Growers, researchers report mixed results with soil fungicide

01/01/2012 02:00:00 AM
Tom Burfield

Serenade Soil has been touted as a “new approach for soil fungicides” by Denise Manker, vice president of global product development for Davis, Calif.-based AgraQuest Inc.

Introduced in January 2010, the product is the first soil fungicide based on its patented ingredient Bacillus subtilis (strain QST 713), the company says.

It is designed to protect potatoes, tomatoes, cucurbits and other plants from diseases, such as rhizoctonia, fusarium, pythium and Phytophthora.

But how well has Serenade Soil actually performed so far?

Growers and researchers report mixed results with the product, and most want to give the biological fungicide more time to prove itself.

Fighting common scab

Wysocki Produce Farms of Bancroft, Wis., used Serenade Soil to fight common scab on its potatoes for the past two seasons, says Gary Barten, agronomy operations manager.

“Scab costs us a lot of money,” Barten says.

The company grows fresh-market potatoes and, since scab is a visual blemish, tubers can become unmarketable if the condition gets serious.

Serenade Soil does not control scab, he says, but it suppresses it.

“If we get some suppression, it certainly pays for itself,” Barten says.

He estimates that applying Serenade Soil costs about $20 per acre, in line with the cost of similar conventional products.

Wysocki Farms also has used Blocker (PCNB) fungicide, and Barten says Serenade Soil typically is comparable.

AgraQuest says the product increases yields and plant size. Although Barten did not formally evaluate Serenade Soil on those criteria, he says he did not notice an increase in tuber yields or plant size.

Time will tell whether the company stays with Serenade Soil, but Barten says he’s leaning in that direction.

“I think Serenade will always be some part of Wysocki’s program,” he says.

Varied onion results

Bill Gasser, pest control adviser and consultant for Basin Fertilizer & Chemical Co. in Merrill, Ore., has been involved with tests of Serenade Soil on dehydrator onions for two seasons.

He noticed good results in 2010.

But preliminary indications as digging began in mid-October this season showed no difference on white rot or yields.

“The [return on investment] was favorable,” he says about last year’s trials. He saw a 15 percent increase in yields.

This year, he tried two different rates but did not see any difference in yields or incidence of white rot. But white rot pressure was low this season.

The product did serve as a good tool to fight white rot and rhizoctonia disease in potatoes last season, Gasser says. He plans to try it again with onions next year, perhaps applying it at a higher rate.

“I’m not willing to give up,” he says.

Post-harvest tests

Willie Kirk, a plant pathologist at Michigan State University, has conducted trials with Serenade Soil in post-harvest potatoes. Kirk inoculated tubers with four pathogens: late blight, pink rot, dry rot and pythium leak.

While the untreated check had a 22 percent incidence of late blight disease, the crop treated with Serenade Soil had only a 2 percent to 5 percent disease incidence.

When tubers were inoculated with pythium leak, the untreated check had 40 percent incidence. Of the diseased potatoes, the fungicide Phostrol provided 17 percent suppression and Serenade 20 percent.

With a fairly light incidence of pink rot, Serenade Soil offered about the same control as Phostrol.

In a test involving dry rot, 56 percent of untreated potatoes had the disease while 50 percent of the Serenade Soil-treated were infected. That compared with about 10 percent infection when the tubers were treated with other conventional products.

AgraQuest’s Manker says tests involving inoculated potatoes can be misleading, since extremely high, artificially induced disease pressure can be difficult for any biological fungicide to overcome.

Growers typically contend with low to moderate disease pressure, she says.

“In that situation, the product works really well,” she says. “It’s been a very successful product for us.”

Kirk’s recommendation for growers: Try Serenade Soil on some acreage to see if it works for you.

Testing white mold

At the University of Wisconsin, plant pathologist Amanda Gevens tested Serenade Soil to see how it affected white mold on snap beans.

Last year, Serenade Soil “showed some promise numerically,” but there was no significant difference in controlling white mold.

Gevens hoped to try the test again this year, but conditions weren’t favorable for white mold.

“The story in snap bean white mold is that there’s some promise, and we’d like to further evaluate the use of Serenade Soil as a soil-incorporated treatment,” she says.

She saw conflicting results in tests involving potatoes.

Last year, “We did have significantly better common scab control with Serenade Soil than we had in the untreated control and when compared to a few of the other conventional treatments,” she says.

Things were different this year.

“We actually had much greater disease in our Serenade treatments than we saw in the untreated control,” she says.

The conflicting results could be the result of a change in the product’s performance or simply the idiosyncrasies of biological fungicides.

“Conditions which may or may not favor disease can also favor or detract from the efficacy of the biological control,” Gevens says.

Because of the favorable results of the 2010 tests, Gevens plans to evaluate Serenade Soil again this coming season.

AgraQuest continues to have big plans for Serenade Soil.

“We’re going to be expanding our label as we gather enough data to be able to properly guide the growers on rates,” Manker says.


The nuts and bolts behind Serenade Soil


Serenade Soil is a biological fungicide that builds a disease protection zone around the seed, says its manufacturer, Davis, Calif.- based AgraQuest Inc. as the seedling grows, the beneficial bacteria in the product continue to grow, attaching themselves to the plant roots, expanding the disease-protection zone.

The results are higher-yielding fields and better quality fruits and vegetables, the company says.

Serenade Soil has a one-two punch that traditional chemical fungicides lack, says Denise Manker, vice president of global product development for AgraQuest.

It has the immediate effect of drenching the soil. Then the bacteria colonize the plant roots as the plant continues to grow.

It also has a multi-site mode of action that can fight pathogens resistant to other fungicides, she says.

The product can be applied in-furrow at planting, drenched in-furrow with seed pieces, put in with fertilizers or run through chemigation.

The goal, Manker says, is to “get it to the zone where the roots are.”

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