Rotate Or Tank Mix To Avoid Resistance

In this, the final article in our series on making the most of your fungicide dollars, I am considering fungicide resistance management. There are some key topics that should be addressed, and I am covering them by answering questions. Obviously, if your fungicide fails due to resistance, your dollars are wasted.

Which pathogens become resistant the quickest?

The pathogens that become resistant to fungicides most quickly are those that reproduce quickly and in high numbers. These include powdery mildew fungi (e.g. Oidium), downy mildew fungi (e.g. Peronospora), Botrytis, Pythium, Phytophthora and bacteria (e.g. Pseudomonas, Xanthomonas, Erwinia, etc.). It is interesting that although bacteria develop resistance to copper quite readily, fungi don’t seem to. The FRAC (Fungicide Resistance Action Committee) actually has copper listed as low risk of resistance development.

Which fungicides are most likely to have resistance concerns?

In this case, the more narrow the mode of action the more likely the target fungi can develop resistance to that fungicide. Fungicides like chlorothalonil and mancozeb actually have multiple sites where they attack the fungus, making them less likely to have resistance problems.

In contrast, some of the newest fungicides have very narrow, specific modes of action, making resistance development more likely. That has led to very strict instructions on their labels concerning the number of times they may be used on a crop and/or if they must be tank mixed.

How can you reduce the potential for resistance development?

The most important method is to do everything in your power to reduce disease, including using alternative methods–practice integrated pest management (IPM). If you do nothing but spray fungicides, you are placing too much strain on them and they are more likely to fail. Even the best fungicides work poorly when cultural and environmental controls of IPM are ignored. Don’t wait, be preventative when necessary.

Downy mildew and some bacterial diseases are not easy to control if preventative applications are not made. Use products according to their labels–the fungicide manufacturers really do know more about how to use their products than anyone else does. Learn more about important diseases of your crops so you can find their Achilles heel.

Botrytis can be controlled without any fungicides if humidity and temperature are firmly under your control. Some diseases must be present on the seed, cutting or liner because they do not blow in with the wind. Finally, rotate or tank mix products.

Is tank mixing or rotation best?

Most studies show both methods work for resistance management, so the preference is yours. If you make a tank mix with two products for the same disease, then you are doing so to manage resistance. If, however, you combine products with different spectrums, you are simply using a shotgun approach. This gives you some assurance you will control an undiagnosed situation, or one that is caused by more than a single pathogen.

I find many growers like to use tank mixes. They think they can reduce costs by using lower rates of the fungicides if they mix them. Sometimes this is true, but not always. You can reduce the rate of fungicides in a tank mix when you are treating preventatively, disease pressure is low, both products work on the target fungus and you are sure you do not have resistance to either product.

You should not go below labeled rates in most circumstances. Do not reduce rates when you do not know the cause of the disease, more than one disease is present, the fungicides have a narrow or similar mode of action or the product is new to you. Pre-mixes can make the entire question moot.

Leave a Reply

More From Disease Control...
Researchers Study Rose Varieties

October 17, 2017

Rose Rosette Update: Research into Detection and Management Continues

Halfway through a five-year, $4.6 million grant to combat rose rosette disease in the U.S., a national research team is encouraged by the amount of information learned, but admits having a way to go before finding how to overcome the deadly problem.

Read More
Botrytis Symptoms on Leaves

October 17, 2017

How One Grower is Battling Botrytis with a New Biological

CropKing in Lodi, OH, recently began using a new beneficial fungus in its fight against Botrytis in its greenhouse tomatoes. So far, the results have been promising.

Read More
BASF Pageant

September 29, 2017

New Fungicide Provides Production and Postharvest Disease Control in Ornamental Crops

Pageant TR from BASF controls seven key diseases, and can be used both in the greenhouse and in trucks that are on their way to a retail site.

Read More
Latest Stories
Researchers Study Rose Varieties

October 17, 2017

Rose Rosette Update: Research into Detection and Manage…

Halfway through a five-year, $4.6 million grant to combat rose rosette disease in the U.S., a national research team is encouraged by the amount of information learned, but admits having a way to go before finding how to overcome the deadly problem.

Read More
Botrytis Symptoms on Leaves

October 17, 2017

How One Grower is Battling Botrytis with a New Biologic…

CropKing in Lodi, OH, recently began using a new beneficial fungus in its fight against Botrytis in its greenhouse tomatoes. So far, the results have been promising.

Read More
BASF Pageant

September 29, 2017

New Fungicide Provides Production and Postharvest Disea…

Pageant TR from BASF controls seven key diseases, and can be used both in the greenhouse and in trucks that are on their way to a retail site.

Read More
Ascochyta in chrysanthemum

September 27, 2017

14 Common Chrysanthemum Diseases to Monitor

Penn State University Extension features a section on its website devoted to diseases commonly found in chrysanthemums.

Read More
Boxwood Blight

September 19, 2017

Concerned About Boxwood Blight? Here Are Some Updated M…

AmericanHort’s Horticultural Research Institute has released an updated version of its boxwood blight Best Management Practices document.

Read More
Powdery mildew on rosemary. Photo credit: SHS Griffin

September 9, 2017

Howler Biological Fungicide from AgBiome Gains EPA Appr…

Howler provides preventive, long-lasting activity on a broad spectrum of soilborne and foliar diseases, with no special handling or storage required.

Read More
Aphids

July 7, 2017

New Tools for Your Crop Protection Arsenal in the Green…

Over the past few months, crop protection companies have developed several new products designed to help you manage a wide range of insect and disease pests. Here’s a look at some of them.

Read More
Primula acaulis, Botrytis, Disease, Griffin Greenhouse Supplies

May 30, 2017

BioWorks Launches New Biofungicide for Botrytis Control

BotryStop was developed for the control of pathogens such as Botrytis, Sclerotinia, and Monilinia in several crops, including ornamentals.

Read More
Botrytis Blight Geranium

May 10, 2017

A Refresher on Botrytis Management in the Greenhouse

When the weather is moist and humid, susceptible greenhouse plants may need to be protected from Botrytis cinerea, a fungus that causes leaf spots, blighting, and stem cankers.

Read More
Downy mildew sporulation on underside of leaf

May 5, 2017

New Bactericide/Fungicide from BioSafe Systems Helps Ma…

BioSafe Systems has introduced PerCarb, a broad-spectrum bactericide/fungicide for use in greenhouse fruits and vegetables, as well as other crops.

Read More
Pythium

March 27, 2017

Florida Ornamental Growers Took a Hit in 2016 Thanks to…

While damage figures from the 2015-2016 winter rains are still being compiled, researchers have found that Phytophthora and Pythium caused severe destruction in many plants.

Read More

March 20, 2017

AgBiome’s New Zio Biofungicide Receives EPA Regis…

The new biofungicide is the first product from AgBiome, and will be marketed by SePRO Corp. in the ornamentals market.

Read More

February 26, 2017

AgBiome Will Enter the Ornamentals Market With a New Bi…

AgBiome, a young company with teammates steeped in decades of experience in the crop protection world, sees an opportunity to bring products to market that fill the existing gaps in plant protection. The company has partnered with SePRO to market and distribute Zio, a biological fungicide expecting EPA registration this spring.

Read More
Tomato Spotted Wilt Virus on Osteospormum

February 23, 2017

4 Pathogens to Prepare For in 2017

Early detection of disease and virus symptoms in the greenhouse is critical. One expert says there are a few pathogens in particular that growers should be monitoring.

Read More
Boxwood Blight

February 7, 2017

Boxwood Blight Detection in Illinois Has Growers on Ale…

Symptoms of boxwood blight, which can spread quickly in production facilities, include leaf spots, stem cankers, and defoliation.

Read More
downy-mildew-impatiens-feature

December 24, 2016

How Agronomic Programs Can Help You Successfully Manage…

To prevent problems before they start, make an agronomic program an essential part of your production plan.

Read More

December 19, 2016

Funding Allocated for Several Horticulture Pest Researc…

The USDA Animal and Plant Health Inspection Service has allocated millions in funding to research plant pests such as boxwood blight, downy mildew, and phytophthora.

Read More
Phytophthora On Poinsettia

November 23, 2016

Tips On How To Prevent Aerial Blight Spread In Poinsett…

According to Michigan State University experts, certain species of the pathogen Phytophthora, which is typically thought of as a root rot, can also cause issues above-ground.

Read More