Why do I have to wait 2 weeks to spray sulfur after copper spray?

I have an A. pear (20th Century) that suffered blossom blight previously and I plan to spray copper (Kocide 3000) at a delayed dormant stage.

I have E. pear trees that have suffered pear blister mites so I plan to spray lime-sulfur when blossoms swell.

I read an article by Oregon State U. for home gardeners to “allow two weeks between applications of copper and any sprays containing sulfur”.

From the time I will spray copper and spray lime-sulfur, it could be less than two weeks.

What will happen if I spray them less than two weeks apart? What kind of damage?

I know lime-sulfur can help with fire blight, too. But my question is why it should not be spray within 2 weeks of each other?

Disclaimer: Any scientific education/knowledge some may think I have is a rumor. :smile:

Copper and sulphur should be compatible. See this chart:


I wonder if there is not a typo in what you read, its oil and sulphur you need to keep two weeks apart.

Note that most compatibility issues are not issues for dormant spraying, e.g. oil and lime-sulphur is fine for a dormant spray. I also spray copper and lime-sulphur together occasionally as a dormant spray.


Thank you, Scott. Below is what I read it from, under Fixed Copper heading.


Starting this Sunday, the weather and the tree condition is ready for dormant sprays.

I just sprayed copper and sulfur together with oil and Daconil…just this evening. Dormant spray…most of my trees are at pretty much full bud swell.