Production Practices & HLB
Impacts on Fruit Marketability
Mark RitenourUniversity of Florida
Indian River Research and Education Center
The Importance of High Packouts
• Higher packouts = more $$ to grower
• There comes a point when economics dictate taking the
crop straight to the processor
VS
What Influences Packout?
• Age of Trees
• Climate & Weather
• Disease
• Cultural Practices
• Harvest Practices– Spot picking = lower packouts in subsequent picks
• Postharvest Handling Practices
The Importance of Satisfied Markets
• Claims or
rejected loads
at destination
markets are
EXTREMELY
COSTLY!
Three Focus Areas
• Peel Breakdown
• Fruit Decay
• Pesticide Residues
Diplodia stem-end rot
Stem-end Rind Breakdown
Possible Causes of Peel Breakdown
• Water stress?
• Nutrient
Imbalances?
• Low RH postharvest or
sudden changes in
relative humidity (“RH
shock”)?
Water Stress Results
• White grapefruit harvested 48 days after withholding water,
held for 3 d at 70F (60% RH), washed (no wax), and then held
under ambient conditions on the air-conditioned room floor
~73F.
Days after
harvest
Treatment
13 Control 91.33 az 3.33 1.33 3.33 2.67 3.33 6.00 a
Water def. 78.67 b 5.33 4.67 5.33 10.00 6.00 16.00 b
Significance
25 Control 81.00 a 4.67 1.33 5.33 3.33 a 13.00 14.33
Water def. 60.00 b 15.33 6.00 17.33 11.33 b 13.33 24.00
SignificancezValues within each column followed by unlike letters are significantly different by Duncan's multiple range test at P < 0.05.
yIrrigation and rain witheld for 49 days prior to harvest.
NS,*Nonsignificant or significant at P < 0.05, respectively.
Stem-end rind
breakdown (%)
Total peel
breakdown (%)
Marketable
(%)
Stem-end
rot (%)
Penicillium
(%)
Total decay
(%)
Peel pitting
(%)
NS *
* NS NS NS * NS NS
* NS NS NS NS
Roots & HLB
Johnson et al., 2014
weig
ht
sta
rch
weig
ht
sta
rch
weig
ht
sta
rch
Roots & HLB
Johnson et al., 2014
density
sta
rch
density
sta
rch
density
sta
rch
LAS detected
Treatments
• Control – normal grove practices
• Foliar MKP Treatments (23.5 lb MKP/acre + 4 lb/acre
low-biuret urea, 125 gal/acre)
– 8 lb K2O/acre
• Foliar Magnesium (6% Epsom salts)
• Foliar MKP + Mg
• Vapor Gard® (1% or 2%)
• WashGard (1%)
• Polymer Delivery System (1%)
Results – Foliar MKP• Star Ruby red grapefruit harvested two weeks after commercial
MKP application, held for 4 d at 73F (60% RH), washed (no wax),
and then held under ambient conditions on the air-conditioned
room floor ~73F
Harvestz
(weeks)
Days after
harvesty
Treatment
2 25 Control 70.50 ax 1.00 1.00 27.50 a 27.50 a
MKP 86.50 b 1.00 1.50 11.00 b 11.00 b
Significance
3 27 Control 82.58 10.25 1.67 7.67 a 9.33 a
MKP 85.70 9.66 0.67 2.64 b 2.97 b
Significance
4 12 Control 64.32 b 2.52 6.87 25.32 a 32.10 a
MKP 72.89 a 3.19 4.61 18.89 b 23.50 b
Significance
Marketable
(%)
NS
Total peel
breakdown (%)
** NSNS ** **
Total decay
(%)
Pitting
(%)
Stem-end rind
breakdown (%)
*
*** NS NS *** ***
NS NS *
Results - 2009
• Fruit held 2 to 4 days at 70F (60% RH), washed & waxed
(carnauba), and then held under ambient conditions on the air-
conditioned room floor ~73F
Peel Breakdown (%)
Grapefruit 1 Grapefruit 2 Valencia
Control 40.3ab 46.2 33.9a
MKP 29.1abc 28.2 22.7ab
Mg 21.6abc 27.8 19.5b
MKP + Mg 2.6c
Vapor Gard® 12.5c 17.6 10.7bc
• Postharvest peel breakdown can be promoted by tree water
stress before harvest
• Since HLB damages tree roots, it may also increase tree/fruit
water stress and peel breakdown– THIS NEEDS TO BE TESTED!
• Foliar application of K can significantly reduced peel
breakdown
– BUT NOT ALWAYS!
• Vapor Gard (1% or 2%) has performed well over several
seasons in reducing postharvest peel breakdown
Conclusion
Fruit Decay - on Tree!
• Diplodia (Lasiodiplodia theobromae)causes fruit stem-end rot and was:
– Consistently detected in the abscission zone and juice of HLB-infected fruit
– Greater abundance of Diplodia was positively correlated with lower fruit detachment force
– Fruit ethylene production is positively correlated with Diplodia infection levels
Zhao et al., 2015, 2016
Preharvest Materials Tested
• Benlate (Benomyl) – 2 lb/acre
• Topsin M (Thiophanate-methyl) – 2 lb/acre
• Topsin F (Thiophanate-methyl) – 16 oz/acre (liquid)
• Headline (Pyraclostrobin) – 16 oz/acre
• Kocide DF (Copper) – 4 lb/acre
• Abound (Azoxystrobin) – 16 oz/acre
• Enable (Fenbuconazole) – 8 oz/acre
• Aliette (Fosetyl-Al) – 5 lb/acre
Preharvest Materials Tested
• Phosphorous acid (Nutriphite or Phostrol) – 4 pints/acre
• Pristine (Pyraclostrobin + Boscalid) - 18.5 oz/acre
• Actigard (Acibenzolar-S-methyl) – 100ppm + 0.025% Silwet
• Scholar (Fludioxonil) – 8oz/acre
• Switch (cyprodinil & fludioxonil) – 14 oz./A
• Bravo (chlorothalonil) – 6 pts./A
• OxiDate or HDH Peroxy (H2O2) – 1%
• PAA (15%) – 85 ppm
Compound
Control 42.5 aw
48.2 79.9 18.8 a 21.2 a 34.1 ab 37.8 ab
Ferbam 43.7 a
Acibenzolar-S-Methyl 65.5 78.8 16.2 a 15.6 a 51.2 a 45.1 a
Fenbuconazole 51.6 a 50.6 76.2 18.7 a 24.3 a 37.0 ab 46.0 a
Fosetyl AL 59.9 a 50.2 77.6 16.4 a 14.1 ab 30.0 b 34.1 abc
Phosphorous acid 29.3 ab 44.7 84.8 20.9 a 36.4 a 51.6 a 22.0 bc
Copper hydroxide 39.6 a 48.2 78.7 13.3 a 37.9 a 40.6 ab 26.0 bc
Azoxystrobin 39.7 70.2 13.5 a 25.5 a 37.2 ab 38.0 ab
Benomyl 6.2 b 40.1 74.0 3.0 b 1.4 b 2.9 c 18.2 c
Significance * *** **
41 d 86 d 79 d
--- --- --- --- --- ---
58 dx
34 d 78 d 77 d
*v
NS NS **
---
---
23 Nov.y
20 Sept. 9 Oct. 13 Dec. 21 Dec. 19 Mar. 2 Apr.
18 Sept. 2000 11 Dec. 2000 16 Mar. 2001
'Sunburst' 'Fallglo' 'Sunburst' 'Marsh'
Percent Total Decay
4 Nov. 1999z
Compound
Control 60.0 71.8 ay
41.7 a 31.8 a 30.5 60.2 a
Pyraclostrobin 51.8 50.8 b 36.5 ab 17.7 ab 28.3 48.2 a
Phosphorous acid 46.4 45.9 b 29.1 ab 16.7 ab 29.9 47.2 a
Thiophanate methyl 45.1 47.2 b 14.1 c 6.1 b 17.2 15.0 b
Benomyl 42.4 41.3 b 22.5 bc 14.2 ab 12.3 14.0 b
Significance
25 Apr. 6 May.6 Dec.y
18 Dec. 27 Feb. 11 Mar.
NSw
* * * NS **
122 d84 d 118 d 123 d 133 d81 dx
25 Feb. 2002 23 April 20024 Dec. 2001z
'Sunburst' 'Marsh' 'Valencia'
Percent Total Decay
Summary of ExperimentsPreharvest application
Healthy fruit 1999-2005
Treatment Tangerine Orange Grapefruit
Benomyl 4z/6
y 1/2 5/6
Thiophanate-methyl (WSB) 2/3 1/2 3/5
Thiophanate-methyl (FL) 1/1
Pyraclostrobin 1/1 0/1 1/3
Phosphorus Acid 1/4 0/1 0/4
Pyraclostrobin + Boscalid 0/2
Copper hydroxide 0/3 0/1
Azoxystrobin 0/2 0/2
Fenbuconazole 0/3 0/1
Fosetyl AL 0/3 0/1
Acibenzolar-S-methyl 0/2 0/1zNumber of trials the treatment resulted in significantly (p <0.05)
more healthy fruit than the control in at least one of the two harvests.yTotal number of trials the material was tested.
Quadris Top
(Azoxystrobin & Difenoconazole)
• Applied 4 time (twice each in spring and fall) each on 5 different cultivars of citrus
• Diplodia levels
– Significantly reduced in ‘Early Gold’ orange and ‘Murcott’ tangor
– Tended to reduce in ‘Midsweet’ orange
– No significant differences for ‘Navel’ orange and ‘Ray Ruby’ grapefruit
• There was a consistent positive correlation between Diplodia infection and fruit drop
Zhao et al., 2016
Conclusions• Benlate and Topsin
= best, but no longer available
– Efficacy unknown in HLB era
• Fludioxonil products (Scholar & Switch – not
registered) = occasional control
– Efficacy unknown in HLB era
• Quadris Top = intermittent control under HLB
conditions
• Further work is needed
Pesticide Residues & Fruit
Marketability
• Maximum Residue Limits (MRLs)
– Represent the legal tolerances for residues of
different chemicals (often pesticides) on fruit &
vegetables
– Country specific
FL Fresh Grapefruit Shipments
Source: FDOC-EMRD
0%
10%
20%
30%
40%
50%
60%
1987 1992 1997 2002 2007
Domestic Canada
Europe Japan
Other Pacific Rim Other
Source: FDOC-EMRD (Economic Market and Research Department)
2013
3%
8%
20%
42%
27%
MRLs & Different Countries
• A variety of MRLs for different countries greatly
complicates pest control choices for growers and
packers
• Japan (2006)
– Implemented positive list for MRLs
• EU (2008)
– MRL Harmonization Regulation (EC) No 396/2005
MRLs & Different Countries
• South Korea
– Now switching to a positive list system
• China
– Moving to a positive list system
• Taiwan
– Has many missing MRLs (backlogged) and a
restrictive sanctions policy
MRLs & Different Countries
• Industry vigilance is required when MRLs for
export markets are lower than U.S. MRLs
– Especially critical because countries change
MRLs periodically
– Limited knowledge of how fast residues of various
compounds decline under different
production/postharvest conditions
Secondary Standards
• Even more confusing can be individual buyer residue tolerances that are more restrictive governmental MRLs
– These include food processors
• Such tolerances are not widely reported, but must be obtained through communication directly with the buyer
– Close and frequent communication with buyers is essential
GlobalMRL.com
Thank You!