Is it too dry for disease to develop?

In moist years, the decision to use fungicide is a no-brainer. High moisture means bigger yield, but more chance of disease spreading throughout the crop. What about applying fungicides in a dry year? It may not seem so clear, but you can realize several important benefits.

Increased water use efficiency 

A plant becomes stressed when there is a lack of moisture, which kickstarts their defense mechanisms, including premature ethylene production. This causes the plant to limit unnecessary energy draws such as the development of new buds, flowers or pods. Applying a fungicide will help a plant overcome drought and heat stress by reducing the amount of ethylene produced and increasing its water use efficiency. When a plant is more effective at using the available water, it keeps the plant from shutting down and aborting pods. 

Increased nutritional capacity 

Fungicide applications reduce moisture stress on the plant. This allows the plant to put more energy into building a larger root system, which in turn enables the uptake of moisture and vital nutrients. A fungicide helps a plant grow to its full potential, so it doesn’t dry down before it has the chance to fill seeds properly. It has also been shown to increase root biomass, which is important in dry conditions. The more robust the roots, the better they are to seek moisture and vital nutrients. 

In previous trials across several farms near Lethbridge, Alberta, some farmers claimed up to an 8 bu/ac increase in yield where they used a fungicide on peas, compared to where they did not.

In addition to general plant health benefits there is still the potential for the spread of disease in dry conditions. While it is true that most diseases require higher moisture levels, humidity and rainfall to spread through the crop canopy, they may not need as much moisture as we think, because:

• A closed canopy will have a higher humidity level even if it hasn’t rained in a few days. The small amount of dew on the plants in the morning is enough to create the perfect environment for disease.
• Some diseases such as powdery mildew will actually break down when there is high rainfall. Fusarium head blight spores can be distributed with the wind and rainfall and only requires high humidity to become activated.

*Trials conducted in 2016.