By Tom Burfield

Weed control in citrus groves is not a task you should put off.

All of Florida’s groves require some type of weed control—either by chemical or mechanical means, says Steve Futch, Extension agent with the University of Florida’s Citrus Research and Education Center in Lake Alfred.

There are myriad reasons why it’s important to attack weeds in an effective and timely manner.

“It’s been well documented that weeds compete with citrus trees for space, water, nutrients and light, and they impede the harvesting of a crop,” Futch says.

They also harbor insects, serve as hiding places for rodents and interfere with the irrigation pattern of low volume irrigation systems.

“In some cases, regardless of the weed type, they can completely cover the tree—especially a younger tree,” he says.

Despite the dire consequences of ignoring weeds, “they are manageable if you do it correctly,” Futch says.

Young trees more susceptible Weeds pose a greater threat to young trees than older ones because the canopy of mature trees can help shade out the unwanted plants.

“A thick, well formed canopy can restrict light to soil surface under the tree canopy by up to 90 percent,” Futch says. But a young tree, with its small canopy, allows more light to reach the grove floor, increasing weed pressure.

When Futch tests new herbicides, he conducts them in young groves.

“If an herbicide is effective in a young grove, it will provide weed control in a mature grove,” he says.

By Tom Burfield Some weeds, such as Spanish needles and selected vines, are becoming more difficult to control, he says.

They’re not resistant to weed killers, but they may require higher rates than in the past because the plants may be building tolerance.

For example, a weed that a grower could control with 2 quarts of glyphosate per treated acre may now require 3 quarts.

“It’s taking more to get the same control,” he says.

Total per acre cost for weed control in central Florida is about $225. In the southwest production area, it’s about $186 and in the Indian River region, it’s about $216. Those figures are from a report prepared last fall by Ron Muraro, Extension economist based at the Citrus Research and Education Center. Popular herbicides Among the herbicides used in Florida are Treevix from BASF, which kills weeds on contact but does not have a long residual; Chateau, a residual herbicide from Valent USA that works best for broadleaves and is registered for non bearing citrus; and Alion, a new product from Bayer CropSciences that isn’t yet registered. Bayer hopes to have federal registration of Alion by June.

All work differently than glyphosate, which is marketed under numerous brand names and to which weeds in parts of the United States are becoming resistant.

More frequently used preemergence products include Diuron (diuron), Krovar (Hyvar plus Diuron), Princep (simazine), Solicam (norflurazon) and Prowl (pendimethalin), Futch says. In addition to the brand name products, other off patent formulations are available.

Herbicide combo Haines City Citrus Growers Association, a Haines City based cooperative that also manages groves, uses a combination of contact and residual materials to control weeds, says Charles Counter, director of field operations.

Weeds are not a huge problem on the 5,700 acres that the cooperative operates, he says. Nonetheless, citrus is a perennial crop, so there is constant weed pressure.

Growers in the cooperative spend $100 to $150 per acre annually on weed management, he estimates.

“We generally apply [herbicides] three to four times a year under the trees,” Counter says.

In addition, the grove middles also require treatment several times a year, either through a chemical burn down or a mowing and disking process.

Like Futch, he points out that weed management practices vary by the age of the tree.

“Young blocks require more aggressive herbicide programs, because of the sunlight hitting the ground, and mature blocks require a little less because of the shade under the trees,” he says.

A top 5 concern Faced with pests, such as Asian citrus psyllid and the citrus greening it vectors, controlling insects has become a greater priority than controlling weeds at Ben Hill Griffin Inc. in Frostproof, says Steve Farr, vice president of the company’s growing operation.

remains among the top five priorities for the company, which grows thousands of acres of citrus, Farr says. The company spends $100 to $150 per acre per year on weed management.

The specific herbicides the company uses vary.

“We use an assortment of things, depending on location and soil types—flatwood versus the ridge,” Farr says.

The firm uses glyphosate as well as postemergent materials, such as Princep, Solicam and Krovar. Farr says he typically applies herbicides three times per year.

The key, he says, is to evaluate your own situation and select the product that works best for your groves.

Selection criteria Futch agrees, adding that no matter what herbicide you plan to use, there are certain factors to take into account.

Consider your grove location and the weeds at that site. Soil type, tree age and type are also important factors.

“In some instances, products can only be used in the flatwood and not on the ridge,” Futch says. “Others can be used in both ridge and flatwood citrus groves.”

The best time to apply an herbicide typically is late winter or early spring because most products, especially residuals, need to be incorporated into the soil with rainfall or irrigation.

“If herbicide is not properly incorporated, the material will just lie on the surface and may allow weeds to emerge,” Futch says.

Application rates and methods can vary by tree age or, in rare cases, by citrus variety, so always follow label directions, Futch warns.

The label also will list any use restrictions, dictate the type of personal protective equipment to wear and provide other important information.

“The label is paramount in any management program, and it’s the law,” he says.