|Crop Knowledge Master|
|Rhizoecus Root Mealybug|
Arnold H. Hara, Extension Entomologist
Ruth Niino-DuPonte, Research Associate
Department of Entomology
Since 1990, Rhizoecus hibisci, has spread to major potted foliage production areas. Its introduction to Hawaii is much more recent than the coffee root mealy bug, Geococcus coffeae, whose presence was recorded in the early 1900s. Potted palms and other slow-growing plants are more susceptible to infestation by root mealybugs because they require lengthy bench time to attain marketable size.
Rhizoecus hibisci have been found on palms, calathea, and Serrisa spp.
Rhizoecus hibisci is widely distributed in east and southeast Asia, and has also been found in Puerto Rico and Florida. In addition, R. caladii has recently been intercepted by California in rhapis palms from Hawaii.
Damage by the root mealybug is nonspecific in that the most common symptoms are slow plant growth, lack of vigor and subsequent death. Root mealybug is not evident unless the root ball is examined by removing the plants pot. White, waxy substance and adult females will be noticeable especially between the pot and root ball (Figs. 1 & 2). Plants that are slow-growing, root-bound, or under environmental or nutritional stress are more susceptible to mealybug infestation.
The life cycle from egg, crawler, nymph to adult is about 2 to 4 months (Figure 1). It is during the crawler stage that mealybugs spread and disperse. The adult female lives from 27 to 57 days depending on species and can give birth to 17 to 83 young in 1, 2, or 3 litters. White, cottony-like masses containing egg-laying females and/or eggs are normally visible on the outside of the root mass when an infested plant is lifted from its container. Males were not observed.
Figure 3. General biology of a root mealybug
(Adapted from: North Carolina Agric. Exten. Serv., 1978
White, cottony-like masses containing egg-laying females and/or eggs are normally visible on the outside of the root mass when an infested plant is lifted from its container. Eggs hatch less than 24 hours after being laid.
It is during the crawler stage that mealybugs spread and disperse.
The adult female root mealybug is bluish-grey, elongate-oval, up to 2.35 mm in length. It can be distinguished from the coffee root mealybug, Geococcus coffeae, by the absence of the anal hooks. The adult female lives from 27 to 57 days depending on species and can give birth to 17 to 83 young in 1, 2, or 3 litters. White, cottony-like masses containing egg-laying females and/or eggs are normally visible on the outside of the root mass when an infested plant is lifted from its container. Males were not observed.
Fig. 1. Enlarged view of root mealybugs. Fig. 2. Root mealybugs on outside of rootball
[Photo: Linquist (1991)] [Photo: Linquist (1991)]
Crawlers are the dispersal stage and are highly mobile. Once crawlers find a suitable spot, they settle down and begin to feed on roots with their sucking mouthparts. The initial root mealybug infestation into bench plants greenhouse is often from purchasing infested plants or from crawlers on host plants within or outside the greenhouse. The coffee root mealybug is known to spread by: 1) irrigation water, 2) re-use of previously infested pots, 3) re-use of contaminated media, or 4) crawlers moving from infested plants to other plants.
There are no known natural predators of Rhizoecus hibisci present in Hawaii.
Because the root mealybug is very difficult to detect and control, every effort should be made to prevent its spread and establishment. The following practices are recommended:
Research conducted by the University of Hawaii at Manoa, College of Tropical Agriculture and Human Resources has demonstrated that hot water dips alone are as effective as insecticides. Submerging potted Rhapis palms in 120 o F (49 o C) water until the internal root ball temperature reaches 115 o F (46 o C) is 100% effective in killing root mealybugs and does not significantly affect the potted palms. Drenching potted palms in hot water at 120o F for 15 minutes will not only control mealybugs, but will also eliminate burrowing nematodes.
Chemical control of root mealybugs by dipping or drenching with liquid insecticides is more effective than granular insecticides. Dursban TNP (4EC) applied twice at 2 week interval as a drench or dip controls the coffee root mealybug; however, it may take 4 to 6 months before the cottony waxy secretions deteriorate completely. This may pose a potential risk of shipment rejection by quarantine inspectors. Research trials ranked Dursban 50 WP and TNP (4EC) the least phytotoxic to palms and indicated that watering palms prior to drenching application significantly reduced insecticide phytotoxicity. A small group of plants should be treated at the recommended rate under the anticipated growing conditions and observed for phytotoxic symptoms for at least 14 days before a large number of plants are treated. In the dip method, the entire potted plant container is submerged in a diluted Dursban solution (1 pt per 100 gallons) submerging the roots for about 30 seconds. In the drench method, after pre-moistening with irrigation or rainfall, the diluted Dursban solution is poured into each potted plant container to saturate the soil at a rate of 10 to 12 fl. oz. per gallon of container size. Do not remove container from plants prior to treatment.
Marathon 60 WP is applied only as a drench and can be applied with a surfactant or wetting agent to assure thorough distribution of solution in the potting medium. Drench rates are determined by plant container size. Over 95% control has been observed for up to 12 weeks. Contact activity and systemic activity will reduce high root mealybug populations within 5 to 7 days. Residual activity of Marathon should control most emerging larvae.
FOLLOW SAFETY PRECAUTIONS GIVEN ON MANUFACTURERS LABELS.)
Consult a chemical sales representative, the Hawaii Department of Agriculture, or the University of Hawaii Cooperative Extension Service for correct formulation of insecticides, more information, or updated recommendations. The user is responsible for the proper use, application, storage, and disposal of pesticides.
Reference to a product does not imply approval or recommendation by the College of Tropical Agriculture and Human Resources, Cooperative Extension Service, University of Hawaii, or the United States Department of Agriculture and does not imply its approval to the exclusion of other products that may be suitable. All materials should be used in accordance with label instructions.
This information is the culmination of a series of interviews with researchers, extension agents, chemical sales representatives, and growers in Hawaii and a worldwide literature search.
FOR QUESTIONS OR COMMENTS PLEASE CONTACT:
Arnold Hara: 461 West Lanikaula St. Hilo, HI 96720, Ph: (808) 974-4105 Fax: (808) 974-4110 E-mail: firstname.lastname@example.org
Baker, J. R. (ed.) 1978. Insect and Related Pests of Flowers and Foliage Plants. North Carolina Agricultural Extension Service, AG-136, Raleigh, NC.
Beardsley, J.W., Jr. 1966. Hypogaeic mealybugs of the Hawaiian Islands (Homoptera: Pseudococcidae). Proc. Hawaii. Entomol. Soc. 14: 151-155.
Linquist, R.K. 1991. Identification of Insects and Related Pests of Horticultural Plants. Ohio Florists Association, Columbus, OH.
Snetsinger, R. 1966. Biology and control of a root-feeding mealybug on Saintpaulia. J. Econ. Entom. 59: 1077-1078.
Williams, D.J. 1996. Four related species of root mealybugs of the genus Rhizoecus from east and southeast Asia of importance at quarantine inspection (Homoptera: Coccoidea: Pseudococcidae). J. Natural History 30:1391-1403.