Black knot for plums - Ask Extension
Why does Michigan States extension say sulfur is NOT protective against black knot on edible plums but I recently paid for the OSUs agriculture extens...
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Black knot for plums #865370
Asked April 22, 2024, 12:07 AM EDT
Why does Michigan States extension say sulfur is NOT protective against black knot on edible plums but I recently paid for the OSUs agriculture extension PDF with info about fruit trees and in it states sulfur IS a preventative against black knot. So who is right ?
I'm already using chlorothalonil in the early spring until shuck split but need something after shuck split and according to OSU, sulfur works. Any tips appreciated.
Lake County Ohio
Expert Response
Jeremiah,
The answer to your question is not necessarily that one is right and the other is wrong. The label for a Lime-sulfur product (https://www3.epa.gov/pesticides/chem_search/ppls/<personal data hidden>0-20181105.pdf) lists black knot of plum as a disease for which it can be applied as well as for several other pests. Since it is listed on the label, it was included in the OSU publication. No determination was made as to its effectiveness against the disease. The author(s) of the Michigan State publication has made the judgement that lime-sulfur is not overly effective against black knot of plum based on research and/or personal observation. The complete answer may be somewhere in between being not effective and effective. There are numerous additional factors that could influence the outcome of using lime-sulfur including timing of applications, concentration used, weather, severity of infections, inoculum in the area, susceptibility of the plum variety, whether or not old knots were pruned out of the trees, and what other fungicides might be used on the trees through the growing season.
The answer to your question is not necessarily that one is right and the other is wrong. The label for a Lime-sulfur product (https://www3.epa.gov/pesticides/chem_search/ppls/<personal data hidden>0-20181105.pdf) lists black knot of plum as a disease for which it can be applied as well as for several other pests. Since it is listed on the label, it was included in the OSU publication. No determination was made as to its effectiveness against the disease. The author(s) of the Michigan State publication has made the judgement that lime-sulfur is not overly effective against black knot of plum based on research and/or personal observation. The complete answer may be somewhere in between being not effective and effective. There are numerous additional factors that could influence the outcome of using lime-sulfur including timing of applications, concentration used, weather, severity of infections, inoculum in the area, susceptibility of the plum variety, whether or not old knots were pruned out of the trees, and what other fungicides might be used on the trees through the growing season.
