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Home , Fire blight, Golden Russet

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, 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 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 , , , , under control. Smoothee Golden, Fortune, NY 674, , and more. A list of varieties sus- ceptible 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 inci- dence of 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. 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 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 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 reported was in a an established 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 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 . 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 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 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 Susceptible1 Very Susceptible1 Very Susceptible2 Resistant-Susceptible1,2 Cameo Susceptible3 NY674 Susceptible4 Susceptible1 NY75414-1 Susceptible3 (BC8m15-10) Susceptible3 Orin Susceptible3 Delicious (Red, all strains) Resistant1 Susceptible-Very Susceptible1,2 Elliot ? ? Resistant1 Pioneer Mac Susceptible3 Susceptible3 Prima Resistant1 Fortune Susceptible4 Priscilla Resistant1 Fuji Very Susceptible2 Pristine Susceptible3 Fuji 2 Susceptible3 R.I. Greening Very Susceptible1 Gala (all strains) Very Susceptible2 Redfree Resistant-Susceptible1,2 GingerGold Very Susceptible2 Rome Beauty Very Susceptible1 Gold Rush Susceptible3 Sansa Susceptible3 Resistant-Susceptible1,2 Senshu ? Golden Russet ? Shizuka ? Golden Supreme Susceptible4 Smoothee (Golden Del.) Resistant-Susceptible1,2 Very Susceptible1 Susceptible1 Susceptible1 Spigold Very Susceptible1 Honeycrisp Susceptible4 Stark Bounty Resistant1 Idared Very Susceptible1 Stark Splendor Resistant-Susceptible1,2 Jerseymac Susceptible1 Starkspur (Delicious) Susceptible1 Jonafree Resistant-Susceptible1,2 Resistant-Susceptible1,2 Jonagold Very Susceptible1 Suncrisp ? Jonamac Susceptible1 Sunrise Susceptible3 Very Susceptible1 Twenty Ounce Very Susceptible2 Resistant1 Tydeman Susceptible1 Very Susceptible1 Viking Resistant1 Macfree Resistant1 Susceptible1 Macoun Susceptible1 Yataka Susceptible3 McIntosh Resistant-Susceptible1,2 Zesta! ?

1 Ratings from MSU Web site, Nancy J. Butler, “Disease on ”. 2 Ratings from WV University, Kearneysville website, K.S. Yoder and A.R. Biggs. 3 Ratings from Drs. Steven Miller and Alan Biggs in NE183 plot, WV. 4 Ratings from other field observations.

move any infections noted in the trees model. However, streptomycin-resistant sistance development. Dr. Tom Burr has to prevent spread to other trees. The strains of E. amylovora have developed in shown reduced efficacy of streptomycin closer the planting is to an infected many parts of the country due to too fre- when mixed with calcium and phosphate orchard, the more closely the new trees quent use of streptomycin. ions. Streptomycin should not be applied should be scouted. Streptomycin is effective in fire blight with foliar nutrients. Tank mixing with 5) Control aphids and leafhoppers, control because it limits the multiplication mancozeb has not been documented to which are suspected to spread fire of bacterial cells. Bacterial diseases require reduce control. Thorough spray coverage blight. a certain number of bacterial cells to re- is critical. sult in disease symptoms. One bacterium Alternatives to streptomycin for con- Blossom Blight—The Most Powerful does not result in disease. Streptomycin trolling blossom blight, such as copper, are Phase Of The Disease is only locally systemic—it is only ab- limited in their usefulness due to inferior sorbed by blossoms that are open at the efficacy and phytotoxicity, especially rus- Control Materials: Blossom blight is time of application. Slow drying condi- seting. Other alternatives such as a the epidemic phase of the disease that pro- tions increase the absorption of streptomy- biocontrol agent (BlightBan C9-1), SAR vides the inoculum for shoot blight, cin and make it more effective. Current (systemic acquired resistance) inducers trauma blight, and rootstock blight for recommendations for streptomycin are to (e.g. Actigard 50 WG and Messenger), a years to come. The most effective mate- apply it at a rate of 8 oz/100 gal dilute rate, growth regulator (Apogee 125 11W), and rial for blossom blight control is strepto- or at 4 oz/100 gal if mixed with Regulaid. new formulations of copper (Phyton 27) mycin sprayed during bloom, when infec- Using lower rates will not give reliable re- and antibiotics (Pace-17) are being evalu- tion is predicted by the MARYBLYT tm sults, and may increase the chance of re- ated for blossom blight control in repli-

8 NEW YORK STATE HORTICULTURAL SOCIETY cated plots at Geneva, NY. BlightBan C9- Cougar Blight Vs. MARYBLYTtm (Albion 98) 1 is a living bacterium that colonizes the 4 habitats of E. amylovora on the plant when applied before the infection takes place and inhibits the pathogen from multiply- -H -H -H -H ing. An SAR inducer is a chemical agent 3 which activates natural resistance in the plant, but does not have direct antibacte- rial activity. Most of these products are in the experimental phase of development 2 Risk Rating and still require EPA and/or NYS-DEC registration for orchard use. The materials listed above were 1 evaluated in 1997-99 for control of blos- som blight on ‘Idared’ apple trees in a re- 24-Apr 1-May 8-May search orchard at Geneva, NY. Treatments Date were replicated five times with 150-200 CB-FB locally CB-FB in orchard MARYBLYT blossom clusters per replication in a ran- domized complete block design. The products were applied at 1/2-inch green, tm pink, 10 percent bloom, 24 h before inocu- Cougar Blight Vs. MARYBLYT (Albion 99) lation and 24 h after inoculation, depend- 4 ing on their mode of action, using a single nozzle handgun sprayer at 150 psi and sprayed to run off. The blossom clusters were inoculated at full bloom with E. 3 amylovora using a Solo backpack sprayer. -H -W -T Infected and healthy blossom clusters were recorded three weeks after inocula- tion and fruit russeting was assessed seven 2 -WT weeks after the last spray. Risk Rating The results of 1997 field trials showed a significant reduction in blossom infec- tion when trees were sprayed with SAR 1 inducers and biocontrol agents compared 4-May 11-May 18-May 25-May to untreated trees (Table 3). The disease Date control by biocontrol agents (BlightBan CB-FB locally CB-FB in orchard MARYBLYT C9-1 and A506) alone was approximately half the control achieved with Agrimycin tm Figure 4. Comparison of MARYBLYT blossom blight prediction with prediction by Cougar Blight at 14.7 g and 29.4 g/50 L (4 oz and 8 oz/ in orchard with fire blight in orchard last season and fire blight in local area last season. 100 gal dilute) treatment. A significant re- duction of blossom blight incidence was observed in Actigard and Messenger treated trees compared to the untreated TABLE 2 check, but control was not as good as it Effect of copper and blossom removal on fire blight development in a newly planted was with the Agrimycin treatments. Al- Jonagold orchard. though Mankocide and Kocide treatments significantly reduced blossom blight infec- % trees with blossom blight % trees with shoot blight tion, fruit russeting was observed in both Treatment # trees 1997 1998 1999 1999 the treatments. In 1998 the weather dur- z ing bloom was favorable for blossom + Copper , - bloom 587 0.2 0.3 0.2 1.4 + Copper, + bloom 32 3.1 3.1 0.0 3.1 blight infections with 50 percent infected - Copper, - bloom 52 0.0 0.0 0.0 0.0 blossom clusters in the untreated inocu- - Copper, + bloom 26 0.0 3.8 11.5 23.1 lated check. Blightban A506 was not sig- z nificantly different from the check. A 32 In 1997 Kocide DF applied at budbreak + 2 weeks. In 1998 Kocide DF applied at budbreak. percent reduction in blossom blight was observed in BlightBan C9-1 treated trees. dition of mancozeb to Kocide 2000 im- The results from 1997 and 1999 field Less blossom blight was observed in proved control over either treatment trials were similar in the control of blos- Actigard and Messenger treatments but alone, but was not significantly better than som blight infections. In 1999, the weather was not significantly different from the Microsperse, Nu-Cop 50DF, or Agrimycin during bloom was hotter than usual and check. Kocide 2000 and Nu-Cop 3L, gave 4 oz/100 gal). Agrimycin at 4 oz/100 gal bloom lasted for 20 days (7 May-26 May). tm similar control to Agrimycin 4 oz/100 gal gave the best control, reducing infection During this period the MARYBLYT pro- treatment (52-57 percent control). The ad- by 73 percent. gram predicted two high-risk days but no

NEW YORK FRUIT QUARTERLY • VOLUME 8 NUMBER 1 • 2000 9 infection period. In our trials, inoculation coupled with high risk days for fire blight infection during bloom resulted in 25.7 percent of blossom clusters infected, and allowed for efficient screening of prod- ucts for activity against blossom infection. Pace 17 (streptomycin) at 14.7 g/50L (4 oz /100 gal) with Regulaid applied 24 h before and after inoculation gave the greatest control (71.8 percent), closely fol- lowed by the same treatment with Agrimycin-17 (streptomycin at 4 oz/100 Figure 4. Black speckling and russet resulted from copper applications in cover sprays on Twenty gal). Lower rates (7.35 g/50L (2 oz/100 gal Ounce apples. These are destined for the processor because they are not acceptable for fresh fruit. dilute) of Pace 17 and Agrimycin 17 with Regulaid were tested at Geneva to com- TABLE 3 pare the control of these treatments alone with the same rates used in combination Effect of antibiotics, copper compounds, biocontrol agents and SAR inducers on blossom blight control in Idared trees, Geneva , NY 1997 with a biocontrol agent such as BlightBan C9-1. These rates are not recommended as Time of Infected blossom x standard practice for growers due to re- Treatment Rate/50Lz applicationy clusters % sistance development issues and normally Untreated inoculated check 50.0 a provide less effective control. BlightBan Agrimycin 29.4 g 3,4 6.9 gh C9-1 applied at 10 percent bloom and 24 h before inoculation gave 40.5 percent con- Agrimycin 14.7 g 3,4 6.1 gh trol. When BlightBan C9-1 was applied Vigor-Cal 500 ml 2,3,4 8.8 fgh during bloom, and followed with strepto- +Agrimycin 14.7 g 3,4 mycin at the experimental low rate after Mankocide DF 79.75 g 3,4 12.0 cdef inoculation, there was only slight improve- GWN-9200 10W 37.5 g 3,4 10.7 defg ment in control. Research from other states GWN-9200 10W 75.0 g 3,4 9.7 efgh showed improved control from biocontrols if integrated with recommended rates of GWN-9200 10W 100.0 g 3,4 8.5 fgh streptomycin. Sprays of Mankocide DF, Kocide 101 77W 47.8 g 3,4 10.4 defg Nucop 50 DF and Phyton 27, 24 h before BlightBanC9-1 12.6 g 2,4 14.1 bcde and 24 h after inoculation all resulted in significant (50 percent) control of the dis- BlightBan A506 13.1 g 2,4 16.4 bc ease. Mankocide and Nucop caused the BlightBan A506 13.1 g 2,4 18.7 b greatest amount of fruit russeting, al- +Actigard 50 WG 6.0 g 1,4 though russeting was significantly less BlightBan A506 13.1g 2,4 7.5 fgh when Mankocide was applied once, 24 h +Agrimycin 17 14.7 g 4 pre-inoculation, followed by Pace treat- BlightBan A506 13.1g 2,4 5.2 h ment. Phyton 27 is a very unusual copper +Agrimycin 17 14.7 g 3,4 compound that caused very little russet- Actigard 50 WG 6.0 g 1,4 15.3 bcd ing. Messenger at 26 g/50L applied at 1/ Messenger 5.0 g 1,4 18.4 b 2-inch green and pink resulted in 46 per- cent control, which was numerically but Messenger 10.0 g 1,4 15.9 bc not statistically different from streptomy- z All treatments were tank-mixed with Break-through (50 ml/50L), a surfactant from Plant Health cin. The level of infection in Apogee treated Technology Inc. blossoms was not significantly less than in z Time of application 1 = pink (8 May); 2=10% bloom (14 May); 3= 24 h before inoculation (20 May); the untreated inoculated check. Greater 5= 24 h after inoculation (22 May) disease control was obtained with y Treatments followed by the same letter did not differ significantly (P=0.05) as determined by Waller biocontrol agents when combined with grouping. SAR inducers or antibiotics suggesting that the alternative materials are compatible and have good potential for an integrated In field trials on commercial farms in vided superior control under high blos- management of a blossom blight program. western New York without artificial inocu- som blight disease pressure without the The biocontrol agents and SAR inducers lation, the use of copper/mancozeb to con- poor fruit finish that results from copper are still experimental and not registered trol fire blight during bloom gave compa- applications. If copper is used it must be in New York, but show considerable rable results to plots treated with strepto- applied at the lower rates stated on the promise, especially if used in combination. mycin in low disease pressure conditions labels (Champ 2F at 2/3 pt/acre) starting Further research on combination of (no blossom blight infection predicted). at 10 percent bloom, at 5-7 day intervals. biologicals and SAR inducers is being However, commercial plots with natural Research data in trials at Geneva suggest done in the lab, greenhouse and field in inoculum and a blossom blight infection better control when the copper is mixed 2000. period showed that streptomycin pro- with mancozeb. 10 NEW YORK STATE HORTICULTURAL SOCIETY TABLE 4 If the MARYBLYT tm infection risk is “high” (three of four requirements for blossom in- Effect of antibiotics, copper compounds, SAR inducers on shoot blight control in Idared trees, fection are met) with the only missing fac- Geneva , NY 1999 tor being the average temperature of 60°, the %%model will recommend the consideration of blighted % russeted a streptomycin application to protect open Surfactants Time of shoot russeted fruit blossoms. If a wetting event is the only fac- Treatment (rate/50L) (rate/50L) application1 length fruit surface tor missing, growers need to do some criti- Untreated control 89.7 a 0.2 c 1.0 bc cal thinking about the potential for dew in Empire (inoculated) 7.2 g low spots in orchards or note any spray ap- Pace 17 14.7 g Regulaid 15 ml 4,5 35.2 f 0.3 c 0.5 c Agrimycin 17 14.7 g Regulaid 15 ml 4,5 39.9 ef 0.0 c 0.0 c plications that are made that could wet the Mankocide DF 79.75 g. Regulaid 15 ml 4,5 55.8 bcd 21.3 a 4.5 a blossoms resulting in an infection. When Phyton 27 13.3 ml Regulaid 15 ml 4,5 61.0 b 6.9 b 4.1 a growers are inputting maximum and mini- Actigard 50 WG 10.0 g Regulaid 15 ml 2,3 50.8 bcde 0.6 c 0.6 c mum temperatures to run the models, it is Messenger 26.0 g Reguard100 ml 2,3 43.9 def 0.6 c 3.0 ab important they run a range of temperatures 1 1 = Petal fall + 5 days (May 21), 2 = 2 weeks after #1 (June 4), 3 = 1 week before inoculation (11 June), in the forecast to cover differences across the 4 = 24 h before inoculation (16 June), 5 = 24 h after inoculation (18 June), 6 = 10 days after inoculation. microclimates of the farm. There are always 2 Treatments followed by the same letter did not differ significantly (P>0.05) as determined by Waller warmer spots on a farm that will grouping. us with fire blight infections. It is important to remember that all models rely on accurate weather data and Timing of Control Sprays Smith. It is not a computer model, but can forecasts. All models have some flexibility be set up on a spreadsheet. The model uses in risk prediction for growers to adjust risk Blossom blight control using streptomycin a lookup chart to determine daily degree according to variety, rootstock, inoculum hinges on critical timing of the application. hours accumulated based on the maximum source, etc. Based on three years of compari- The old standard timing in the mid-1980s and minimum temperatures. Users calculate son, the two models correlate well when was to apply streptomycin when the tem- the sum of degree hours over four days dur- enough heat units have accumulated and perature was above 65°F and rainfall or rela- ing bloom leading up to a potential wetting there is a wetting event. Accuracy of the tive humidity was above 60 percent during period. Users must select the appropriate in- model predictions is evident from the severe bloom. In the absence of anything better, oculum potential based on proximity to the level of fire blight incidence in blocks not some growers sprayed and some didn’t. inoculum source. Neither of these models treated with streptomycin when they pre- Many times, growers got away without will predict how many infections may result dicted infection in 1999. In order for either spraying and had very little incidence of fire if the risk of infection is high. model to be useful for blossom blight con- blight in apples. This gave growers a false We have collected weather data since trol, streptomycin must continue to be bothe sense of security when they ignored the sys- 1997 from weather sensors across the region. available and effective. When we start to use tm tem. However, more sophisticated predictive The data were entered in the MARYBLYT the new SAR inducers and biocontrols, the models have been developed that are risky 4.3 model for many sites, and into the Cou- models will need to be modified to recom- to ignore when they predict blossom blight gar Blight spreadsheet as well. The predic- mend applications earlier than 24 hours be- infections. tions of both models were entered into a fore or after an infection. In New York, we have been working spreadsheet for comparison of blossom tm with MARYBLYT since 1992, and Cougar blight predictions. Comparison of predic- Shoot Blight Control Blight since 1997, and have gained experi- tions from both models for two seasons ence and confidence in their predictions. showed that the models are closely corre- If blossom blight is completely pre- tm MARYBLYT 4.3 is a computer-based lated in terms of heat units accumulated. vented, shoot blight will usually be mini- model, developed by Dr. Paul Steiner, de- Both models rely on growers to determine mal. To date, there is no effective registered signed to predict blossom blight infection the occurrence of a wetting event. control for shoot blight. We recommend potential and symptom development of MARYBLYT tm 4.3 requires data entry for the streptomycin be sprayed after bloom to con- most phases of fire blight. The model as- wetting event; Cougar Blight assumes a wet- trol shoot blight only in the case of or sumes an abundance of inoculum in the or- ting event has occurred or will occur. Fig- severe and rain. Repeated applications chards. It predicts the potential risk of infec- ures 1 and 2 show the risk prediction of both of streptomycin in a heavily infected orchard tion based on the occurrence of certain en- models on the Y axis, where 1 = low, 2 = will quickly lead to selection of resistant vironmental conditions in sequence. These moderate, 3 = high, and 4 = “Infection” for strains of E. amylovora and loss of this valu- conditions include: MARYBLYT tm or “Extreme” risk for Cou- able material for blossom blight control. Al- 1) The presence of blossoms. gar Blight. The “-H” (insufficient heat units), ternative controls have been tested in repli- 2) The accumulation of 198 DH (>65 F) “-W”(lack of wetting event), “-WT”(lack of cated inoculated plots in Geneva and in two from start of bloom. wetting event and temperature below 60), replicated commercial plots with natural in- 3) A wetting event including rain, dew or etc., indicate the required factor missing for oculum. a spray application, or 0.1 in. of rainfall MARYBLYT tm when it predicted a lower risk Note: exciting results on control of the day before. potential than Cougar Blight, in 1998 and shoot blight with the growth regula- 4) The average temperature of 60 F the day 1999. tor, Apogee, are reported in a sepa- of infection. One factor that seems to reduce the cor- rate article in this issue, and are not A second model, Cougar Blight, was relation between models is the MARYBLYT repeated here. developed in State by Tim tm requirement for 60°F average temperature.

NEW YORK FRUIT QUARTERLY • VOLUME 8 NUMBER 1 • 2000 11 The efficacy of two antibiotics, two cop- Actigard or Messenger treatments applied controls, but changes may be on the hori- per compounds, and two SAR inducers prior to inoculation. The Mankocide and zon. The one big change that has occurred against infection of shoots by fire blight was Phyton 27 treatments were both signifi- over the past ten years is the increase in dis- evaluated on ‘Idared’ trees in a research cantly better than the untreated check, but ease pressure and an increase in the urgency orchard at Geneva. Treatments were repli- not as effective as the streptomycin treat- for maintaining a tight, full season manage- cated five times with each replicate consist- ments. Both resulted in fruit russet, al- ment program for fire blight on the whole ing of a single tree in a randomized com- though Phyton 27 caused significantly farm. At present, the use of precise disease plete block design. All treatments were ap- fewer russeted fruits than Mankocide. prediction models is critical in timing ap- plied to run off using a single nozzle hand- Copper does not have systemic activ- plication of streptomycin for blossom blight gun sprayer. Following the treatments, 20 ity against fire blight and will not control and resistance management. In the growing tips of current season shoots, 20- provide control of the internal spread of E. future, integrating antibiotic sprays with 40 cm long, from each tree, were inoculated amylovora within the tree once a shoot is other “softer” plant protection methods like by bisecting the two youngest leaves with infected. However, it does have the poten- biocontrol agents, SAR inducers and scissors dipped in E. amylovora inoculum. tial to reduce the population of epiphytic growth regulators is a potential option to Shoots of Empire were inoculated as an bacterial populations from oozing infec- keep the development of antibiotic resis- untreated moderately resistant check. All tions to limit further spread to wounded tis- tance and fire blight under control. Unfor- inoculated shoots were labeled. Six weeks sue in the tree. In 1999 there were no differ- tunately, the cost of these integrated pro- after inoculation the lengths of necrotic in- ences in levels of shoot blight in replicated grams with antibiotics will be more expen- fection and of the whole shoots, including commercial plots where Champ 2F (2/3 pt/ sive. For now, streptomycin continues to be the infected length, were determined. A acre) cover sprays were applied starting at the critical control material to manage fire week later, the proportion of fruit with rus- 1-2 weeks after petal fall and 10-14 day in- blight. set and of the russeted fruit surface area was tervals. However, 1999 was a very dry sea- estimated. son causing terminal buds to set early, shut- In inoculated untreated checks, 89 per- ting down succulent growth that probably Deborah Breth is an Area Extension Educator cent of shoot length became blighted, which limited the spread of fire blight. There was with the Lake Ontario Area Fruit Team located was significantly higher than for all other significantly more fruit russet in copper in Albion. She specializes in integrated pest treatments (Table 4). Pace and Agrimycin treated plots than in the plots without cop- management. B. Reddy is a Postdoctoral Fel- treatments, which are both streptomycin per. low in Herb Aldwinckle’s group at Geneva. formulations, applied before and after in- Jay Norelli is a Senior Research Associate in oculation, gave the highest level of control Summary Plant Pathology working with Dr. Aldwinckle. (61 percent and 56 percent, respectively). Herb Aldwinckle is a Professor of Plant Pa- There was no significant difference in the In conclusion, there are very few new thology and leads the fire blight team at level of control obtained with Agrimycin, options to apply on the farm for fire blight Cornell.

12 NEW YORK STATE HORTICULTURAL SOCIETY