Southwick, Stephen :

Grant, Joseph A

Glozer Dr, Kitren

Project Title : Reduction of stem loss in Bing sweet cherry , 2004 Project Leader : Steve Southwick , Pomologist , Pomology Department , U . C . Davis Cooperators : Joe Grant , Farm Advisor , San Joaquin County Kitren Glozer , Staff Research Associate , Pomology Department , U . C . Davis Summary : We evaluated the effects of several plant growth regulator products and concentrations that had shown promise in increasing stem pull force in > Bing = sweet cherry in trials in 2003 . Based on the 2003 study of PF change in untreated fruit , we suggested that treatments be applied prior to color break / pink fruit stage . Treatments in 2004 were applied at green fruit ( April 23 ) and straw ( May 3 ) stages . Average PF on the first application date was 1671g and on the second date was 1383 g . In 2003 , the highest increase in PF compared to the untreated control was found with compounds having cytokinin - like activity : MaxCel ( 25 ppm ) and Promalin ( 75 ppm ) , using limb replicates . In 2004 we used whole tree replicates and again found the greatest improvement in PF with MaxCel and Promalin , with a slight positive effect for MaxCel as concentration increased from 25 to 75 ppm . No concentration effect was found with Promalin . Further studies should concentrate on refining the application timings of these products . In 2004 , we evaluated changes in stem removal force , or > pull force = ( PF ) , of untreated fruit over time , as in 2003 . The degree to which PF = s changed from one color class ( green , straw , color break / pink , light red , dark red ; light red , dark red ) to the next in 2003 tended to be approximately 20 - 30 % ; 2004 observations verified 2003 results . There was variation in stem pull force within a color from season to season . Problem and its significance : Customers generally prefer cherries with the stem attached and fruit without stems may be more susceptible to decay with shipment and storage . Sweet cherry packers and shippers have noticed significant stem loss in cherries prior to and during packing in many cases . Some have thought stem loss was due to increased use of gibberellin ( GA ; gibberellin A ) . We found concentrations of GA over 32 g / acre coincidental to 3 increased stem loss in our survey conducted in 2002 . However , the use of GA in relation to stem loss was not clearly connected . Other factors than GA use seem to contribute to stem loss in > Bing = and other sweet cherry cultivars . California cherry growers have been routinely using GA in orchards for more than 10 years to improve fruit quality . In recent years , GA use has increased as export markets have favored cherries treated with GA . With the increased use growers , packers and buyers have noted that GA - treated cherries have stems that are loose or detached ; at times fruit maturity has been delayed by GA use . Stem loss will continue to be a problem because of > Bing = susceptibility to stem loss under California conditions . To continue our efforts to better understand and reduce stem loss in > Bing = sweet cherry we continued our investigation of chemical sprays to reduce stem loss , focusing on chemical sprays that were effective in 2003 and refining treatment timing and concentration . Introduction : We conducted a survey in 2002 of 23 orchards in the Lodi / Stockton area where GA was being used in order to assess GA treatment ( s ) and conditions that lend themselves to the production of fruit without stems . We also sampled fruit from GA - treated orchards where the range of GA used varied from 10 to 40 fluid oz or grams active ingredient per acre with volumes of water used to deliver the GA ranging from 100 to 350 gallons per acre . We found in a general sense that stem loss varied by orchard with some high loss and some low loss , ranging from ~ 1 % to as high as 15 to 20 % stem loss in 2002 ; all orchards had some stem loss . We found that , in a very general sense , the later in the season that harvest occurred , the greater the stem loss , but there were some orchards with high stem loss relatively early in the season . Our survey also suggested that cooling the fruit through reducing temperature in cold storage or hydrocooling after picking and prior to packing helped to reduce stem loss . We also found that there was tendency for concentrations of GA over 32 g / acre to increase stem loss , although the relationship of stem loss with increased GA concentration was not strong . In 2003 , we followed the change in stem pull force for untreated fruit in > Bing = sweet cherry over time as fruit matured on the tree at two locations ( Linden and Lodi ) . The major contributor to PF reduction in untreated fruit was maturity change . Time spent on the tree may contribute to PF reduction as it is affected by maturity , but may not inherently reduce pull force ( i.e . as > time spent on the tree = ) . Pull force at harvest in both locations ranged from the 300 ' s to 500 ' s g , across all marketable colors and treatments . Based on our study of PF change over time and maturation in untreated fruit , we suggested that treatments to enhance fruit / stem attachment should be applied prior to color break / pink . We also evaluated the effects of plant growth regulator and calcium sprays on stem pull force . The trials were exploratory and only limbs were treated . Treatments applied in 2003 limb tests that showed the highest 7 7 increase in PF compared with the untreated included chemicals with cytokinin - like activity ( MaxCel , Promalin 7 7 ) and KelPak , as well as ReTain , an ethylene biosynthesis inhibitor . To further test the effects these chemicals might have on PF , we conducted a trial in a commercial orchard in the Lodi area in which whole tree replicates were treated with these compounds . Objectives : 1 . Continue to determine if pre - harvest sprays might increase stem retention and reduce stem loss in > Bing = cherry . 2 . Refine pre - harvest sprays to better define spray timing and concentration for maximal effectiveness with regard to improving stem retention . 3 . Determine if a positional component to sun / shade exposure of fruit affects stem removal force . Plans and Procedures : Plant materials , experimental design , fruit sampling and statistical analyses : The orchard used in this trial was off of Harney in the Lodi area and consisted of > Bing = on mahaleb rootstock , planted in 1992 . Pollenizers were > Black Tartarian = , > Lapins = and > Rainier = . Trees were planted at a 20 x 20 = spacing , 100 trees per acre . The orchard was on Hanford sandy loam soil and was micro sprinkled for irrigation . Full bloom was approximately March 15 . Pollenizers were > Lapins = , > Rainier = and > Black Tartarian = . This orchard was well maintained and had a history of good production of large fruit , but stem loss is often as high as 30 % in the packout . Pull force change over time in untreated fruit ; relationship to maturity : As in 2003 , we sampled untreated fruits of all color classes found on trees over time to better understand the dynamics of stem removal force ( pull force ; PF ) change and a maturity index ( color ) for predicting PF reduction timing . We sampled fruits from several untreated trees selected at random on April 16 , 23 , 28 , 30 , May 3 , 6 , 14 , 21 and 25 , graded fruit into five color classes ( green , straw , color break / pink , light red , dark red ; light red , dark red = CTIFL color chips 3 and 4 , respectively ) , and measured stem PF , using an Imada DPS11 - R digital force gauge with a cam - type attachment to hold cherry stems . Fruit size was also measured on each cherry sampled for PF . Sample size for each date ranged from 10 to 60 fruit per color grade per tree . Samples were collected from both the interior and exterior portions of the canopy , at a height of 1.5 to 2 m above ground level . Pull force relationship to type , concentration and timing of chemical treatments : Treatments applied to entire trees included : 1 . Untreated control 2 . ReTain , 50 g a.i . / acre 3 . MaxCel , 25 , 50 , 75 ppm 4 . Promalin , 25 , 50 , 75 ppm 5 . KelPak ( seaweed product with cytokinin and gibberellic acid activity ) - 1 All treatments were applied at a volume of 100 gallons per acre ( water pH 7.0 ; 936 LÎ?ha ) with a Stihl SR 400 mist blower ( Andreas Stihl , Waiblingen , Germany ) . We used a complete random block design with 4 single tree replicates per treatment ( 4 blocks ) ; 2 blocks were contiguous within each of 2 tree - rows . Treated trees were guarded by unsprayed guard rows . Sprays were applied approximately 6 to 7 am . Experimental treatments were applied at green fruit ( April 23 ) and straw ( May 3 ) stage ( two applications on the same trees ) . Average PF on the first application date was 1671 g and on the second date was 1383 g . Application of MaxCel , Promalin and KelPak included 0.1 % Regulaid and 0.25 % RNA Activator 85 ; ReTain was applied with 0.1 % RNA Si 100 . Fruit were randomly collected from treated trees , sampling from the canopy periphery at a height of 1.5 to 2 m above ground level . On May 25 , at commercial harvest , fruit firmness and fruit size were evaluated using a FirmTech2 device ( measures grams force / mm and diameter in cm ) for relationship to PF . As no difference in PF due to color among marketable fruit ( light red to mahogany ) was found on May 21 , grading by fruit color was not applied on May 25 , however , all fruit evaluated on that date were dark red to mahogany . Sample size was 15 fruit per tree . Statistical Analysis Systems software ( SAS Institute , Cary , NC ) was used to perform the analysis of variance ( PROC GLM ) . Mean separation was by LS Means and by Duncan = s Multiple Range Test , 5 % level of significance . Pull force relationship to position of fruit : On May 25 , fruit were sampled from 4 untreated trees , with fruit divided by exposure in the canopy to sun ( > sun = fruit ) or shade ( > shade = fruit ) . Ten dark red or mahogany fruit from each exposure from each tree 1 were evaluated for pull force and results tested statistically using two - sample t - tests . Results and Conclusions : Pull force change over time in untreated fruit ; relationship to maturity ( Table 1 ) : In 2003 and 2004 , the degree to which PF = s changed from one color class to the next tended to be approximately 20 % . It appears that reduction in stem removal force is a gradual process over the maturation period of > Bing = cherries , although somewhat greater reduction ( 26 - 36 % ) in stem removal force can occur with red color development and physiological maturity . Reduction in pull force , under California growing conditions , begins relatively early in sweet cherry fruit development , based on two years = data in three sites . Untreated fruit at a single orchard site in 2004 tended to have pull force measurements that were much higher within a given color group than those found in either orchard tested in 2003 ( considered on a color group basis ) . Green fruit averaged 400 - 500 g higher PF in 2004 and all but the ripest fruit tested on the last two dates ( May 14 and 21 ) had much higher PF = s than those fruit evaluated in 2003 . These differences might be attributed to orchard soil or irrigation differences , chemical management differences , or climatic differences among the three orchards and two years ( temperatures were higher in 2003 prior to and during harvest ) . To better understand the phenology of stem attachment with fruit maturation in > Bing = cherry , a number of orchard sites and trial years , representing a range of soils , management practices and climatic conditions , is required because of the variation noted in stem pull force change with fruit maturity as a function of season . Pull force relationship to type , concentration and timing of chemical treatment ( Table 2 ) : Pull force was improved by treatment with MaxCel and Promalin at all concentrations . No concentration effect was found with Promalin , and when a potential concentration effect was suspected in MaxCel , a statistical analysis revealed no concentration effect with that treatment either ( Table 2 ) . Effect on pull force was clearly a treatment effect that was highly significant and fairly uniform among replicates ; there was no block effect . Fruit size was also quite uniform , averaging 10 - 10.5 row fruit , independently of treatment . Future trials should continue to investigate spray timing , concentration and both single and multiple sprays , looking at various indicators for treatment , such as maturity ( color ) , pull force change , days after full 1 A two - sample t - test ( also called an unpaired t - test ) compares results from two treatments applied to different experimental units while a paired t - test evaluates subjects that have each received both treatments at differing times . bloom . While a single spray application may be appropriate when maturity is uniform throughout an orchard , at the time of application ( green fruit to straw stage ) , range of maturity can = t be accurately predicted . A split application may address the problem of some fruit developing the ability to assimilate the product or develop a response more readily than others . Treatment effects should also be followed through the commercial picking and packing process , to evaluate actual stem loss at each step . Pull force relationship to position of fruit : When position of fruit with relation to the outer part of the canopy and exposure to sun was investigated , no positional differences were found in pull force ( Table 3 ) . Summary : Our work suggests that sprays of MaxCel or Promalin help to increase stem pull force . Future work should focus on determining the best spray timing linking that timing to either stem pull force or fruit color . Additional work should focus on refinement of chemical concentration . Acknowledgements : We appreciate the support of the California Cherry Advisory Board in funding this project and the cooperation of Pat Hale , grower . % Decrease 17 17 16 26 16 fruit 21 . untreated and ( g ) 14 bc ab ab 6 , c c b a force 2004 all 589.1 531.6 702.8 951.8 1671.0 1383.1 1147.7 May of Pull Stockton , and mean 30 # Fruit a 23 , is 26 66 59 56 46 36 16 number 16 , April % Decrease Each on 18 19 18 12 2004 2004 . in ( g ) 11 ; and c b b d d a force 2003 746.8 991.4 923.7 615.8 545.2 1209.3 and 2003 Pull 2 , 5 1 , years Location June # Fruit for 102 79 58 68 81 46 27 , 0.05 % . y 19 , combined 15 , % Decrease = May P 21 36 27 Test , sampling on Range orchards ( g ) x of c c b d d a a dates 581.7 591.4 909.9 434.4 424.4 1127.5 1149.8 force Multiple 2003 both Pull color , 1 , from Location Duncan = s grade . by 2003 # Fruit time , 79 18 66 63 66 32 16 in color by vs collected separation force a break \ pink mahogany within Pull grade were mahogany 1 . sampled red Means red Fruit Color green Table color straw light dark dark x y y Table 2 . Treatments , concentrations and timings , harvest on May 25 , 2004 . All treatments applied at 100 gallons per acre and , with the exception of ReTain , which was applied with 0.1 % Regulaid + 0.25 % RNA - 85 ; ReTain applied with 0.1 % RNA Si 100 . Chemical Concentration Stem pull force ( g ) x 1 Untreated control 399.4 d 399.4 b 7 2 ReTain 50 g a.i . / 100 gal / acre 390.6 d 1 qt / 100 gal / acre ( 5 7 Kelpak ppm ) 357.2 d 3 4 25 ppm 455.8 c 455.8 a 7 MaxCel 5 50 ppm 462.2 bc 462.2 a 75 ppm 496.2 abc 496.2 a 6 7 25 ppm 501.4 ab 7 Promalin 8 50 ppm 512.9 a 75 ppm 486.2 abc 9 Source df MSIII df MSIII Model 11 122203.4 * * * 224 11454.5 * * * Treatment 8 164119.6 * * * 3 71665.1 * * * Block 3 10742.7 3 18410.7 Error 498 11975.8 218 10400.3 x Means separation by Duncan = s Multiple Range Test , P = 0.05 % ; * * * = P = 0.001 . y Applied to the same trees on April 23 and May 3 . Table 3 . Effects of canopy position on stem pull force in > Bing = sweet cherry , May 25 , 2004 . Stem pull force y Position g x > Sun = 448.4 ( 23.2 ) > Shade = 473.9 ( 13.5 ) ns x Mean separation by Student = s t - Test ( â?? SE ) ; P = 0.05 ; ns = non significant . y > Sun = fruit were sampled from sunny exposures on outer canopy perimeter ; > shade = fruit were sampled from shady exposures within the interior of the canopy . All fruit sampled from height of approximately 1.5 - 2 meters above ground .