CHEMICAL DEFOLIANTS ON BARE ROOT HARVESTED NURSERY CROPS

Authors: MOORE, BENJI - TENNESSEE TECH UNIV; Fare, Donna; DEYTON, DENNIS - UNIVERSITY OF TENNESSEE; SAMS, CARL - UNIVERSITY OF TENNESSEE

Submitted to: Southern Nursery Association Proceedings
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/2/2003
Publication Date: 12/15/2004
Citation: Moore, B., Fare, D.C., Deyton, D., Sams, C. 2004. Chemical defoliants on bare root harvested nursery crops. Southern Nursery Association Proceedings. 48:275-279.

Interpretive Summary: Natural defoliation of field-grown nursery stock is frequently later in the fall than desired for efficient harvest for bare root plants. Delayed fall defoliation and plant harvest can delay fall shipping and expose plants to early fall freezes which may result in increased cold damage. Leaves retained on plants during storage result in increased disease incidence, thus producers take on the laborious task and expense of hand stripping plants to decrease the disease occurrence. A project was initiated to study the effect of chemical defoliants on nursery crops that typically have a late leaf drop or has historically had freeze damage from early fall freezes. In mid October prior to fall leaf drop, chelated copper at 0.3, 0.5, and 0.8 a.i., ethephon growth regulator, 21.7 percent, at 1000 and 2000 ppm, and a soybean oil mix of 6 percent a.i. were applied to yellow delicious apple, Aristocrat flowering pear, and redbud. One week after application of copper at 0.8 a.i., yellow delicious apple and redbud had 38 and 44 percent leaf drop, respectively. Naturally defoliating control plants retained 97 percent of their leaves. Aristocrat pear was least affected by defoliant treatments and had less than 50 percent leaf drop by 6 weeks after application. However, delayed spring bud break and terminal damage was evident on Aristocrat pear 4 weeks after replanting the following spring. Redbud and yellow delicious apple had no visual damage from defoliation treatments.

Technical Abstract: Natural defoliation of field-grown nursery stock is frequently later than desired for efficient harvest for bare root plants. Delayed fall defoliation and plant harvest can delay fall shipping and expose plants to early fall freezes which may result in increased cold damage. Leaves retained on plants during storage result in increased disease incidence, thus producers take on the laborious task and expense of hand stripping plants to decrease the disease occurrence. A project was initiated to study the effect of chemical defoliants on nursery crops that typically have a late leaf drop or has historically had freeze damage from early fall freezes. In mid October prior to fall leaf drop, CuEDTA, 14 percent, at 0.3, 0.5, and 0.8 a.i., ethephon, sold commercially as Florel 21.7 percent, at 1000 and 2000 ppm, and a soybean oil mix of 6 percent a.i. were applied to Malus spp. Mill. 'Yellow Delicious' apple, Pyrus calleryana Decne. 'Aristocrat' pear, and Cercis canadensis, redbud. 'Yellow Delicious' and redbud had 38 and 44 percent, respectively, leaf drop within one week of CuEDTA at 0.8% a.i application. Naturally defoliating control plants retained 97 percent of their leaves. 'Aristocrat' pear was least affected by defoliant treatments and had less than 50 percent leaf abscission by 6 weeks after application. However, delayed spring bud break and terminal damage was evident on 'Aristocrat' pear 4 weeks after replanting the following spring. Redbud and 'Yellow Delicious' apple exhibited no adverse visual affects from defoliation treatments.