March 12, 2008

Citrus Questions?

By Jane Morse
University of Florida, IFAS Pinellas County Extension Agent

rust miteA common occurrence this time of year is to see oranges that have brown areas. This is most likely rust mite damage (unless it smells rotten). Rust mite damage is nothing to worry about as it doesn’t affect the taste of the fruit; it just makes the outside rind not be perfectly orange.
If you want perfectly orange rinds, spray your trees in March or April with a horticultural oil (use an oil that lists paraffinic oil as the active ingredient). Always read and follow directions exactly as indicated on the label of pesticides.

leafminerAnother common problem on citrus is leafminers. Leaves will look misshapen and one can see serpentine tunnels on the leaf surface. For mature trees this will not harm them and little control is available. Either leave them alone or during the spring growth flush spray the tree with horticultural oil twice, spaced two weeks apart. Very young trees can be hurt by the loss of leaf surface that leafminers cause. Young trees should be treated with a horticultural oil during the spring growth flush.

Fertilization is necessary to keep your tree healthy and producing well. Bearing trees should be fertilized 3 times per year with a good quality 8-8-8 citrus or palm fertilizer that supplies micro nutrients (i.e. zinc, manganese, boron and copper) as well as the macro nutrients (i.e. nitrogen, phosphorus, potassium). The amount applied at each application is about five pounds. A tree that is 5 years or older would receive three separate applications of 5 pounds for a total of 15 pounds of fertilizer per year. A bathroom scale can be used to determine fertilizer weight. If your trees are surrounded by turf and you are fertilizing your turf, then you probably don’t need to apply extra fertilizer to your trees.

The recommended 3 applications per year can be made in January-February, May-June and October-November. Be sure to evenly spread the fertilizer. A general guideline is to spread the fertilizer as many feet beyond the drip line of the canopy as the age of the tree in years (up to ten). For trees younger than 5 years call the Extension Service at 727-582-2100 to get their recommended fertilizing schedule.

The soil pH is also important. Citrus prefer a soil with a pH between 5.5 and 6.5. If you live near the beach or have an alkaline soil (above pH 7.0) then minor element deficiency symptoms may develop. The only way to supply these minor elements when the soil pH is alkaline is by applying a nutritional spray to the leaves (foliar application). These sprays should contain zinc, manganese, boron and copper. Spraying once per year should be sufficient. Local garden supply stores should be able to recommend a spray for you.

Watering is also important to tree health. Too much water or too little water can damage your tree. Trees in a well-drained soil usually need about 3/4 inch of water per week (if there is no rainfall). Too much water can cause foot rot to occur. Watch out for flooding, or soggy soils. Citrus do not like to have wet feet!

What about pest and disease management? Homeowners usually only need to apply horticultural oil, insecticidal soap or copper fungicide to control pests and disease.

There are many beneficial-bugs that help to keep pest-bug populations under control and by using horticultural oils and insecticidal soaps most of the beneficial-bugs are saved while the pest bugs are killed. Beneficial-bugs do us a great service and help to keep most pest-bug populations well under control. Using hard chemicals that kill all bugs, including the beneficial-bugs, can actually cause an explosion of pest-bugs to occur. So stay away from the hard, conventional pesticides, especially those that keep killing for a long time. You do NOT need them and they usually make the problem worse.

For other questions about plants:

Information for this article was obtained from: Citrus Culture in the Home Landscape Control Of Insects, Mites And Disease Of Florida’s Dooryard Citrus

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