Common citrus problems in north Florida

Citrus leafminers do not kill the tree but can cause unsightly damage. You can manage leafminer by using horticultural oil sprays labeled for citrus.

I continue to receive questions about citrus leafminer, citrus rust mite and leaf spot disease on locally grown citrus trees. Below is info on these common citrus pests.  

The mated citrus leafminer female lays a single egg on the underside of the leaf close to the leaf stem. Upon hatching, the flat larva works its way through the leaf, feeding, leaving a trail (also called a mine) that’s visible as a squiggly line. The mines cause the leaf to curl.

Citrus leafminers do not kill the tree but can cause unsightly damage. You can manage leafminer by using horticultural oil sprays labeled for citrus.

Use the oil as a preventative measure by targeting new growth and getting good coverage underneath the leaves as well as on the upper surface. The oil will make the leaf surface slick making it difficult for eggs to stick. Look for one of the year-round or summer horticultural oils.

Spray the tree shortly after a flush of new growth. Sprays to control adults usually are not successful.

Mated females more actively lay eggs when there is a lot of young tender growth. This typically happens when there is a flush of new growth such as in the spring. Avoid fertilizing too much or too often as fertilizations can result in “artificial” flushes of new growth, which is what attracts the mated female moths to the tree.

Also factor in the fertilizer that the tree is getting from nearby lawn areas. The tree’s roots extend out 2 to 3 times beyond the end of the branches, growing into nearby lawn areas. Many homeowners unknowingly over-fertilize their citrus and other fruit trees as a result of the tree roots taking up fertilizer applied to surrounding lawn grass.

Citrus rust mite is an extremely small mite. Their feeding causes dark discolored areas on the surface of the fruit (outer peal/skin). This is basically a cosmetic problem, not affecting the edibility of the fruit. This mite can be controlled with horticultural oil, as described above with citrus leafminer.

Wet weather provides perfect conditions for fungal leaf spot diseases. With frequent rains, it’s common to have foliage diseases (leaf spot diseases) on citrus and many other landscape plants. These foliage diseases don’t cause long-term problems for citrus trees. Some of the heavily infected leaves may fall prematurely.

To control these types of diseases, it is necessary to begin a spray program early in the year (spring) and spray every 7 to 14 days while weather conditions favor disease development (during frequent rains). A copper-based fungicide labelled for use on citrus can be used. Good coverage of the foliage throughout the entire tree is required.

Always follow label directions and precautions for any pesticide product you use.

Below are links to UF/IFAS Extension publications with more info.  

https://edis.ifas.ufl.edu/hs141, http://edis.ifas.ufl.edu/pdffiles/CH/CH15900.pdf, https://edis.ifas.ufl.edu/ch179

Larry Williams is the Extension horticulture agent with the Okaloosa County Cooperative Extension Service, University of Florida. Contact Larry at 689-5850 or email lwilliams@myokaloosa.com.