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2008 Florida Citrus Pest Management Guide: Brown Rot of Fruit1
J.H. Graham and L.W. Timmer2Management of brown rot, caused by Phytophthora nicotianae or P. palmivora, is needed on both processing and fresh market fruit. While the disease can affect all citrus types, it is usually most severe on Hamlin and other early maturing sweet orange cultivars. See also PP-156 Phytophthora Foot Rot and Root Rot .
Phytophthora brown rot is a localized problem usually associated with restricted air and/or water drainage. It commonly appears from mid-August through October following periods of extended high rainfall. It can be confused with fruit drop due to other causes at that time of the year. If caused by P. nicotianae, brown rot is limited to the lower third of the canopy because the fungus is splashed onto fruit from the soil. P. palmivora produces airborne sporangia and can affect fruit throughout the canopy.
Early season inoculum production and spread of Phytophthora spp. are minimized with key modifications in cultural practices. Skirting of the trees reduces the opportunity for soil-borne inoculum to contact fruit in the canopy. The edge of the herbicide strip should be maintained just inside of the dripline of the tree to minimize the exposure of bare soil to direct impact by rain. This will limit rain splash of soil onto the lower canopy. Blocks with overhead irrigation should be converted to undertree microsprinklers to avoid the promotion and spread of inoculum in the canopy. Boom application of herbicides and other operations dislodge low-hanging fruit. Fruit on the ground becomes infected and produces inoculum of P. palmivora that can result in brown rot infection in the canopy as early as July while fruit are still green. The beginning stages of the epidemic are very difficult to detect before the fruit are colored and showing typical symptoms. Application of residual herbicides earlier in the summer may reduce the need for post-emergence materials later and minimize fruit drop throughout this early stage of inoculum production from fallen fruit.
Usually a single application of Aliette, Phostrol or ProPhyt before the first signs of brown rot appear in late July is sufficient to protect fruit through most of the normal infection period. No more than 20 lb/acre/year of Aliette should be applied for the control of all Phytophthora diseases. Aliette, Phostrol and ProPhyt are systemic fungicides that protect against postharvest infection and provide 60-90 days control. Copper fungicides are primarily protective but are capable of killing sporangia on the fruit surface and thus reducing inoculum. They may be applied in August before or after brown rot appearance and provide protection for 45-60 days. If the rainy season is prolonged into the fall, a follow-up application of either systemic fungicides at one-half of the label rate, or copper in October may be warranted. With average quality copper products, usually 2-4 lb of metallic copper per acre are needed for control.
Precautions should be taken during harvesting not to include brown rot-affected fruit in the field containers as this could result in rejection at the processing or packing facility.
Recommended Chemical Controls
READ THE LABEL.Rates for pesticides are given as the maximum amount required to treat mature citrus trees unless otherwise noted. To treat smaller trees with commercial application equipment including handguns, mix the per acre rate for mature trees in 250 gallons of water. Calibrate and arrange nozzles to deliver thorough distribution and treat as many acres as this volume of spray allows.
Table 1. Recommended Chemical Controls for Brown Rot of Fruit
Pesticide
FRAC
MOA2
Mature Trees
Rate/Acre1
Aliette WDG
13
5 lb
Phostrol
13
4.5 pints
ProPhyt
13
4 pints
copper fungicide
M9
Use label rate.
1Lower rates may be used on smaller trees. Do not use less than minimum label rate. 2Mode of action class for citrus pesticides from the Fungicide Resistance Action Committee (FRAC) 2003. Refer to ENY624, Pesticide Resistance and Resistance Management, in the 2008 Florida Citrus Pest Management Guide for more details.
Footnotes
1. This document is PP-148, one of a series of the Plant Pathology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Date printed: December 1995. Date revised: November 2007. This publication is included in SP-43, 2008 Florida Citrus Pest Management Guide. A copy of this publication may be found at http://edis.ifas.ufl.edu/CG022. Please visit the EDIS Web site at http://edis.ifas.ufl.edu. For a copy of this handbook, request information on its purchase at your county extension office.2. J.H. Graham, professor, Soil and Water Science Department, and L.W. Timmer, professor emeritus, Plant Pathology Department, Citrus REC, Lake Alfred, Florida; Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, 32611.
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U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, Dean.
Copyright Information
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