Washington Tree Fruit Research Commission

Research Reports

WTFRC internal pear projects (2009)

FINAL PROJECT REPORT
WTFRC Project #
YEAR 0/0
Organization Project #
Title:WTFRC internal pear projects
PI:Ines Hanrahan
Organization:WTFRC; 104 N 1st St., Suite 204; Yakima, WA 98901 509-669-0267 hanrahan@treefruitresearch.com
 PDF version of report

Cooperators

Jim McFerson, Tom Auvil, Felipe Castillo, Tory Schmidt, WTFRC,                                        Wenatchee, WA; Jonathan Toye, Extenday, NZ

Objectives

1. Investigate the effects of chemical thinners on pear crop load and fruit quality. 

2. Determine the effects of Daybright reflective groundcover on horticultural performance of pear orchards.

Significant findings

Chemical thinning: The most consistent performers in Washington pear chemical thinning trials are ammonium thiosulfate (ATS) applied during bloom and benzyladenine (BA) applied postbloom. Increases in individual fruit weight are often observed after benzyladenine application, even without significant fruitlet thinning. 

Reflective groundcovers: Daybright reflective groundcovers improve yields in Bartlett by increasing fruit set and/or size.

Methods

Chemical thinning: Within a set of 6 trials in 2008 we evaluated ammonium thiosulfate (ATS), and urea as bloom thinners, as well as BA (Exilis Plus, MaxCel, 6-BA) and NAA as postbloom thinners. ATS (4%) and urea (5%) were applied at 20 and 80% bloom (only 80% at grower-applied sites, both timings at PropTec sites), BA (1%) and NAA (3.6oz/100gal) at 10 mm fruitlet size.  All experiments employed randomized complete block designs with 4 replicates. Two of last years trials were small plot trials sprayed with a Proptec tower sprayer operated by WTFRC staff. The remaining four trials were applied by grower-cooperators with their own commercial spray rigs, typically airblast sprayers.           

Initial bloom counts were taken prior to treatment and compared to actual fruit set counts taken after June drop. From these data, we calculated the number of fruit set per 100 blossom clusters. We also recorded the quantity of fruit set in each cluster initially counted, allowing us to calculate how many clusters were blanked, thinned to single fruits, two fruits, etc.  Return bloom counts of the same experimental units are recorded in the spring following treatment.  Standard fruit quality parameters are assessed at commercial harvest, including: fruit size, soluble solids content, titratable acidity and firmness. Sampled fruit was visually graded for defects including: sunburn and russet.  

Reflective groundcovers: Trials were conducted in two locations over three seasons (2006 - 2008).  The first site (Sunnyside) was a mature Bartlett/seedling block with 4 x 13 ft. spacing, and trained to a v-trellis structure.  The second site (Cashmere) was a young ‘Bartlett’ block, on an OH x F 87 rootstock, with 7 x 14 ft. spacing, and trained to a central leader structure.  Daybright was applied from early bloom until harvest in both experiments.  The general layout consisted of variable length strips of reflective ground cover applied in four or six plots across several orchard rows alternating with untreated control plots of approximately equal dimensions. Daybright reflective groundcover was placed in orchard alleyways and attached to the tree trunks with elastic bands (ca. 4 inches above ground), covering approximately 80% of intra-row space.

All samples were taken from trees in the middle row.  For each experiment, yields and fruit maturity were determined from several individual trees per plot at harvest (4 in Cashmere, 8 in Sunnyside); the Cashmere block was strip-picked at harvest, while the Sunnyside block was picked twice, once for fresh market, and again for cannery pears.  Fresh market pears were chosen  based on fruit size (minimum 2.55 inches diameter). The remaining pears (cannery) were harvested immediately following the first pick. Fruit maturity parameters were assessed from 10 fruit per tree for each pick, including: fruit weight, firmness, starch, titratable acidity, soluble solids concentration, russet incidence, degree of sunburn.             

Results and discussion

Chemical thinning: The Mt. Adams, Buena and Tonasket trials were sprayed by grower-cooperators, while those at Sawyer and Cashmere were applied with the WTFRC Proptec tower sprayer (Table 1).  

Table 1. Crop load and fruit quality effects of WTFRC pear thinning trials. 2008.

Treatment Fruitlets/LCSAcm2Fruitlets/100 blsm clustersFruit diameter (in)Fruit weight (g)Box sizeSugars  (% brix)Acids  (% m. acid)Firmness  (lbs)
                                                       Bartlett / Seedling – Sawyer                                      
ATS2.3 ns52 ns2.6 ns200 b10010.2 b0.316 a17.6 a
6-BA1.4482.7212 a9410.2 b0.270 c16.7 b
NAA1.8642.6198 b10110.7 ab0.280 bc17.1 b
Urea2.1492.6203 ab9811.4 a0.307 ab17.7 a
Control2.2612.6202 ab9910.6 ab0.279 bc17.0 b
Bartlett / OHxF.87 – Cashmere
ATS2.3 ab34 a2.7 b211 b9513.1 ns0.354 ns18.4 ns
6-BA1.6 b21 b2.8 a232 a8613.10.35218.0
NAA1.8 b28 ab2.7 b206 b9713.10.35917.6
Urea1.8 b29 ab2.7 ab214 ab9313.00.35918.1
Control2.9 a36 a2.6 b201 b9913.30.35617.8
Bartlett / OHxF.87 - Mt. Adams
ATS6.1 ns73 ns2.6 c160 b12511.0 ns0.243 ns18.0 a
6-BA4.6732.6 a171 a11711.10.24917.0 c
Urea5.0762.6 b167 ab12011.20.24917.2 bc
Control4.9802.6 b166 ab12010.90.23717.6 ab
Bartlett / OHxF.97 - Mt. Adams
ATS3.6 ns76 ns2.6 b171 ab11711.2 ns0.311 a17.1 ns
6-BA3.4672.7 a178 a11211.10.286 ab17.0
Urea3.4752.6 b170 b11810.80.259 bc17.2
Control4.5842.6 ab170 b11810.70.243 c16.9
Bartlett / Seedling – Buena
ATS0.7 ab44 ns2.7 ns214 ns9311.4 ns0.305 ab17.4 ns
Exilis Plus0.7 ab482.72139411.40.334 a17.1
Urea0.5 b392.72129411.20.265 b17.3
Control1.0 a522.72069711.50.292 b17.3
Bosc / OHxF.97 - Tonasket
ATS1.3 ns85 bno data251 a8011.3 ns0.159 ns14.0 b
MaxCel1.597 ano data219 c9111.50.15114.8 a
Urea1.579 bno data237 b8411.00.15014.5 ab
Control1.798 ano data211 c9512.40.14214.8 a

 Fruit set (fruitlets/100 clusters) was significantly reduced once with urea or ATS (Tonasket) and 6-BA (Cashmere), translating into higher individual fruit weight at harvest (Table 1). Although BA did not thin fruitlets effectively, it generally improved final fruit size.  Soluble solids, titratable acidity and fruit finish were not affected by any treatment.  Chemical thinning effects on fruit firmness are inconsistent: firmness was increased once with ATS and urea, and decreased once with 6-BA and ATS. 

Since 2003 we have conducted 25 pear thinning trials, testing an array of bloom (ATS, urea, CFO+LS, LS) and postbloom (BA, NAA) thinners. Table 2 summarizes our results. The overall goals when using crop load adjustment methods are: reduction of fruit set (indicated by fruitlets/100 blossom clusters); increase in mean fruit weight; and consistent annual bearing (indicated by return bloom). ATS and BA products have shown utility in pear blossom and fruitlet thinning. More importantly, BA typically improves final fruit size even in the absence of fruitlet thinning (Table 2). 

Table 2. Incidence of statistically significant results for three key crop load parameters. WTFRC pear chemical thinning trials 2003-2008.

THINNING AGENTFRUITLETS/100BLSM CLUSTERSMEAN FRUITWEIGHTRETURNBLOOM
NAA0/6 (0%)0/6 (0%)0/2 (0%)
ATS7/25 (28%)5/24 (21%)2/17 (12%)
Urea1/17 (6%)3/17 (18%)0/11 (0%)
CFO + LS0/3 (0%)1/13 (8%)1/2 (50%)
LS1/13 (8%)3/13 (23%)0/13 (0%)
BA3/12 (25%)6/10 (60%)2/5 (40%)

  

 

 

 

 

Reflective groundcovers: Daybright, a reflective groundcover manufactured by Extenday, was applied for the third consecutive year in 2008 in an established Bartlett block on a V-trellis (Sunnyside) and a young Bartlett block (Cashmere) from early bloom to harvest. Each year of the trial, fruit was harvested in two picks at Sunnyside and a single pick in Cashmere.  Timing and duration of commercial harvest was not affected by Daybright at either site in 2008. Significant results include (Table 3, 4):

      Table 3. Yield effects of WTFRC pear reflective groundcover trials. 2008.
Treatment Total yieldkg/treeTotal fruit ctfruit/treeYield efficiency  fruit/TCSA     kg/TCSA1st pick kg % of total2nd pick kg % of total
Bartlett / Domestic - Sunnyside
Daybright25.1 ns128 ns1.1 ns0.21 ns92 ns8 ns
Control25.61361.10.218911
Bartlett /OHxF.87 - Cashmere
Daybright71.3 a383 a4.6 ns0.85 nsno datano data
Control64.5 b342 b4.40.83no datano data
  Table 4. Fruit quality effects of WTFRC pear reflective groundcover trials 2008.
Treatment Sugars(% brix)Acids(% malic acid)Firmness(lbs)Weight(g)Diameter(in)
Bartlett / OHxF.87 - Cashmere
Daybright11.4 b0.329 a17.3 ns203 b2.66 b
Control11.9 a0.313 b17.0217 a2.70 a
Bartlett / Domestic – Sunnyside (Fresh pick)
Daybright10.8 a0.256 b17.6 a199 a2.64 a
Control10.2 b0.279 a17.4 b190 b2.57 b
Bartlett / Domestic – Sunnyside (Cannery pick)
Daybright10.5 ns0.255 b17.9 ns123 ns2.26 ns
Control10.30.273 a17.7 1222.25

 During the three year trial period, Daybright application resulted in consistently higher yields in two years at both sites (Figure 1).  2008 results suggest that Cashmere fruit set gains were offset by smaller fruit size (10% higher yields with loss of ½ box size). In Sunnyside, yields were comparable, but fruit was ½ box size larger (Table 4). 

Reflective groundcovers have shown utility in modern pear plantings and young orchards. Trials with Daybright reflective groundcover demonstrate yield gains in Bartlett due to increased fruit set and/or size. Better light distribution spurred renewed fruiting in lower portions of tree canopies, allowing more of the crop to be managed from the ground.             

Figure 1:  Percent change in yield (kg/tree) after Daybright application in two pear orchards over a three year period.   

Figure 2:  Percent change in individual fruit weight (gram) after Daybright application in two pear orchards over a three year period.          

OUTREACH

Posters

Schmidt, T. 2006-2008. Crop load management. Posters at WSHA annual meeting. 

Castillo, F. 2006-2008. Update on reflective groundcover evaluation in Washington. Posters at WSHA annual meeting.  

Talks at industry meetings

Castillo, F. 2007. Reflective groundcovers in tree fruit. GS Long Grower Meeting.  

Castillo, F. 2007-08. Reflective groundcovers. Okanogan Field Day. 

Hanrahan, I. 2008. Crop load management in pears. Presentation at Wenatchee Pear Day.  

Schmidt, T. 2007.  WTFRC Research Programs. Presentation at D & M Growers’ Annual Meeting, Yakima, WA. 

Schmidt, T. 2008.  WTFRC Research Programs. Presentation at D & M Growers’ Annual Meeting, Yakima, WA. 

Schmidt, T. 2008.  Horticultural benefits of reflective materials. Presentation at Cascade Ag Services Growers’ Annual Meeting, Chelan, WA.  

Scientific publications

Hanrahan, I., Schmidt, T. R., Castillo, F., McFerson, J.R.. 2008. Reflective Ground Covers Increase Yields of Target Fruit. Poster and paper at ISHS in Geneva, NY, August 2008.  

Other

Hanrahan, I. 2009. Increasing yields of target fruit with reflective ground covers in pear. Presentation at IFTA conference, Potsdam, Germany. 

Schmidt, T. 2007. Improving fruit quality with reflective fabrics and sunburn suppression. Presentation at British Columbia Fruit Growers’ Association Hort Forum, Penticton, Canada.              

EXECUTIVE SUMMARY

1. Pear crop load management 

Since 2003 we have set-up 25 pear thinning trials, testing an array of bloom (ATS, urea, CFO+LS, LS) and postbloom (BA, NAA) thinners. Our overall goals were:-          reduction of fruit set (indicated by fruitlets/100 blossom clusters);

-          increase in mean fruit weight;

-          consistent annual bearing (indicated by return bloom).

The most consistent performers in Washington pear chemical thinning trials are ammonium thiosulfate (ATS) applied during bloom and benzyladenine (BA) applied postbloom. Increases in individual fruit weight are often observed after benzyladenine application, even without significant fruitlet thinning. 

 2. Reflective groundcovers in pear Daybright, a reflective groundcover manufactured by Extenday, was applied for three consecutive years in an established Bartlett block on a V-trellis (Sunnyside) and a young Bartlett block (Cashmere) from early bloom to harvest. Daybright results demonstrate yield gains in Bartlett due to increased fruit set and/or size. Better light distribution spurred renewed fruiting in lower portions of tree canopies, allowing more of the crop to be managed from the ground. 

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