GIBBON, Minn. – For years, farmers have been testing and trying different foliar products. While foliar fungicides have a proven track record, the results from foliar applied nutrients tend to have a great deal of variation. There is even some limited variation with the fungicides. Research from Beck’s suggests that the time of day could be causing some of that variation.
“We started the study about three years ago, it was actually by accident, we messed up a study and started investigating the time of day to spray certain products,” said Jim Schwartz, director of Practical Farm Research and agronomy at Beck’s, during a recent phone interview. “It seemed like we were getting some response to a specific time during the day to spray.”
The research Beck’s is doing across multiple sites in six states is focusing on time of day of applications of fungicides and foliar nutrition.
“When we started digging into this, we found there are two ways that products can get into the leaf, one is through the pores on the cuticle,” said Schwartz. “And the other way is through the stomates.”
Cuticular pores have polarity and carry a negative charge. Any products being sprayed on the leaf with a negative charge will have a harder time entering through those pores.
“The leaf surface has a waxy layer and that wax layer is designed to keep stuff out,” he said. “So, the other way then is these stomates.”
New research is indicating that the guard cells that open and close the stomates are lined with pores. It is through these pores that much of the foliar applied products enter the leaf.
“Why that is important as it relates to time of day is, if you think about it, guard cells typically are more open in the cool of the day, in the morning or the evening,” he said. “As the heat of the day comes, in order to prevent moisture loss, they close.”
So, it makes sense that for products that need to get inside the leaf, whether or not the guard cells and the stomates are open will affect how well the product works. That means there is a benefit to spraying those products in either the early morning or late evening.
Many fungicides, for example, are considered locally systemic. They enter one side of the leaf and can move to the other side. They really cannot move throughout the whole plant.
“Then, of course foliar nutrition products as well, we want to get them in the leaf to get them into the plant,” he said. “Herbicides, it doesn't take much, especially those that are fully systemic.”
A small amount of a systemic herbicide can easily enter the leaf and move throughout the entire plant. Herbicides are still best sprayed in the heat of the day.
The other factor to consider as it relates to the time of day is the survivability of the droplets.
“With a fungicide, it can be any droplet size, but typically we crank up our pressures when we spray fungicides to 40-50 psi, to try to get more penetration in the canopy,” he said. “When we do that, we get more 70-100-micron droplet size.”
With higher temperatures and more sun, those small droplets are at greater risk of evaporating before they ever touch the leaf. They can evaporate very quickly.
“The other side of that is as humidity is higher, then droplets survive longer in the environment,” he said. “So again, more pressure to spray on the canopy gives us more droplets, but we also know that high temperatures and low humidity limit the lifetime of that droplet.”
As part of Beck’s Practical Farm Research program, they’ve tested time of day of application of foliar nutrition products across multiple locations for the past three years.
“At each location, we are seeing anywhere from a 4-9-bushel increase by spraying foliar nutrition products in the morning,” he said. “We still see yield increases in the afternoon, but they are muted, they are 2-3 bushels and then the curve goes back up again in the evening, not as much as in the morning.”
Last year was the first year they tested the theory with fungicides and the results were similar.
“In beans, it was a $ 21 positive return on investment to spray in the morning,” he said. “And for corn, it was $14.”
Keep in mind, there is no additional expenses associated with this. It does not cost the grower any more money to spray in the morning versus the afternoon.
“We are not telling guys, oh you have to rush out and change everything the way you do it,” said Schwartz. “But we are saying, if you have a choice, if you have the choice to spray a fungicide or a foliar nutrition product in the morning, give it a shot.”