Vol.3, No.7, 962-970 (2012) Agricultural Sciences http://dx.doi.org/10.4236/as.2012.37117 Use of carnauba based carrier for copper sprays reduces infection by Xanthomonas citri subsp. citri and Diaporthe citri in Florida commercial grapefruit groves Jan Narciso 1* , Wilbur Widmer 1 , Christopher Ference 1 , Mark Ritenour 2 , Ricardo Diaz 3 1 USDA/ARS, US Horticultural Research Laboratory, Fort Pierce, USA; * Corresponding Author: jan.narciso@ars.usda.gov 2 IFAS, IRRC, University of Florida, Fort Pierce, USA 3 PACE International, Wenatchee, USA Received 18 August 2012; revised 21 September 2012; accepted 3 October 2012 ABSTRACT Citrus canker, caused by Xanthomonas citri subsp. citri (Xcc), is a bacterial disease of citrus and results in peel blemishes rendering fresh fruit unsalable. Xcc is most active in warm, wet Florida summers where tissues are infected during periods of active growth. Melanose, caused by Diaporthe citri, is common in citrus producing countries, but, like canker, is only important for fresh market fruit. To control can- ker and melanose, Florida growers spray trees with copper formulations (Cu), but these sprays are removed by strong rains and intense radia- tion of Florida summers. A study was under- taken in FL commercial grapefruit groves in 2009 and 2010 to assess the efficiency of a spray combining copper with a specially formu- lated, 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 ap- proximately 10 and17% more canker free fruit in 2009 and 2010 respectively compared to trees sprayed with copper alone. Compared to control trees the canker free fruit incidence was in- creased by ≈10% in 2009 and 57% in 2010. 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. Keywords: Citrus Canker; Melanose; Protective Sprays; Adjuvant; Coatings 1. INTRODUCTION Citrus canker, caused by Xanthomonas citri subsp. ci- tri (Xcc) is found on all citrus cultivars, with grapefruit, Mexican lime and lemon being the most sensitive [1-4] (Figure 1(a)). All parts of the plant are susceptible but young tissue is the most vulnerable [1,2]. In warm, wet, weather the bacteria ooze from the lesions and are car- ried in wind driven rain to susceptible tissue. On fruit, canker affects the peel producing superficial lesions, which render the fruit unmarketable for fresh sales. One of the strongest impacts of canker is that it causes severe restrictions on fruit movement to some markets [4]. Melanose (Diaporthe citri F. A. Wolf; anamorph Pho- mopsis citri H. Fawc. Non (Sacc.) Traverso & Spessa) is a fungal disease of citrus that causes a superficial blem- ish on the peel reducing acceptability in the fresh market [5] (Figure 1(b)). All citrus varieties grown in Florida are susceptible but as in canker, grapefruit are the most sensitive [5-7]. Disease severity is regulated by tempera- ture and rainfall conditions during leaf expansion [6-9]. In humid and wet weather, conidia exude from pycnidia in dead wood and are washed down the tree from the canopy [5,6,8,9]. Copper formulations (e.g. copper hydroxide) are rou- tinely sprayed on citrus in Florida on a 3-week (21 day) schedule for control of canker, melanose and other fungal diseases [6]. MCGuire [3] found that copper containing sprays were effective in reducing epiphytic populations of Xcc. However, copper dries to a powder and is easily washed away with rains; it also erodes in the harsh UV light and dry conditions in Florida groves. Since the bac- terial and fungal pathogens are most problematic during rain and wind events in the summer, the dissolution of copper under these conditions leads to unprotected sus- ceptible tissue. It is critically important that successful protective sprays are available to reduce infection as well Copyright © 2012 SciRes. OPEN ACCESS