Extension Service: Watch your citrus and ornamentals for tiny insects that may carry disease

The citrus industry was hit with more bad news in late August 2005. Another devastating disease, called huang long bing, “yellow dragon disease,” because of foliage symptoms — was confirmed in Miami-Dade County. This disease is commonly known as citrus greening.

It has spread throughout South Florida and there are suspect cases in Collier County awaiting lab verification. This is a bacterial disease that affects the vascular system of citrus. It kills the tree over time (six to eight years) and affects fruit ripening, lowers fruit production and ruins the taste of the fruit. The symptoms are difficult to distinguish from several other diseases. Several key characteristics are:

-- yellowing that crosses the veins(micronutrient yellowing tends to stay between veins).

-- only one branch exhibits yellow mottling, then it spreads throughout the canopy.

-- fruit drop.

-- small, lop-sided fruit.

-- fruit only half-ripens, that is, the bottom half of the fruit remains green, which is the symptom that sparked the common name citrus greening.

This disease is spread by the Asiatic citrus psyllid, Diaphorina citri. The Asiatic citrus psyllid is a sucking insect that was found in June 1998 on the east coast of Florida and has become widespread throughout the state. The adult resembles a miniature, 1/8 inch long cicada with mottled brown wings.

Characteristically, they perch at a raised angle on the shoot or leaf as they feed. The immature feeding stages, are called nymphs, they are yellow and can be found along with the yellow eggs on the new, tender growth. Look for little white waxy filaments (see the photo) on the tip of the nymph’s abdomen, these stand out and are more readily visible than the insect.

What makes this pest a season-long concern is that females may deposit more than 800 eggs during their lifetimes and there are nine to 10 generations per year.

Favorite psyllid hosts include citrus, key lime, ornamentals (39 species listed so far), including orange jasmine (Murraya paniculata) and Chinese box-orange (Severinia buxifolia). Fortunately, the disease-causing bacterium doesn’t seem to survive in most of these ornamentals, except for the Chinese box-orange.

Check the new growth on your citrus plants weekly. Check the new growth on your citrus plants weekly. One solution, if you see the psyllids, is to use a 2 percent mixture of an appropriately labeled horticultural mineral oil on the new growth. The oil only gets what it hits, that is, there is no residual effect. If a psyllid lands an hour later it won’t be killed by the oil residue.

The Division of Plant Industry has been involved with some parasitic wasp releases. Examine host plants carefully before purchasing and if this psyllid is found at a retailer, notify the owner, as the plants per Division of Plant Industries regulations, will have to be quarantined until the psyllids are eliminated.

The Division of Plant Industry has been involved with some parasitic wasp releases. Examine host plants carefully before purchasing and if this psyllid is found at a retailer, notify the owner, as the plants per Division of Plant Industries regulations, will have to be quarantined until the psyllids are eliminated.

More info and pictures of symptoms and maps of outbreak areas:

www.doacs.state.fl.us/pi/chrp/greening/citrusgreening.html

Also, to help with diagnosing disease symptoms see, A Guide to Citrus Disease Identification, at: edis.ifas.ufl.edu/CH159.

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Doug Caldwell is commercial landscape horticulture extension agent for the Collier County Extension Service. For more information on home gardening, contact the Master Gardener Plant Clinic at 353-2872. For specimen identification, the Extension Plant Clinic is open 9 a.m. to noon and 1-4 p.m. at 14700 Immokalee Road Monday, Wednesday and Friday and some days at the Naples Central Avenue branch library; call 353-2872. For more landscape information, visit: collier.ifas.ufl.edu.

© 2006 marconews.com. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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