Recorded Pest Message – May 6, 2008

Today I am just going to report on apple scab protection and the results from the scab fungicide sensitivity testing from 2007.
Bloom is the most important time to protect your trees from scab. We have been experiencing intense apple scab infection periods and there is the threat of another one Thursday into Friday. The best defense is to apply a protective fungicide right before the next wet weather. Use a protective fungicide like Captan, Polyram, Manzate or Dithane. Sovran or Flint also protect your trees well against scab.

I got the results from the scab samples I took in June 2007. Cornell tested scab from 8 orchards in RI and another 12 orchards throughout New England. The scab was tested to see how sensitive it is to Syllit, Nova or Rubigan and Sovranor Flint. If the scab is sensitive, the chemical can still control scab. If the scab is resistant, the fungicide is no longer effective. There is also the category of “shifted”. This means that the fungus is moving towards resistance. If a fungicide is used in the Shifted category, the fungicide should be used at full strength and probably not beyond this season.

So for the 8 RI orchards and Syllit – 6 orchards are Sensitive to Syllit; 1 orchard is Resistant; and 1 orchard is Shifted.

For Nova or Rubigan – No orchards are Sensitive; 4 orchards are Resistant; and 4 orchards are Shifted.

For the Strobies, Sovran or Flint – 2 orchards are Sensitive; no orchards are Resistant; but 6 orchards are Shifted. This Shifted status for 6 RI orchards may seem very surprising since these fungicides have not been used much in RI. Unfortunately, once there is resistance to Rubigan and Nova, resistance to the Strobies follows very quickly.

The results in the other NE states are very similar to our results in RI.

Indar and Inspire are 2 new fungicides very similar to Rubigan and Nova. Perhaps they will control scab this year – or perhaps they won’t. To be safe, most orchards in RI should not use the SI, also called DMI fungicides. This includes Rubigan, Nova, Indar or Inspire. Indar can still be used for brown rot control in peaches.

Our next Twilight meeting will be May 22 at an orchard in MA. Where the meeting will be has not been determined yet.
Thanks for calling and next message will be recorded Tuesday May 13.