Louisiana Rice: When To Apply Fungicides During The Day?

    In the past I have written about fungicide timing based on rice growth stages, which is critical to fungicide performance. Today, let’s discuss what could be as critical – fungicide timing based on the time of day.

    The rice canopy and the environment in a rice field vary greatly between sun up and sun down. Temperature increases as the day progresses and then starts to cool as evening approaches. The canopy is normally wet in the morning and dries as the day progresses.

    Wind is normally low in the early morning and increases as the day progresses. Rainfall can occur at any time of the day. All of these conditions can affect fungicide deposition, drift, redistribution, volatility, weathering and absorption.

    Research projects have tried to determine the best time to apply a fungicide to rice.

    Studies were conducted where various fungicides were applied at 6 a.m., 8 a.m., 10 a.m., noon, 2 p.m., 4 p.m. and 6 p.m. to separate treatments. Fungicides were applied with a backpack sprayer to plots of very susceptible varieties inoculated with sheath blight at the Rice Research Station in Crowley, Louisiana.

    The fungicides used were Rovral and Benlate at boot and heading and Tilt at panicle initiation and boot. Disease development was evaluated and the plots were harvested.

    Disease control was not significantly affected by time of fungicide application. Yield performance was affected by time of spraying. However, there was no clear pattern.

    The only significant effect environment had on fungicide performance was associated with rain. During a one-fourth-inch rain between 4 p.m. and 6 p.m., fungicide treatments applied just before the rain event were washed off while fungicides applied soon after the rain landed on wet foliage and tended to roll off the plants.

    Two to four hours of drying was enough to allow the fungicide to become unaffected by rainfall in this test.

    Although this information is based on older fungicides, it does show a wide window for fungicide application during the day. More importantly, it points out the need to avoid rain fall either after or before fungicide applications.

    Normally, you do not have control of when a fungicide is applied by an aerial applicator, but avoiding rain is important to get the most out of your fungicides.

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