progress report: cultural and chemical methods for the management … progress... · 2013-01-24 ·...
TRANSCRIPT
Kelly Ivors, NC State University
PROGRESS REPORT: Evaluating cultural and chemical methods for the management of box blight, a new disease to the U.S. boxwood industry
These trials were conducted at our new shaded container pad built in April 2012 solely for boxwood blight research at the Mountain Horticultural Crops Research Station (MHCRS) in Mills River, NC (Figure below). Studies were conducted by members of the Ivors lab, including technician Landis Lacey and M.S. grad student Miranda Ganci, in collaboration with Dr. Michael Benson, under strict sanitary protocol so that the disease stays contained at this facility. This pad is located on over 200 acres of land owned by the MHCRS, and secluded from commercial boxwood production. Weather conditions during the 2012 summer up until mid‐September were conducive for boxwood blight infection and progression. Pasted below are the summaries of the trials we conducted during the summer, fall and winter of 2012. For more in depth details regarding all of these trials, as well as numerous photo albums providing pictures of boxwood blight symptoms and other look‐a‐like diseases on boxwood, please refer to: http://go.ncsu.edu/boxwood_blight_links
Susceptibility of Commercial Boxwood Cultivars to Cylindrocladium buxicola Box blight can impact the appearance and aesthetics of boxwood because the foliage typically becomes blighted. Young plants can be killed by the pathogen. Symptoms of box blight include dark‐ or light‐brown, circular leaf spots often with darker margins; dark stem cankers (streaks); straw‐ to bronze‐colored blighted foliage; and leaf drop. Leaf spots may grow together to eventually cover the entire leaf. Sometimes only the lower stems become infected, leaving the tops green; in those cases the plant may appear top‐heavy. Blighting and defoliation can occur suddenly with complete leaf loss under warm (64 to 80°F) and humid conditions. While the full host‐range of this fungus is not yet fully defined, there appears to be levels of tolerance to this fungus in some boxwood cultivars. Until now, only laboratory assays have been conducted on the susceptibility of less than 10 Buxus cultivars. Therefore this study was conducted to determine the susceptibility of commercially available boxwood cultivars under more natural conditions for box blight infection in outdoor container trials.
METHODS: Susceptibility to box blight was evaluated for 23 cultivars of boxwood at the MHCRS during summer 2012. Cultivars were arranged in a randomized complete block design consisting of four
replications of six 1‐gal plants per cultivar (24 plants total). Disease assessments were performed based on a Horsfall‐Barratt scale including percent leaf area diseased and percent stem streaking. RESULTS: The graph below indicates a wide range in susceptibility of Buxus spp. to the boxwood blight pathogen; however B. sempervirens types were more susceptible in general (a 2011 publication reported ‘Justin Brouwers’ to actually fall within the B. sempervirens cluster). The cultivars listed as tolerant had minimal lesion development caused by C. buxicola. This is possibly due to plant genetics, as well as physical features of the plant, such as more open and upright leaf canopies. Buxus sempervirens ‘Suffruticosa’ (English) and Buxus sempervirens ‘American’ were especially susceptible. It is important to note that some boxwood cultivars are limited in their optimal plant hardiness zones; make sure to look up specific growing requirements for each variety before recommending them in specific regions.
Evaluation of fungicides for the prevention of boxwood blight, 2012 This trial evaluated the efficacy of several commercially available fungicides for preventive activity against boxwood blight caused by Cylindrocladium buxicola. Treatments were arranged in a randomized complete block design consisting of four replications of six 1‐gal English boxwood plants per treatment
on a container pad at the Mountain Horticultural Crops Research Station in Mills River, NC. Treatments were applied as foliar sprays until runoff with a CO2‐pressurized backpack sprayer equipped with a handheld boom and a single, hollow‐cone nozzle (TXVS‐26) delivering 50‐60 psi. Treatments were applied on 13 Sep, 28 Sep, and 13 Oct. Inoculum was prepared by flooding Petri‐dishes of 10 day cultures of the pathogen growing on PDA. Plants were spray inoculated with 5,000 spores per ml until run off one day post treatment on 14 Sep, and again on 30 Sep, two days after the second fungicide treatment with 8,000 spores per ml until run‐off. Disease assessments were conducted on 1, 16 and 26 Oct. Percent leaf area diseased was recorded using the standard Horsfall‐Barratt scale. Disease pressure was not high enough to evaluate percent leaf drop or percent stem streaking. AUDPC for percent leaf area diseased across the entire timeframe of the trial was calculated. Air temperatures during the trial was suboptimal for high rates of infection with average daily high and low temperatures of 77.7 and 55.4°F for Sept; and 66.3 and 43.5°F for Oct.
Phytotoxic symptoms were not observed for any of the treatments. Although disease pressure was low, with the exception of three products, all other products were effective at preventing leaf infection by C. buxicola when applied one to two days before inoculation. The most effective products contained the active ingredient chlorothalonil (Daconil Weatherstik, Spectro, Disarm C and Concert II) or the active ingredient fludioxonil (Medallion and Palladium) as either premixes or solo. Plants sprayed with Terraguard, Trinity, or Banner MAXX had statistically less leaf area diseased due to boxwood blight in comparison to the non‐treated control plants, although these would be considered less effective products since they reduced, but did not prevent infection.
Treatment and rate /100 gal FRAC code*
Geometric midpoint:percent leaf area
diseased AUDPC percent leaf
area diseased
Non‐treated, inoculated control ......... NA 1.38 a ** 24.60
Daconil WeatherStik 1.375 pt ............. M5 0.0 d 0.0
Cleary 3336F 16.0 fl oz ........................ 1 0.03 d 0.54
Spectro 1.5 lb ...................................... M5 + 1 0.0 d 0.0
Affirm 0.5 lb ........................................ 19 0.02 d 0.64
Torque 10.0 fl oz ................................. 3 0.03 d 0.54
Compass O 2.0 oz ............................... 11 0.03 d 0.46
Terraguard 16.0 fl oz ........................... 3 1.04 ab 14.42
Disarm O 2.0 oz ................................... 11 0.36 cd 6.68
OHP 26019 2.0 lb ................................ 2 0.36 cd 6.37
Disarm C 11.0 fl oz .............................. M5 + 11 0.0 d 0.0
Tourney 4.0 oz .................................... 3 0.03 d 0.85
Insignia 10.0 oz ................................... 11 0.03 d 0.64
Pageant 14.0 oz .................................. 7 + 11 0.03 d 0.67
Trinity 12.0 fl oz .................................. 3 1.04 ab 14.42
Banner MAXX 12.0 fl oz ...................... 3 0.7 bc 12.72
Concert II 35.0 fl oz ............................. M5 + 3 0.01 d 0.03
Medallion 4.0 oz ................................. 12 0.01 d 0.03
Palladium 6.0 oz .................................. 9 + 12 0.0 d 0.0
Heritage 50 WG 8.0 oz ........................ 11 0.03 d 0.36
Investigating the survivability of C. buxicola microsclerotia in commercial boxwood fields Since its first detection in fall 2011, boxwood blight has been identified in multiple boxwood fields in Western North Carolina. Since NC is the largest field producer of boxwood in the U.S., our goal is to implement effective disease eradication strategies to stop the spread of the pathogen and eliminate the disease from our industry. Therefore we are interested in identifying ways the fungus overwinters in naturally‐infested sites. One evolutionary adaptation that enables other Cylindrocladium species to survive long periods of time in plant material and soil is the formation of specialized structures called microsclerotia; some Cylindrocladium species have been reported to survive as long as 15 years in soil. Studies currently being conducted by NCSU graduate student Miranda Ganci are focusing on the viability of C. buxicola microsclerotia in both the organic and soil fractions of samples collected from naturally infested boxwood fields. We are currently trying to optimize this sieving technique as a first step in order to evaluate the effectiveness of potential disease mitigation strategies (fumigation, flaming, solarization) in box blight infested fields.
Pictures above show the development and production of microsclerotia in Petri dishes colonized by C. buxicola.
IMPACT STATEMENT The NCSU website (go.ncsu.edu/boxwood_blight_links) that provides fact sheets covering these studies has already received over 1300 hits as of January 22, 2013 (see picture below). This new information on managing boxwood blight has the potential to save growers hundreds of thousands of dollars by helping to prevent and manage boxwood blight, and to equip the US and NC boxwood industries with better strategies on cultivar selection and preventive fungicide applications.
The mycelium is starting to differentiate into a thicker, darker mass in order to
produce microsclerotia. The dark structures in this picture
are microsclerotia.