For the past few weeks we have continued to see an escalation of disease identified as Target Spot in our float plant systems. In the past we have had little or no control of this and have encouraged producers to get the plants into the fields. Later in the season we see this disease show up in our crops and continually lose weight and production. Dr. Kenny Seebold, Plant Pathologist at the University of Kentucky, has worked to get an emergency label or Quadris in the greenhouse and on the float system. The following is an article that Seebold sent to the agents last Friday.
Over the past two weeks, we’ve seen an explosion of target spot on tobacco transplants around Kentucky. I’ve sent out updates and tips for management recently, and wanted to give an update on the current situation.
Even with a couple of days of good weather, target spot is plenty active right now. And with rain in the forecast for a few days more, we can expect disease pressure to stay high. Currently, we recommend taking steps to maintain good ventilation, adequate fertility, and application of mancozeb fungicides (like Dithane, Manzate, or Penncozeb) on a five-seven day schedule. Mancozeb is not specifically labeled for target spot, but is fairly suppressive when applied in a preventive manner. The problem we have now is that disease pressure is so high that mancozeb just can’t keep up. And the problem is worse for people who started spraying after target spot fired up. We know about the “unmentionable” products that show up in the float system, and we’d all agree that the best possible situation would be to find an active, legal means to control target spot.
The fact is, a legal option has been in place for a while. Quadris fungicide, labeled for target spot and other diseases like frogeye and blue mold, does not have specific restrictions on greenhouse use on its label. However, there is not specific guidance on using the product on transplants, and the manufacturer (and myself) did not particularly want to see Quadris in the float system. The main reasons were potential for resistance development (especially with blue mold), and the potential for crop injury. The current crisis, though, dictated that we find something that could help stem the tide of target spot. I really think that, had we not found a solution, we were looking at a train wreck for a bunch of growers. After a few phone calls late last week, it became clear that Syngenta was willing to support the use of Quadris in the greenhouse, and I was in complete agreement. To that end, thanks to the hard work of folks at Syngenta and Kentucky Department of Agriculture, a Special Local Need [24 (c)] label for the use of Quadris on tobacco in the greenhouse was approved this afternoon.
Effective now through July 30, 2009, growers will be able to make one application of Quadris at a rate of six fl oz/A, which is the equivalent of 0.14 fl. oz. (4 ml) of product per thousand square feet of float bed (roughly 400 trays), applied in a recommended volume of five gallons – enough to get good leaf coverage. Thus, a grower mixing 20 gallons of spray solution would add 16 ml of Quadris, or roughly three teaspoons of product. After making the Quadris treatment, producers should switch back to mancozeb until plants are set in the field. This is critical to stay in compliance with the label, and to minimize the risk of resistance developing.
It’s important that growers who use Quadris in the greenhouse have a copy of the 24(c) label in their possession. It is equally important to remember that the greenhouse application counts toward the seasonal limit (four-five applications) allowed on tobacco. As I mentioned earlier, this label will expire at the end of July, 2009. It is not clear at this time if we’ll renew this for next year, but I will keep you posted. In the meantime, please let me know if you have any questions. You can contact me by phone at (859) 229-2420, or by email at email@example.com. The Quadris greenhouse label for Kentucky will be posted on the KY Tobacco Disease page at www.uky.edu/Ag/kpn/kyblue/kyblue.