Crop issues during summer’s dog days

BLOOMINGTON, Ill. — The Illinois Soybean Association’s agronomy team is spending the dog days of summer scouting for problems in fields that have, could or will impact plants.

During a recent Field Advisor podcast, Stephanie Porter, ISA outreach agronomist, shared with Kelsey Litchfield, ISA agronomic outreach manager, what she has seen in soybean fields.

Litchfield: What are you seeing in fields from a disease standpoint in your area?

Porter: Even in those areas, that are really, really dry, there’s still humidity there. One of the misconceptions is you have to have rain for humidity. We have a lot of humidity still, and that’s apparent, but now we have even more.

There was a mention by one of our ISA board members of fog. That’s one of those red flags that there’s going to be disease.

Another one is if you start to have condensation on your windows — any kind of leaf wetness is when you have disease.

The other thing that we focus on with the disease triangle is temperature, knowing there are differences between northern and southern Illinois.

You have to be careful when we talk about certain diseases because tar spot and northern corn leaf blight are popping up into areas and that tends to be sometimes in a little bit of cooler temperatures.

They like cooler temperatures compared to gray leaf spot, for example, or others that blow up like rust would blow up. Southern corn leaf rust blows up from the south and it likes warmer temperatures.

We were in a field in Crawford County (during the second week of July) and we started to see some frogeye leaf spot lesions show up and that’s a big deal.

The first thing is you want to make sure you look at the variety, because a lot of the varieties do have differences of susceptibility to frogeye leaf spot. That’s a big one for fungicides in soybeans.

The other disease that was popping up (in late June), and we tended to get it a lot worse in our fields for some reason, is septoria leaf blight. That is usually in the lower canopy.

We tend to not worry about it as much, but once it works its way up more than halfway through the canopy, that can start to cause some issues. I think we probably need to do more research on that disease.

Normally, we just try not worry about septoria leaf blight, but it’s definitely another factor out there in the fields.

Litchfield: Those are some things to look for out in the field to see if fungicide is needed. We hear that since commodity prices are lower, should we make that fungicide pass or not? It differs from soybeans to corn. Can you talk about that and the growth stages when considering a fungicide application?

Porter: With all this heat and rain that we’ve had, we’re really starting to progress quickly and get tassels out there. So, we need to make the decision quickly because we don’t want to get past the time where a decision would be too late to be made, especially on corn.

Another factor also to take into consideration, especially this year, and I know we are on our farm, is that later-planted crops tends to get a little bit more disease and sometimes insects. So, really make sure you’re scouting for certain things like that.

I guess I’ll also throw in seeing Japanese beetles. I have not seen anything really heavy. We tend to see one or two every time we go into a field, maybe a cluster.

I was in one field maybe in Crawford County. We were also seeing a lot of stink bugs in the south, too.

I really think they’re a factor, as well, especially later in the season, especially in the south. That’s something to watch out for, as well.

We’ve also been fighting grape colaspis beetles. They’re not normally a huge foliar feeder.

We haven’t seen huge amounts of those, but there’s more of them this year, and I’m sure there could be a random field that could have a lot in them if they had them earlier in the season feeding at roots.

Litchfield: Can you talk about throwing the insecticide in with fungicide as an option?

Porter: A lot of decisions have already been made on the farm. Fungicide and insecticides are often bought earlier in the winter to get some discounts. There’s a lot of farmers that are trying to make that decision.

Typically, unfortunately, or fortunately, depending on how you want to look at it, a lot of people in Illinois tend to just throw in that insecticide in with a fungicides at the same time because typically insecticides cost less.

There are also decisions being made between generics and non-generics, which is kind of a big deal with fungicides. And then oftentimes, if you want to make a decision for an insecticide, there are some thresholds for some insects, and there aren’t some for others.

I would say the main one that we’re concerned at this time would be Japanese beetles. Mainly, you want to watch for foliar feeding at this time with Japanese beetle. Look at the whole plant and make sure that 10% to 15% is not being fed on.

The other thing with Japanese beetles is with corn is we’re mainly concerned with those silks. There are a lot of parts of the state that are droughty and they’re worried about pollination with silks and maybe tassels not coming out at the same time in sync.

We’d also have to worry about Japanese beetles, because in droughty situations, we aren’t getting a lot of silks popping out. If the Japanese beetles are feeding on those, then that’s even more a bigger issue that we could disrupt pollination.

The last thing, I would be remiss if I didn’t say this, but Japanese beetles a lot of times are on just field edges. I know we don’t like to be in the field when it’s 100 degrees out, but if you want to take a look at the rest of the field, it may just be a lot of them are on the edges, so don’t panic.

Litchfield: Going back on the disease side, you mentioned some of those diseases from frogeye leaf spot, gray leaf spot, septoria to leaf blight. What are some of the things farmers should be looking for going into the next couple of weeks?

Porter: Normally this is the best time to be scouting. This is probably the hottest time that most people are scouting. If we’re going to look forward, I would again focus on some of the later-planted fields, as well.

Make sure that we’re not getting, for example, bean leaf beetles later in the season in soybeans. I also mentioned stink bugs, as well. Those are just some things I would watch out for.

Tar spot is always a factor, and it can show up later and get you. There’s been some work done at Iowa State that found generic fungicides might not give you as much efficacy, and so you may need to do another application depending on when you apply the first time.

Let’s say, for example, you decided not to spray a fungicide on corn, and all of a sudden, our temperatures got cooler, which it can happen, that’s a little bit more conducive for tar spot.

Then you would want to make sure you kept scouting and maybe if it started to blow up, you may want to apply another fungicide later in the season, which is very possible. I would have never said that a couple years ago before we had to tar spot, but that’s another thing to watch out for.

Litchfield: You’ve been to some fields in western Illinois where red crown rot has been detrimental. It’s an absolute terrible disease. Talk about the importance of getting a diagnosis that will help make future decisions for those fields knowing the disease is possibly present and that is carries on.

Porter: You are not going to get rid of it. It’s there. One of the factors that’s popped up in making decisions is that red crown rot has a lot of alternate hosts. We’re still learning those and one is alfalfa.

So, for example, my neighbor found red crown rot. They also have a dairy farm, and so that was one of the things that first popped up in my mind that they can’t grow alfalfa, either. It really affects your rotation.

The other thing is they might want to try to use some of the seed treatments out there that maybe they weren’t normally using. It might be a higher rate, depending on the label.

Make sure you know that, but it’s not going to be a cure-all for sure, but it’s one of the tools we have to use against red crown rot at this time.

There’s other cultural things as with all root rots. You may want to improve drainage in the field. That’s going to help you a lot.

You may want to clean some field tools and harvest that field last. There’s just a lot of different decisions if you don’t want to spread it to other fields.

Litchfield: Based on what you’ve seen so far this season, are there any lessons you’ve learned that you might want to share because there are times when you see something in the field and there’s nothing you can do about it this year, but you can prepare for next year. We’ve been in fields with Phytophthora and there’s nothing that you can do about it right now.

Porter: There’s so many different things, but I think that fields with Phytophthora was one of the main things that popped in my head. Phytophthora is something we’re seeing in a lot of different fields.

We need to start really diving into whether or not some of the varieties that we’re buying have the correct score, and if we think that they have good tolerance or if they have the right RPS gene for Phytophthora, is that RPS gene working? Do you have the right stack in there?

The fact that I’ve already seen frogeye makes me think that maybe you should start making sure that you have some resistance against that. We just had the weather for that disease, as well.

The other thing is we continue to have issues with weeds and something’s going to have to give. We’re to the point now where I talked to somebody a week ago and they had the cultivator out.

We preach against that, but once you get past that R1 stage where we can’t make any more herbicide applications, or we shouldn’t, they’re off label, what do we do now? And you see a lot of people out there with hoes walking beans again and the weeds are an issue.

I think that a lot of the populations are lower. We had later planting. We didn’t have row closure by the Fourth of July, many fields that weren’t planted early, and we have a weed issue. This is nothing new.

We are getting resistance to glufosinate and different ones are popping up in the state. These are commonly used herbicides in the state, and so we’re going to have to start thinking about different ways to combat weeds going forward.