Oil sprays increase the phytotoxicity of captan to apple foliage. The purpose of this study was to determine if oils increase the penetration of captan through leaf cuticles. Enzymatically isolated apple leaf cuticles were used as a model system to study captan penetration. A bioassay was developed using the inhibition of growth of Penicillium cyclopium on potato-dextrose agar as a measure of captan penetration through the cuticle. Captan penetrated through both surfaces, but significantly more penetrated through the abaxial cuticles than the adaxial cuticles. Increasing the captan concentration increased the captan penetration through the abaxial cuticle in a linear relationship. Captan penetration through the cuticle was increased by 63% when cuticles were treated with captan plus 1% emulsified soybean oil. Abaxial cuticles treated with captan plus emulsified soybean oil or with captan plus SunSpray Ultra-Fine oil had >125% greater captan penetration than cuticles treated with only captan. Cuticles treated with captan plus dormant oil (petroleum oil) had 220% more captan penetration than the captan only treatment.
B.R. Bondada, C.E. Sams, and D.E Deyton
Kitren Glozer and Franz J. Niederholzer
Use of rest-breaking chemicals may partially substitute for chill requirement in “French' prune. Many California prune growers use oil in the dormant season to tighten and advance bloom, with application timing judged by experience and calendar date. Other rest-breaking agents have become commonly used in California cherry production and their application is generally timed by chill portion accumulation, calculated by the Dynamic Model. We evaluated the effects of treatments of dormant oil or CAN17 (calcium ammonium nitrate) + Entry on budbreak and bloom progression in `French' prune with applications timed at regular intervals. While most treatments improved fruit set and reduced reproductive bud death, an optimum range for both types of rest-breaking treatments was found for advancement and compression of bloom. All rest-breaking treatments advanced fruit maturity equally, compared to the untreated control, as measured by fruit firmness. Although chill hour (hours ≤7°C) calculations might also be used for timing these treatments, when chill portion and chill hour accumulations are compared for the 2004–05 dormant season at several different sites, differences from site-to-site are small for chill portions, and much greater for chill hours. This fact supports experimental evidence from numerous California trials in sweet cherry in which rest-breaking treatment timings based on the Dynamic Model tend to be more consistent than the timings based on the “chill hour” model.
Anish Malladi and Peter M. Hirst
Peach production is significantly reduced and severely limited by frost injury in regions frequently exposed to late spring freeze conditions. Peach flower buds become increasingly susceptible to low-temperature damage from the period of completion of rest through fruit set. Delaying dehardening and/or flower bud development is an effective way to avoid frost damage. Bio-regulator applications, affecting dormancy or bud development, can delay flowering and dehardening of the buds and can help in avoiding spring freeze injury. Spring applications of AVG and dormant oils on 8-year-old `Redhaven' peach trees were evaluated. AVG applications effectively delayed bloom by 2 to 5 days. The most effective treatment was two applications of 2000 ppm AVG, which delayed bloom by almost 5 days. Repeat applications of AVG were more effective than the single dosage treatments. The 1000 ppm, repeat application delayed bloom by 4 days. A single application of 5000 ppm AVG resulted in severe phytotoxicity. The wetting agent levels were also varied and AVG applications were most effective in combination with 0.2% `Sylgard'. AVG, apparently, delayed bloom by delaying bud development following the completion of rest. The dormant oil sprays were ineffective in achieving bloom delay. The specific leaf weight characteristics of the treated trees were not affected except for the 5000-ppm AVG application, which reduced SLW. Fruit characteristics such as maturity, weight, and soluble sugar concentration were not affected by any of the spring applications (except for the 5000-ppm AVG application, which was phytotoxic). Our studies indicate that AVG is effective in delaying bloom in peaches by up to 5 days. This has the potential to substantially increase peach yields in years with a late spring freeze.
Rachel Leisso, Bridgid Jarrett, Katrina Mendrey, and Zachariah Miller
( Buthelezi et al., 2021 ). An extension guide by Alfuth (2019) indicates plastic bags can be effective but does not indicate the level of control. Bessin and Hartman (2019) combined Japanese apple bags or paper bags with dormant oil and two early
Michele R. Warmund, Jeanne D. Mihail, and Kaley Hensel
above the medium surface, leaving three canes per plant. Dormant oil (Damoil; Drexel Chemical Company, Memphis, TN) was applied to elderberry plants at 7.5 mL·L −1 to control overwintered eriophyid mites ( Phyllocoptes wisconsinensis Kiefer). On 14 Mar
E. Barclay Poling
cold event ( Dami et al., 2005 ). Application of oils at nontoxic rates in the dormant season may also be effective ( Dami, 2007 ). Dormant oil sprays used in this way to slow bud deacclimation and delay grapevine budburst would be considered a passive