Southwick, Stephen :

Glozer Dr, Kitren

Hansen, Randy :

Bonin, Al :

Control of Shoot Growth in â?? French â?? Prune by Apogee in 2003 Steve Southwick , Pomology Department , UC Davis Kitren Glozer , Pomology Department , UC Davis Randy Hansen , Weddle , Hansen & Associates , Inc . , Placerville Al Bonin , Farm Manager , Pomology Department , UC Davis Summary : We used vigorously growing â?? French â?? prune trees growing on marianna 2624 rootstock that had been planted in 1991 and utilized in our continuing Apogee trials . We applied Apogee as - 1 a single treatment of 250 mg � L ( ppm , applied at 200 gallons per acre ) on April 8 , approximately 2 weeks after full bloom ( average current season shoot length ~ 4 inches ) . We also - 1 applied Apogee as multiple treatments of 250 mg � L ( per application ) on April 8 and April 29 , on April 8 and May 20 , or on April 8 , April 29 and May 20 at 200 gallons per acre spray volume . All Apogee treatments reduced shoot growth at the last date of measure , 65 days after full bloom ( March 25 ) . The single application on April 8 reduced shoot growth overall by 19 % and all split applications reduced growth approximately 25 % . Return bloom in 2003 after treatments made in 2002 was not affected by Apogee . Unfortunately , it does not appear that BASF will label Apogee for use on prunes and plums in California , so we will discontinue this work . Problem and its significance : Shoot growth of prune trees can be highly variable and sometimes excessive in prune orchards throughout California . To remedy excessive shoot growth , pruning is often necessary , but pruning is one of the highest costs in prune production . Apogee â?¢ , a shoot growth inhibitor ( prohexadione calcium ; BASF Corp . , Research Triangle Park , NC ) , has been shown to reduce shoot growth of apples , pears , and sweet cherry . Apogee works as a gibberellin biosynthesis inhibitor . Apogee sprays have been reported to reduce secondary growth by as much as 50 % in apples ( Yoder et al . , 1995 ) , and shoot growth reduction appears to be concentration - and species - dependent . Apogee may have a relatively short active period in the plant after application ( BASF estimates approximately 10 to 14 days with repeat applications at 3 to 5 weekly intervals . ) , therefore timing of application and the possibility that a repeated treatment would be efficacious was investigated . Our preliminary work with back pack mist blower sprayers indicated that Apogee may have promise for shoot growth reduction in â?? French â?? prune . Consequently , our more extensive 2002 and 2003 orchard sprayer trials were initiated . Materials and methods Experimental location and plant material , sample procedures and experimental design : Experiments were conducted at UC Davis â?? Wolfskill Experimental Orchard ( Masson addition ) in Winters , CA . We used a complete randomized design of four replicates with four - tree plots x six treatments and treated trees blocked by treatment along three rows per replicate . Treated trees were â?? French â?? prune trees planted in 1991 on M2624 rootstock at 183 trees per acre density . These trees had been used in 2002 trials and the control treatment and early single treatment ( Apogee at 250 ppm , April 8 ) were applied to the same trees that had received these treatments in 2002 . Treated trees were fully guarded against spray drift . Application of Apogee â?¢ ( prohexadione calcium , BASF Corp . , Research Triangle Park , North Carolina ) , a - 1 growth retardant , was at 200 gallons per acre ( 936 L � ha ) using a speed sprayer ; 0.1 % Regulaid was added as an adjuvant . Ten shoots per tree , from approximately 1 m above ground level to approximately 2.5 m above ground on all sides of the tree , were tagged on April 8 , prior to treatment . On this date shoots averaged ~ 4 inches ( 10.2 cm ) in length . Apogee was applied either as a single application on April 8 ( approximately 14 days after full bloom ) , or as split - 1 treatments of 250 mg � L ( per application ) on April 8 and April 29 , on April 8 and May 20 , or on April 8 , April 29 and May 20 . Shoot growth was measured April 8 , May 5 and May 30 . Return bloom measurements for comparison of 2002 treatment effects was measured on March 25 . Statistical Analysis Systems software ( SAS Institute , Cary , NC ) was used to perform the analysis of variance ( PROC GLM ) . Mean separation was by Duncanâ??s Multiple Range Test , 5 % level of significance . Results : Return bloom measured on March 25 ( full bloom ) did not vary among Apogee treatments applied in 2002 ( Table 1 ) . Shoot growth responses to Apogee had shown from year to year that application timing and concentration affected the amount of shoot growth measured in â?? French â?? prune ( Figures 1 - 3 ) . Results in 2003 were consistent with previous years â?? work in that total shoot growth was found to - 1 be reduced approximately 19 % by the first treatment with 250 mg � L Apogee , applied on April 8 , and by 25 % by all split applications when measured on May 30 ( Figure 4 ) ; a split application - 1 of 125 mg � L Apogee had reduced shoot growth in 2002 compared to most single treatments and the untreated control ( Figure 3 ) . In all years of this trial , we found that a large number of treated shoots set terminal buds within one month of treatment , when Apogee was applied shortly after bloom . Summary Remarks : Apogee has a federal registration and is labeled in California for use on apples ( we expect a lable on pears in 2004 ) . Apogee is normally applied with multiple sprays at either 125 or 250 - 1 mg � L from 100 to 200 gallons per acre . Results with â?? French â?? prune suggest Apogee may be an effective plant growth regulator for reducing shoot growth under California conditions . Pertinent literature : Costa , G . , C . Andreotti , F . Bucchi , E . Sabatini , C . Bazzi , S . Malaguti and W . Rademacher . 2001 . ® Prohexadione - Ca ( Apogee ) : Growth regulation and reduced fire blight incidence in pear . Hortscience 36 : 931 - 933 . Yoder , K.S . , S.S . Miller and R.E . Byers . 1995 . Suppression of fireblight shoot blight by prohexadione calcium under experimental and natural inoculation conditions . Proprietary publication , BASF . ® Table 1 . Effect of Apogee on return bloom of â?? French â?? prune . Applications made in 2002 ( full bloom was on March 28 , 2002 ; March 25 , 2003 ) . - 1 Apogee ( ppm , mg � l ; 100 gal / A ) ; date of y application in 2002 No . of flowers per cm shoot length x 250 , April 8 0.52 125 , April 8 0.47 250 , April 22 0.49 125 , April 22 0.55 125 + 125 April 8 & April 22 0.47 Control 0.64 ns x Mean separation by Duncanâ??s Multiple Range , P = 0.05 , ns = non significant . y All applications made with 0.1 % Regulaid . 30 Control 250 ppm April 3 250 ppm April 7 25 250 ppm , April 11 250 ppm April 19 ( cm ) 20 length 15 Shoot 10 5 0 0 5 10 15 20 25 30 35 Days after full bloom ( March 31 ) ® Figure 1 . Effect of Apogee on mean lateral shoot growth ( ± s.e . ) of â?? French â?? prune in 2000 . Arrows indicate dates of application of Apogee . 60 a 50 ( cm ) 40 b length 30 Shoot 20 250 ppm , April 11 250 ppm x 2 , April 11 & 25 Control 10 0 0 20 40 60 80 100 120 140 160 180 200 Days after full bloom ( March 31 ) ® Figure 2 . Effect of Apogee on mean lateral shoot growth ( ± s.e . ) of â?? French â?? prune in 2001 . Arrows indicate dates of application of Apogee . Figure 3 . Shoot growth with Apogee treatment of ' French ' prune in 2002 250 ppm , April 8 125 ppm , April 8 250 ppm , April 22 45 125 ppmx April 22 125 ppm April 8 & 22 a Control 40 35 ( cm ) ab ab length30 b b Shoot 25 20 15 10 0 10 20 30 40 50 60 Days after full bloom ( March 28 ) ® Figure 3 . Effect of Apogee on mean lateral shoot growth ( ± s.e . ) of â?? French â?? prune in 2002 . Arrows indicate dates of application of Apogee . 50 Control April 8 , 250 mg·L - 1 April 8 + April 29 , 250 x 2 mg·L - 1 40 April 8 , May 20 , 250 mg·L - 1 a April 8 + April 29 + May 20 , 250 x 3 mg·L - 1 ( cm ) b 30 length c - Shoot 20 10 â?? â?? â?? 0 0 10 20 30 40 50 60 70 Days after full bloom ( March 25 ) ® Figure 4 . Effect of Apogee ( applied at 200 gallons per acre ) on mean lateral shoot growth ( ± s.e . ) of â?? French â?? prune in 2003 . Arrows indicate dates of application of Apogee .