agriculture, IPM, vegetables

And the results are in…from Year 1. What do biofungicides add to vegetable disease management Part 3

Cucurbit powdery mildew on a winter squash leaf.
One of our goals for this project was to understand what biofungicides might add to a cucurbit powdery mildew management program.

Introduction

In 2018 we conducted field trials using biofungicides in cucurbit powdery mildew and snap bean white mold management programs. Hopefully you’ve read part 1 and part 2 of this biofungicide story. If not, now might be a good time.

Part 1 will give you more details about the trial design. We wanted to know whether adding biofungicides would improve disease control, plant health, or yield. For cucurbit powdery mildew, we were adding one of three different biofungicides to a conventional chemical spray program. We also included a treatment that was all OMRI-listed (organic) products. For white mold on snap beans, we were curious about using an in-season biofungicide (Double Nickel, Bacillus amyloliquefaciens strain D747) in combination with a pre-season biofungicide (Contans, Paraconiothyrium minitans strain CON/M/91-08). In 2018, our white mold treatments were just Double Nickel and Cueva (an OMRI-listed copper). In 2019, we’ll add the pre-season Contans treatment.

Part 2 explains more about the modes of action of the five biofungicides we are looking at. The post also includes practical information about how to use these biofungicides to maximize their efficacy – compatibility with other products, best way to store them, when to apply them, etc.

Now it’s time to talk about what we learned from this first year (of a two-year project).

The bottom line

We don’t want to keep you in suspense, so here’s a quick summary of what we learned. Fortunately for the eastern NY grower who graciously allowed us to run the trial on his farm (but unfortunately for us), the snap bean field had very little white mold in 2018. Even the plots that were not sprayed with Double Nickel or Cueva had almost no disease. So we weren’t surprised when there were no differences in disease, plant health, or yield among the white mold treatments. Results from Sarah Pethybridge’s efficacy trials with OMRI-approved products for white mold are available online.

A healthy field of snap bean plants.
Our snap bean trial in eastern NY in 2018 had very little white mold. (Photo credit: Crystal Stewart)

Cucurbit powdery mildew was a bit more severe than white mold (low pressure in eastern NY, moderate pressure in western NY and on Long Island), but we were not able to detect statistically significant benefits from adding biofungicides to a conventional spray program. Disease severity, plant health (as measured by NDVI), yield, and fruit quality (Brix) were the same whether you used a conventional spray program, or a conventional spray program plus a biofungicide. We didn’t measure significant differences in yield among any of the treatments at any of the three sites.

The conventional powdery mildew spray program alone, or when combined with LifeGard, Regalia, or Serifel significantly reduced disease compared to no treatment for cucurbit powdery mildew. Adding any of the biofungicides to the conventional spray program did not improve control compared to using only the conventional sprays. The organic (OMRI-listed products) treatment was not significantly different from either no sprays at all, or the conventional spray program.
Severity of powdery mildew on the upper sides of the leaves in the Western NY trial. Here, disease severity is quantified using the area under the disease progress curve (AUDPC). This number summarizes disease severity from multiple dates, and the larger the number, the worse the disease. If two treatments share the same letter, the average disease in those treatments is not significantly different. The error bars give you an idea of how much variability there was in each treatment.

NDVI results

NDVI (normalized difference vegetation index) values did not detect cucurbit powdery mildew early. (Since there was so little white mold, we couldn’t test NDVI for early detection.) There was some inconsistent correlation between NDVI readings and disease, yield, and Brix in winter squash. In WNY we used both a handheld GreenSeeker and a gator-mounted Crop Circle to measure NDVI. Both devices had similar results. Based on this first year of testing with these two devices, NDVI measurements were not useful as an early indicator of cucurbit powdery mildew.

In addition,  NDVI measurements did not  detect subtle differences in plant health among treatments. At only one of our three sites (Long Island) were there any significant differences in NDVI among treatments. This was only on the last two rating dates in the season, when powdery mildew was visibly more severe in the non-treated control than the conventional fungicide treatments.

On the last two rating dates of the season (August 31 and September 17), NDVI values were significantly higher in the conventional powdery mildew spray program treatment and all three of the conventional + biofungicide treatments, compared to the plots that were not treated for powdery mildew. Adding the biofungicides did not significantly improve NDVI, compared to using only conventional products.
Normalized difference vegetation index (NDVI) measured on winter squash in the Long Island trial on three dates at the end of the season. NDVI values closer to 1 indicate more healthy, green foliage. If two treatments have the same a letter on the same date, the average NDVI readings on that date were not different between the two treatments. Data from August 31 are labeled with uppercase, while data from September 17 are labeled with lowercase letters. There were no differences among any treatments on August 24. The error bars give you an idea of how much variability there was in each treatment. We couldn’t do statistics on the organic treatment because too many plants were killed by Phytophthora blight in the plots that received this treatment.

Some caveats

The non-treated control (received no powdery mildew fungicide) was often not significantly different from the conventional fungicide control (our best management program). We know that controlling powdery mildew on cucurbits is important, so if we don’t detect a significant difference between the non-treated control and the treatment that should have provided the best control, it is then hard to draw further conclusions from the data.

We didn’t measure statistically significant differences in marketable yield among any of the treatments at any of the sites. Data for eastern NY are shown in this graph.
We didn’t detect statistically significant differences in marketable yield among any of the treatments in any of the trials. Here are the data from eastern NY. Notice that all six bars are labeled with the letter “a”. As with previous graphs, the error bars give you an idea of how much variability there was across the different plots in each treatment.

When disease pressure is low (as it was in Eastern NY), we would expect not to see many differences between treatments. Similarly, if the conventional fungicide program provided excellent disease control (as it did on Long Island), it would be hard to detect an improvement in control from adding a biofungicide. Another challenge we dealt with in the Long Island trial was Phytophthora blight. By the end of the season, we had lost two of the four plots receiving the organic treatment to this disease. This limited our ability to statistically analyze the biofungicide data. On Long Island, the organic spray program initially performed well – as seen on August 31  – comparable to the conventional treatments. But by the final assessment on September 17, the organic program was no longer as effective. This was not surprising since it was 10 days after the last application. Suffoil-X was the final organic product applied, and it has little residual activity.

In the Long Island trial, there was very little disease on August 16 or 24. On August 31, disease had increased in the non-treated control, but the organic treatment was still suppressing disease well. Control in the organic treatment had declined by September 17, but this was 10 days after the last spray was applied.
Average severity of powdery mildew on the upper surface of leaves on the last four assessment dates in the 2018 Long Island trial. All of the treatments (except the non-treated control) suppressed powdery mildew well through August 31. Control in the organic treatment had declined by September 17, but this was 10 days after the last spray was applied.

In WNY, we had an epic aphid outbreak. An entomologist colleague identified them as probably melon aphids, and also that 2018 was generally a bad year for aphids. It’s also possible that while trying to control cucumber beetles earlier in the season, we killed some aphid natural enemies, contributing to an aphid outbreak later in the season. I know cucumber beetles are tough, but if you can manage them without decimating your local natural enemies, you’ll be doing yourself a favor!

The underside of a squash leaf covered with aphids; an acorn squash fruit covered with shiny honeydew from aphids; a close-up picture of an adult aphid and some young aphids.
The severe aphid outbreak in the western NY trial may have made it more difficult to detect differences among treatments. In late August, some of the leaves were covered with aphids (A), and many fruit were covered with honeydew (B). Getting a close look at the aphids is essential for correct identification (C).

We deliberately used a very intensive spray program, starting our biofungicide applications early, and continuing to apply them as we added conventional fungicides later in the season. This was an expensive powdery mildew management program. But, in this first year of the project, we didn’t want to be left wondering if a lack of differences was due to underapplication of the biofungicides.

If you want to see more of the data we collected from the cucurbit powdery mildew trial, you can find it in the Proceedings from the 2019 Empire State Producers Expo.

What does this all mean?

First, this is only the first year of our project and one year of data. It’s a start, but we’ll hopefully learn more in a second year. Since we didn’t measure a significant improvement in yield, we didn’t see evidence that adding biofungicides to a full chemical spray program for powdery mildew justified the cost. The relative costs of the treatments we used are listed in the table below, and the approximate per acre costs of each product are in the Proceedings from the 2019 Empire State Producers Expo. Replacing a chemical spray or two with a biofungicide could be a more economical option. That’s something we’re planning to look at in 2019.

Treatment
Date Non-treated Conventional Conventional + LifeGard Conventional + Regalia Conventional + Serifel Organic
7/19/18 – LifeGard Regalia Serifel LifeGard
7/27/18 – LifeGard Regalia Serifel LifeGard
8/3/18 – Vivando LifeGard + Vivando Regalia + Vivando Serifel + Vivando MilStop
8/10/18 – Quintec LifeGard + Quintec Regalia + Quintec Serifel + Quintec Serifel
8/17/18 – Luna Experience LifeGard + Luna Regalia + Luna Serifel + Luna SuffoilX
8/24/18 – Vivando LifeGard + Vivando Regalia + Vivando Serifel + Vivando MilStop
8/31/18 – Quintec LifeGard + Quintec Regalia + Quintec Serifel + Quintec Serifel
9/7/18 – Luna Experience LifeGard + Luna Regalia + Luna Serifel + Luna SuffoilX
Total cost (per A) – $228.28 $343.32 $536.28 $696.28 $257.76
Cost increase vs. conventional (per A) – $  – $115.04 $308.00 $468.00 $29.48

Based on results from this year, we can’t yet recommend that you run out and buy a handheld NDVI sensor for early detection of cucurbit powdery mildew. We’ll collect NDVI data again in 2019, and let you know what we learn. Although our results from the field trials were somewhat inconclusive in this first year, we’re hopeful that the information we’ve compiled about how these biofungicides work and how to use them will be useful. If you’re thinking of using Contans, Double Nickel, LifeGard, Regalia, or Serifel in 2019, first take a look at these fact sheets related to our white mold and powdery mildew trials. And if you have used biofungicides, we’d be interested in hearing about it; click here to send an e-mail.

This post was written by Amara Dunn (NYS IPM), Elizabeth Buck (Cornell Vegetable Program), Meg McGrath and Sarah Pethybridge (both Plant Pathology & Plant-Microbe Biology, School of Integrative Plant Science, Cornell University), Crystal Stewart (Eastern NY Commercial Horticulture Program), and Darcy Telenko (Department of Botany & Plant Pathology, Purdue University). Thank you to the New York Farm Viability Institute for funding.