Getting The Most From Your Fungicides: Application Rate, Interval & Timing

Getting The Most From Your Fungicides: Application Rate, Interval & Timing

I am sure you’re thinking the headline is somewhat dull, but if you do not pay attention to these aspects of disease control, you will be wasting a lot of money and wind up irritated. This article is part of the series to make the most of your fungicide/bactericide dollars in order to keep your profit margin up. I hope the thoughts I pass on will help some of you make better, more cost-effective decisions regarding fungicide/bactericide use.

Does Rate Really Matter?

I always ask which rates are being used to treat a disease before I try to suggest a control strategy. It is interesting to me how often the rates being used are too low to be effective. You might as well be spraying water if you use too low a rate. Remember, water is not neutral but something fungi and bacteria thrive on. So spraying very low rates can end up with more disease and not less.

Deciding The Right Rate

After conducting fungicide trials for more than 30 years, I have seen some cases in which a lower rate is more effective than a higher rate. One of the best examples in our trials has been the negative effect of using the highest labeled rate of Aliette for downy mildew.

When I first moved back to California, I heard how this fungicide was not effective on downy mildew–even when used at 5 pounds/100 gallons. I set out to find out the reason and discovered that after a couple years, the most effective rates were 1-2 pounds/100 gallons. If the rates were increased to 5 pounds/100 gallons, the degree of disease control was less. Only testing in your facility will tell you what the best rate is, so I always suggest starting in the middle of label rates when testing a new product.

Higher efficacy at a lower rate may be due to unseen or undetected phytotoxicity. Some pathogens, such as botrytis, take advantage of stressed plants and are worse when the plant is damaged. This is seen when copper fungicides are used when they cannot dry quickly. The resulting burn can end up infected with botrytis and actually more disease. Read the labels and stay in the middle of the road–at least the first time around.

In a rhizoctonia cutting rot trial, we saw one of the three fungicides tested was slightly more effective at the highest rate tested while the other two gave the same degree of control at all labeled rates tested. Rates on fungicide labels reflect the summation of many trials conducted all over the United States, and sometimes all over the world.

Rarely, I find that the rates are not what our trials have shown. Sometimes, they might be lower than our trials indicate are effective. At other times they are higher. The bottom line is you must use the rates on the labels, and if they are not working for you, switch fungicides.

Can I Reduce Rates When I Use A Tank Mix?

Nope! This is especially true if you are adding two mode of action groups to manage development of resistance. One of the ideal ways to develop resistance is to use a low rate of an active ingredient many times without rotation. This stresses the fungus or bacterium just enough to allow the strains with higher resistance to that active ingredient to develop. Because you probably do not want to promote fungicide resistance, try to avoid using lower-than-labeled rates. In other cases, tank mixes are designed to expand the range of the spray. For instance, if you are applying something for pythium and something different for rhizoctonia and you decrease both rates, you are once again applying water.

Stretching The Interval To The Breaking Point

This is another experiment commercial growers should not do. The result of applying products less frequently than suggested on the label is an outbreak of the disease. It is always harder to stop a disease that is active than to prevent one. Unfortunately, we have seen some situations, such as certain anthracnose diseases and fusarium crown rot, in which applying products too frequently makes the disease worse. This is due to a combination of the fact that every application adds water and, as mentioned earlier, fungi like water and phytotoxicity on the crop. Fusarium, botrytis and anthracnose fungi like phyllosticta take advantage of damaged leaves and stems. Phytotoxicity is always a function of rate and interval with a sensitive plant.

The interval must be based on how severe disease pressure is. The interval changes with the crop age and weather, and only experience can tell you when a one-week interval is needed instead of two to four weeks.

When Should I Start Spraying?

The old saying, “An ounce of prevention is worth a pound of cure,” has been around for a very long time because it is right. The key question is when will disease start? Knowing the weather that promotes certain diseases allows us to time treatments right before disease might occur.

You can avoid this guessing game somewhat if you are an excellent scout. If you can see the very first signs of disease, many times, that is the best time to start treatments. However, there are some diseases that cannot be cured no matter how fast you react, and they should always be prevented.

It is especially critical for crops like poinsettias that have a narrow target market time. I always suggest applying products when the particular disease is most likely to be present or at the final date you can apply an effective treatment. On poinsettias, rhizoctonia cutting and stem rot only causes significant losses during rooting and the first month of production.

Treating for this disease for the entire three-to-four-month production cycle is a costly and wholly unnecessary step. The late-season botrytis stem rot that is sometimes found is often confused for rhizoctonia stem rot. Once poinsettias have closed their canopies you cannot apply a spray to their stems for botrytis stem rot. So an application of something for this disease must occur before the canopy closes for best effect.

Conclusion

Deciding what to spray, how much, how often and when to start is a tough set of answers to come up with. It takes years of experience and constantly learning to be a great grower. Remember, if being a great grower was easy, even researchers could do it.

Leave a Reply

More From Disease Control...

March 13, 2018

Greenhouse Biocontrol Goes Mainstream

Biological control has moved into the mainstream for greenhouse growers. And the timing couldn’t be better, as consumer demands for more sustainable production methods for the plants they buy are moving back upstream.

Read More
Downy mildew sporulation on underside of leaf

March 10, 2018

Segovis Fungicide Now Available to Ornamental Growers in California, New York

Segovis, from Syngenta, features a unique active ingredient that helps control downy mildew and Phytophthora.

Read More
Sample-collecting-for-Virus-Testing-Feature

March 3, 2018

How to Keep Your Greenhouse Crop Free of Disease

All growers deal with the possibility of damaging disease issues in the greenhouse. Here’s how Pleasant View Gardens makes sure its greenhouse crops stay disease-free.

Read More
Latest Stories

March 13, 2018

Greenhouse Biocontrol Goes Mainstream

Biological control has moved into the mainstream for greenhouse growers. And the timing couldn’t be better, as consumer demands for more sustainable production methods for the plants they buy are moving back upstream.

Read More
Downy mildew sporulation on underside of leaf

March 10, 2018

Segovis Fungicide Now Available to Ornamental Growers i…

Segovis, from Syngenta, features a unique active ingredient that helps control downy mildew and Phytophthora.

Read More
Sample-collecting-for-Virus-Testing-Feature

March 3, 2018

How to Keep Your Greenhouse Crop Free of Disease

All growers deal with the possibility of damaging disease issues in the greenhouse. Here’s how Pleasant View Gardens makes sure its greenhouse crops stay disease-free.

Read More
Greenspire-Procidic

December 25, 2017

New Fungicide Helps Control Mildews and Rot in Ornament…

Greenspire Global, Inc. has developed Procidic, a bactericide and fungicide that provides effective disease control without synthetics.

Read More

December 21, 2017

Dümmen Orange Confirms Presence of Xanthomonas in Begon…

In a December 16 letter to its customers, Dümmen Orange said it had encountered an issue in its El Salvador-based Las Mercedes production facility, where bacterial leaf spot had been confirmed in begonia production.

Read More

December 21, 2017

Plantpeddler Provides Guidelines for Xanthomonas Bacter…

A leading producer of Begonia young plant liners and finished plants, Cresco, IA-based Plantpeddler has issued the following informational guidelines on Bacterial Leaf Spot in Begonias.

Read More
BASF Orkestra Intrinsic

December 18, 2017

California Growers Have a New Disease Control Tool

BASF’s Orkestra Intrinsic fungicide has been approved in California for control of several ornamental plant diseases.

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

December 14, 2017

New Biofungicide Approved for Disease Control in Orname…

Certis USA recently introduced Carb-O-Nator, a new broad-spectrum foliar fungicide that works on contact to control powdery mildew, Alternaria, Anthracnose, Botrytis, Septoria leaf spot, and other diseases.

Read More
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