Univerisity of Florida IFAS Extension Reprint
Control of Insects,
Mites and Diseases of Florida's Dooryard Citrus Trees
Insects, mites, and
diseases are common problems to the Florida homeowner with a
dooryard planting of citrus. The object of this circular is to aid him
in the control of these pests.
Frequently, more harm than good comes from an attempt to control these
pesticides. To be successful, the right material should be applied at
the right time using the right amount in the right manner. If any of these
conditions cannot be met, it is usually better not to spray at all.
In order to acquaint the home citrus grower with insects, mites, and diseases
and their control, the subjects are discussed in the following order:
individual problems; beneficial insects, mites, and fungi; approaches
to the control of citrus pests; dooryard pest control chart; suggested
spray programs; sprayers; and precautions in the use of pesticides.
Citrus rust mites have an annulate, wedge-shaped body, lemon-yellow in
about 1/200 inch in length. They have 2 pairs of legs and piercing-sucking
mouthparts. They can just barely be seen with the naked eye and can be
seen better with a 10-power magnifying glass.
The life cycle of the citrus rust mite is completed within 5-7 days during
the summer. Eggs are spherical (round), transparent, and laid singly on
leaves, stems, and fruit of all commercial citrus varieties. The mite
has 2 immature stages that are similar to the adult in appearance. Although
present throughout the year, in Florida the citrus rust mite is most prevalent
during the summer months.
Injury from extensive citrus rust mite feeding causes surface blemish
to the fruit . This can reduce the external quality of marketable fruit,
and reduce yield by causing premature fruit drop and reduced fruit size.
None of these affects the internal fruit quality.
Citrus red mites (purple mites) are only about 1/50 inch long. They are
bright red to
deep purple in color and infest leaves, fruit, and new growth. Injury
results from feeding and appears as a scratching or etching of fruit and
the upper surface of leaves. In periods of prolonged dry weather, they
can cause a collapse of leaf cells and even leaf drop. Use a 10X magnifying
glass to inspect for citrus red mites and eggs on the upper surface of
the leaf, looking especially along the midrib, as well as in angular crevices
of the leaf stems and the young, tender twigs. Citrus red mites are more
numerous from May through July, but can be the most damaging in the fall
and winter months during periods of low rainfall or inadequate irrigation.
Texas citrus mites are about the same size as citrus red mites, but are
brownish-green in color with dark brown to greenish spots or bars near
the lateral margins (edges). Numbers of mites are generally much heavier
along the midrib on the upper surface of leaves . They also are most numerous
May through July, and most damaging October through February.
Six-spotted mites are also about the same size as citrus red mites but
are white-yellow to sulfur-yellow in color. Adults usually have six dark
spots that are barely visible with a 10-power magnifying glass, arranged
in two rows on the back or abdomen. These mites live in colonies on the
under surface of leaves, especially along the veins and midribs. Injury
appears as yellow spots, often cupped toward the top of the leaf. Six-spotted
mites prefer grapefruit, but can be found occasionally on other varieties
of citrus. They usually appear in early February and have disappeared
by mid July.
Purple scale and Glover scale (long scale) are very similar in appearance
but Glover scale is longer and narrower. The covering of the mature scale
purplish-brown in color and about 1/8 inch long. These scales suck juices
from leaves, fruit, twigs, and branches. Injury to leaves results in yellow
or chlorotic spots. These scales can cause leaves and fruit to drop, as
well as cause twigs and branches to die. They are often overlooked because
they are found primarily on the inner parts of the tree.
Chaff scale forms a light brown, nearly round armor closely resembling
a piece of wheat chaff. Where abundant on the bark, the limbs appear to
be covered with chaff. This scale infests leaves, fruit, and bark, causing
green spots on the fruit.
Citrus snow scale is a pest in most parts of citrus growing areas of Florida.
Male scales have elongated white armor, while females are mahogany colored,
making them inconspicuous and hard to see against tree bark. They are
largely confined to the trunk, limbs, and twigs.
If its parasite is not active in your area, chemical control may be necessary.
Be sure to thoroughly wet all infested bark.
Florida Red scale and Yellow scale are armored scales of similar size
and shape. The
armor or covering of the adult female is almost circular in outline for
however, the yellow scale is yellow to light orange in color, while Florida
Red scale is dark reddish-brown with a nipple-shaped center that is grayish
to reddish-yellow. These insects infest leaves and fruit, and can cause
them to drop.
Do not mistake Florida Red scale for fungus killed whiteflies.Cottony
cushion scale is rarely of economic importance except in nurseries and
on young trees. The mature female is conspicuous because of her fluted
white egg sac. The Vedalia ladybeetle feeds on this scale and usually
keeps it under control but cannot always be depended upon on young trees.
Whiteflies primarily attack new growth. The nymph (immature stage), which
transparent and seldom recognized, infests the underside of the leaves,
copious quantities of sap, resulting in some injury to the trees. Dooryard
growers also object to sooty mold fungus, which in turn grows in the honey-dew
excreted by the immature stages of the whitefly. Never spray the trees
when a large number of adult whiteflies are present. Instead, wait 10
to 12 days until most of the adult whiteflies have disappeared. This will
allow enough time for the eggs to hatch and the young to be killed before
they can cause much damage.
The citrus blackfly is a close relative of the common whitefly often seen
in Florida. The adult fly is about 1/25 of an inch long and slate blue-black
in color. Eggs are laid in a distinctive spiral pattern on the underside
of leaves with about 28 to 34 eggs in each spiral. The larvae change from
dusky color through dark brown to black as they grow. The pupae are shiny
black, spiny, and oval in shape. Homeowners should look for this insect
on the underside of leaves and report suspected infestations to the local
county Extension office.
Mealybugs have a segmented body which is covered with mealy white wax.
most common during the spring and early summer, but are frequently found
during the winter in tree crotches and under loose bark. Mealybugs may
become so numerous following fruit set that their feeding under the button
of young fruit may cause the fruit to drop. They also collect in masses
between fruit clusters. Sooty mold can also be severe following a mealybug
Aphids or plant lice attack young, tender growth and cause leaves to wrinkle
and curl .
Insecticides should be applied to infested young growth before the leaves
curl. There is little value in applying an insecticide after many leaves
are curled or new growth is nearly mature.
The orange dog is often a pest of young citrus trees. As an adult, the
species is a large black and yellow swallowtail butterfly. However, it
is named from the larva , which is an ugly brown and white caterpillar
which grows to a length of 1 1/2 to 2 inches. During the summer and early
fall, these caterpillars may be quite destructive on young trees. Pick
caterpillars off young trees by hand.
Several kinds of grasshoppers and katydids feed on the leaves of citrus
usually are not important pests of dooryard trees. Eggs of the broad-winged
katydid are laid along the leaf margins and arouse the interest of many
SOME BENEFICIAL ORGANISMS
There are many beneficial parasites (tiny, wasp-like insects), predators
(insect and mite) and pathogens (predominantly fungi) that attack various
pests of citrus. In many cases, natural enemies regulate potential pests.
This is referred to as biological control.
Parasitic wasps. Many wasp-like parasites, particularly of the genus Aphytis,
effectively control a wide range of armored and soft scale pests. Most
noteworthy are the parasites of purple scale, Florida Red scale (Plate
33), and citrus snow scale.
Fungi. Two parasitic fungi, Aschersonia spp. and Aegerita sp. are commonly
infecting immature whiteflies of citrus. Red Aschersonia forms pink and
reddish pustules 1/8 inch or less in diameter on the underside of leaves.
It is so colorful that many growers are quite concerned when it appears
and usually think it is harmful. Aegerita or brown whitefly fungus appears
as cinnamon pustules about 1/8 inch in diameter on the underside of leaves.
This fungus is often confused with Florida Red scale.
Other fungi such as Hirsutella thompsonii and Triplosporium floridana
rust mite and Texas citrus mite, respectively. H. thompsonii is particularly
important in reducing citrus rust mite populations in the summer.
Predators. Several insect and mite predators such as the ladybeetles (adult
and larvae ) and lacewings (larvae) feed upon eggs and other stages of
insects and mites. Most are general in their feeding habits and exhibit
an overall effect on pests throughout the year.
Scab is a fungus disease that attacks young leaves, small fruit, and tender
grapefruit, Temple , Murcott honey orange, lemons, sour orange, Satsumas,
and some varieties of tangelos. It causes raised, light brown, corky areas
on fruit and leaves.
Melanose is a fungus disease that attacks young fruit primarily
of grapefruit, however, other citrus varieties may be affected. The injury
to fruit is often confused with rust mite injury, which has a smoother
feel. This rind blemish does not affect the quality of the fruit. While
scab is more important on young trees, melanose is more injurious to older
trees.Trees are usually over 10 years of age before melanose becomes a
problem. Since melanose grows in dead wood, keeping the trees free of
such wood will aid in the control of this disease.
Greasy spot is a fungus disease that attacks all varieties of citrus grown
Infection occurs mostly in the summer, but symptoms do not appear until
two to nine
months later. Symptoms first show up as yellowish-brown spots on the leaves.
The spots develop a slightly blistered appearance on the underside of
the leaves, and ultimately become oily brown or black. Spots vary in size
from small dots to 1/4 inch in diameter. Where several spots coalesce
(grow together), the areas covered may be considerably larger. This disease
can cause serious premature defoliation during the winter. This disease
may also infect the fruit rind, especially on grapefruit, causing specks
to appear in areas between the oil glands. Good spray coverage of the
lower leaf surface is essential for satisfactory control.
Sooty mold may blacken leaves of the entire tree. Aphids, mealybugs, certain
soft scales, and particularly immature whiteflies excrete a sweet, syrupy
material known as honey-dew. The sooty mold fungus grows wherever this
material falls. Controlling these insects will prevent sooty mold, and
oil sprays will usually cause it to flake off, making the leaves and fruit
bright and shiny.
APPROACHES TO THE CONTROL OF CITRUS PESTS
Homeowners with a few citrus trees should follow one of the following
courses in the control of insects and diseases:
1.Do not apply pesticides. Depend entirely on natural control of predaceous
insects and mites, parasitic insects and diseases, weather, and other
factors. There are many instances where dooryard, and even commercial
plantings are never sprayed or dusted, and yet the trees survive and produce
good crops of satisfactory fruit. Under this program, yield may be reduced
and external quality will usually be low.
2.Control individual problems when they first appear. Make frequent inspections,
identify the problems, and apply the recommended pesticides before infestations
can become severe. These steps require: 1) learning to identify the more
common pests of citrus; 2) detecting their presence early; 3) sprays timed
to give effective control. Unfortunately, most homeowners do not find
this practice easy to follow and the results are often unsatisfactory.
Frequently, the pests cause severe damage before they are detected.
3.Follow the spray program suggested in this circular. This schedule may
need to be supplemented in the event insects such as grasshoppers, katydids,
and other less common pests attack citrus trees between the regular sprays.
Suggested Spray Program
There is no simple rule one can follow which will always result in bright
fruit and vigorous trees. However, there is a rather simple spray schedule
that can be followed which will control most pests and result in thrifty
trees producing fruit of good quality, but not necessarily always of a
bright color. A schedule of this type usually requires three or possibly
four spray applications per year. A suggested spray program follows.
(Substitutes can be made - see Table 1.)
Postbloom (4 weeks after petals fall) - Copper plus a recommended miticide.
Summer (July) - Benlate or copper plus Ethion plus .5% spray oil.
Fall - Recommended miticide for citrus rust mite and spider mite control.
Table 1. Dooryard Citrus Pest Control Chart.
Other Pests Controlled
Rust mitesSpider mites
snow scale only.
Rust mitesSpider mitesAphids
species of scale
Does not control
WhitefliesSpider mitesGreasy spotLoosens
Does not control
snow scale. Do not
apply if trees are
wilting or in a near
wilt state. Do not
apply within 3
weeks of sulfur.
Oil applied after
trees to cold
damage and may
reduce the crop
the following year.
Oil applied in the
fall may inhibit
and retard fruit
Spider mitesCitrus snow scale
Most species of scale insectsSpider mites
Rust mitesMost species of scale insects
Scale (does not control citrus snow
scale)WhitefliesGreasy spotLoosens sooty
under scale pests.
ScaleSpider mitesGreasy spotLoosens sooty
Apply before new
growth starts in the
spring and when
2/3 of petals have
young fruit, 4
weeks after the
July. Sprays of
corky areas of the
rinds, but this will
not affect eating
1Read label thoroughly; follow label directions for mixing and application
Many of the failures to control citrus pests that are charged against
the pesticide are quite often the result of improper application and timing.
A gardener who has a substantial number of citrus trees is advised to
get a good sprayer. One to three-gallon compressed air models can be used
while trees are small. These models are not expensive. Air pressure is
pumped up by hand, and the nozzle, which is at the end of a short wand,
delivers a fine spray which can be accurately directed to all surfaces.
When trees become large and cannot be thoroughly covered by this type
dooryard citrus growers should either obtain a small power sprayer or
hire someone with adequate equipment to insure thorough coverage of the
entire tree. If these conditions cannot be met, i is generally better
not to apply sprays at all.
Sprayers which attach to the end of garden hoses are generally not satisfactory
for use on mature citrus trees. The spray pattern is usually coarse, and
it is very difficult to direct the spray to reach and adequately cover
the undersides of the leaves, especially those near the ground, and the
side of plants close to a building or fence. If a hose attachment sprayer
is used, the emulsion concentrate formulation of insecticide is preferred
over the wettable powder.
PRECAUTIONS IN THE USE OF PESTICIDES
Care in Handling Pesticides. Treat all pesticides as poisons and handle
the cautions on the manufacturer's product labels. Always read the label
completely before using any pesticide.
Pesticide Residues. Citrus consumed by the producer should be prepared
generally accepted practices of washing, peeling, etc. Dooryard fruit
that is offered for sale must conform with federal and/or state food and
drug pesticide residue regulations. Copper and oil emulsions are exempt
from a tolerance, and no waiting period is required. Waiting periods between
last application of certain pesticides and harvest of fruit are as follows:
Benlate - no time limitation; Ethion - 21 days on lemons and limes; no
time limitation on orange, grapefruit, tangelo, tangerine; do not repeat
application within 90 days; Kelthane - 7 days; Malathion - 7 days.
Oil Emulsion Sprays. Do not apply oil emulsion sprays during the fall
or winter months or to a tree that shows signs of wilting. Allow at least
6 weeks to elapse between applications. Do not mix oil with sulfur. Apply
the two separately, allowing at least a three-week interval between applications,
or injury to fruit and foliage may result.
Herbicides (weed killers). Another problem that should be of concern to
citrus growers is the use of weed killers on lawns. If a weed killer is
used, be sure it is not used close enough to citrus to result in residues
in the fruit; or be sure it is approved for use around citrus trees.
Household Sprays. Several homeowners have made the mistake of spraying
citrus trees and other plants with sprays formulated specifically for
use inside homes to control household pests. These sprays, in general,
have the insecticide dissolved in some type of petroleum solvent such
as refined (deodorized) kerosene and should not be applied to plants because
injury to the plants usually results.
This document is Circular 139, a series of the Pest Management Department,
Research and Education Center, Lake Alfred, FL, Florida Cooperative Extension
Service, Institute of Food and Agricultural Sciences, University of Florida.
Publication date: May 1992. Reviewed: August 1993. Revised: June 1994.
Joseph L. Knapp, professor, entomologist, Department of Entomology and
Nematology, Citrus Research and Education Center, Lake Alfred, Florida,
a branch campus of the University of Florida, Gainesville, Florida.
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