Why You Can Stick with Overhead Irrigation to Prevent Powdery Mildew

Powdery mildew is a common name for hundreds of different related but different mildews that each target just a few different plants. All of these mildews form a similar white or gray coating on infected leaves and stems, and they all drain nutrients from the plant and block the process of photosynthesis.

It has been common agricultural advice for decades to avoid overhead irrigation techniques in order to control powdery mildew in crops that are sensitive to it. However, it's not actually necessary to switch away from this effective irrigation technique. Learn the facts before making a big investment in a whole new irrigation system.

It’s Hard to Control Mildew and Moisture

As with practically every form of mildew, all powdery mildew diseases require a relatively high humidity level to actively grow and release spores to spread. Overhead watering of any kind, including natural rainfall, does increase the humidity around a plant's leaves and stems for a short amount of time. This has led to both gardening and agricultural sources recommending that only drip and buried irrigation should be used for plants in danger of powdery mildew development.

Yet it's not as simple as keeping moisture away from the leaves. First, you can't control overhead watering that comes from rain unless you're growing in enclosed greenhouses or field hoop houses. Second, moisture from overhead watering evaporates surprisingly quick in an open field, which results in a drop to a safer humidity level soon after watering is complete. Third, applying moisture from the top down during the right part of the day may actually help prevent powdery mildew from growing and spreading rather than encourage it.

Humidity Fluctuations

It's not just high humidity alone responsible for powdery mildew growth. The fungi responsible for plant damage react to humidity cycles rather than just spikes in moisture levels. The disease grows best when there's a lot of evening moisture, such as dew fall on the leaves, and a drying cycle during the day with low humidity levels.

Keeping moisture levels higher as temperatures rise in the morning actually prevents the mildew from growing. This is easily accomplished with overhead irrigation during the morning hours, which also allows noon and afternoon sun and breezes to thoroughly dry out lingering moisture before the sun sets and temperatures drop again.

Surface Water

Aside from affecting the humidity cycle that triggers mildew growth, overhead watering creates a coating of moisture on the surface of the leaf. If it was moisture alone responsible for triggering powdery mildew growth or spread, then growers would see an immediate increase in visible mildew after each watering. Instead, testing shows that a direct coating of moisture on existing mildew colonies prevents spore germination.

Spores usually form on humid nights, so direct water application is of limited use as a control method, but at the very least you can trust that overhead watering during the morning isn't responsible for spreading the disease.

Overhead Irrigation

Since overhead irrigation doesn't automatically cause or help spread powdery mildew, you're free to enjoy its many benefits:

Easy application of chemicals, including fungicides for powdery mildew control, through chemigation
High uniformity of irrigation coverage, resulting in less wasted water and fewer crops lost to stress
Reduced labor costs for maintenance compared to drip and buried irrigation, with maintenance requirements varying between the types of overhead equipment
Easier expansion of the system as establish and plant new fields, including pumps to increase water pressure far from the well
Limited soil erosion, which is often caused by drip or buried irrigation.

If you're ready to switch back to time-tested and reliable overhead irrigation, we've got everything you need here at Waterford Irrigation Supply Inc.

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