Citrus Greening Effects on Fruit Size Distribution in Citrus Trees Chris Oswalt Extension Agent, Polk County & Tim Spann CREC, Lake Alfred Chris Oswalt Extension Agent, Polk County & Tim Spann CREC, Lake Alfred

Introduction Greening causes fruit to be small, misshapen, lopsided, develop an off flavor and abscise prematurely Groves can become unproductive in as little as 2-4 years (Ke et al. 1988) Yield can be reduced by 10 to 80% depending on percent of canopy affected (Bassanezi et al. 2006) Greening causes fruit to be small, misshapen, lopsided, develop an off flavor and abscise prematurely Groves can become unproductive in as little as 2-4 years (Ke et al. 1988) Yield can be reduced by 10 to 80% depending on percent of canopy affected (Bassanezi et al. 2006)

Fruit Symptoms

Introduction Quantitative data about how yield is reduced is limited Hypothesis: greening infected trees have a shift in fruit size distribution, being more heavily skewed toward smaller fruit, and that this may be a possible method for detecting greening infected blocks as well as for eliminating greening fruit from loads Quantitative data about how yield is reduced is limited Hypothesis: greening infected trees have a shift in fruit size distribution, being more heavily skewed toward smaller fruit, and that this may be a possible method for detecting greening infected blocks as well as for eliminating greening fruit from loads

Experimental Site 9-year-old ‘Valencia’ on carrizo First greening find Dec –109 trees, removed immediately Jan. 2007, second find –102 trees, 100 removed in August 2007 Jan. 2008, 74 trees with visible symptoms 9-year-old ‘Valencia’ on carrizo First greening find Dec –109 trees, removed immediately Jan. 2007, second find –102 trees, 100 removed in August 2007 Jan. 2008, 74 trees with visible symptoms

Healthy tree Greening tree found 1/08 Greening tree found 1/07

Methods Trees hand harvested April 9-11, 2008 –5 healthy (symptomless) trees –6 PCR+ –2 trees from Jan find Fruit sized by hand based on fresh fruit size standards –<125, 125, 100, 80, and 64s Fresh weight by size and total FW were recorded 125 fruit were sorted into symptomatic and asymptomatic Trees hand harvested April 9-11, 2008 –5 healthy (symptomless) trees –6 PCR+ –2 trees from Jan find Fruit sized by hand based on fresh fruit size standards –<125, 125, 100, 80, and 64s Fresh weight by size and total FW were recorded 125 fruit were sorted into symptomatic and asymptomatic

Results Total fresh weight and fresh weight by size category per tree for ‘Valencia’ fruit from healthy trees and trees infected with greening disease for either 1 or 2 years. Fruit yield (lbs fresh weight) per tree Total< Healthy year infected year infected z P =0.0692N/A z P values represent the results of t-test comparisons between healthy trees and 1-year infected trees. Analysis for fruit size >125 could not be performed because there were no fruit in that category on the healthy trees. 2-year infected trees were not included in the analysis due to the lack of replicate trees, these data are shown for discussion purposes only. Greening reduced total yield by ~25% (1 box) 125 fruit on 1-year infected trees were 35% symptomatic Greening reduced total yield by ~25% (1 box) 125 fruit on 1-year infected trees were 35% symptomatic

Results 50-60% of total yield was 125 or smaller fruit on infected trees compared to healthy trees

Significance to Processors/Packers Due to smaller fruit size total juice volume produced will be less from greening trees Potential off-flavors in greening fruit For fresh fruit ~5% of fruit is lost due to size (<125), another 10-15% is lost due to symptoms (poor fruit quality) Due to smaller fruit size total juice volume produced will be less from greening trees Potential off-flavors in greening fruit For fresh fruit ~5% of fruit is lost due to size (<125), another 10-15% is lost due to symptoms (poor fruit quality)

Significance to Growers In the block used in this study 15% of trees have been removed since first greening find Direct loss of nearly 1500 boxes in 18 months The 3 grove inspections to date have each found 4.5 – 6% infection In the block used in this study 15% of trees have been removed since first greening find Direct loss of nearly 1500 boxes in 18 months The 3 grove inspections to date have each found 4.5 – 6% infection

Conclusions For Valencias greening can be detected based on fruit size distribution Data can be used to develop better economic models Data indicate that processors and packers may be able to help ID unknown areas of greening For Valencias greening can be detected based on fruit size distribution Data can be used to develop better economic models Data indicate that processors and packers may be able to help ID unknown areas of greening

Additional Research Determine if these effects are the same for Hamlin and grapefruit Determine yield loss due to premature fruit drop as well as from reduced fruit size Determine if these effects are the same for Hamlin and grapefruit Determine yield loss due to premature fruit drop as well as from reduced fruit size