We are having numerous questions concerning the use of Sulforix or lime sulfur at this specific time. For the remainder of this note, I will reference lime sulfur only, but know that I am referring to either lime sulfur or Sulforix when I do so.
Relative an application of lime sulfur at this time (early to mid-December), I would prefer that producers wait till a later timeframe so as to potentially maximize the lime sulfur impact on Exobasidium leaf and fruit spot. I can’t say for sure that lime sulfur would not have activity against Exobasidium during this timeframe, but we do not have research data to support that an early-dormant application will be as effective as a late-dormant application. In addition, producers will likely damage remaining leaves with the lime sulfur; chemical defoliation is not natural, and I don’t like going against nature unless there is a good reason to do so. A rule of thumb (by variety) for planning the lime sulfur application would be to ask the question, when was the earliest budbreak that occurred in previous years at this location (buds that actually would produce leaves or fruit), and back up the lime sulfur to 1-2 weeks prior to that for planning purposes; at the same time, keep an eye on the weather and the plants for movement or predicted movement based on chill hours and temperatures.
Application of lime sulfur is truly an individual judgment call, and predicting budbreak is difficult at best. The current recommendation is for application of lime sulfur at stage 2 (visible swelling of bud, scales separating, flowers still completely enclosed), but some limited stage 3 may be present (bud scales separated, apices of flowers visible) when the vast majority of buds are in stage 2; this is how we are defining late dormant for the purposes of lime sulfur applications. If a producer applied lime sulfur three weeks prior to budbreak, I think this would be just fine; getting it out exactly within the 1-2 week pre-budbreak timeframe is not my concern, but I think December will generally be too early for lime sulfur applications in Georgia. Mid- to late January is more likely the correct target for southern highbush varieties. Lime sulfur is not the only solution for Exobasidium, so if greentip or bloom happens earlier than expected, producers can apply Captan + Indar for management at that time.
Some folks are also asking about putting out lime sulfur prior to Dormex, and I would personally want to do the reverse; in other words, you should apply Dormex first and then lime sulfur (based on currently available information). Producers need to be very sure of the right answer relative timing when using Dormex; applying too early is not effective and waiting too late to apply Dormex is dangerous for blueberry plants. A Dormex warning in the Southeast Regional Blueberry Horticulture and Growth Regulator Guide [(Gerard Krewer (University of Georgia), Bill Cline (North Carolina State University) and D. Scott NeSmith (University of Georgia)] indicates that Dormex will kill flower buds if applied after bud swell, and application must be based on bud development. While Dormex timing studies reveal some advantages in terms of increased foliation, caution needs to be exercised, as flower buds at stage 3 of development or beyond are very susceptible to chemical burn by the product. The current recommendation for Dormex in Georgia is to apply a concentration of 1 to 1.5% of Dormex to poor leafing cultivars when 50 to 60% of their chilling requirement has been met. Typical application dates for southern highbush in south Georgia are late December or early January. Rabbiteye applications are usually in late Jan. or early Feb. Use only on a small scale until you gain experience with the material. Do not apply within 14 days of oil application or within 30 days of copper fungicide application.
Relative close timing of Dormex and lime sulfur applications, we do not have a firm answer, but it scares me to think of having these applied too closely together as well. I can’t find anything on either label that precludes them being applied within a certain period of time from each other, but with Dormex, there is a warning about oils and coppers: “Dormex should be applied 30 or more days before normal budbreak and the oil and/or copper spray should be made as a delayed dormant spray, which coincides with early budbreak. This practice will give three or more weeks of separation.” Without knowing better, I am assuming the same would be true of lime sulfur. Lime sulfur should not be applied within 14 days of an oil application, so there can be some complications with any/all of these materials in the late-dormant timeframe.
I also had a question about putting out oil, Dormex, and lime sulfur. I think the order would have to be oil, Dormex, and then lime sulfur to make that work, with each being separated by at least 2-3 weeks for safety. That is the only way that I think all three can be applied in a single season. However, the temperatures and timing of oil applications could be problematic, as well as the Dormex timing. The lime sulfur is locked in (~2 weeks prior to bud break).
I hope the above information helps a little. However, the application timings of all these materials can be confusing and difficult. Please ask if you have questions, and we will work our way through the answers.
