Evaluation of fungicides for the control of Rhizoctonia root rot in blueberry cuttings, 2008

摘要

In recent disease surveys of blueberry propagation systems in Georgia, Rhizoctonia root rot (RRR) was associated with diseased rooted cuttings. RRR prevents rooting by development of stem lesions which can result in girdling and/or necrosis of developing root systems, often resulting in plant mortality. To determine the efficacy of select fungicides for control of RRR, two trials were conducted in a shade house on the Griffin campus of the University of Georgia. Cuttings were taken from mature field-grown plants, stored overnight in an icewater filled cooler, and stuck the following day, 24 June (trial 1) or 23 Aug (trial 2), into cell packs filled with finely milled pine bark. The pine bark had been infested with inoculum of a pathogenic Rhizoctonia sp. producedon V8/vermiculite growth medium; a final pathogen concentration of ~140 and~ 300 colony-forming units/cm3 was attained in trials 1 and 2 respectively. Fungicides were applied the day after sticking and again 2 weeks later by drenching 0.5 L of the fungicidal suspension to an experimental unit of 36 cuttings. Treatments were applied to a randomized block design with four replications; they included an untreated control (water drench), HeritageWDG (50% azoxystrobin), ProStar 70WP (70% flutolanil), Terraguard SC (42.1% triflumizole), Medallion 50WSP (50% fludioxonil), and an additional negative control consisting of cuttings stuck in non-inoculated bark with no fungicides applied. Fungicide applications were made at sticking and again 14 days later. Data on lesion incidence, lesion length, and stem girdling incidence were collected for both trials 27 days after sticking. As expected, non-inoculated cuttings did not develop disease symptoms ineither trial; thus, only data from the inoculated plants were subjected to analysis of variance and means separation by Fisher's Protected LSD test (P = 0.05).