Management of Rugose Spiraling Whitefly on Gumbo Limbo in South Florida

Joseph Doccola1, JB Torrish2, Jim Maler3, Douglas Bush4, Stephen Wyka1, and Donald Grosman5

1Arborjet Inc., Woburn, MA 01801, 2Arborjet Inc., Mt. Dora, FL 32757, All Florida Pest Control, Hollywood FL 33021, 4Douglas Pest Control, Inc., Homestead FL 33033, 5Arborjet Inc., Lufkin, TX 75904

Figure 3. Reference Severity Scale used to rate percent coverage of plate with growth of sooty mold (photos by J. Doccola). Plate opacities greater than 10% exceed the threshold tolerance in these studies.

0%, Very Low 10%, Low 33%, Moderate 100%, Severe Introduction

Trial 1 – Miami, FL

Methods. In Miami Florida, eight randomly-selected Gumbo Limbo trees were assigned to each of seven treatments: ACE-jet (97.4% w/w acephate), IMA-jet (5% w/w imidacloprid), IMA-jet 10 (10% w/w imidacloprid) and ACE-jet + IMA-jet, ACE-jet + IMA-jet 10, IMA-jet + IMA-jet 10 (Arborjet, Inc., Woburn, MA), and untreated. The systemic insecticides were applied on December 20, 2011 using Arborjet’s QUIK-jet at label rates based on tree diameter at breast height (DBH): ACE-jet and IMA-jet applied at 8 mL per 2.5 cm DBH, IMA-jet 10 applied at 6 mL per 2.5 cm DBH. When applied in combination, the doses were reduced by half per insecticide, with the exception of the IMA-jet + IMA-jet 10, where the 10% was applied at the full (6 mL per 2.5 cm DBH) rate. The injection sites were installed in the trunk flare and placed ~15 cm apart around the tree.

Fig. 1. A. Rugose spiraling whitefly (RSWF) adult, top left, (photo by H Glenn, UF/IFAS); B. RSWF-infested Gumbo Limbo, Hawks Cay Resort, Duck Key, FL, lower left, (photo by J. Doccola); C. Gumbo Limbo in southern Florida is planted as a shade and ornamental tree, right (photo by J. Doccola).

Conclusions

Results

Mannion, C. and H. Glenn. 2010. Rugose Spiraling Whitefly (previously Gumbo Limbo Spiraling Whitefly): A New Whitefly in South Florida. UF/IFAS Factsheet. 5 pp. (webpage accessed 08/06/2012).

Frank J. Byrne, Anthony A. Urena, Lindsay J. Robinson, Robert I. Krieger, Joe

Doccola, and Joseph G. Morse. 2011. Evaluation of neonicotinoid, organophosphate a d avermectin trunk injections for the management of avocado thrips in California avocado groves. Published online in Wiley Online Library. DOI 10.1002/ps.2337.

Acknowledgments We thank the Amaretto Homeowner Association, Miami, FL and Hawks Cay Resort, Duck Key, FL for providing the study sites. This research was supported, in full, by Arborjet, Inc. Woburn, MA.

In 2009, the exotic Rugose Spiraling Whitefly (RSWF, Aleurodicus rugioperculatus) (Hemiptera: Aleyrodidae) (Fig. 1b) was reported in Miami-Dade County (Mannion and Glenn, 2010). RSWF has a broad host range which includes palms and woody ornamental trees such as gumbo limbo (Fig. 1 b&c). Like other piercing sucking insects (e.g., aphids), RSWF exudes honey dew which supports the growth of sooty mold. Tolerance of honey dew and sooty mold in home owner association (HOA) landscapes and in resort properties is low.

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Insecticides such as acephate and imidacloprid can be applied by tree injection for control of piercing-sucking insects. In Avocado, acephate and imidacloprid were shown to accumulate in the canopy at differential rates following tree injection (Byrne et al. 2011). Acephate was active in the foliage 1 week (7 days) after injection and has a short residual (6 weeks), whereas imidacloprid accumulated more slowly, over 16 weeks. Combining the quick knockdown of an organophosphate (acephate) with the longer residual activity of the neonicotinoid (imidacloprid) serves to introduce two modes of action and to potentially reduce the frequency of treatment. The goals of these studies are (a) to manage RSWF infestation for one year with a single injection treatment and (b) to recommend the best management practices using Arborjet tree injection methodology. Here we report on two studies in southern Florida (Miami and Duck Key) on RSWF-infested Gumbo Limbo using two systemic insecticides.

Trial 2 – Duck Key, FL

Methods. At the Hawks Cay Resort on Duck Key, eight randomly-selected Gumbo Limbo trees were assigned to each of three treatments: ACE-jet high + IMA-jet high, IMA-jet 10 high, and untreated controls. The systemic insecticides were applied on May 21, 2012 using QUIK-jet: ACE-jet at 9 mls, IMA-jet at 16 mL per 2.5 cm DBH and IMA-jet 10 at 6 mL per 2.5 cm DBH. The injection sites were installed in the trunk flare and placed ~15 cm apart around the tree. A clear vinyl plate was fixed to each tree for 65 DAT. The vinyl plates were evaluated as in Trial 1. This study is ongoing and will run for 365 DAT. Statistical analyses were conducted in MINITAB Version 15 (Minitab, Inc. State College, PA, USA), one-way ANOVA and 2-sample t-tests were conducted; statistical significance accepted at p=0.05. Percent data were arcsine transformed using the formula: arcsin (sqrt (x/100), prior to analysis.

Clear vinyl plates (Figure 2) were fixed to each tree for 30 d to 60 d periods. The vinyl plates were collected and scanned on a CanoScan8800F flatbed scanner. The scanned images were assessed visually for opacity. The plates were given a numeric rating from 0 to 100, where 0 = clear plate or no sooty mold, and 100 = plate completely covered by sooty mold. The degree of infestation may be implied by the degree of blackening of the plates, and the sooty mold growth qualified as low, moderate or severe (Figure 3). We established a nuisance level at opacity greater than 10%. Successful control of RSWF therefore was at 10% or lower. This study ran for 365 DAT.

Figure 2. Inverted clear vinyl plate affixed to tree bole using a binder clip to collect honey dew and sooty mold (photo by J. Doccola)

Figure 4A-B Percent sooty mold on clear vinyl plates in Trial 1 at 28 DAT (A) and 274 DAT (B). All the trees were infested by RSWF. The 10% line is the threshold of tolerance ; above the line is unacceptable.

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Figure 5A-B Percent sooty mold on clear vinyl plates in Trial 2 at 65 DAT (A) and 120 DAT (B). All the trees were infested by RSWF. The 10% line is the threshold of tolerance; above the line is unacceptable.

The two studies applied variable rates of imidacloprid according to the treatment protocol, from 0.2 to 0.8 g ai per 2.5 cm dbh. In Study 1, treatments did not differ statistically from the untreated checks in assays up to and including 274 DAT (Figure 4). In Study 2, statistical differences were observed among the treatments through 120 DAT (Figure 5). The highest rate of imidacloprid (to 0.8 g ai) was equivalent in each study. Difference in dose rates or amount of formulation applied do not account for treatment differences observed. The more plausible explanation for the differences in efficacy is timing of application. Two factors may be at play, that is, (a) increase in whitefly activity with warmer temperatures, and (b) the role of tree phenology with respect to retention or loss of foliage in which the imidacloprid has accumulated. Treatments based on tree phenology and expected whitefly activity proved most effective in our studies. It is our recommendation to apply treatments to Gumbo Limbo trees for Rugose Spiraling Whitefly approximately 30 days before expected peak activity and after trees have refoliated. Administering ACE-jet + IMA-jet sequentially (i.e., IMA-jet first, followed by ACE-jet into the same injection site) provides quick knockdown, two different modes of action and greater residual activity.

Literature Cited

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