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We have investigated a number of instances of the apple 

 replant problem in Massachusetts. At the present time we are 

 determining which potential pathogens are involved and planning 

 greenhouse work \\?ith rootstocks and seedlings to determine 

 pathogenicity. Future work will involve screening major root- 

 stocks and rootstock/scion combinations for reaction to the 

 agent(s) of the replant problem. 



2. Biomonitoring of Fungicide Residues on Apple Leaves 



As part of the Integrated Pest Management Program, we have 

 been developing in the laboratory a method for determining bio- 

 logically-active fungicide residues on apple leaves. This is 

 done by plating leaf discs on agar plates seeded with spores 

 of Gloeosporium or Saccharomyces . Zones of spore germination 

 inhibition indicate the relative concentrations of biologically- 

 active fungicide residues on the leaves. This information can 

 be used to predict fungicide spray timing. Limited field results 

 were obtained last year and more extensive data will be obtained 

 from field tests this year. 



3. Disease Resistant Fruit Trees 



Apple cultivars that are immune to scab, and varying in 

 their resistance to powdery mildew, rust and fireblight, have 

 been planted at the Horticultural Research Center in Belchertown. 

 These include 4 trees each of: NY613452, Liberty, Priscilla, 

 Sir Prize, Mac Free, Nova Easygro and Prima. 



Imperial Mcintosh trees are used as disease-susceptible 

 comparison trees. 



Pear Cultivars that are resistant or tolerant to fireblight 

 have also been planted. Four trees each of HW602, HW603, and 

 Highland have been planted. Bartlett trees are used for compari- 

 son. 



We plan to evaluate these trees under our conditions and to 

 begin looking at possible differences in leaf surface microflora 

 between resistant and susceptible trees, as a prelude to biolog- 

 ical management of apple scab and other diseases. 



4. New Disease Investigations Block 



A new block has been established to do research on integrated 

 chemical and biological management of apple diseases: 15 trees 

 each of Cortland, Empire, Roger's Mcintosh, Double Red Delicious, 

 and Yellow Delicious were planted in 1978 for a total of 75 trees. 

 Trees are in randomized units of three, \\'ith 5 replications. 



