Combatting Fungicide Resistance in Strawberry Nurseries

UF/IFAS and Clemson University use peach research to benefit strawberry industry

Sweet, succulent strawberries have to start out somewhere, and that generally means the nursery. Before they make it onto shelves throughout the U.S. and the world from fields in Florida and California, they have to survive and thrive. Proper care in the nursery will lead to healthy, productive plants in the growers’ fields. Unfortunately, early introduction of pesticides and fungicides can result in disease resistant plants making it into the fields. A joint research project between the University of Florida and Clemson University in South Carolina seeks to eradicate this problem.

Strawberry anthracnose affects crops throughout the world, but is especially prevalent in southern locales because the optimal development temperature for the pathogens is about 80°. According to the USDA, 40 percent of Florida farmers are affected each year by anthracnose. Anthracnose is a general term that describes several diseases. It can be caused by any member of the fungi group Colletotrichum. The result can be crown rot, fruit rot, black leaf spot, or irregular leaf spot.

A big part of the problem with controlling strawberry anthracnose is that the chemicals being used in the growers’ fields are the same ones being used in the nurseries. This has resulted in unintentional selection for pesticide resistant pathogens going from the nurseries into the fields.

Dr. Guido Schnabel, plant pathologist at Clemson University, describes the problem, “In the past, the nursery men have used the same pesticides as the growers, and they started selecting for resistance in the pathogens and shipping those resistant strains on the plants to the fruit growers. Then growers were stuck with what they had, and had to try to figure out how to manage the diseases with fewer materials. We’re trying to eliminate this problem and give them some other tools to use.”

Dr. Schnabel is part of a collaborative effort between Clemson University, the University of Florida, Cornell University, and the USDA. He is working closely with Dr. Natalia Peres, professor of plant pathology at the University of Florida Gulf Coast Research and Education Center, to develop alternative means of controlling strawberry anthracnose. Dr. Peres’ research team has received grant funding from the USDA Specialty Crops Research Initiative program. The goal is to reduce resistance to pesticides so that the chemicals will still work in the fields.  Several alternative fungus control methods are being investigated.

Some of the alternative treatments involve the application of heat. Research shows that steam is less damaging to plants than dry heat is. Plant saunas are proving to be a vital part of the treatment process.

“It’s not a new concept,” says Dr. Peres, “but we are trying to make it work in the large setting that is a nursery, while doing as little damage to the plant as we can. So instead of applying heat with hot water, which can be damaging to the plants, we are applying steam.” A large chamber is used to apply steam to the plants, thereby killing the resistant population of pathogens on the plants. Growers then receive plants with lower levels of inoculum on them.

Application of UV lighting is another approach that is testing favorably. UVC lighting sterilizes the plants, including resistant populations. “Again this is not something new,” says Dr. Peres. “This is already being done in some greenhouses especially in Europe. We’re just taking it to the next step and trying to implement it in the open field and on a larger scale.”

That’s not to say that chemical control is completely out the door at the nursery level. The goal is to maintain the effectiveness of conventional chemicals out in the fields. To this end, there are various chemicals and organic compounds being investigated for use in nurseries.

Dr. Peres has already been instrumental in helping growers reduce the usage and cost of fungicide. She and her team have created an online tool called the Strawberry Advisory System which alerts farmers when weather conditions are ripe favorable for fungal inoculum to take hold. This tool helps decrease the amount of pesticide wasted through unnecessary application.

Overall it is expected that an integrated approach will be the most effective. Rather than suggesting that nursery growers adopt one particular means of control to replace fungicide use, using a series of alternative techniques will be most effective.

There will be some investment required on the part of nurseries. New equipment will be needed to provide the benefits of steam and UVC treatment. It’s hard to say at this point what the cost per nursery could be, but the return on the investment is practically guaranteed.

Strawberries are a $366 million per year industry in Florida, second only to California. We need our nurseries and fields to be healthy and productive. Drs. Schnabel and Peres and their teams are working hard to make sure the tools we currently have at our disposal remain effective. Their work may change the look of strawberry nurseries in the future, but it is all to preserve the image of the luscious berries we’ve come to know and love.


By Teresa Schiffer