Integrated Pest Management, Plant Pathology

Episode 1: Cercospora Leaf Spot on Sugar Beets

Join Emily and Bob as they discuss the Cercospora leaf spot in sugar beets.

00:30 Emily: Hi everyone! Welcome to Farm Sci-Ed. My name is Emily Stine and today I’m interviewing plant pathologist Dr. Bob Harveson, who’s doing some really interesting work on cercospora in sugar beets. So sit back, relax, and let’s go learn.

00:43 Emily: So Bob, what are sugar beets?

Bob: Sugar beets are plants that are greatly a result of breeding. It was found that this particular beets – in general, fodder beets and other types of beets – had sucrose in them, which is the same product that is produced by sugar cane.

So it allowed temperate areas to produce sugar, which then enabled everybody to be able to – it made it more available to the general public. Because previously, it had all come out of the tropics – you know from the cane – and so it was exorbitantly expensive. So it’s a crop that they have bred to the general plant that they have now. So there are high, high levels of sucrose within that plant and it’s the same type of product that is by the totally unrelated sugar cane. Which is kind of odd, but that’s I think, an interesting fact.

1:35 E: Where are they commonly grown?

B: Well they’re grown out here the western part of Nebraska, but then it’s also in Colorado, Wyoming, and there’s a great deal around the Great Lakes, Michigan and then Minnesota. North Dakota is the largest number of acres. So it is grown in various places. It’s grown up in the northwest and same in Idaho as well.

2:00 E: What is cercospora?

B: Cercospora is a fungus. It’s the generic name for a fungus that causes – it’s an airborne thing. The spores fly through the air. It just causes a foliar disease of sugar beets and other beet related: table beets,
those sorts of things, they’re still susceptible to this.

The other thing that I wanted to point out is that it can be confused with a number of other foliar type diseases that we might see here, but it’s the only one you have to be worried about. It’s the only one that causes economic damage, but it could be confused with alternaria leaf spot or with bacterial leaf spot.

It can be very very devastating, not only to to yield, but also in that it doesn’t sit well in the piles, so it doesn’t process very well. So you just, you just lose a lot of the sucrose because of this infection. Not only in yields, but later on for processing.

2:56 E: What kinds of environmental conditions favor cercospora development in the field?

B: Well it’s – it does have a very specific set of conditions that it needs. It needs a long period of water, duration of at least 11 hours of standing water on the leaves and so forth.

It also needs a [specific] temperature range. If it gets down below 60 degrees Fahrenheit, then then it won’t be a problem. And then if it gets up higher to 95 to 100 then it’s not going to be as much of an issue either. So you need the combination of warm temperatures with  a lot of water.

3:31 E: How do sugar beet growers manage cercospora in the field?

B: Well, there’s a number of ways. One of the first things, like I mentioned a while ago, is you need to make sure that it is cercospora that you’re looking at. ‘Cause if it’s one of those other diseases, you’re going to waste your money because they weren’t going to be economically damaging anyway. And then you’re just out the cost of the chemical.

I guess the most effective way, or the most cost effective way, is through genetic resistance. They have done a really good job of doing – of finding resistance – and then incorporating it into new varieties which are agriculturally successful.

Other things you can do: different types of tillage so it it it can – it basically survives in residues, plant residues. So if you can get that buried or if you can get it out of the way, then that’s going to also help you to a great extent. It’s going to remove that source of inoculum. It doesn’t move a great deal, but it can move through wind patterns.
So, what the idea is to not – if you’ve had a field that had a severe amount of disease, then don’t put another crop the next year within a hundred yards of that.

Fungicides are another option that are routinely used and if you combine those with with the resistance then that that’s even better. But the problem with the fungicides is that there’s populations that have built resistance towards these fungicides and so that’s something you always have to keep in mind. And it’s something that we are continually trying new things to see just to look at different chemistries or different products so that we don’t all – we don’t lose products because of the genetic resistance to that. And that’s so, that’s a huge part of that is not to use the same chemistry multiple times in a year.

5:21 E: How do they track these environmental conditions?

B: Well, we – they do have – we do have a predictive system that has been in place since the 1980’s. It was developed by my predecessor Eric Kerr, and then another UNL faculty member. It’s basically an alert system that that tells you the environment. Its advantage is that it tells you whether the temperature and the moisture has been right for infection to occur. So it doesn’t tell you that the pathogen is present, it just says “hey”.

It’s a monitor, you take it and put it in the fields, and then each day you go and take a look at it. And then it gives you a numerical value of 0 to 14, which is a formula and it’s based on a hourly time for for for the temperatures. Then it spits out a number through a formula of 0 to 14 and so you take that number, that’s the the daily value for disease for that particular day. And the idea is that when you get two successive days in a row where the sum of those two daily infection values reach 7 or higher, then that means the previous 48 hours have been conducive for disease to occur. It doesn’t mean the pathogen is there, doesn’t mean disease is there, it just means that it has been conducive for that to happen. So it makes you have to get out and go check and see if there’s any any of those types of things. So when you do see something and it is building up into the upper part of the canopy, then that’s probably a good idea if if that system told you that it’s time to pull the trigger on it, then you need to you need to have – be prepared to do that.

7:11 E: How has this alert system improved over time?

B: Well I don’t know if we’ve improved it, but we’ve been working with Xin. It was his idea to take this system – he’s not changing the system – but he’s made a a device that allows people to access that information remotely and not having to go out into the field to pick it up. So that’s the key to that thing.

Another thing that we are looking at this year for the first time is essentially a spore catcher and so we put that out there with the the monitor for the for the environmental stuff. And so it should tell us: are the spores present of the pathogen? And so you combine that together with the environment, then that would – I think – be a more effective way of determining whether you need to spray or not.

Because again, spraying indiscriminately is not a good idea. There are chemicals that are available that we can use if things come to that situation.

8:10 E: Does the kind of fungicide a producer use matter?

B: What I’ve found in the past, is that the fungicides that you use are not as critical as using them at all. So if if you don’t do it and you have big problems then that’s worse than than using the wrong product I guess. So that is a critical thing. But you don’t want to wait too late, but you also don’t wait too early too. Because that’s not gonna –
most of these fungicides are contact, so they’re not going to get in the plant and last a long time. So this would be considered a short-term solution, and that that’s why it’s so difficult to work with. Its that you’ve got to be cognizant of the fact that “hey the last 48 hours have been conducive for this so I need to get out there and see if any infections have moved up the plant.” Because if you get them on the newer leaves, that’s when you start to see the issues with the yield drop and all that.

9:13 E: Well folks, there you have it. In talking to Bob about sugar beets and cercospora, we learned what sugar beets are, what cercospora is, and what some of the management techniques are, including using fungicides for short-term management.

See you next time on Farm Sci-Ed, where we go into the science and education behind farming. Be sure to subscribe and follow us for more science and education behind farming. Comment below if you have any questions about cercospora in sugar beets and we’ll be sure to answer it in an upcoming episode. Until then, subscribe to our channel, like this video, and be sure to follow us on our social media. Have a good one!

This transcript has been edited slightly for grammar.