Tag Archives: disease

What do biofungicides add to vegetable disease management? Part 1 – Introducing the project

butternut squash plants grown on a black plastic-covered raised bed
This summer we compared three biofungicides added to a conventional cucurbit powdery mildew management program in field trials conducted in western and eastern NY and on Long Island. Photo credit: Caitlin Vore, Cornell Vegetable Program

What we’re doing

This summer I have been working with great colleagues (Elizabeth Buck, Dr. Julie Kikkert, Dr. Margaret McGrath, Jud Reid, and Crystal Stewart) on a project funded by the New York Farm Viability Institute looking at the use of biofungicides (Remember what biofungicides are?) in vegetable disease management. Dr. Darcy Telenko (formerly of the Cornell Vegetable Program) helped plan the project before starting her new position at Purdue University, and Dr. Sarah Pethybridge has provided valuable advice based on her extensive work with white mold (including control with biofungicides). BASF, Bayer, BioWorks, Certis, Dow, and Marrone BioInnovations provided product for the field trials.

The project has two goals:

  1. Quantify what biofungicides add to management of cucurbit powdery mildew and white mold in terms of…
    – disease control
    – yield
    – plant health
    – economic value (comparing yield gains to fungicide costs)
  2. Evaluate the utility of NDVI (normalized difference vegetation index) as a measure of plant health and disease detection in fresh vegetables

Why this project?

For both diseases (cucurbit powdery mildew and white mold), we’re considering biofungicides used with other pest management – other biofungicides, conventional chemical fungicides, and/or cultural practices. Biofungicides are not expected to be silver bullets, and they work best when used in an IPM strategy. But when deciding whether or how to use them in your operation, it’s good to know what value you’re getting for the extra costs of purchasing and applying the products. This summer we ran trials in three major vegetable-producing regions of the state: western New York, eastern NY, and on Long Island.

Biofungicides for cucurbit powdery mildew

cucurbit powdery mildew on the upper side of a squash leaf
Cucurbit powdery mildew looks like a dusting of powdered sugar on the cucurbit leaf. These powdery spots start on the underside of the leaf, and then develop on the upper surface of the leaf, so excellent spray coverage is important. Photo credit: Amara Dunn, NYS IPM

For combatting cucurbit powdery mildew, we’re comparing three biofungicides: LifeGard (Bacillus mycoides isolate J), Regalia (extract from the giant knotweed plant Reynoutria sachalinensis), and Serifel (Bacillus amyloliquefaciens MBI 600). All three were applied weekly starting when the plants were small. Then, when the first signs of powdery mildew showed up, we started a rotation of conventional fungicides (Vivando, Quintec, and Luna Experience). These three treatments plus a rotation of all-organic fungicides (LifeGard, MilStop, Serifel, and a mineral oil) are being compared to two control treatments: the conventional fungicides alone, and plants that received no treatment for powdery mildew. We ran the trials on a variety of bushing acorn squash (‘Honey Bear’) that has intermediate resistance to powdery mildew.

Biofungicides for white mold

bean pod half rotted by white mold fungus
Most vegetable crops are susceptible to white mold, with legumes being among the most vulnerable. The name comes from the dense white “tufts” that the fungus forms. These develop into dark, hard sclerotia that can survive for years in the soil. Photo credit: Amara Dunn, NYS IPM

In the white mold trial, we’re looking at Double Nickel (Bacillus amyloliquefaciens strain D747) alone or in combination with Contans (Paraconiothyrium minitans strain CON/M/91-08; formerly Coniothyrium minitans). Next year we’ll look at these biofungicides in combination with reduced tillage at one site. Reduced tillage is another IPM strategy for white mold. The active ingredient in Contans is a fungus that eats the resting structures (sclerotia) of the fungus that causes the disease white mold. Because of this, it needs time to work, and is applied either in fall or spring. The goal is to reduce the number of sclerotia present in the next crop. Next year we’ll collect data on whether application of Contans reduced disease. In the meantime, during the 2018 growing season treatments we tested were Double Nickel, Cueva (an OMRI-approved copper) and no treatment for white mold on snap bean. Previous research by the EVADE Lab at Cornell AgriTech at The New York State Agricultural Experiment Station, Geneva, New York, has shown that Double Nickel is a promising biofungicide for white mold.

What is NDVI, anyway?

In a nutshell, the “normalized difference vegetation index” (NDVI) is a way to quantify how much healthy, green foliage is present. The device we used emits different types (wavelengths) of light (red and near infrared), and measures how much of each type of light is reflected back from the leaves of the plant. Leaves that are dark green and healthy reflect more infrared light and absorb a lot of red light. Less healthy leaves reflect less infrared light. A NDVI value closer to 1 indicates healthier plants. A NDVI value closer to 0 indicates less healthy plants (or more bare ground).

GreenSeeker device over a dark green (healthy) cucurbit plant and a light green (less healthy) cucurbit plant. Arrows show that red and infrared light are reflected differently from these two plants. NDVI values closer to 1 indicate a lot of healthy green leaves. NDVI values closer to 0 indicate less healthy (or fewer) leaves.
NDVI (normalized difference vegetation index) quantifies the amount of dark green foliage based on how much light of different wavelengths is reflected. It is used in some crops to decide when to apply fertilizer, or to help detect below-ground pests. Photo credit: Amara Dunn, NYS IPM

NDVI and similar indices are already used in other crops and in other places to help growers make decisions about when to fertilize, or to help detect parts of a field where a pest may be present. So far in NY, NDVI is not being widely used by fresh market vegetable growers for disease detection. Collecting NDVI data from this project will do two things:

  1. Help us quantify the health of plants. Even though NDVI is not a measure of disease, we would expect to see more healthy foliage if biofungicides are contributing to disease control.
  2. Provide some preliminary data to help us determine whether NDVI measurements could be useful to NY fresh vegetable growers.
people walking through a winter squash field
Growers and industry reps had a chance to visit the 2018 cucurbit powdery mildew field trials shortly before they were harvested. Photo credit: Amara Dunn, NYS IPM

Field meetings were held at each powdery mildew trial location so that local growers could see the trials and hear about the project. We’re currently wrapping up data analysis from the 2018 field season. You’ll be able to learn about results from the first year of this two-year project at winter meetings around NY, in extension newsletters, and here on this blog. Also, stay tuned for Part 2 of this post with details about how these biofungicides work (modes of action), and how to use them most effectively.

This post was written by Amara Dunn (NYS IPM), Sarah Pethybridge (Plant Pathology & Plant-Microbe Biology, School of Integrative Plant Science, Cornell University), and Darcy Telenko (Department of Botany & Plant Pathology, Purdue University).

But does it work? Efficacy of biological control

yellow sticky card for monitoring insect pests in a greenhouse
Biocontrol should be preventative. This yellow sticky card lets you monitor which pests are present and when so that the correct biocontrol (or other management tool) can be used at the right time. It will also help you assess whether your management strategy is working.

If you are thinking about trying biological control, of course you want to know if it is effective. The short answer is, “Yes!” But of course it depends on which biocontrol organism you want to use (and how), which pest you want to manage, and where.

First, you should ask yourself a question: What do I hope to achieve? Some great reasons to use biocontrol for pest management include:

  • Protecting the environment and human health by using more environmentally-friendly pest management strategies
  • Reducing the number of chemical pesticide applications to a crop
  • Preventing (or dealing with) pesticide resistance
  • Meeting a need for a short REI (re-entry interval) or PHI (pre-harvest interval) on the crop
  • Biocontrols are the most effective (and cost-effective) management strategy (definitely true for some pests and settings!)

Second, in what context are you using biocontrol? Biocontrol is best used within a larger integrated pest management strategy. Are you using good sanitation and cultural practices (e.g., adequate but not excessive nutrition and water) that promote healthy plants? Are you regularly checking your plants so that you will notice pests when they are still infrequent (scouting)?

peppers in flooded field
Biocontrol should be used as part of an IPM plan. The excess rain and poorly-drained soil in this field make it unlikely that a biocontrol will be able to protect these peppers from a soil-borne disease.

Biocontrol should also be preventative (before pest pressure becomes high). If you are expecting to use only biological control to solve an already out-of-control pest problem, you will probably be disappointed. Similarly, if environmental conditions are very favorable for a pest, a biocontrol solution will probably be insufficient.

Each year, university researchers, extension staff, and private companies conduct efficacy trials to quantify how well pest management strategies work. Knowing how a biocontrol product/organism performed in these trials can help you decide if you want to try it on your farm or in your yard. It helps to know a little about how these trials are structured. Efficacy trials typically include some combination of the following types of control treatments:

  • non-treated control – plants are exposed to pests (either naturally, or deliberately by the researcher), but no pest management strategy is used; disease/damage severity should be highest in this treatment
  • chemical control – plants are exposed to pests, and a chemical pesticide is applied to manage the pest; sometimes an “industry standard” (what is typically used to manage that pest in that crop and setting) is designated by the author of the study; if no industry standard is designated, comparisons can still be made to the chemical treatment that worked best; disease/damage severity should be very low in this treatment
  • non-inoculated control – no pest pressure (i.e., plants were not deliberately exposed to the pest); sometimes disease or damage still occurs because of natural pest pressure, or because disease or insects spread from other treatments in the trial; disease/damage severity should be lowest in this treatment

Efficacy trials also include statistical analysis. In a nutshell, this analysis tells you whether two values are really different (often described as “statistically different”), or not. If two numbers are not statistically different from each other, it means that only by chance is one larger or smaller than the other. If you did the same experiment again, you might see the opposite relationship. One common way of expressing these differences is by using letters. If two treatments are assigned the same letter, then they are not statistically different. So in the example below, “Bio1” is statistically different from “Bio3” but neither is different from “Bio2”.

graph of sample efficacy trial results
An efficacy trial may compare biocontrol products (Bio1, Bio2, Bio3, and Bio4) to non-treated (high disease/damage), chemical (low disease/damage), and non-inoculated (low disease/damage) controls.

 

When interpreting an efficacy trial, you should compare a biocontrol of interest to the control treatments. Of course, it would be great to see biocontrol products that are just as effective as the chemical control (like “Bio1”), and sometimes they are. Sometimes, a biocontrol may be less effective than the chemical control, but more effective than the non-treated control (like “Bio3”). Sometimes there’s so much variability (represented by the lines extending above and below the blue bars on the chart), that a biocontrol product is not statistically different from either the non-treated control, or the chemical control (like “Bio2”). This makes it difficult to draw conclusions about how well the product worked.

But, it’s not always quite that simple. For example, in these efficacy trials, researchers deliberately expose plants to pests, and often they manipulate the environment to favor pest populations (for example, over-watering plants to promote a soil-borne disease like damping off). While there can be value in assessing product efficacy in a “worst case scenario”, this may be much higher pest pressure than you are likely to encounter on your farm or in your yard. When looking at efficacy trials, you should consider:

  • How much disease/damage was observed on plants that were not protected in any way (non-treated/control)? If it’s too low, it’s hard to be confident that the biocontrols being tested were effective, since even unprotected plants were pretty healthy.
  • How much did the most successful treatment (chemical control) reduce disease/damage? If even the “best” pest management strategy in the trial was not very effective, then pest pressure may have been too high, and it’s not surprising that the biocontrol was ineffective. If you practice good IPM, you likely won’t experience such high pest pressure.
  • How was the biocontrol applied (alone, or as part of a spray program with other products)? Applying single products in an efficacy trial can simplify interpretation, but may not mimic how you plan to use a biocontrol product. If a biocontrol was applied in combination with other products, you should compare the “biocontrol + other products” to the “other products alone” to see what the biocontrol added to pest management.
  • What was your goal, again? For example, if you are hoping to replace one or two chemical applications in a larger spray program with a biocontrol, then a moderately effective biocontrol product (like “Bio3”) may meet this goal.

Because the efficacy of a biocontrol can depend a lot on the environment in which it is used (temperature, humidity, soil conditions, etc.), it’s also a good idea to initially try a new biocontrol in a small area of your farm or yard, and keep notes on what you did and how well it worked for you. You can modify your plan to find what works best for you. The manufacturer or distributor should be able to provide you with important details on how (and for how long) the biocontrol should be stored, and exactly how and when to apply it. And (as always!) if you are using a biocontrol that is also a pesticide (see previous post), make sure that you read, understand, and follow the label.

The following resources summarize efficacy results for biocontrol of plant diseases. As I find efficacy summaries of insect and mite pest biocontrol, I will add them. Or, feel free to suggest efficacy resources you know of in the comments!