The University of Florida has rolled out a new interactive web-based model that helps citrus growers determine when they need to reapply copper sprays.

Megan Dewdney, an assistant plant pathology professor at the Citrus Research and Education Center in Lake Alfred, led a team that brought an earlier copper scheduling system into the 21st century by making it more user-friendly and Web accessible. It can be found at www.agroclimate.org.

Based on petal fall, weather conditions, fruit and leaf expansion, and spray volume and copper content, the model provides a warning or danger alert when copper residual levels fall and growers need to reapply.

“I think it’s really easy,” says Tim Hurner, one of several county Extension agents from citrus-producing areas who provided feedback to Dewdney. “With the final version, we did quite a bit of work with Megan to dummy proof it. You follow the bouncing ball, and it gives you the decision-making tools that are needed.”

Many growers apply copper based on a calendar or at their convenience, says Hurner, who’s based in Sebring in Highlands County. But the model will guide them to when a copper application will be most effective.

If their groves received significant rainfall during the past week, for example, then growers may need to reapply sooner than expected because the rain washed off some of the copper residue, he says. But if the area has been unseasonably dry, they may be able to extend spray intervals without sacrificing efficacy.

Jim Snively, vice president of grove operations for Southern Gardens Citrus in Clewiston, says he’s “absolutely” interested in learning about the copper scheduling model and views it as another tool he and colleagues can use to make better decisions.

Currently, Southern Gardens bases copper applications on knowing the timing and the life cycles of the diseases.

“It’s not just, O.K., it’s June 25, and we need to spray,” Snively says.

Building on earlier research

The original copper spray scheduling recommendation system, or CuSSRS, was developed in the late 1990s and early 2000s by a team of Florida-based researchers.

They included Gene Albrigo and Pete Timmer, University of Florida professors at the Citrus Research and Education Center in Lake Alfred; Howard Beck, a UF professor of agricultural and biological engineering in Gainesville; and Ed Stover, formerly of the UF Indian River Research and Education Center in Ft. Pierce and currently the curator and research leader with the U.S. Department of Agriculture’s National Clonal Germplasm Repository in Davis, Calif.

Most of the data that went into the original copper model is still valid, Dewdney says. The researchers tested it with grower-cooperators for six years, according to an October 2005 peer-reviewed article the group wrote for the Journal ASTM International. They also compared actual and predicted copper residues over a three-year period.

The original program did not improve disease control, and results were similar to calendar date scheduling, according to the article. The program did save one or two sprays per season, however, especially during low rainfall years.

Back then, the researchers reported that growers found the program most useful for lengthening or shortening the calendar interval based on rainfall and to start spraying blocks in different order if rain occurred in one area and not another.

But the older copper model lost favor with growers as newer computer operating systems, such as Windows XP, Vista and 7, and changes to the FAWN system made it too cumbersome.

To use the original model, growers had to download the program and run it off their own computers.

In addition, the original model was designed for copper use only through June or early July when melanose, alternaria brown spot and greasy spot were the predominant diseases, Dewdney says.

Now with the addition of black spot in some areas and widespread citrus canker, most growers apply copper through the summer and into September. Grapefruit growers may even apply copper through October.

Dewdney says she began collecting fruit expansion data for the later months last summer, so she’s not as confident in their validity as she is with data that went into the petal-fall through June period. She plans to collect additional data this summer and fall.

She credits Clyde Fraisse, an Extension specialist and coordinator for the web-based www.AgroClimate.org, and his group for their work in taking the original computer coding and modeling and reprogramming it for the Web.

Seeking grower input

Dewdney conducted several grower training sessions throughout the citrus belt in June and July to inform growers about the new Web-based model, give a demonstration and allow them an opportunity for hands-on simulation.

As part of the sessions, she asked growers for feedback about the site’s appearance, its features and possible other options they’d like to see.

If there’s enough grower interest in a mobile version of the copper model, she says the team also may develop that for a future season.

One area Dewdney says she’s especially interested in is how growers might be able to store their own weather data on the website rather than inputting it each time. Users currently have the option to select a nearby FAWN weather station site or input actual rainfall and temperatures.

“We want to discuss what might be the easiest way if they’re interested in that,” she says. “The easiest way might be signing into a password-protected account and uploading a file. But it has to be something that’s workable for them [growers] and us.”

One of the goals this year, Dewdney says, is to see if the team can incorporate a new type of rainfall data from the National Oceanic and Atmospheric Administration into the copper application model for more site-specific data.

“We want to see if we can obtain better rainfall estimates, so you don’t need to have your own rainfall gauge or rely on a FAWN station that’s maybe too far away,” she says.