2024 has been a challenging year for lawn care, especially in regions like the Northeast where cool season grasses are abundant (cool season grasses are more susceptible to Pythium). If your lawn has been struggling despite your best efforts, you are not alone. This year’s weather conditions have been a perfect storm for Pythium disease, causing it to be an issue across many lawns in Connecticut.
The 150 Rule of Pythium Disease
Most simply put - Pythium is a fungus that is a soil-borne organism. It’s out there lurking in so many of our lawns, just waiting for the perfect moment for it’s spores to flare up and spread when this pathogen is present.
Two main factors that contribute to a Pythium disease flare up are heat and humidity. This is where the “150 Rule" comes into play.
According to the 150 rule - pythium is very likely to flare up (when the pathogen is already present) when, for three consecutive days, the combined daytime temperature plus humidity levels exceed 150.
Another easy way to follow this rule is to combine daytime and nighttime temperatures. When this exceeds 150 degrees, we are in prime pythium blight disease territory.
Here are some examples of the 150 rule with pythium disease:
Daytime high of 90 degrees F plus nighttime low of 60 degrees F
Daytime high of 80 degrees F plus humidity levels of 70%
65% humidity plus daytime highs of 85 degrees F
In Hartford, CT in 2024, around 60 of 75 days between June 1st and August 15 have met this criteria.
This means that for the majority of the summer, we have had perfect conditions for this aggressive lawn disease to thrive and spread. Between June - August in Connecticut we can typically see an average humidity level of 70%. We have had excessive heat in 2024 which has made this year especially tough for lawn diseases.
Why Are We Seeing So Much Pythium This Year?
The 2024 summer has been unusually hot and humid, which are the exact conditions that Pythium thrives in. When these conditions persist, the spore counts can explode.
This year’s weather patterns have created what is known as the "Disease Triangle," where the combination of a susceptible host (your grass), a pathogen (Pythium fungi present in the soil), and the environment (hot, humid weather) has triggered an increase in lawn diseases.
Why Young Lawns Are More Susceptible to Pythium
Young lawns, in particular, are more susceptible to weeds, diseases, insect damage…and pythium is no exception to this. This is because they lack the established root systems and resilience that older, more mature lawns have.
What Can You Do About Pythium?
If you’re noticing signs of lawn stress, it’s crucial to determine whether it’s drought stress or Pythium. Many people think their lawn is suffering from drought and try to compensate by watering more. However, if the issue is Pythium, additional watering can make this problem worse.
In going back to the Disease Triangle - we need 3 things for a lawn disease to be present. Of these 3 criteria, we need to control what we can control.
Host (grass): We can control this by planting A-list certified grasses that are tested to see which best withstand pressures like drought and disease.
Pathogen (soil-borne pythium)
Environment (hot/humid)
Stop Watering Your Lawn: If you suspect Pythium, halt watering immediately. Pythium thrives in wet conditions, so continued watering can accelerate its spread.
Ensure proper drainage. Avoid water logged root zones. Manage thatch, manage compacted soil and manage shade to make sure you have no pooling areas in your lawn.
Call Your Lawn Care Company: Reach out to a professional lawn care company to diagnose the problem. They can determine whether it’s Pythium or another issue and apply the appropriate fungicide to stop the spread.
The summer of 2024 has created the perfect conditions for Pythium to flourish, particularly in areas like Hartford, CT. By understanding the 150 Rule and the environmental factors that contribute to this disease, you can take proactive steps to protect your lawn. Remember, early detection and proper management are key to minimizing the impact of Pythium on your lawn. If you’re unsure about what to do, don’t hesitate to contact a lawn care professional for expert advice.