Lee from West Yellowstone, Montana writes
The timing to stop needlecast from occurring on trees is tricky sometimes but its important to try and be as accurate as you can. Optimal conditions for needlecast are during times of excess moisture and humidity. This disease is common in the spring but can also happen during other times of the year if the conditions for the disease to thrive are favorable. We have linked an article below that is extremely informative on needlecast and how/when to treat for it, and the best management practices to help keep the trees healthy and from being re-infected by spores each year. The excert from the article below refers specifically to growing stages for when the Fung-onil Multi Purpose Fungicide should be applied.
Iowa Extension Article
When all other management is not enough, fungicides can be used to help manage rhizosphaera needle cast. Precise timing is necessary for this method to help, since protection of new growth is the motivation for spraying. Due to the variability of typical spring weather from year to year, it is better to time sprays by observing the new growth. When needle length of the new growth is roughly half the size of old growth, the first spray should be applied. A second spray should then be applied 3-4 weeks later. Sprays may need to be made for 2-3 consecutive years depending on severity. Products containing chlorothalonil or other active ingredients listed for rhizosphaera needle cast can be used for treatment. Remember to always follow the instructions on product labeling.
Answer last updated on: 04/27/2021
