Using preharvest sprays to control postharvest decays on Cameo apples, 2006-2007.

摘要

Postharvest activity from preharvest sprays of Pristine, Scala, Flint, and Topsin M were compared in a trial involving two preharvest intervals. Treatments were applied to 5-yr-old trees of Cameo on Budagovski 9 rootstocks. The trial involved a randomized complete block design with four replications for each fungicide treatment. In addition, each replication included an unsprayed control plot. Trees in this orchard were maintained during the early part of the season using routine fungicide applications. All plots received fungicides as follows: 20 Apr and 18 May – Dithane 75DF 3 lb/A; 1 Jun – Penncozeb 75DF 3 lb/A + Nova 40W 3.8 oz/A; 8 Jun – Polyram 80DF 2.7 lb/A + Nova 3.3 oz/A. No other fungicides were applied except for the treatments described below. Test fungicides were applied on either 25 Sep with no further sprays prior to harvest or on 12 Sep and again on 2 Oct. Preharvest treatments were applied to drip using a handgun. Fruit were harvested at commercial maturity. Rainfall between 25Sep and 5 Oct when fruit were harvested totaled 0.63 in. Rainfall from 12 Sep to 2 Oct totaled 3.06 inches, with no additional rainfall between 2 Oct and harvest on 5 Oct. To ensure that all fruit would be exposed to high inoculum during the harvesting process, fruit were inoculated on 3 Oct using conidia of Penicillium expansum and Botrytis cinerea produced in lab cultures. Conidia of B. cinerea were collected from 35-day-old cultures growing on calcium-enriched V-8 juice agar and conidia of P. expansum were from 12-day-old cultures growing on acidified potato dextrose agar. The spore suspension applied to trees contained 10,000 spores/ml for P. expansum and 157 spores/ml for B. cinerea. Approximately 1.25 gal of spore suspension were sprayed on eachtree using a handgun and a high-pressure sprayer, so each tree received approximately 4.73 X 107 and 7.45 x 105 spores of P. expansum and B. cinerea, respectively. On 5 Oct, an arbitrarily selected sample of 60 fruit were harvested from each test tree. As they were harvested, each fruit was wounded on a single face using a cork with 3 nails 9.5 mm apart in a triangular pattern. Wounds on the fruit were approximately 3.2 mm deep by 1.6 mm diameter. The wounded fruit were placed into storage crates and were moved to a cold air storage room within four hours of harvest. After 24 hr of cooling, the crates of fruit were enclosed in polyethylene garbage bags, 100 ml of water was added to the bottom of each bag, and bags were closed to ensure that fruit wouldbe held at 100% relative humidity. The polyethylene bags were removed on 30 Oct and fruit were exposed to normal air in the storage room thereafter. Fruit were held at 36 °F throughout the cold storage period. Fruit were evaluated for decays on 4 Jan and again on 9 Mar. The causes of decays were tallied based on fruit symptoms. Most, but not all, of the decays originated at the nail punctures we created at harvest. Fruit that developed decay at any position on the fruit were counted as decayed fruit,and fruit with decays at multiple locations were not differentiated from those that had a single decay.