ARS | Publication request: Preharvest measures for postharvest improvement in marketable fresh citrus

Submitted to: Proceedings of Florida State Horticultural Society
Publication Type: Proceedings
Publication Acceptance Date: December 5, 2010
Publication Date: December 29, 2010
Citation: Narciso, J., Ference, C., Peeples, W. 2010. Preharvest measures for postharvest improvement in marketable fresh citrus. Proceedings of Florida State Horticultural Society. 123:252-254.

Interpretive Summary: Citrus canker caused by the bacterium Xanthomonas citri supsp. citri, (Xcc), was once the scourge of the Florida citrus industry from the early 1900’s on and off until the early 1990’s. It has been replaced, for the most part, by citrus greening but still continues to be a problem for Florida fresh citrus. The most recent canker outbreak peaked soon after the 2004 hurricanes, where the rains and winds spread the disease more quickly than it could be controlled. Although some of the strict quarantines placed on the Industry at the beginning of the latest canker epidemic have been lifted, there is still a problem with shipping fruit from cankered areas out of the country. While work is continuing on post harvest measures to insure that no live canker bacteria leave the packing houses, pre-harvest measures are also being improved to decrease the disease pressure in the groves as well as lower incidence of infection on the fruit. Most commonly, a copper formulation is sprayed on the trees soon after petal fall for control of canker. Copper has long been used as an effective fungicide, since fungi are sensitive to metals. However, the sprayed copper tends to be powdery and a good deal of it is removed from the leaves and fruit when it rains. Since rain and wind are the chief means of carrying the bacteria from diseased to healthy plants, this curtails the efficiency of the copper. In 2009 we began mixing the copper with a carnauba wax based “sticking agent” and using this formulation to spray experimental trees in a commercial grove. At the end of the growing season we had a significant reduction in canker lesions on the fruit as well as a dramatic reduction in melanose. With the emergence of yet another fungal disease on citrus (citrus black spot, Guignardia citricarpa Kiely), the increased exposure of these several citrus pests to a prophylactic that is maintained and protects the plant surfaces during times of great disease pressure, will facilitate the harvest of more unblemished and marketable fruit.

Technical Abstract: Citrus canker caused by the bacterium Xanthomonas citri supsp. citri, (Xcc), was once the scourge of the Florida citrus industry from the early 1900’s on and off until the early 1990’s. It has been replaced, for the most part, by citrus greening but still continues to be a problem for Florida fresh citrus. The most recent canker outbreak peaked soon after the 2004 hurricanes, where the rains and winds spread the disease more quickly than it could be controlled. Although some of the strict quarantines placed on the Industry at the beginning of the latest canker epidemic have been lifted, there is still a problem with shipping fruit from cankered areas out of the country. While work is continuing on post harvest measures to insure that no live canker bacteria leave the packing houses, pre-harvest measures are also being improved to decrease the disease pressure in the groves as well as lower incidence of infection on the fruit. Most commonly, a copper formulation is sprayed on the trees soon after petal fall for control of canker. Copper has long been used as an effective fungicide, since fungi are sensitive to metals. However, the sprayed copper tends to be powdery and a good deal of it is removed from the leaves and fruit when it rains. Since rain and wind are the chief means of carrying the bacteria from diseased to healthy plants, this curtails the efficiency of the copper. In 2009 we began mixing the copper with a carnauba wax based “sticking agent” and using this formulation to spray experimental trees in a commercial grove. At the end of the growing season we had a significant reduction in canker lesions on the fruit as well as a dramatic reduction in melanose. With the emergence of yet another fungal disease on citrus (citrus black spot, Guignardia citricarpa Kiely), the increased exposure of these several citrus pests to a prophylactic that is maintained and protects the plant surfaces during times of great disease pressure, will facilitate the harvest of more unblemished and marketable fruit.