Braeburn and Fuji were both quite susceptible to 

 apple scab. 



Results of this test were similar to those in for- 

 mal disease analyses done in Connecticut, Michi- 

 gan, New York, Virginia, and West Virginia 



All apple cultivars do not get scab to the same 

 degree. The key question, for which we do not yet 

 have an answer, is how much less can we spray the 

 less susceptible cultivars? That will have to be re- 

 searched. 



%r ^r \r ^r ^r 

 *^i ^C •'k •'k •'k 



Testing Various Methods of Timing 

 Summer Fungicides 



Kathleen Leahy 



Polaris Orchard Management, Colrain, Massachusetts 



Thomas Clark 



Clarkdale Fruit Farm, Deerfield, Massachusetts 



Ezekiel Goodband 



Alyson's Apple Orchard, Walpole, New Hampshire 



The summer diseases, sooty blotch and flyspeck 

 are the cause of most of the fungicide use after 

 June in New England orchards. Using an improved 

 understanding of the biology of these diseases, and 

 specifically the wetness-hour model developed by 

 Turner Sutton and his colleagues , has allowed 

 growers to reduce fungicide usage in North Caro- 

 lina and other mid-Atlantic states. We wanted to 

 test this model to see whether it is viable in New 

 England conditions. 



In a nutshell, the method developed by Brown 

 and Sutton in North Carolina is based on the biol- 

 ogy of the sooty blotch and flyspeck fungi. It al- 

 lows the first summer fungicide to be delayed until 

 200-250 hours of wetness (counting only wetting 

 periods of 4 hours or more) after the last scab fun- 

 gicide. With our relatively dry summers, we gen- 

 erally reach this threshold in early to mid-August. 

 Thus, using this method, we could, in most years, 

 save a couple of fungicide applications and have 



greater flexibility in timing summer fungicides with 

 respect to insecticides and miticides/summer oils. 

 We also decided to try a somewhat less radical 

 method, based on work by David Rosenberger in 

 New York, showing that fungicide retention dur- 

 ing the summer is such that fungicides need not be 

 re-applied until 150 hours of wetness (no mini- 

 mum threshold) having occurred since the previ- 

 ous fungicide. This would still provide a measure 

 of flexibility in summer fungicide use. 



Materials & Methods 



The two cooperating orchards were located in 

 the Connecticut Valley, one in Walpole, NH and 

 the other in Deerfield, MA. In these orchards, the 

 test blocks were divided into three Vi acre plots, 

 and each plot was treated according to one of three 

 summer fungicide programs: 1) the 'standard' pro- 

 gram of a fungicide application every three weeks 



Fruit Notes, Volume 63 (Number 4), Fall, 1998 



13 



