Integrated Pest Management, Plant Pathology

Episode 5: The Disease Triangle

Join Emily as she talks to Dr. Bob Harveson about the Disease Triangle: what it is, why it matters and how important it is when determining Cercospora management.

This transcript has been edited for clarity.

0:21 Hi everyone, and welcome to Farm Sci-Ed, the show where we go into the science and education behind farming. I’m Emily Stine and today we’ll be talking to Dr. Bob Harveson about the disease triangle and what cercospora needs to flourish. So sit back, relax, and let’s go learn!

0:38 So Bob, what is the disease triangle?

Bob: Well it’s a concept that’s been used by plant pathologists for a while and it just describes the the things that are that are needed for disease to occur.

So with the three points you would need a conducive environment, you would need a pathogen present and then a susceptible host. All three of those need to be going on at the same time or disease just isn’t going to occur.

1:06 E: Why is this something important to plant pathologists?

B: Well, that’s kind of what we do; is that we study the organism. We study what it needs to do so that we can potentially identify that point on the triangle which we can then access or we can take advantage of and and and reduce the disease.

1:26 E: Can you give some examples?

B: Genetic resistance for the susceptible host and then we look at either fungicides or some other kind of process that would help remove or reduce the the pathogen. Or we can also modify the environment with the various types of cultural practices.

1:44 E: Now you’ve mentioned a couple methods of control that you use. Genetic resistance and and fungicide use are fairly understandable, but what is cultural control?

B: Well it’s it’s probably, with irrigation, okay, you need to uh limit the amount. I mean in other words, you need to find a nice amount that wouldn’t be overly wet. You know, just reduce it to – don’t let it get out of control with a a large number of – uh large volume of – don’t over water, I guess.

2:15 E: What’s cercospora’s disease triangle look like?

B: Cercospora needs – there are a certain amount of environmental conditions that it needs. It needs to have temperatures of 80 to 90 during the day, warm temperatures, and then at night something greater than 60. It also needs extended periods of leaf wetness, up to 10 to 11 to 12 hours and in order for the spores to germinate. So those those two factors have to be there at the same time.

2:45 E: How’s the alert system and the spore-nado catcher you’re using help you make decisions?

B: The alert system basically just tells you what the environment’s like. So when whenever you read those each morning, they would tell you a certain – based upon this algorithm in in a form – it would give you a specific number which which then would uh tell you whether the conducive the the environment was was conducive over the previous 48 hours, whether it was or was not. So that one concentrates on the environment. And the spore-nado was – is a structure or a mechanism for measuring if the spores are present or a relative number of them in that that respect. So that that gives you the the presence or absence of the pathogen and then the the alert system just tells you whether the environment is good enough for disease to occur.

3:45 E: Are there post harvest options for producers to use to minimize cercospora in the future?

B: Well, it would be helpful to – you know a lot of people don’t use the any kind of a cultivation – but yeah, if you can get rid of the residue then that would that would certainly help to reduce the the chances of disease the next year.

4:01 E: Well folks, there you have it. Today we talked to Dr. Bob Harveson about cercospora and the disease triangle, and how all three points of the triangle: the environment, the host, and the pathogen all play an important role in disease prevention. Join us next time as we go into detail on some of our other projects. Be sure to follow us on twitter @TheFarmSciEd and check out our website for transcripts and other information. Have a good one!