One reason I moved to Florida 10 years ago was to have the ability to leisurely stroll out the back door on a warm Florida winter day and pick a few tangelos and squeeze some fresh orange juice for breakfast. 2011 wake-up call! We have been dealing with a nightmare of a disease which is almost in every community I’ve been to in Naples.
The citrus industry was hit with the bad news in late August 2005 that a devastating disease, called HLB (short for huanglongbing, which means yellow shoot disease, one of the early foliage symptoms). But it is more commonly known as CG or “citrus greening” because the fruit doesn’t ripen evenly and stays green on the bottom end. This is a bacterial disease which affects the phloem portion of the vascular system; the pipelines which carry carbs produced by leaf photosynthesis downward are blocked. It debilitates trees, causing severe dieback and may eventually cause death of the tree over time (within six to eight years).
It affects fruit ripening, lowers fruit production and ruins the taste of the affected fruit on any given tree. Dr. Phil Stansly, of UF/IFAS, Immokalee Research Center, notes that the most-affected fruit fall from the tree and what is left, looks and tastes normal. The symptoms are difficult to distinguish from several other diseases and nutrient deficiencies.
Several key citrus greening characteristics are: blotchy mottle, an asymmetric yellowing that crosses the veins (micronutrient yellowing tends to be symmetrical and stays between veins); nutrient deficient, dwarfed foliage; initially, one branch exhibits yellow mottling, then it spreads throughout the canopy; fruit drop; small, lop-sided fruit; and the fruit only half-ripens, that is, the bottom half of the fruit remains green, which is the symptom which sparked the common name, citrus greening.
This disease is spread (vectored) 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, and they are yellow and can be found along with the yellow-orange colored eggs on the new, tender growth. Look for little white waxy filaments (see picture) on the tip of the nymph’s abdomen; these may standout 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 lifetime and there are nine to 10 generations per year. However, there is little reproduction during the winter when the trees are not flushing.
Another complicating factor is that besides the favorite psyllid hosts of citrus including key lime, it will feed on ornamental citrus relatives including orange jasmine (Murraya paniculata) and Chinese box-orange (Severinia buxifolia). Fortunately, the disease-causing bacterium doesn’t kill the ornamentals and Dr. Stansly reports the ornamentals are a transitory host. But having the plants in the landscape are like having a “typhoid Mary” in the neighborhood which harbors the psyllids. What used to be the dirt common to orange jasmine is now hard to find because the Florida Division of Plant Industries requires nurseries to grow it in screen-houses.
The citrus grove management strategy for citrus greening disease is a two-pronged attack: first, control the vector and, second, reduce stress factors such as poor nutrition and drought. It may also be helpful to supplement the poor nutrient status of the citrus trees. Maury Boyd, a local grove owner, has prolonged the life of his trees by using repeated spray applications he developed containing salicylate, and nutrients (about 12 to 14 ingredients, see: tinyurl.com/3tw8y95).
The best concoction for the homeowner may consist of foliar applications of soluble fertilizers high in potassium and include all macro and micro nutrients. One homeowner product is a Keyplex formulation tinyurl.com/42lu3gb. (This website lists locations where it can be purchased). It is recommended it be sprayed at least six times during growing season. More frequent applications (there to four weeks) should give even better results.
Check the new growth on your citrus plants weekly. If you see the psyllids, use a 2 percent mixture of an appropriately labeled horticultural mineral oil on the new growth or a neem oil or malathion plus oil product. However, mineral oil only gets what it hits, that is, there is no residual effect. If a psyllid lands on your plant an hour later, it won’t be killed by the oil residue.
Because psyllids are active all year, another approach rather than frequent spraying (who can keep up with that?) is a one-shot treatment of a soil drench insecticide called imidacloprid.
The product labeled for citrus is called Bayer Advanced Fruit, Citrus & Vegetable Insect Control (see label: tinyurl.com/3nt6bb8). It claims season-long control.
The Division of Plant Industry has been involved with some parasitic wasp releases, but I haven’t noticed them at all in our area. 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.
Because I won’t be making all of the nutrient and insect control applications, to achieve my dream of fresh Honey Bell orange juice from the backyard, I may need to look at my citrus trees as short-timers, maybe only lasting seven to eight years or so. I may have to look at a cycle of replanting a new citrus tree every five to ten years to replace the declining trees.
More info and pictures of symptoms: tinyurl.com/3lwwcnw.
Also, to help with diagnosing disease symptoms see, A Guide to Citrus Disease Identification, at: edis.ifas.ufl.edu/CH159.
We need to start looking at planting other fruit which will grow in our unique subtropical climate whether it is low-chill peaches or plums (tinyurl.com/3zwhhaq) or papyas for that breakfast smoothie!
See more about alternative fruit choices at: trec.ifas.ufl.edu/fruitscapes/
Doug Caldwell, Ph.D., is the commercial landscape horticulture extension agent and landscape entomologist with the University of Florida Collier County Extension Service. Email
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