sclerotinia levels

[olinfarms]

We just got back petal test results that show 20-40% infection. what is the best strategy for spraying? Spray now,40-50% bloom,with Ronilan or wait until petal drop and go with Roval Flo for additional alternaria control?

[mhartman]

20-40% petal infection is actually a low reading. Given the wet weather, this level of infection will probably result in a 10-20% yield loss. 20% yield loss from a 40 bu/ac potential crop is 8 bu/ac. At $6/bu, that's $48/acre. A 10% yield loss would be $24/acre. I recommend spraying if the predicted benefit outweighs the cost by 1.5. Now about the choice of products - Ronilan vs Rovral. If sclerotinia is your main concern, I would advise using Ronilan now. If alternaria blackspot is your main concern, then spray later with Rovral. However, the late application timing with Rovral will not provide much sclerotinia control.