to treat diplodia shoot blight
Diplodia shoot blight is best treated by a professional arborist. The arborist will apply three spray rounds of chlorothalonil. The first application should occur before bud break, followed by two more applications at 14-day intervals.
When timed right, these spray applications are very effective. If a tree is too infected, it can take a couple of years for the tree to re-grow enough foliage to look healthy again. Assuming there isn’t severe branch death, recovery is very likely.
Dothistroma Needle Blight
Dothistroma needle blight (Dothistroma Septosporum) is a fungal disease that affects Austrian Pine and Ponderosa Pine trees. It can look like or co-occur with diplodia shoot blight, pine needle scale or salt damage.
How it spreads
Fruiting bodies on infected needles produce spores during the growing season, which move to mature needles during cool, wet weather. While new needles are resistant until midsummer, old needles are susceptible.
Spots develop at the point of infection, which expand to form reddish-brown bands. The needle past the band dies and turns brown. Eventually the entire needle dies and falls early.
How to prevent Dothistroma needle blight
As with diplodia shoot blight, ensure that irrigation isn’t spraying the tree foliage, water trees in dry conditions and mulch around your trees to conserve soil moisture. Also, prune your trees at the appropriate time to improve air circulation through the canopy.
How to treat Dothistroma needle blight
A professional arborist will apply two spray rounds of chlorothalonil. The first application should occur before bud break, followed by a second application at full needle development.
Spray applications are very effective when timed appropriately. It can take several years for infections to become serious, so if caught early damage is very preventable. If a tree is heavily infected, it can take a couple years for the tree to re-grow enough foliage to look healthy again. Assuming there isn’t severe branch death, recovery is very likely.
Rhizosphaera Needle Cast
Rhizosphaera needle cast (Rhizosphaera Kalkhoffii) is a fungal disease that affects Colorado blue spruce, white spruce, and Black Hills spruce trees. It can look like and co-occur with Stigmina Needle Cast (Stigmina lautti), Spruce Spider Mites, Cytospora Canker or salt damage.
How it spreads
During wet conditions, spores transfer from older, infected needles to succulent new growth. The needles will turn yellow and mottled by mid-summer and brown or purplish-brown by late fall or winter. Infection usually starts in the lower canopy and gradually moves up and out, with lower branches eventually dying due to stress.
How to prevent Rhizosphaera needle cast
As with Diplodia shoot blight and Dothistroma needle blight, don’t water the foliage. To increase airflow and speed up the drying process, prune trees at the correct time of the year. Do not shear trees as shearing increases canopy density.
How to treat Rhizosphaera needle cast
A professional arborist will administer three spray applications of chlorothalonil to protect new growth. They will apply the first application at caps off or two-inch shoots, followed by two more applications at 14-day intervals.
Spraying will only protect the current year’s growth, so it’s best to assume that all previous foliage is infected and likely to cast off. It generally takes four to five years of spraying for the tree to regrow enough foliage to look unaffected.
Have you spotted any of these issues on your trees?
If you’ve spotted any of these spring fungal diseases on your trees, or need help identifying or treating them, contact our expert arborists.