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​Strawberry Anthracnose: Managing a Hidden Menace
     
     
   

Part B

Customers push for a change

The past few years have brought Jack an increasing chorus of questions and complaints from strawberry customers about his rigorous program of fungicide spraying. Alarmed by media reports of health hazards associated with pesticides, many parents have expressed concern to Jack about the possible dangers of eating strawberries that could have pesticide residues on them. One day Jack got complaints from his neighbor and friend Anna Nasser, a long-time customer who always brings her children to his farm to pick their own strawberries.

“Jack,” Anna said, “we love to bring our family out to pick strawberries, but we’re worried about all that fungicide you use. I want to keep my kids safe, so I may have to start buying berries from farms that use fewer chemicals. But I’d really rather buy from Sunny Patch Farm; is there any way you can cut back on the fungicides?” Anna’s concerns remind Jack that he has been having similar conversations with other customers, neighbors, and friends. Even at the farmers market, more and more customers want to know about Jack’s fungicide program on the berries.

Jack already knows that fungicide use has some potential for risks to human health and the environment. But he wants to argue that not all of the fungicides pose the same risk. For example, pyraclostrobin (Cabrio), a fungicide in the strobilurin group that is designated by the U.S. Environmental Protection Agency (EPA) as ‘reduced risk,’ is much less damaging than Captan, an older fungicide that Jack also uses. Even though Cabrio is more effective against AFR than Captan, Jack can’t just rely on Cabrio for every spray, because there is a high risk that C. acutatum will become resistant to it after many consecutive sprays.  In fact, resistance has already started to appear. Growing customer pressure is forcing him to re-evaluate his disease management practices in order to remain in business. How can he cut down on fungicide use and still produce top-quality strawberries? Looking for answers, Jack phones Nancy Muller, the plant pathologist.

Disease-warning system

“Hi Nancy, is there a way I can control anthracnose fruit rot with less fungicide? My customers are on my back all the time about this.”

 


Figure 4. Example of fungicide spray timing according to two management systems: calendar-based (every 10 days) and a disease-warning system (applying only when a weather-based threshold is reached).

“It’s good to hear from you, Jack. There may be a way around this problem. We’ve been field-testing a disease-warning system for anthracnose fruit rot that can help you time fungicide sprays based on the weather conditions. A disease-warning system is a tool for optimizing plant disease management. It uses the information about one or more components of the disease triangle - environment, host, and pathogen – to predict the risk of a disease epidemic (Campbell and Madden, 1990). Warning systems have been used successfully on a range of vegetable and fruit crops, including tomato and cantaloupe.

A warning system for AFR on strawberry, called the Florida Advisory System (FAS), was originally developed in Florida (MacKenzie and Peres, 2012). Growers can access the website to get fungicide spray guidance. Recently, FAS has shown promise for use in the Midwest. Based on our results, you can save an average of two fungicide sprays per season, and still keep AFR under control. Maybe you’d like to try it out?” Nancy then emails Jack some details about the FAS warning system:

  • Using an equation developed from results of studies of C. acutatum biology (Wilson et al. 1990), the FAS warning system rates the risk of an AFR outbreak based on the number of hours per day when plants are wet (referred to as leaf wetness duration, or LWD) and the average air temperature during these wet periods. It then advises you whether or not a fungicide spray is needed.
  • You can monitor the weather for the warning system using a weather station that includes sensors to track the weather conditions, a datalogger to record the weather data, and a built-in computer chip that runs the equation to convert the weather data into an AFR risk rating. The risk rating can be accessed by simply pressing a button on the datalogger. The price of the equipment ranges from $500 to $3,000, depending on quality: the higher-priced equipment is more reliable and lasts longer. Location of the weather station also affects risk prediction, because some locations on the farm stay wet for longer periods after rain or dew than other locations.

  • There are pros and cons to consider in deciding whether to try out the AFR warning system:
    • On the positive side, you can show your customers that fungicide usage is reduced by 40% (by eliminating an average of 2 fungicide sprays from your usual total of 5 sprays per season). You will save some money and time by avoiding two fungicide sprays per year as well as protect the environment, yourself, and your customers. On top of that, using less fungicide may also reduce the risk of developing C. acutatum that is resistant to fungicides.
    • On the negative side, you may worry that the risk of an AFR outbreak is increasing by abandoning your “tried and true” practice of making 5 fungicide sprays per season and placing your trust in a new, weather-timed spray system. The calendar sprays are more predictable than the disease-warning system sprays, so you can schedule them more efficiently. Warning-system spray alerts, on the other hand, may come at less convenient times, such as when the farm is open for fruit picking or when the weather is too wet to spray fungicide. As you know, a serious outbreak of AFR could cost you far more in lost sales than what you would save by applying 2 fewer fungicide sprays per season. In addition, tending a weather station will take some additional time and trouble during a busy growing season.

Should Jack trust his strawberry crop to the warning system and the weather monitoring equipment? Is it worth the extra time and trouble? Strawberry is such a high-profit crop that Jack really doesn’t want to make any mistakes. But he doesn’t want to lose customers either. What should he do?

PART B QUESTIONS:

  1. Describe how the AFR warning system works.

  2. Based on the disease triangle concept:

    1. Are there strategies that Jack could use to keep C. acutatum from getting into his fields?

    2. If the fungi were confirmed NOT to be present in the field, would it make sense to spray fungicides against AFR anyway? Why or why not?

  3. Based on the information presented in the case:

    1. Would you use the warning system if you were Jack O’Neil?

    2. If yes, how can he make sure that the warning system is working in his field? What are possible problems associated with using it? What additional information would be useful to help you decide?

    3. How will using the warning system help Jack to reduce the risk of resistance development?

    4. If Jack decides not to use the warning system, how can he meet his customers’ demands that he cut back on fungicide use?


Answers to these questions are available to instructors here.​