Potato Production And The Environmental Component Of Plant Disease

As a plant pathologist, one of the first things I was taught was a fundamental concept called the “Disease Triangle.” This model contains the key elements required for a plant disease to occur and includes three components:

• You must have a susceptible host;
• You must have a virulent pathogen; and
• These two must come together under suitable environmental conditions.

Throughout my career as a potato specialist, the importance of this basic relationship has been demonstrated time and time again.

Each of these three components can be manipulated to some extent by producers. We can influence the host component by our choice of variety, for instance. On the pathogen side, a great deal of time and money is spent on seed certification in an effort to eliminate or greatly reduce the presence of seed-borne pathogens.

These first two components are certainly sig-nificant in their own right but for this discussion, I thought I’d go into some-what greater detail on the all-important environmental component.

Know The Disease Environment
Knowledge about the environmental conditions required for a disease to occur can be exploited to our advantage. In many of the potato-producing regions of North America, growers and their advisors know that some diseases, like late blight, will almost certainly show up when a certain set of environmental conditions occur.

Studies on these conditions have allowed the development of predictive models (such as Blitecast) that indicate the need for fungicide applications to begin even if no disease has been observed as of yet. Such models can also provide information on conditions wherein disease pressures are low and fungicide applications can be safely delayed.

But what happens when the climate within a given area begins to warm up? Not only would some pathogens start causing problems earlier in the season, some of them would be able to overwinter in areas where they couldn’t before. The ability to survive because of milder winter conditions means that we could see the range of some pathogens extend northward. Keep in mind that plant diseases wouldn’t be the only things affected; warmer conditions could well have similar detrimental effects on other serious pests like insects and nematodes.

Weird Weather
Lately, we have been seeing some very unsettled weather patterns throughout the continent. I’m going to sidestep any discussion about climate change and what might be causing it, but some of the changes in weather that we are experiencing appear to be real, and our agricultural industries must take this factor into account as we move forward.

Here’s an example. Out here in Idaho last season, we experienced several weeks of greater than average rainfall during August. As a result, there were some regions in the Southeastern part of the state that reported potato
late blight. While this occurrence would be routine and easily handled in many parts of the country, the inexperienced growers in the affected area responded with fungicide pro-grams, but many applied too little, too late, and some were not able to get the disease under control.

Be Ready For This Season
We could be facing similar problems in other parts of the country with other pathogens and other pests. We’re still trying to come to grips with the potato psyllid/zebra chip issue in the Southern and Western U.S.

Was there some subtle environmental change that was responsible for the appearance of this new problem? I don’t want to be a purveyor of doom and gloom but, with the unsettled climate we are experiencing throughout the country, we need to keep our eyes open wide and our ears firmly to the ground. Those diseases and other pests that your production area are not supposed to have could wind up surprising you, and not in a good way.