strobilurines that may be applied. There are differ- 

 ences between the two labels in these respects. The 

 Flint label uses a more cautious approach. For Sovran, 

 the manufacturer "recommends" no more than three 

 applications in a row. The Flint label states "use a 

 maximum of two consecutive applications." The 

 Sovran label says "do not make more than six applica- 

 tions per season". The Flint label carries a five appli- 

 cation limit. The Sovran label states that Sovran should 

 not be used as the last fungicide application of the sea- 

 son, while Flint does not have that restriction on the 

 label. 



At the very least, the label recommendations and 

 limits should be followed strictly. A conservative ap- 

 proach would be a four application per season limit, 

 with a maximum of two consecutive applications. All 

 strobilurins have the same mode of action, so the limit 

 of four applications per season would apply to the to- 

 tal number of Sovran and Flint sprays. Because 

 strobilurines work well on fruit scab and other diseases, 

 there is no compelling reason to tank-mix them with a 



broad-spectrum protectant as there is with the sterol 

 inhibitor fungicides. Rather, the manufacturers have 

 chosen to recommend alternating pairs of applications. 

 Pairs of applications made 7 to 10 days apart sounds 

 similar to the "back-to-back" applications recom- 

 mended for the SI fungicides such as Rubigan and 

 Nova. However, the important point with the 

 strobilurines is to use a different class of fungicide af- 

 ter making two strobilurine applications in order to 

 reduce the chances that resistance will develop. There 

 certainly are a number of unanswered questions about 

 the best way to manage resistance, but that probably 

 argues for taking a relatively cautious approach to us- 

 ing the strobilurines. 



Both products exhibit excellent post-infection ef- 

 ficacy, similar to the 4-day activity of the SI fungi- 

 cides. As you might expect with this sort of post-in- 

 fection efficacy, the strobilurines are somewhat sys- 

 temic. The strobilurines show some protectant activ- 

 ity, probably on the order of 3 to 6 days. Therefore, 

 recommended intervals between applications are 7 to 



Fruit Notes, Volume 64 (Number 2), Spring, 1999 



