Jude Boucher, UConn Extension
There is a new fungicide registered for powdery mildew (PM) control of cucurbit crops for 2015. Vivando was formerly only registered on grapes but has received a national supplemental label for all major groups of cucurbits, apricots, cherries, hops and peaches. Vivando has a different mode of action from other registered fungicides on cucurbits and is in a new resistance group (U8).
Meg McGrath, from Cornell’s Long Island Horticultural Research Station, has included it in her fungicide efficacy trials for pumpkins, winter squash and muskmelons for the last few years and has shown that it “exhibits excellent control” of PM. It now represents another family of mobile fungicides that is capable of targeting this disease on the underside of leaves where PM gets started. Because mobile fungicides tend to be very prone to resistance problems and this product targets only powdery mildew, it will be necessary to rotate to other groups of mobile fungicides often and to mix it with a good preventative fungicide for resistance management and to control other important diseases on cucurbit crops.
The IPM program in CT has advocated starting your fungicide program when you find PM on the bottom of one leaf out of 50 older leaves scouted per week, then rotating through each family of mobile fungicides over the course of the summer for full-season crops like pumpkins and winter squash. The mobile fungicide should be mixed with a fungicide that will provide some control of PM and the other major fruit rot diseases, such as black rot, Plectosporium and scab. When you run out of mobile fungicide groups switch to sulfur for PM and a broad spectrum fungicide to control the fruit rot disease complex. Sulfur will provide the best under-leaf control of PM of all the protectants. This type of program has been providing IPM growers with 95-100% marketable fruit for years (see ‘Effects of Fungicide Timing and Tillage on Resistant Pumpkins’ on the UConn IPM Web Site, www.ipm.uconn.edu/).
One example of this type of spray program that combines great efficacy and resistance management would be to make applications at 10-day intervals with: Vivando (group U8) + Bravo, Torino (U6) + Bravo, Quintec (13) + Cabrio, Procure (3) + Bravo, then sulfur and Bravo. Note: Quintec is not registered for summer squash and cucumbers, but is registered for all the full-season cucurbits (pumpkins, melons, gourds, and winter squash).
Meg McGrath lists the following PM products for organic producers: sulfur, copper, horticultural oils (i.e. JMS Stylet-oil), potassium bicarbonate (ie. MilStop), and biologicals /microbials (e.g. Actinovate, Double Nickel, Regalia, Seranade Opti, and Sonata). Note: copper may cause phytotoxicity on many pumpkin varieties. Do not mix Vivando with horticultural oils.
McGrath, M. T. . 2015. Managing Cucurbit Powdery Mildew Successfully in 2015. Cornell Extension Fact Sheet. hhtp://vegetablemdonline.ppath.cornell.edu/
McGrath, M. T. and K. A. LaMarsh. Efficacy of Fungicides for Managing Powdery Mildew in Pumpkins, 2014. Plant Disease Management Reports 9: V030
McGrath, M. T. and K. A. LaMarsh. Efficacy of Fungicides for Managing Powdery Mildew in Pumpkins, 2013. Plant Disease Management Reports 8: V204
McGrath, M. T. and L. K. Hunsberger. Efficacy of Vivando for Managing Powdery Mildew in Cucurbit Crops, 2011. Plant Disease Management Reports 6: V007