Understanding the plant disease triangle

Have you ever been caught off guard by a disease outbreak in your farm or garden that just seemed to come out of nowhere? You aren’t alone. It only takes a few days for dormant disease to suddenly wipe out an entire crop. In fact, an estimated 20-40% of all crops are lost to pests and disease each year. The first step in managing disease is to understand what it is and what causes it.  

There are three factors that must all be present for plant disease to occur: 1. A pathogen, 2. A favorable environment and 3. A susceptible host plant. Again, each must be present, two is not enough. This is why disease can appear so rapidly. When two of these conditions are present then all it takes is the introduction of the third to cause an outbreak. And these factors can change rapidly, such as a sudden rainstorm or a pathogen blowing in from the farm next-door. 

It is important to consider and track each of these factors as part of your pest and disease management plan. Addressing these factors proactively instead of reacting to an outbreak will save time, money, stress and potentially your entire crop. Knowing these factors can even help identify nutrient or water issues that were mistaken for disease. So, what do each of these factors mean and what can we do as growers to track and actively manage them? 

1. A Pathogen

First, you need to have a pathogen to have disease. This seems obvious but there is more to it once you look a little closer. Did you know a pathogen can be present without ever causing disease? Without the other two factors present, a pathogen can remain dormant in the soil or a plant. 

Pathogens come in the form of many different microorganisms including but not limited to certain species of bacteria, fungi, nematodes and oomycetes. There are many non-pathogenic species of these organisms, with some even being beneficial, so it is important to distinguish between the two. 

They can be introduced to your plants in many ways. They can travel in the air, water and even irrigation lines. Infected soil can be blown in or carried in by water runoff. You could also get a bad batch of soil from a supplier. Other common causes of introduction include infected seeds and tissue culture. We suggest buying materials and inputs from trusted and reputable suppliers as much as possible. 

Sometimes pathogens may survive from prior seasons. They can survive inclement weather in the soil, on plant debris and on old tools.  

Some routes for pathogen entry are easier to control than others but it is best to stay aware of the risks and track them when possible. Regular scouting and testing are a terrific way to stay aware of your disease risk. It supplies the data over time to identify when and where pathogens appear. Testing can also be used to screen inbound materials. We recommend testing yourself using an on-site test. Cubed Labs offers an on-site test for botrytis, which can be used to track the presence of fungal spores or hidden infections.  

2. A Favorable Environment

The second factor is having a favorable environment. Every pathogen has a different ideal condition that allows for infection, growth and spread. Most pathogens favor wet and temperate conditions including some soil borne ones. For example, botrytis thrives at 71-77°F and 85% humidity while phytophthora prefers overwatered soils. 

Most growers already track this factor by simply checking the weather forecast every day. This simple step allows you to know when you need to be on alert for potential outbreaks. 

Other control methods are dependent on your grow type but are always done with the goal of creating unfavorable conditions. Reduce excess moisture on plants by using drip irrigation when possible. Remove weeds and debris where some pathogens can reside. Maximize air circulation by planting to allow natural airflow and by removing excess leaves or adding fans. Ensure your soil drainage is adequate and that there is no pooling water. You can even add hay or wood chips drainage areas to keep soil-borne pathogens from splashing on plants or fruits. 

3. A Susceptible Host Plant

The third factor, a susceptible host, boils down to plant and soil health. Like humans, healthy plants have a stronger immune system and can resist pests and pathogens naturally, while imbalanced nutrients can make plants susceptible. Healthy soil and the beneficial organisms within it can naturally stimulate a plant’s immune system and out-compete pathogens. 


Just like with pathogens, we recommend regular testing to keep track of soil and plant health. On-site plant and soil health tests are starting to become more available. These tests allow you to produce this data in real-time without having to wait for off-site results. Cubed Labs is currently developing N-Sight™, a testing system designed to track NPK levels as well as sugar, protein and lipids with a simple non-destructive scan. 

Some other common causes of susceptibility are physical damage and a lack of natural resistance. Breaks and cuts on stems, roots or leaves create openings for pathogens to infect a plant. We recommend regular scouting to help you identify damage and at-risk plants. Some species of plants or cultivars have a natural resistance to local pathogens. Check with your area extension office or seed provider if you need help finding which varieties of plants do better in your region. 

It takes all three factors for disease, each of which you can track and take pro-active measures against. Knowing about each is the first step in controlling them and there are many measures growers can take to manage them. We believe regular scouting and testing are key to tracking each of these factors. Check out why we think testing is so important.

Interested in learning more or want to hear what Cubed Labs is all about? Schedule some time to talk with us!

Our own Brent Nichols would be happy to help – Click Here to schedule a meeting!

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