Dr. Heather Kelly discusses seedling disease symptoms and scouting in our latest Call of the Week.
Ginger Rowsey: Thank you for listening to call of the week I’m Ginger Rowsey and our guest is Dr. Heather Kelly. Heather it’s been a pretty wet spring—it’s pouring down rain as we’re recording this podcast—are we in a high-risk year for crop disease?
Heather Kelly: Definitely with the rain and warmer temperatures we’ve had there’s definitely some diseases that could be prevalent. It’s really going to depend on multiple factors, so hopefully seed treatments have been put on the seed. We don’t always need an overtreatment, but field history will play a role in that. Soybean, corn and cotton are at risk without a seed treatment, most of the time everything does come with the treatment on it already, and sometimes the base is good enough, but knowing what’s on your seed will really help you if you do end up in a situation where you’re thinking you might have a seedling disease issue. And so with that, you might initially just see weaker seedlings or areas that are not emerging where the majority of the field is. So, we have the general terms of “dampening off,” there’s seed rot, and really for the most part most of the symptoms you see for seedling diseases won’t tell you what specific pathogen is actually the problem. You actually have to get samples into the lab or we isolate it in in the lab with media and look at it under a scope to say, “Yes it was fusarium, or pythium, or phytophthora, or rhizoctonia, and actually rhizoctonia may be the one exception where you might see what we call “sore shins” that are lesions on the stems that can cause dampening off, but it can also call seed rot. And so first and foremost, assess your situation.
Rowsey: Specifically what symptoms are you looking for this time of year for seedling diseases, and then talk a little bit about how to look for those symptoms. Is it as simple as looking, or do you need to get out there and dig some plants up?
Kelly: Initially you should be fine just looking. If you’re walking and have a pretty uniform stand, you should be fine if everything looks pretty vigorous. Obviously, there’s probably different areas of the field that just might contain weaker soils that just regardless are going to have weaker stands, but that also might be the area where you have a seedling disease issue. If you do see problems with stands and vigor in the field, notice what’s the pattern. Because what I have received so far was a suspect seedling issue, but it turned out to be a herbicide injury issue. So definitely looking at the overall pattern in the field can be a good indicator of seedling disease or herbicide injury. And that injury is either from what went out this spring or what was sprayed even last year with the residual holdover. So, that’s where it can get a little tricky because obviously the lower-lying areas of the field that hold water would be your higher-risk areas for seedling disease, but also you might have herbicides settle in those areas that could also be showing up.
Know that you had a fungicide on the seed with at least two different active ingredients. One needs to cover fungal pathogens usually fusarium, rhizoctonia, then another component that covers the oomycetes they are fungal-like pathogens, that would be your phytophthora and pythium. And so as long as you at least know that you had that protection, then we start to investigate to make sure we rule out other things. We probably get samples and start to isolate in the labs to identify the specific pathogen, but unfortunately if the stand is damaged enough, your options are going to be to replant, and that’s always kind of situationally dependent.
Rowsey: I know it’s hard to get into specifics about the replant, but do you have a general rule or recommendation about at what point you do make that replant decision?
Kelly: It really comes down to the economics of it, and what can go back into the field. Also, what the yield potential is. Usually around 30% in general across the board, but that can be crop-specific. It might change, going up or down and depending on is it just one area. Usually you don’t want to spot replant. That’s not always the best because then you are going to have plants at different maturities. But it just varies. A lot of times with soybean, (and depending on the time difference) it might even out and catch up and wouldn’t be that big a deal, but with corn and cotton it can be much more problematic. If you do need to replant it would be better to do the entire area or just the quarter of the field or the half of the field that’s the most damaged to ensure you still get a very good crop from that area.
Rowsey: Lastly, any comments about wheat disease?
Kelly: With the rain we’re getting now shortly after bloom our risk for head scab has increased to moderate in most areas of West Tennessee and much of Middle Tennessee. But right now it’s just going to be a watch and wait game. Bloom is the last time period you can put out a fungicide. We do have some stripe rust in the area, and so if a fungicide was not sprayed that could easily blow up, and as the temperatures get warmer we could see some leaf rust in the area and then again as the season progresses you don’t actually see the fusarium head blight symptoms until after bloom but before maturity you might see some kernels or heads that look like they’re maturing ahead of time and at closer examination there might be some orange or salmon colors along with those kind of bleached out areas and that is the fusarium that causes the head blight or head scab. Again, nothing to do at that time, but still take note of it and take record to see if a fungicide was sprayed, when was it sprayed and what variety. Also, take into consideration the field history because all of that will play a role in if you will have an issue with that disease in coming seasons in the same location.
Rowsey: Heather, where can people go to get information about these issues throughout the year?
Kelly: Our mobile-friendly website is guide.utcrops.com. We’re always updating and adding more information not just about diseases but also insects, our fungicide efficacy tables and insecticide tables are there. Again, that’s guide.utcrops.com.
