120% 



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c 



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■c 



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— 60% 



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 o. 

 en 



^ 40% 



20% 



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7/28/99 8/4/99 8/11/99 8/18/99 8/25/99 9/1/99 9/8/99 9/15/99 9/22/99 9/29/99 



Date 



Figure 1 . Percentages of fruit showing flyspeck symptoms following sprays with calcium chloride 

 and three different fungicide treatments, Kingston, RI, 1999. 



The strobilurines may represent a real opportunity 

 to improve our summer-disease managment. So far, 

 no interactions with mite management have appeared. 

 Residue problems with the strobilurines, as compared 

 to Benlate or captan, might be expected to be minimal. 

 Rather than focusing the strobilurines on scab, it might 

 be useful to reserve at least a couple of applications 

 for flyspeck. 



So, should Flint or Sovran be purchased for the 

 2000 growing season? Both materials have performed 

 very well against scab and flyspeck, so the limiting 

 factor will probably be price. The chemical compa- 

 nies are aware of this, and will probably price the 

 strobilurines to be competitive with the combined cost 

 of an SI plus protectant. Captan or mancozeb alone 

 probably will be cheaper. If price is an issue and grow- 

 ers cut strobilurine rates below the label minimums, 

 then control may not be very good, especially without 

 a protectant to act as a back-up. 



Strobilurines are good antisporulants. That is, they 

 prevent active scab from producing large numbers of 



viable conidia that can cause more infections. They 

 will do a good job stopping or slowing an epidemic. 

 However, more than 96 hrs after the start of an infec- 

 tion, it is unlikely that strobilurines will stop symptom 

 development. With the SI fungicides, applications a 

 few days beyond the 96-hour post-infection recommen- 

 dation would usually stop symptom development, or 

 limit it to yellow spotting. This will probably not be 

 the case with the strobilurines. In addition, post-in- 

 fection use will hurry the process to resistance devel- 

 opment. 



Another factor to consider is what might be called 

 "new product caution." With any new product, un- 

 foreseen circumstances may yield unexpected perfor- 

 mance problems. While the strobilurines look great, it 

 might be prudent to use them on a limited basis for a 

 year or two. A lot will be learned about the strobilurines 

 as commercial growers begin to use them. In short, 

 use them where the price and timing fits your needs, 

 but do not abuse them by cutting rates, or applying 

 extra applications. 



Fruit Notes, Volume dA (Number 2), Spring, 1999 



11 



