Scouting for Diseases, VBC
July 30, 2021
Lesions on the Leaf
Late leaf spot is starting to be found in more fields this week, including those with timely and expensive fungicide programs. Switching modes of action and/or including Bravo or sulfur in with the next fungicide application, or tank mixing a systemic product with bravo (e.g., if the previous spray was bravo) are all options to buffer ourselves from any one product potentially being a weak link. Crop oil burn can raise an eyebrow or two and can be found in the mid-upper canopy following an herbicide spray. Spots from oil or surfactant do not have raised spores on the underside as LLS does.
Fields that have a rotation history with legumes are at an increased risk for soil diseases such as white mold/stem rot and Cylindrocladium black rot. We have several effective fungicides for in-season management of white mold, including elatus, excalia, convoy/umbra, fontelis, and provost, whereas our most effective options for CBR get applied in-furrow at planting. If some of these have been applied and we still see disease, it likely would have been much worse if we did not do what we did. We’ll let slide the analogy of a bowl of soup and an ice cube. A few pictures including examples of characteristic symptoms/signs for white mold and CBR are included.
Fields nearing the 90 or the later 105 DAP fungicide spray, especially in our southwestern counties, may consider including a preventative application of Dimilin 2 fl oz/A when the sprayer is going across the field for velvetbean caterpillar control. This is a relatively inexpensive treatment with a good residual. Do we need it this year? Maybe not, though I at least want to mention it after the last two years with VBC coming in about a month earlier than was typical for many moons before. Worms generally are more of a concern during extended dry periods, and while many areas have been fortunate with rains, not all have. Dimilin has a 28 day PHI and is not intended to control established populations. VBC are easy to kill if they do show up and start eating uninvited, but if left to their own devices, they can defoliate a canopy quickly. May not need to spray for VBC early this year, but good to keep an eye out nonetheless.
The week ahead looks encouraging for rain.