Successful Fire Blight Control Is in the Details

Successful Fire Blight Over the past 10 years there has been an increase Control is in the Details in fire blight pressure giving urgency to the Deborah I. Breth1, M.V.Bhaskara Reddy2, Jay development of better 2 2 control programs. There Norelli and Herb Aldwinckle are very few new options 1 Lake Ontario Fruit Team, Cornell Cooperative Extension, Albion, NY to apply on the farm, but 2Dept. of Plant Pathology, New York State Agricultural Experiment Station Cornell University, Geneva, NY changes may be on the horizon. At present, the use This research is supported in part by the New York Apple Research of precise disease predic- and Development Program and the USDA Special Grant. tion models is critical in timing application of streptomycin for blossom ontrolling fire blight is an essential susceptibility of the rootstock. Susceptible blight control and aspect of apple production in both varieties on susceptible rootstocks require resistance management. C young and old plantings. Since estab- the most comprehensive management pro- lishment costs for high-density plantings are gram. In the future, integrating as high as $5000 per acre, fire blight control The basic fire blight management pro- in a new planting is even more critical than gram is not described here in detail. The antibiotic sprays with in an old established orchard. The intensity purpose of this article is to address specific other “softer” plant of the control program should be based on fire blight problems and report results of protection methods like the susceptibility of the scion variety and the ongoing research to solve these problems. biocontrol agents, Susceptibility of Varieties and SAR inducers and growth Rootstocks regulators offers promise Most of the new varieties demanded to keep the development by the market and planted in New York of antibiotic resistance in high density plantings are susceptible to fire blight. They include GingerGold, and fire blight Gala, Fuji, Honeycrisp, Jonagold, under control. Smoothee Golden, Fortune, NY 674, Cameo, and more. A list of varieties susceptible to fire blight rated in previous re- ognizing the potential for disaster and pre- search is included in Table 1. New variet- venting it. Don’t let fire blight get estab- ies have not been rated experimentally as lished in a new planting! to the level of susceptibility. But the incidence of infections under natural inocu- Fire Blight Control for New lum conditions have been reported in the Plantings table from personal communication with consultants, and with Drs. Steven Miller Site selection is a critical component and Alan Biggs from a variety trial in of an integrated fire blight control program Kearneysville, WV, part of regional project for new plantings. Pick a planting site with NE183 to evaluate varieties. well-drained soil, and good air drainage. Rootstock susceptibility is discussed Before planting, add soil nutrients such as in another paper in this issue of the Fruit potash, phosphorus, and lime to provide Quarterly. The combination of highly sus- calcium and magnesium and to correct ceptible scion varieties on highly suscep- Figure 1. Weather stations are used to moni- pH. These nutrient deficiencies are harder tor maximum and minimum temperature and tible rootstocks such as M.9 and M.26, of- to correct after planting. Set the planting wetting periods from rain and dew. The data ten results in rootstock blight and tree as far as possible from an infected apple are entered into a disease prediction model death. In an ideal world, the market would or pear orchard. Isolation always helps. to time streptomycin application to control only demand varieties that are resistant to Many times, however, we have to plant blossom blight, and to predict symptom de- fire blight. In the real world, however the that new orchard right next door to a pro- velopment for all phases of the disease. first step in controlling fire blight is rec- cessing orchard that has plenty of fire 6 NEW YORK STATE HORTICULTURAL SOCIETY 3) No copper with blossoms removed. where blossoms were removed (Table 2). 4) Copper with blossoms removed. There was no apparent difference between The plantings were followed through treatments with and without copper. In 1999. Orchard A was set up in eight rows Orchard B with randomized plots of equal of Jonagold on M.9 located windward of size, the only infection reported was in a an established Idared orchard infected with plot with no copper applied and with blos- fire blight. This block was not a replicated soms intact. Under natural inoculum lev- trial because the grower wanted to keep els, these data do not show striking differ- unprotected parts of the block very small ences between treatments. But as we con- to reduce the risk from fire blight. Orchard tinue to follow these plantings into the 4th B was a block of Gala and Fuji on M.9 lo- leaf, observations will be made concern- cated on the windward side of a pear or- ing the potential for rootstock blight de- chard with minimal fire blight infection velopment. So far, the major contributing due to cool bloom periods. Orchard B was factors for fire blight establishment in a replicated across varieties, and subsamples new planting are the presence of blossoms of treatment plots were evaluated for each and inoculum in nearby orchards. Over the treatment. years, there have been new plantings that Copper applications were made the have not had fire blight controls applied first year using Kocide DF at 4 lb/100 gal and no infection has resulted. Expensive dilute applied to drip at budbreak and two disasters are becoming more common, weeks later. In the second leaf, only one though, and once established, fire blight abccopper application was made at budbreak. will be a menace for the new planting for In the 1st and 2nd leaf, the blossoms were years to come. Figure 2. This newly planted orchard of Gala removed by pinching them off at the stems Recommendations drawn from field on M.9 with multiple blossom blight infections. to prevent removal of any potential apical experience and demonstration plots in- bud that would develop into a growing clude: point. Timing of blossom removal preceded 1) Apply copper to “sanitize” the new blight. This is often a recipe for disaster. weather conditions that were conducive for trees at budbreak. There are two major concerns that blossom blight infection conditions. Both 2) Remove blossoms in 1st and 2nd leaf may contribute to the risk of fire blight in orchards were mapped to identify all trees plantings before the blossoms open or newly planted blocks. First, many nurs- in the block. These maps were used to before the occurrence of a blossom ery trees are purchased with “feathers” document where blossoms were intact, and blight infection. This can be done (scaffold branches) that produce some where any fire blight infections occurred. when central leader shoots are se- flower buds in the first year. Some variet- Although insufficient incidence of in- lected. ies like Gala and GingerGold flower on fection occurred for statistical analysis, 3) If blossoms are not removed, monitor one-year-old wood. Newly planted trees there was a trend in Orchard A that had weather conditions for blossom blight come into bloom after established or- more inoculum pressure from a nearby or- conditions and apply streptomycin as chards have bloomed, when growers have chard. Plots with blossoms left intact had needed. stopped monitoring for blossom blight more fire blight infection than in those 4) Monitor the planting weekly and re- conditions on the remainder of the farm. The blossoms in the new planting are then very vulnerable to infection. Second, many nursery trees come from areas where there may be streptomycin-resistant Erwinia amylovora. Resistance to streptomycin has not been documented in New York except for an isolated incidence. Most nurseries do a thorough job of controlling fire blight with streptomycin and copper as needed for high-risk infection conditions. But E. amylovora is a successful epiphyte, surviv- ing on the surface of bark and leaves. So to get a theoretical “clean start” in the new orchard, an application of copper at budbreak after planting may kill any bac- teria on the surface of the new trees. To test management strategies for pre- vention of fire blight in susceptible high- density orchards, demonstration plots were established in newly planted blocks on two farms in 1997. Treatments were: 1) No copper with blossoms intact. 2) Copper with blossoms intact. Figure 3. Experimental material is sprayed for control of fire blight. NEW YORK FRUIT QUARTERLY • VOLUME 8 NUMBER 1 • 2000 7 TABLE 1 Cultivar susceptibility to fire blight compiled from several sources. very resistant = no control needed; resistant = control needed only under high disease pressure; susceptible = control usually needed where disease is prevalent; very susceptible = control Apple cultivar Relative susceptibility Apple cultivar Relative susceptibility Ambrosia ? Mollies Delicious Susceptible1 Arlet ? Monroe Susceptible2 Beacon Susceptible1 Mutsu Very Susceptible1 Braeburn Very Susceptible2 Northern Spy Resistant-Susceptible1,2 Cameo Susceptible3 NY674 Susceptible4 Cortland Susceptible1 NY75414-1 Susceptible3 Creston (BC8m15-10) Susceptible3 Orin Susceptible3 Delicious (Red, all strains) Resistant1 Paula Red Susceptible-Very Susceptible1,2 Elliot ? Pinova ? Empire Resistant1 Pioneer Mac Susceptible3 Enterprise Susceptible3 Prima Resistant1 Fortune Susceptible4 Priscilla Resistant1 Fuji Very

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