Read a Q&A about the bactericide Oxytetracycline, marketed under the name Mycoshield.


Bactericides are the talk of the citrus industry in Florida. Citrus growers have been watching the developments with bactericides ever since they were granted emergency use in spring of 2016. Citrus Industry Magazine published a Q&A recently with Dr. Bob Bruss, the Director of Technical Services for Nufarm. Nufarm is the manufacturer of the bactericide Oxytetracycline, sold under the trade name Mycoshield. Read an excerpt of that Q&A below.

Q&A for Bactericide Oxytetracycline


Q: How should Mycoshield be applied when treating Florida citrus trees for HLB?

A: Bruss: At present, Florida growers are operating under a Section 18 (specific exemptions), which spells out use instructions and restrictions. FFVA is now working with FDACS seeking a renewal from EPA of the Section 18. Nufarm recommends applying 1½ pounds of Mycoshield per acre along with a high-quality penetrating surfactant. Growers have the flexibility to apply up to eight times per season with a 21-day preharvest interval.

Q: When are applications of Mycoshield most effective?

A: Bruss: The last two years of research demonstrate Mycoshield is taken into citrus trees most effectively during periods of active leaf flushing. Generally, the greatest flushing occurs in spring and fall. This timing also corresponds to greater activity of HLB in plant tissues vs. summer when bacteria may drop naturally.

Q: Can Mycoshield be tank-mixed with other standard products without impacting performance?

A: Bruss: It appears many growers are tank-mixing Mycoshield with a wide variety of other products normally used in a spray program. We have not received reports of either compatibility or phytotoxicity issues. Foliar applications of Mycoshield alone are not phytotoxic. However, some combinations of Mycoshield — plus other pesticides, surfactants and/or fertilizers — may cause crop injury. The crop safety of any Mycoshield mixture must be verified on a few trees before making a commercial application.

Q: What are the recommendations for rotation of Mycoshield when applying to citrus?

A: Bruss: Oxytetracycline is the ultimate active ingredient resulting from an application of Mycoshield. This is a reversible bacteriostat that suppresses protein production in target bacteria. Multiple applications of oxytetracycline at frequent intervals are needed to starve the bacteria of essential proteins until they perish.

Q: What are you hearing from growers regarding the trees’ response to applications?

A: Bruss: Generally, growers are reporting visual improvement in tree health and research consultants working with Nufarm on Florida trials are observing similar patterns. Since Mycoshield is a suppressive tool, we expect some larger, older trees may not respond as rapidly as younger plantings. Additionally, we expect tree health to show continued improvement the second year of treatment due to cumulative bactericide HLB-suppressive effects.

Q: When would you expect to see more visual and/or yield impacts from the applications?

A: Bruss: Our research trial fruit drop/yield data will be evaluated in the near future. As stated, we also expect there to be a cumulative improvement next season into the summer. Hopefully, many of the trees that were treated in 2016 will have an improved leaf flush this spring. This in turn will provide more young foliage to absorb the 2017 applications leading to additional improvement in tree health.

Griffin Fertilizer is committed to helping both growers and ranchers make sound agronomic and economic decisions in order to maximize the health of their grove and pasture. As a full-service custom dry & liquid fertilizer blender and crop protection product distributor, we will continue our mission to further advance Florida agriculture. For questions or concerns about your farm or pasture, contact us and one of our team will be in touch.