January 2013 Update: Village Rugose Spiraling Whitefly Assessment and Treatment
Village staff and consultants continue to monitor trees in public areas for the presence of the rugose spiraling whitefly and natural predators released as part of a Village-sponsored program. Regular surveys are conducted to measure the level of whitefly infestation on the trees and palm species most affected, to assess the effectiveness of treatment programs that began in 2011 and to evaluate the populations and extent of predatory beetles and parasitic wasps released in May-October 2012. Surveys conducted in late 2012 and early 2013 showed that Gumbo Limbo remain the local trees most affected by the whitefly invasion. Other trees and palms showed improvement in response to the Village root-injection insecticide treatment program.
A new treatment plan has been implemented per recommendations by the Village Arborist John Sutton and consulting Horticulturist Richard Murray. All Gumbo Limbos on the Rights-of-Way along Ridgewood Road and Cypress Drive were treated on January 23, 2013 by TruGreen, the Villlage's pest control contractor. Systemic fungicide, systemic insecticide and micronutrients to boost new growth were applied via liquid drenching as opposed to the previous method of root injections. Research has shown that applying diluted chemicals in a drench results in better absorption by the tree. Observations of Village Gumbo Limbo street trees have shown that the previously used injection method may be adding additional stress to the affected trees and causing canker. The treatment schedule will also change to four times per year with the next liquid drench insecticide application at the end of May 2013.
Village Arborist John Sutton has been instructed by the Village Manager to perform a Village-wide assessment of all Village trees and palms on Village property (streets, medians, swales, parks). The scope of work includes scouting for whitefly plus inspection and evaluation of infested areas. The survey will take place in mid-April 2013 since many trees drop their leaves in Winter. A report with recommendations will be submitted within a week of the assessment. The report will show where whitefly is identified in terms of the heaviest infestations to the lowest and include treatment recommendations for each area.
Results of Recent Street Tree Surveys and Treatment Recommendations
Village Arborist John Sutton inspected Gumbo Limbo street trees in several locations after Village Contractor TruGreen applied insecticide on September 9, 2012. In his letter to the Village dated October 10, 2012 (available here as PDF), Sutton noted "I have not observed a reduction in whitefly populations to non-damaging levels" although some trees were doing better. In addition to leaf loss and heavy white residue on the leaves, Sutton observed the development of canker in several Gumbos. Canker is characterized by "cracks in the bark and oozing of sap" and may be caused by "fungal spores or bacteria".
In order to reduce the stress on these affected Gumbo Limbos, Sutton recommended discontinuing the Village's preferred whitefly treatment of chemical injection into roots. This was the preferred treatment in the Village and involved drilling holes into the tree and inserting an insecticide-laden device that releases its contents over time. Arborist Sutton and Horticulturist Richard Murray, who provided a second opinion on January 21, 2013 (see letter (PDF) here), believe drilling holes may further stress and damage trees and also create additional entry points for fungal spores or bacteria that can cause canker. Details of the new recommended treatment program can be found in the consultants' letters referred to above.
Results of Monthly Evaluations of the Presence of Whitefly and Natural Enemies
Dr. Catharine Mannion, an Entomologist at the University of Florida IFAS Facility in South Miami-Dade County, and colleagues continue their monthly assessments of the presence of both whitefly and their natural enemies in the Village. This research will continue through May 2013. Dr. Mannion states that a key period for assessing whitefly populations will occur when temperatures increase in the Spring. Infestations, in general, go down during the cooler Winter temperatures. Cooler temperatures also affect the whitefly's natural enemies. Assessments in those months also will be very important to gauge the presence of natural enemies of the whitefly and if any insecticide applications should be made. A final analysis of data and annual report will be submitted in May 2013.
Dr. Mannion submitted a Whitefly Project Update to the Village on October 15, 2012 (report available here as PDF). The report summarized the results of her work to " enhance the presence of natural enemies to control the Rugose spiraling whitefly through releases of known natural enemies and to ultimately determine the impact of these natural enemies on the whitefly infestation." Her team released 2,490 predatory beetles in nine batches at 17 locations in the Village between May 29 and October 9, 2012. 320 parasitic wasps of possibly two different types were released. The release locations include sites treated with insecticide as part of the Village Whitefly treatment program and areas that were not treated. Intensive evaluations of the predators' presence and locations took place on September 11 and 25 and October 9, 2012. The predatory beetles established themselves at half of the release sites where no insecticide had been used. Little or no populations were observed at treated locations. Parasitic wasps are established at all sample sites that include areas where no wasps were released by the researchers. According to Dr. Mannion, "It appears that the parasitic wasps are less affected by the insecticide". The wasp populations and their migration to new areas of infestation are excellent results.
Dr. Mannion provides this assessment in the October 15, 2012 report (PDF) based on her team's research:
"Using predators and parasites for pest control can ultimately provide a long-term, biologically based solution. But it also requires patience. Thus far, the release of parasites and predators is successful in that there is establishment of one predator and two parasites. These populations should grow, but unfortunately it takes time for the populations to grow enough to show the impact they have on the pest population. [--] Evaluations of whitefly infestations and presence of natural enemies will continue through May 2013. Whitefly infestations, in general, naturally go down during the winter as temperatures cool which will also impact the natural enemies. A key period will be next Spring when temperatures warm. At that time, it will be important to assess if and where any insecticide applications should be made and to determine the presence of natural enemies."
Consulting Horticulturist Murray added these observations in his letter (PDF):
"Whitefly infestations have occurred in other states like California which saw an infestation of Ash Whiteflies which produced large amounts of honeydew and sooty mold similar to the effects of the Spiraling Whitefly. The good news is that the infestation died off in about 5 years as predator insects started feeding on the Ash Whiteflies and that insect is no longer a problem in the landscape. Hopefully the Rugose Spiraling Whitefly will follow the same pattern and it will not be a significant problem in a few more years.
It seems likely that landscape trees susceptible to Spiraling Whiteflies will have to be treated on a regular basis to prevent them from becoming infested with this nuisance insect for the next few years. We do have treatment options that will work well to control this insect but the treatment program must be modified for Gumbo Limbo trees to achieve adequate control."