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ARS Home » Southeast Area » Fort Pierce, Florida » U.S. Horticultural Research Laboratory » Citrus and Other Subtropical Products Research » Research » Publications at this Location » Publication #286210
Title: Use of carnauba based carrier for copper sprays reduces infection by Xanthomonas citri subsp. citri and Diaporthe citri in Florida commercial grapefruit groves

Author
item Narciso, Jan
item Widmer, Wilbur
item RITENOUR, MARK - University Of Florida
item Ference, Christopher
item DIAZ, R - Pace International, Llc - Usa

Submitted to: Agricultural Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/3/2012
Publication Date: 11/23/2012
Citation: Narciso, J.A., Widmer, W.W., Ritenour, M.A., Ference, C.M., Diaz, R. 2012. Use of carnauba based carrier for copper sprays reduces infection by Xanthomonas citri subsp. citri and Diaporthe citri in Florida commercial grapefruit groves. Agricultural Sciences. 3(7):962-970.

Interpretive Summary: Asiatic citrus canker, a bacterial disease of citrus, was first documented in Florida in the early 1900’s. The disease was managed, returned and remains uncontrolled. There is little information on methods to reduce infection/inoculum on the leaves, twigs and fruit. Melanose, a fungal disease, is common in citrus producing countries, but is only important for fresh market fruit. Florida growers spray trees with copper formulations. However, these sprays are removed by strong rains and intense radiation of Florida summers. A study was undertaken in Florida commercial grapefruit groves in 2009 and 2010 to assess a spray combining copper with a specially formulated wax, WashGard®. Fruit from trees sprayed with WashGard and copper has approximately 10 and 17 percent more canker free fruit in 2009 and 2010 respectively compared to trees sprayed with copper alone. For melanose there was 40% more disease free fruit (treated) over fruit from trees with no treatment in 2009 and approximately 20% more in 2010. Controlling infection with this spray significantly reduces citrus canker and melanose, increasing the percentage of marketable fruit.

Technical Abstract: Asiatic citrus canker caused by Xanthomonas citri subsp. citri (Xcc), a bacterial disease of citrus, was first documented on Florida citrus in the early 1900’s. At that time the disease was managed, only to return in the 1980’s and 90’s and to finally remain uncontrolled in 2004. Xcc is most active in the warm, wet summers of Florida where tissues are infected during periods of active growth. There have been numerous studies into the biology of the bacterium, but there has been little applicable information on methods to reduce infection/inoculum on the leaves, twigs and fruit in the field. Melanose, caused by Diaporthe citri, is common in citrus producing countries, but is only important for fresh market fruit. Dead wood on citrus trees is the source of spore production, which affects young tissue in early to mid summer in Florida. To control canker and melanose, Florida growers spray trees with copper formulations (Cu). However, these sprays wash off with the strong rains of Florida summers making protection unavailable to vulnerable tissues when infection rates are highest. A study was undertaken in Florida commercial grapefruit groves in 2009 and 2010 to assess the efficiency of a spray combining copper with a specially formulated, hydrating wax (WashGard®)(WG). Using a 21-day spray schedule for the season, fruit were sprayed with WG/Cu, Cu and Control (no spray). Fruit from trees sprayed with WG/Cu had approximately 10-and17% more canker free fruit in 2009 and 2010 respectively when compared to sprays of copper and compared to control, increases in canker free fruit were ˜10 and 57% in 2009, 2010 respectively. For melanose, disease free fruit increased 40% over no treatment in 2009 and approximately 20% in 2010. Controlling infection with this spray significantly reduces citrus canker and melanose infection and increases percentages of marketable fruit.