Wednesday, May 8, 2013

Flooded Fields and Planting Recommedations

Hello Vegetable and Small Fruit Growers
I am posting items to the WNC Vegetable and Small Fruit Blog temporarily in the absence of a vegetable agent.  Some of you have fields that were recently flooded by the tremendous amount of rain that we have had over the past weekend.  The information following comes from Dr. Kelly Ivors and are her most current recommendations as to how to prepare these fields for the crops you plan to plant in particular tomatoes and peppers.  

"Our NCSU labs  can test water for Phytophthora (that isn't the problem), but the water samples will be variable and very hard to determine what was in the exact flood waters that each field was exposed to when the flooding occurred. Samples would have needed to be taken during the flooding. Flooding also carries debris and anything else that is water soluble or water 'floatable'. You just have to assume that there is a increased potential that Pythium and possibly Phytophthora could have been introduced, or other pathogens that are water dispersable. My chapter on oomycetes in the new APS Press book "Waterborne Plant Pathogens" (IN PRESS!) goes over this variability in detail.
Main point is this: Phytophthora and Pythium infections almost always show up in the wettest spots in the field. In ornamentals, it is where they have water pooling or leaky irrigation heads. In Fraser fir fields, Phytophthora root rot was correlated with soils high in clay. In vegetable fields, these pathogens seem to be most problematic in low spots and areas that drain poorly. I bet the same areas that flooded recently have been flooded before. We have had quite a bit of flooding since I have been working at NCSU.
Hopefully the surrounding soils weren't that warm enough to have active populations of bacterial wilt. I think my main concern in setting transplants in recently flooded fields would be Pythium or Phytophthora crown/root rot (or both organisms... maybe even a complex with Rhizoctonia/Fusarium if contaminated debris / small pieces got under the plastic). I would worry the most about direct-seeding/setting cucurbits in these flooded fields, and also worry equally about setting pepper and tomato transplants in these fields as far as Pythium and Phytophthora goes. While P. capsici isn't a big problem on tomatoes, young plants are very susceptible to Phytophthora crown rot / stem blight.
If you want to still plant tomatoes or peppers in these fields, I think the best bet would be to apply mefenoxam PREVENTIVELY in the drip RIGHT AFTER plants are set. Mina did a study on black shank of tobacco a few years back, and Ridomil worked the best when it was applied on the date closest to transplanting.  The rate for Ridomil Gold is 1 pint / acre. I have attached a screen shot of further application details. RATE IS VERY IMPORTANT when dealing with young plants. Do NOT OVER APPLY MEFENOXAM to young seedlings.
If you are going to set tomatoes, then I would recommend a variety that has Fusarium race 1, 2 and *3* resistance, as Dr.Shoemaker has also suggested. We really appreciate your input and advice Paul. Two pathologists are better than one !!!"

Posted with minor edits by Cliff Ruth, Extension Area Agent.  

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