Spraying Before Daybreak

Bigger droplets, more coverage, longer efficacy means
improved control.

By Amanda Huber

  
Trying to control disease in a peanut plant is a challenge. The plant’s structure makes it a difficult target to cover effectively. For leafspot, the sprayer must cover the entire canopy; limb rot affects the limbs; white mold can be on the pegs, pods and crown; and CBR affects the roots.

To control disease more effectively may require taking advantage of what the plant does naturally.

“When you look at the peanut canopy during the day, it has dense, overlapping foliage,” says Tim Brennemen, University of Georgia (UGA) research pathologist. “It is designed to spread out, capture all the sunlight it can to turn into sugar, and it is really good at doing that.”

Brennemen says, looking at the peanut plant at night, you can see that the leaves fold up and, in many places, you can see down to the soil.

“It’s pretty clear that this type of canopy would be much easier to spray through and penetrate than the canopy during the daytime,” he says. The idea for spraying at night came from a visit to growers in Nicaragua, which Brennemen thought was worth investigating here. This is a good example of the benefits of international information exchange.

Bob Kemerait, UGA Extension pathologist, says at times it is worth exploring creative strategies to manage disease better, and night spraying may be one of those creative strategies.

“The problem in controlling white mold and Rhizoctonia limb rot is getting that fungicide down into the canopy. By spraying at night, you are reaching the target with the product.”

Bigger Droplets, More Coverage
Looking at it from a mechanism standpoint, Brennemen used spray cards to see what kind of coverage he could get with day versus night.

“The canopy, which is good at intercepting sunlight, is also very good at intercepting your fungicide. If you spray during the daytime, that’s where the bulk of your chemical is ending up. Spraying at night, we had more droplets get down through the canopy and reach that bottom part of the plant.”

Brennemen says the droplets were also consistently bigger at night, whereas during the day, the finer spray droplets were more subject to evaporation.

“When you looked at the total overall coverage of the plant surface, it was much better when spraying at night. This is especially true the later in the season you get, when the peanut plant gets bigger and the canopy gets deeper.”

Slower Fungicide Breakdown
Another thing Brennemen and his team looked at was longevity of the fungicide. Once you get the fungicide out there on the plant, how long does it last? How long is it effective?

“Clearly, we found that on the leaves that are high up on the canopy and exposed to all that sunlight and UV rays, the fungicide is broken down faster than it is on leaves towards the bottom of the canopy,” he says. “Also, you get better distribution of the fungicide on the moist foliage.

“There are several biological things that come into play.”

Improved White Mold Control
Brennemen conducted a white mold test with applications at evening, morning and during the day, using Headline, Abound and Provost. The Bravo check plot had 35 percent white mold.

“Headline sprayed during the day had about 30 percent white mold,” he says. “Sprayed in the evening, we had better control, and sprayed in the morning, before sun up, it gave significantly better control. In fact, it was as good as some of our best materials.”

Brennemen says Abound and Provost had similar response, giving significantly better control when sprayed before daybreak. However, Bravo, a straight protectant fungicide, needs to be sprayed during the day.

“Last year, we reported spectacular results and huge increases where we had sprayed at night for controlling white mold,” Kemerait says. “This year, in 2008, the results were not as dramatic as in 2007, but still positive. In one trial, we had an increase in yield of 1,100 pounds per acre where we sprayed at night.”

Early Morning Best
Overall, the researchers agree that morning sprays have tended to show better yield than evening sprays.

“It’s not something that is automatically going to cause a yield increase,” Brennemen says. “But in some problem fields, where you are not getting the level of control that you could, it can make a difference.

“With night sprays, there is clearly a potential to improve white mold control and increase yield. The more disease pressure you have, the more potential there is for that difference.”

Brennemen says his research has shown that the very early morning time is the best time to spray.

“I think the wet leaves and moisture that helps to distribute the fungicide is part of the reason for this.”

He also says spraying at night may have more effect with dryland peanuts than with irrigated peanuts.

Brennemen is continuing to look at other diseases, including the potential night spraying may have for improving Cylindrocladium Black Rot control.

PG