It’s been three years since citrus greening was found in a south Florida grove, the first discovery of its kind in the United States. Greening, also known as huanglongbing or yellow dragon disease, is spread when an infected Asian citrus psyllid transmits greening from an infected tree to a healthy one by injecting the bacterium into the phloem.
If a tree is infected by the bacterial disease it greatly reduces production, destroys the economic value of the fruit, and can kill the tree.
Since the disease’s discovery, the Florida citrus industry has immersed itself in becoming educated about the deadly disease. Although there is no known cure for it, studies show that one way greening can be managed is by controlling the Asian citrus psyllid.
“We have done a lot of field trials and feel like we have a good handle on what does and doesn’t control the psyllid,” says Michael Rogers, entomologist and associate professor with the UF/IFAS Citrus Research and Education Center, Lake Alfred.
According to the “Asian Citrus Psyllid and Leafminer” chapter of the UF/IFAS Extension’s 2008 Florida Citrus Pest Management Guide, evidence shows that in other citrus-producing countries the use of insecticides to control psyllids helps slow the spread greening. Some officials say this may be the best outcome the Florida citrus industry can hope for at this point.
“Nothing is going to eradicate greening,” says one citrus industry leader who wished to remain anonymous. “Our efforts, no matter how hard we try, aren’t going to yield a 100 percent success rate.”
Now that the industry understands that citrus greening is here to stay, the goal has changed from finding a cure to finding a way to live with it.
“With overall low psyllid infection rates, controlling psyllids, not elimination, appears to be obtainable,” Rogers says. “Our goal is to keep psyllids at a minimum by finding the best way to control them at the lowest cost to the grower. This is our No. 1 priority.”
Choose the right chemical
One way to suppress the population of the pysllid, as recommended in the guide, is the use of chemicals. The type of chemical, quantity, when, and how are all details included in the management plan.
When using chemicals to control psyllids, many factors go into selecting what type of chemical should be used and when to use it. The age of the tree is one of the first factors that should be considered.
For young trees, growers should use the soil-applied systemic insecticides, aldicarb and imidacloprid, which provide the longest lasting control of psyllids with the least consequence, according to the Pest Management Guide. Aldicarb is only produced by Bayer CorpScience, Research Triangle Park, N.C., under the product name of Temik. It is a systemic carbamate insecticide that may be used on young trees that have been planted for at least one year. Applications to trees 8 feet and smaller requires two to three weeks for the product to be absorbed into the root system and sent to the leaves. A certified applicator may apply aldicarb from Nov. 15 through April 30.
Imidacloprid, a neonicotinoid insecticide, can be applied either as a foliar application or a soil drench, which has been determined to be the best method by researchers. The chemical is produced by several companies.
According to Roy Morris, Bayer representative for Polk County, the company continually strives to develop and perfect chemicals to combat the psyllid for young and mature trees.
“As soon as greening was detected here in Florida, we started looking for a chemical to produce that would be effective and came up with Temik,” Morris says. “We’ve been very impressed with the results of the trials we’ve done.”
Various growers agree that Temik seems to help control the pest.
“Temik is certainly in our arsenal of weapons,” says Ray Bentley, president of Bentley Grove Service, Winter Haven. The company cares for approximately 2,600 acres in the Polk County area. “We are pleased with the results so far. But, it’s hard to say what the long-term affects and results are going to be since this is only a short period.”
Jerry Newlin, vice president of grove operations for Orange-Co., Arcadia, says that on young trees, AdmirePro is the most effective product he has found. Wayne Douberly, president and chief executive officer of Kahn Grove Management in Sebring, agrees.
The only soil-applied insecticide that has been shown to provide any reduction in psyllid numbers on large trees is Aldicarb, according to the Pest Management Guide. The only other chemical control option that has been demonstrated to be effective for reducing psyllid populations on bearing trees is the use of broad-spectrum foliar insecticide applications, the Guide advises.
“With mature trees, it is important to rotate the mode of action because we don’t want the psyllid to become resistant to the method,” Newlin says. “But, Temik, is, of course, what we use with a variation of other products, with the rotating in mind.”
Choose the right application method
As with other methods of controlling the psyllid, several factors need to be considered when deciding whether to use ground or aerial spraying.
Ground sprays provide the best coverage when new flush is present, however ground spraying does have its disadvantages. It requires a great deal of manpower, it often is hard to coordinate timing of sprays with your neighbors, and the psyllids move quite a bit while the spraying is taking place, Newlin says.
“When coverage is ultra critical, it is better to use ground spraying,” he says. “Ground spraying is good for taking care of other pests at the same time as spraying for the psyllid.”
Aerial spraying has a number of advantages, too. First, it can target adult psyllids when there is very little or no new flush. Second, it can cover a large area in a short amount of time. Third, it is a cheaper means of application. Finally, if using a spreader, the chemicals may reach areas that were previously untouched.
Bentley says this type of application works great for quick knock down of the psyllids.
Aerial sprays can be accomplished with a fixed wing aircraft or a helicopter, both of which have advantages and disadvantages. Fixed wing aircraft is less expensive per acre and can cover the property faster. Helicopters do not need a landing strip like fixed wing aircraft, though, and can get around easier and safer.
If possible, coordinate the aerial spraying with neighboring groves, advises Rogers. This ensures that the treatment is done at the same time, lowering the chance of psyllids moving from grove to grove. This also can reduce the number of sprays required in the long run.
According to Rogers, aerial sprays have better proven results when it is possible to have an entire area on the same psyllid management program.
“It is really a luxury to do the entire block. We have neighbor cooperation and can blanket the entire area in some locations,” Douberly says.
Customize the recommendations
Even though the guide clearly offers suggested chemicals and quantities, many growers have learned that for the best results they must modify the plan accordingly for their specific, individual situation.
“We use the prescribed recommended chemicals in the Pest Management Guide and are pleased with the results,” Douberly says. “However, I can also tell you that you name it, we’ve tried it.”
Newlin says he believes that the best program is one tailored to fit the specific circumstances of one’s grove.
“We follow the basic guidelines and then, depending on specific scouting information or specific harvest times, we go from there,” he says.
The price of juice and fresh fruit, or profit margin, also plays a role in how aggressive a grower’s psyllid management program can be.
“In the past 18 months, our caretaking prices per acre have almost doubled,” Bentley says.
Maintain an optimistic outlook
The outlook for the future of Florida citrus is one of optimism.
“I’m optimistic because of all the information we have already. We’ve learned so much so quickly,” Bentley says. “There are good, smart people working on it.”
Bayer researchers are doing their best to continue developing products that can control the psyllid having introduced two new insecticides already this year, Provado and Movento.
Bayer claims that Provado is a cost-effective and broad-spectrum control of many common and destructive insect pests, including psyllids, that is quickly absorbed and redistributed within the leaves resulting in quick knock down and good residual activity. Provado will be ideal for pre-harvest cleanup, with a short re-entry period and no, or minimal, pre-harvest intervals, the company says.
Bayer says Movento is a systemic foliar insecticide that will offer growers a tool for managing a broad range of sucking insect pests that contains the active ingredient spirotetramat, the first member of the new chemical class of tetramic acids developed exclusively by Bayer.
“I feel like we are starting to get a handle on it,” Newlin says. “We are very hopeful. We’ll do whatever it takes to whip this.”