Washington Tree Fruit Research Commission

Research Reports

Programs to increase yields of target fruit in peach and nectarine (2011)

WTFRC Project #
YEAR 0/0
Organization Project #
Title:Programs to increase yields of target fruit in peach and nectarine
PI:Tory Schmidt
Organization:WTFRC (509) 665-8271 tory@treefruitresearch.com 1719 Springwater Ave. Wenatchee, WA 98801
 PDF version of report


Ines Hanrahan, Felipe Castillo, Tom Auvil, Jim McFerson, WTFRC;                                      Essie Fallahi, University of Idaho, Parma


  1. Evaluate the performance of chemical blossom thinners in peach and nectarine (2009-2010). 

2. Determine horticultural effects of reflective groundcovers on 2 peach cultivars (2009). 

Significant findings

  1.  None of the chemical blossom thinners evaluated in peaches and nectarines (ATS, NC99, Tergitol) reduced fruit set or increased harvest fruit size more than once in six trials over two years. 

2.  Daybright increased yields and enabled the majority of the fruit to be harvested in the first and second pick, whether deployed for the entire growing season or 8 weeks prior to harvest.


Chemical blossom thinning:  We evaluated three chemical thinning programs: Tergitol (1.0%), NC 99 (6%), and ATS (2%) were applied at both 20 and 80% bloom with an AccuTec sprayer. Four randomized complete block trials with four replicates were established in 2009 in one peach (‘Brittany Lane’/Lovell, 6’ x 16’, 9 years old) and three nectarine blocks (‘Scarlet Sun’/Lovell, 6’ x 16’, 9 years old; ‘Red Gold’/seedling, 7.5’ x 15’, 8 years old; ‘Grandbright’/Lovell, 6 x 18, 8 years old). Two trials of similar design were established in 2010 using the same ‘Brittany Lane’ peach and ‘Scarlet Sun’ nectarine blocks.  Data recorded included: initial bloom counts, green fruit set, hand-thinning time, whole tree yields, and standard harvest fruit quality indices.

Reflective ground covers: Two 2009 trials were established near Wapato, WA consisting of 6 strips of Daybright applied in four plots (5 trees long) alternating with untreated control plots of approximately equal dimensions. Daybright 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. Daybright was deployed in a ‘Country Sweet’ peach block (Lovell rootstock, 12’ x 18’ spacing, 9 years old) from full bloom through harvest in early August. The same material was then moved into an ‘O’Henry’ peach block (Lovell rootstock, 7’ x 15’ spacing, 7 years old) until harvest, approximately 2 months later. All fruit samples were taken from trees in middle rows.  For each experiment, yields and fruit maturity were determined from 1 tree per plot at each commercial pick. Standard fruit quality parameters were assessed from 10 fruit per tree at each pick.  

Results and discussion

Chemical blossom thinning:  For stone fruit chemical thinning programs to prove cost effective, they must significantly reduce the need for expensive hand thinning and/or increase the yields of large, high quality fruit.  Unfortunately, significant reductions in fruit set and increases in fruit size were rare from chemical thinning treatments in 2009 (Table 1) and 2010 (Table 2).  Even in cases where treatments produced desired effects, marginal losses in yield efficiency (kg/cm2 TCSA) likely offset any financial benefits of those programs.  Growers would also potentially gain financially from reduced hand-thinning inputs for chemically treated blocks, but these results have been rare in our studies (Tables 1 & 2).  Even in cases where fruit set is significantly reduced, an orchard worker still typically has to make the same number of ladder sets to hand thin a tree, whether he/she has to climb the ladder to remove 2 fruitlets or 20. 

Over 10 years of stone fruit chemical thinning trials, we typically observed more successful results than those of 2009 and 2010.  Unusually cool and damp spring conditions in 2010 may have muted treatment effects during the critical stages of fruit set and early cell division.  Over the course of these studies, frequent losses in yield have often negated the financial benefits of reduced hand thinning and increased fruit size. 

Chemical blossom thinning of soft fruit can be achieved by a variety of chemicals, but ATS has been the most consistent performer in our experiments.  Tergitol has shown some potential, but has been comparatively inconsistent, sometimes over-thinning and often failing to produce significant results.  Other materials including NC99 and lime sulfur rarely demonstrated treatment effects.  

Until new chemistries are identified as potential thinners, the merit of ongoing trials in this area seems marginal.  It is our opinion that the best available option for reducing fruit set and subsequently increasing fruit size is use of mechanized thinners like the Darwin or Bonner.  Even though we are still learning how best to best adopt these new mechanical technologies, they offer the benefit of guaranteeing results independent of weather conditions.  We will continue to work with Karen Lewis to fine tune the use of these machines in the coming seasons.   

Table 1: WTFRC peach and nectarine chemical blossom thinning trials 2009. 

 Fruitlets Fruit FruitHandYield FirmnessSugarAcids
TREATMENT(cm2 TCSA)(%)(in)(min/tree)(kg/cm2 TCSA)(lbs)(% Brix)(% malic acid)
’Grandbright’ Nectarine / Lovell - Basin City
NC995.9 b66 ns2.58 b-0.15 ns21.5 ns9.5 ns1.115 ns
Control7.6 a742.62 a-0.1522.49.01.128
‘Red Gold’ Nectarine / Seedling - Monitor
ATS5.1 b75 ns2.79 ab-0.27 b28.2 b13.2 ns1.397 ns
NC995.3 b742.81 a-0.26 b28.6 b13.41.405
Tergitol6.9 a742.68 ab-0.30 ab28.9 ab13.51.287
Control6.5 ab802.67 b-0.34 a29.5 a13.71.270
‘Scarlet Sun’ Nectarine / Lovell - Wapato
ATS5.5 ab60 ns2.48 ns8.3 ns0.22 ns23.5 ns11.1 ns1.085 a
NC994.9 b582.418.50.2323.310.50.897 b
Tergitol6.4 ab642.327.80.2123.410.90.976 b
Control6.8 a652.379.30.2324.89.70.913 b
‘Brittany Lane’ Peach / Lovell - Wapato
ATS5.4 ns40 ns2.62 ns10.3 ns0.20 ns18.0 ns10.2 ns0.967 ns
 Table 2: WTFRC peach and nectarine chemical blossom thinning trials 2010. 
 Fruitlets Fruit FruitHandYield FirmnessSugarAcids
TREATMENT(cm2 TCSA)(%)(in)(min/tree)(kg/cm2 TCSA)(lbs)(% Brix)(% malic acid)
‘Scarlet Sun’ Nectarine / Lovell - Wapato
ATS1.6 ns17 ns2.65 ns7.9 ns0.10 b6.6 ns12.2 b1.05 ns
NC991.0172.686.90.06 c5.011.8 bc0.94
Tergitol1.0122.586.10.06 c4.013.3 a1.05
Control1.8182.598.80.14 a6.311.4 c1.04
‘Brittany Lane’ Peach / Lovell - Wapato
ATS1.2 b17 b2.58 ns9.5 ns0.09 ns12.7 ns9.9 ab1.20 ns
NC992.7 a29 a2.579.60.1311.910.1 a1.22
Tergitol1.2 b18 b2.647.60.1010.010.1 a1.19
Control1.9 ab32 a2.519.20.1212.19.6 b1.17

Reflective ground covers 2009: Fruit size effects were insignificant except for the first pick of ‘Country Sweet,’ where treated fruit were 10% larger (Table 4). Yields were increased by Daybright in ‘O’Henry’ (Table 3). Sugars and acids were largely unaffected by the Daybright treatment. Firmness at harvest was increased in ‘O’Henry’ and unaffected in ‘Country Sweet’ (Table 4). Daybright shifted more fruit toward earlier harvests based on the percentage of fruit harvested in the first two picks; in both ‘Country Sweet’ (Figure 1) and ‘O’Henry’ (Figure 2), more than 50% of fruit was picked in the first two passes as compared to 30% or less in control plots. 

The most important determinant of profitability for soft fruit growers is reliable cropping of high yields of target fruit. Reflective ground covers such as Daybright consistently increase individual fruit size, as well frequently improving overall yields. In addition, treated fruit can often be harvested in fewer picks. Best results are typically obtained by season-long application; however, we have shown that fruit size and yield gains are possible when applied 8 weeks before harvest. Deploying materials like Daybright across multiple blocks in one growing season considerably increases amortization costs. 

Our program has evaluated the horticultural effects of Extenday and Daybright in apples, pears, cherries, and peaches over several growing seasons.  As with the other crops, our peach results consistently reflect an increase in individual fruit size and/or total fruit set from use of Daybright.  These increases typically produce higher yields of target fruit, but these financial gains must be weighed against the high capital costs of investing in and maintaining this technology.  Even though Daybright can help the production of most stone fruit systems, a grower’s best chance to recoup investment costs would be to use the material in already profitable blocks, rather than using the material to increase the marginal production of a struggling block. 

Table 3: Yield effects of reflective groundcovers for two peach varieties (‘Country Sweet’, ‘O’Henry’). 2009.

 Total yieldTotal fruit ctYield efficiency
TREATMENT(kg/tree)(fruit/tree)(fruit/cm2 TCSA)(kg/cm2 TCSA)
‘Country Sweet’ Peach / Lovell - Wapato
Daybright45 ns215 ns0.9 b0.2 ns
Control412281.0 a0.2
‘O’Henry’ Peach  / Lovell - Wapato
Daybright37 a156 a1.3 ns0.3 a
Control27 b123 b1.10.2 b
   Table 4: Maturity effects of Daybright on ‘Country Sweet’ and ‘O’Henry’ peaches. 2009.
 TREATMENT(% Brix)(% malic acid)(in)(g)(lbs)
‘Country Sweet’ Peach / Lovell - Wapato 
1st pickDaybright11.8 ns0.390 ns3.15 a257 a13.6 ns
 Control12.20.4013.08 b235 b15.4
2nd pickDaybright10.4 ns0.363 a3.04 ns229 ns15.9 ns
 Control10.70.326 b2.9722814.5
3rd pickDaybright9.8 ns0.325 ns2.89 b205 ns13.9 b
 Control10.20.3092.98 a21715.8 a
4th pickDaybright8.8 ns0.376 ns2.86 b199 ns14.2 ns
 Control9.10.3322.92 a20614.3
‘O’Henry’ Peach / Lovell - Wapato  
1st pickDaybright12.5 ns0.678 ns3.17 ns264 ns14.1 ns
2nd pickDaybright12.5 ns0.693 ns3.11 ns252 ns15.8 a
 Control12.30.6913.1526014.0 b
3rd pickDaybright11.4 ns0.636 a3.10 ns247 ns11.1 a
 Control11.60.598 b3.112507.2 b
4th pickDaybright10.8 a0.570 ns2.85 ns195 ns10.2 a
 Control9.9 b0.5602.861997.1 b

Figure 1: The influence of Daybright on the percentage of fruit harvested in each pick for ‘Country Sweet’ peaches. 2009. 

Figure 2: The influence of Daybright on the percentage of fruit harvested in each pick for ‘O’Henry’ peaches. 2009.


I. Hanrahan, T. R. Schmidt and James. R. McFerson. 2009. Programs to increase fruit size and yields in stone fruit. ASHS Annual Conference. Saint Louis. USA (poster)  

I. Hanrahan and T. Schmidt. 2010. WTFRC internal program: Chemical thinning trials in peaches and nectarines. Yakima Valley Soft Fruit Day. Buena. USA. (oral presentation)

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