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Rusty looking citrus problems?

Citrus grown in the home landscape can be attacked by a number of insect  and mite pests.  Some are large enough to  be spotted early in their infestation.   Others are so small that you can’t see them without magnification. Consequently,  you don’t tend to notice their damage until it’s too late to do anything about  it.  One very small pest that delivers an  unsightly punch is the citrus rust mite (CRM).

Mites are arachnids rather  than insects making them related to spiders.   While there are several different types of mites that affect citrus, CRM  is perhaps the most common.

The citrus rust mite is found on all citrus varieties throughout  Florida. Populations of CRM can develop quickly under ideal conditions with a  female laying 20 to 30 eggs over a 20-day period.  Although they can be found anytime of the  year, their peak populations usually occur during June and July.

Rust mites have  piercing-sucking mouthparts and feed on the outside exposed epidermal surface  of fruit that is 1/2 inch or larger and on plant leaves and green twigs. Feeding destroys the rind cells and ultimately  causes a very unappealing and alarming looking fruit.

The appearance and amount of damage depends on when the  infestation occurs.  When a fruit is  injured in summer or fall, the injured surface is smooth and dark brown in  color, commonly referred to as “bronzing”.  Mites feeding on fruit early in the spring  produce a peel referred to as “sharkskin” because of its rough,  grayish color. Blemished fruit  lose water faster than undamaged fruit and will be smaller and appear substandard.

Sun spots result from where the citrus rust mite avoids feeding on the most sun exposed portion of the fruit.

Photo credits:  Theresa Friday

Citrus rust mites prefer the fruit on the tree’s outer canopy that  is exposed to sunlight.  However, the  mite itself will avoid the most sun-exposed portion of the fruit.  This behavior results in a “sun spot” of  undamaged rind on the sunny side of the fruit.   This pattern of damage is helpful in the diagnosis of this pest.

Not all the fruit on a tree will be afflicted and not every citrus  tree in the yard will have an infestation.   Thankfully, this condition has no effect on flavor; it is strictly a  surface blemish. It does make fruit un-saleable (and sometimes even hard to give  away), but still good to eat.   Unfortunately, there is nothing you can do for it once the fruit is damaged.

Since rust mites are not readily visible to the naked eye, by the time the damage has been  observed, spraying would usually be too late to be worthwhile. Therefore, early  scouting is critical to avoid fruit blemishes.   Use a magnifying glass to look for the mites at the times when  infestation is expected to commence.  Mite populations usually begin to increase in April on new  foliage and reach a peak in June to July. Depending on weather conditions and  the occurrence of natural enemies, citrus rust mite populations usually decline  in August and September, but increase again in October and November.

Pay  special attention to trees recently sprayed with insecticides.  The misuse of insecticides can sometime allow  an explosion of mites.

Horticultural oils can be  used to control many pests that attack citrus, including mites, whiteflies and  scales. These products work by suffocating insects and causing them to die. When applied properly, oils provide a  very useful tool for controlling some citrus pests without damage to beneficial  organisms but the sprays require careful use to avoid plant Injury.

In general, be sure to  carefully read any insecticide labels before applying them to your citrus  trees. Before you spray your citrus with any insecticide, make sure citrus is  included on the label. Also make sure the insects or mites you would like to  control are listed on the label.

Contact Information

For more information or if you have a question, call The University of Florida/IFAS-Santa Rosa County Extension, at 850-623-3868, between the hours of 8:00 am and 4:30 pm weekdays.  Hearing-impaired individuals may call Santa Rosa County Emergency Management Service at 983-5373 (TDD).

Extension Service programs are open to all people without regard to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations.  The use of trade names in this article is solely for the purpose of providing specific information.  It is not a guarantee, warranty, or endorsement of the product name(s) and does not signify that they are approved to the exclusion of others.

Permanent link to this article: http://santarosa.ifas.ufl.edu/blog/2011/12/16/rusty-looking-citrus-problems/