Evaluation of Low Rates of Apogee for Shoot Blight Control

Kari Peter and Brian Lehman , Penn State University Fruit Research and Extension Center, Biglerville, PA

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This experiment was conducted at the Western Maryland Research and Education Center in Keedysville, Maryland.  The goal of the experiment was to determine low rates of the growth regulator, Apogee, both alone and in combination with plant defense stimulators, could effectively reduce the severity of fire blight shoot strikes.  The experiment was carried out in a ‘Cripp’s Pink’ and ‘Brookfield Gala’ block that were adjacent to each other.  Each block was laid out the same and contained equal numbers of trees on four Geneva rootstocks: G.41, G.202, G.202TC (tissue culture), and G.935.  This research is building off research conducted at the same site in 2017.
 

Two to three treatment trees were tagged for each treatment replicate in each variety block.  Each cultivar rootstock combination had four replicates in a randomized complete block design.  The treatments consisted of a control with no treatment, Apogee 2 oz/A for the second treatment, and Apogee 2 oz/A combined with Regalia 2 qt/A for the third treatment.  The fourth treatment consisted of Apogee 2 oz/A for the first two sprays followed by one application of Actigard 2 oz/A.  Each treatment was applied with Choice Weather Master as a water conditioner and LI-700 as a penetrant.  The three treatment applications were made starting at petal fall on 7 May, 18 May, and 29 May.  Shoot inoculations were completed three weeks after the first Apogee treatments on 1 June.  Inoculations were done by wounding shoot tips with a scalpel that was dipped in a suspension of local Erwinia amylovora, strain Ea 273 at 1 x 107 colony forming units.  Sixteen shoot tips per multi-tree replicate were inoculated.  Shoots were assessed on 28 June.  Disease severity was calculated by measuring the extent of fire blight symptoms down the shoot vs. the length of entire shoot.  Shoot length assessments of Apogee treatments were made on separate shoots.  Data was analyzed by Analysis of Variance.
 

Conditions were favorable for inoculation and fire blight development at the time of inoculation, with calm winds, overcast skies and temperatures in the low to mid 70’s.  Disease development progressed at a moderately slow pace.  Symptoms became readily visible with the severity reaching 70-80% on the untreated trees.  At four weeks after inoculation in the ‘Brookfield Gala’ block, Apogee combined with Regalia was the only treatment that significantly reduced the severity of fire blight compared to the control (Figure 1).  However, in the ‘Cripp’s Pink’ block, all treatments significantly reduced fire blight severity (Figure 2).  The Apogee and Regalia combination produced the biggest reduction in severity but not significantly more than the other treatments.  The data collected in this experiment suggest it is possible to reduce fire blight severity with low rates of Apogee alone or in combination with other products if several applications are made prior to disease development.