COOPERATIVE EXTENSION WORK IN AGRICULTURE AND HOME ECONOMICS
(Acts of May 8 and June 30, 1914)
Agricultural Extension Service, University of Florida. Florida State University and United
States Department of Agriculture, Cooperating. H. G. Clayton, Director
Control of Insects and Diseases of
Dooryard Citrus Trees
FRED P. LAWRENCE
JAMES E. BROGDON
Dooryard plantings of citrus hold much interest for many
Florida home-owners. These should receive care and attention
if they are to grow and produce fruit properly. Most instructions
and recommendations for citrus have been directed to commercial
growers. The object of this circular is to aid the dooryard citrus
I, iL a small citrus tree with summer oil.
4.. .. ..-
A grower with a few citrus trees can either follow the spray
schedule suggested in this circular or make frequent inspections
and apply pesticides as they are needed. If he chooses the latter
course he should learn to identify the common pests of citrus
and apply the recommended controls before the infestations
become severe. (Extension Circular 137 will be very helpful in
learning to identify the common pests of citrus.)
There are many instances where dooryard, and even commer-
cial, plantings are never sprayed and yet the trees thrive and
produce good crops of satisfactory fruit. This is primarily the
result of the presence of beneficial insects such as ladybeetles
and helpful fungi like the Aschersonias that kill destructive pests.
This is known as biological control. Where this condition exists
and trees maintain a healthy growing condition with satisfactory
fruit, pesticides should not be used. Unfortunately, most grow-
ers can never attain this condition or, if they do, it is frequently
destroyed or thrown off balance in favor of the pests by condi-
tions that are more unfavorable for the friendly insects and
diseases than for the pests. When this occurs artificial or
chemical control measures are usually necessary.
There is no simple rule one can follow which will always re-
sult in bright fruit and vigorous trees. However, there is a
rather simple spray schedule that can be followed which will con-
trol 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 appli-
cations per year.
1. Dormant Spray (usually applied in January).-This is a
most effective spray for controlling insect pests and diseases of
citrus. Use DN, Aramite or Ovex for purple mite and six-
spotted mite control, sulfur for rust mites, malathion for scales
and copper for melanose and scab control. (See chart.) Those
gardeners whose trees are growing on alkaline soils should add
zinc and manganese to this spray mixture. (See section on
2. Post-Bloom Spray.-This is an optional spray and may be
omitted. However, growers who added zinc and copper to their
dormant spray and growers who are especially interested in
bright fruit should apply a post-bloom spray. This spray should
be applied immediately after the flower petals have fallen and
before the young fruits are % inch in diameter. This usually
occurs in April. The post-bloom spray should be: (a) a mixture
of malathion and sulfur, or (b) an oil emulsion spray. A neutral
copper may be added for melanose control on older trees (see
discussion on melanose under diseases). Never mix oil and sulfur
in the same spray. (See (d) under Cautions.)
3. Summer Oil.-Spray all trees thoroughly with an oil
emulsion spray between June 15 and July 15. This spray is
primarily for scale control but will also remove sooty mold from
the foliage and control most other pests attacking citrus at that
time of the year.
4. Fall Miticide (usually applied between October 15 and
November 15).-A combination of DN or Aramite or Ovex plus
wettable sulfur should control all mites.
Specific Insects and Their Control
Florida red scale is an armored scale with a protective cover-
ing that is dark reddish-brown in color with a nipple-shaped
center that is grayish to reddish-yellow in color. The adult
female is about 1/12 inch in diameter and almost circular in
outline. These scales infest leaves and fruit and may cause
them to drop. There are at least four main generations a year.
For control measures, look under "-cal-" on the control chart.
Purple scales also have a protective armor. The mature scales
are shaped somewhat like an oyster shell, purplish-brown in
color and about i/A inch long. Purple scales feed on leaves, fruits
and all ages of wood. They collect especially along midribs and
base of leaves, but may occur on any part, on the upper as well
as the lower surface. Injury to leaves results in a yellow or
chlorotic area or spot. These scales can cause leaf drop, fruit
drop and dead wood. This is Florida's most destructive citrus
For satisfactory scale control, see "scales" on the chart.
Purple mites are only about 1/50 inch long. They are rose
to deep purple in color and infest leaves, fruit and new growth.
Injury appears as a scratching or etching of the upper surface
of the leaf. They may cause a collapse of leaf cells and leaf
drop. Use a magnifying glass to inspect for purple mites and
eggs on the upper surface of the leaf, especially along the mid-
rib and in angular crevices of leaf stems and young, tender twigs.
They cannot be readily seen without a magnifying glass. Purple
mites are more numerous from November to April, but may be
found at other times during the year. For control look under
"red spider" on the chart which follows.
Six-spotted mites are about the same size as purple mites but
are white-yellow to sulfur-yellow in color. Adults usually have
six dark spots which are barely visible with a 10-power magni-
fying glass and arranged in two rows on the back or abdomen.
These mites live in colonies on the under surface of leaves only,
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 are found on other types of citrus.
They usually disappear with rainy weather. (For control see
Rust mites are present most of the year and their injury,
which does not materially affect fruit quality, often results in a
brown, rusty color to the fruit. They are about 1/200 inch long
and cannot be seen with the naked eye and are difficult to recog-
nize with a 10-power magnifying gla,-. Look for mites on green
fruit and both sides of leaves. If one is not especially interested
in bright fruit, it will not be necessary to apply sulfur for rust
mite control. If bright fruit is desired, sulfur should be applied
about every six weeks from fruit set until harvest. (Sulfur
should not be mixed with oil or one used within three weeks of
Whiteflies.-The whiteflies that infest citrus are not considered
serious pests in commercial groves but are disliked by most
dooryard growers. The nymph (immature stage), which is sel-
dom recognized by the grower, infests the under side of the
leaves and withdraws quantities of sap from them, resulting in
some injury to trees. Dooryard growers object to sooty mold
fungus which grows in the large quantities of honeydew given
off by the immature stages of the whitefly. In controlling white-
flies, never spray the trees when a large number of adults are
seen. It is better to wait 10 to 20 days after most adult white-
flies have stopped flying. This will give the eggs time to hatch
and allow the young to be killed before they cause much damage.
(For control see "-- alel and whiteflies" on the control chart.)
Sooty Mold.-Aphids, mealybugs, certain soft scales and par-
ticularly immature whiteflies excrete a sweet, syrupy material
known as honeydew. This falls on leaves and fruit and in it
grows sooty mold fungus. Sooty mold blackens the entire tree
including the fruit and this blackening, which dulls the luster
of foliage, causes the home gardener much concern. By control-
ling these insects you can prevent sooty mold. However, where
sooty mold is present, oil sprays will usually cause it to flake off,
making the leaf bright and shiny.
Aphids or plant lice attack young, tender growth and cause
leaves to wrinkle and curl. Controls 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 nearly mature.
Ladybeetles are small beneficial insects and there are many
different kinds. Some are black with two red spots, and others
are 0,lnrgL with several or no black spots. Both the larvae and
adults feed on harmful insects.
Red Aschersonia, commonly found on citrus trees, is a bene-
ficial or friendly fungus that kills immature whiteflies. It forms
pink and reddish pustules 1/ inch or less in diameter on the
under side of leaves.
Brown whitefly fungus also aids in control of whiteflies. It
appears as cinnamon or brownish colored pustules about 1/8 inch
in diameter on the under side of leaves. This fungus is often
confused with Florida red scale.
Scab is a fungus disease that attacks young leaves, small fruit
and tender twigs of grapefruit, temple oranges, lemons, sour
oranges, Satsumas and some varieties of tangelos and is particu-
larly important in coastal areas. It is very important on young
trees. It causes raised, light brown, corky areas on fruit and
leaves and can be controlled with a copper spray applied just
before growth starts in the spring.
Melanose is a fungus disease that attacks leaves and fruit and
tender t % i The diseased leaves have raised brown lesions that
make them feel like sandpaper. The injury to fruit is often
confused with russeting or rust mite injury, which has more
of a smooth feel. 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. Melanose
is easily controlled by coating the young fruits, leaves and tender
twigs with a copper spray just after the flowers shed (usually
The nutritional or physiological spray is very important and
necessary for citrus growing in alkaline soils. Many growers
DOORYARD CITRUS PEST CONTROL CHART
4 to 5 tablespoons of 80
to 90% oil per gallon of
water (3 pints in 25
5 tablespoons per gal. of
water (1 lb. in 20 gals.)
2 teaspoons per gal of
water (1 pint in 25 gals.)
Oil emulsion sprays may be applied from petal fall in
the spring through September, but the preferred time
is June 15 to July 15. Cover upper and lower surfaces
of all leaves and branches thoroughly. (See cautions on
use of oil sprays.)
Malathion may be used any time insects become numer-
ous. It is not as effective as oil emulsion sprays against
heavy infestations of Florida red and purple scales.
Under these conditions make a second application of
malathion 3 to 4 weeks after the first. Thorough cover-
age of all tree surfaces is necessary.
Use oil sprays at same dosage as recommended above if scales are present. One-half
the above dosage is satisfactory for mites only. (See cautions on use of oil sprays.)
Follow recommendations on the container labels for Aramite, Ovex or DN. Aramite
and Ovex can be used any time of year. DN should not be used when the temperature
is above 88 degrees F. or on young foliage before it hardens. Malathion will kill
mites but not their eggs. If used, a second application should be made 1 to 2 weeks
after the first.
Same as under scales
A second application may be necessary 3 to 4 weeks
after the first. Oil emulsion sprays are not satisfactory
against these pests. The Vedalia or Australian lady-
beetle is an effective predator of cottony-cushion scale.
4 tablespoons per gal.
(1 lb. in 10 gals.)
12 to 11/ lbs. per tree,
depending upon size
As directed on container
As directed on container
As directed on container
Rust mites cause russeting or brown, rusty fruit. Un-
less bright fruit is desired, control usually is not neces-
sary. Apply every 6 weeks from fruit set until harvest
for bright fruit. Do not mix oil with sulfur or use one
within 3 weeks of the other.
Aphids cause a curling of young, tender leaves. Observe
,...iL growth carefully and treat before leaves curl.
'i. i a large percentage of leaves are curled or new
growth is nearly mature, control is not practical.
Sprinkle chlordane dust around base of trees or in nests
or hills about the area. Chlordane sprays may be used.
Sprays may be used. '-o :-.,-.l-r. control these
pests mechanically on ., i trees by catching and
killing them while infestations are light.
Scab is a fungus disease that is very important on many
varieties of citrus trees. (See discussion under dis-
eases.) Apply spray thoroughly to all surfaces just
before new growth starts in the spring.
Trees are usually more than 10 years of age before
melanose becomes a problem. Apply sprays Ih..,uchli,
to young fruits, leaves and tender twigs just ,fttv the
also find it beneficial on all citrus, regardless of soil acidity or
A good nutritional spray can be made by mixing 3 tablespoons
of copper sulphate, 21/4 tablespoons of zinc sulphate, 31/% table-
spoons of manganese sulphate, and 61/2 tablespoons of hydrated
lime in 3 gallons of water. In making this spray, it is better
to make a paste of the copper, zinc and manganese and mix this
thoroughly in the 3 gallons of water. Then make a paste of the
hydrated lime and add it to the mixture. This mixture should
be stirred thoroughly until used. If not used immediately, the
material should be thrown away and a new mixture made.
Where available, neutral copper, zinc and manganese may be
used instead of the sulphate materials and the hydrated lime
will not be needed. Neutral materials are easier to mix and use.
The nutritional spray should be applied in the spring before
growth starts. Between January 15 and February 15 is usually
the most satisfactory time. It can be applied later in the year.
However, it is not a good practice to apply it to new growth.
Cautions in Use of Pesticides
All pesticides should be treated as poisons and handled accord-
ing to the cautions on manufacturer's product label. Always
read the label; it is for your protection. Cautions in use of oil
emulsion sprays include: (a) Never spray a tree which shows
signs of wilt. (b) Do not spray with oil during the winter
months. (c) If two oil sprays are necessary, they should never
be applied nearer than six weeks apart. (d) Do not mix oil with
sulfur or use one within three weeks of the other, as injury to
fruit and foliage may result. DN should never be applied to
unhardened young foliage or when the temperature is above 88
degrees F. Do not mix DN with oil emulsion, as it will cause
foliage and fruit injury.
AGRICULTURAL EXTENSION SERVICE