Here is an old extension article by Lowell F. True written in 1987. Much of it is still relevant.

One exception worth mentioning is the decline in the expertise in citrus trees of the local nurseries that serve the Phoenix area. I personally would only buy citrus trees from two sources. The first and best choice would be from Greenfield Nursery they grow their own trees and are third generation citrus providers. My second choice would be Harpers Nursery.

Also worth mentioning is the fact that many people that have citrus no longer have irrigation so all of the watering data needs to be disregarded. You might want to read an article I wrote on watering.

One other thing to think about is the introduction of Mycorrhizal fungi into the root system to strengthen and protect your citrus trees. We can do that for you.

Warner

The University of Arizona College of Agriculture Tucson, Arizona 85721 Reprinted 7/87
Lowell F. True
Extension Agricultural Agent Steve Fazio
Extension Horticulturist, Retired Terry Mikel
Extension Horticultural Agent

Planting and caring for citrus trees isn't difficult, but success does depend on several things:

Location is a major concern. Plant citrus only in the warner desert and low-frost-risk areas of our state. In many sections of central Arizona, small trees may be stunted or killed unless they are protected from frost and cold winters. In other areas, soil or water may be too salty, and in some places the soil may be too rocky or alkaline.
One way to make sure citrus will grow in your area before you start planting is to check for mature trees. If they grow for someone else, they should grow for you.

CHOOSE THE RIGHT VARIETY AND SITE

It is important to select varieties that will meet your needs and do well where you live. Consider the mature size of your tree when selecting a planting site.

Citrus foliage and fruit differ in their resistance to injury from freezing. Here is a list in increasing degree of ability to withstand cold: lime, lemon, sweet oranges, tangerine types, grapefruit, sour orange, kumquat and calamondin.

Consider harvest time of different varieties so you will have fresh fruit much of the year.

Genetic dwarf varieties, such as Marrs Orange, are good for small spaces. Areas
6-8 feet across should be adequate for most of these.
Oranges

WASHINGTON NAVEL generally bears larger fruit than the Valencia and other sweet varieties, but. is lowyielding in home yard plantings. Trees produce abundant bloom but most drop from the tree. Fruit quality is better in medium to heavy soils. Poorly adapted to sandy Yuma Mesa soils. Recommended for limited production.

VALENCIA grows to medium size and is excellent for juice or eating. Should be planted in warmer areas or protected because fruit matures in March. It is a
good producer, with yields more than 200 pounds of fruit per tree after trees are 8
-10 years old.

SWEET ORANGES include several varieties usually grouped together as "Arizona Sweets." MARRS has the advantage of being an early-maturing, semi-dwarf tree. It produces above-average crops early in the life of the tree. Fruit quality is fair to good. Fruit may sunburn in full sun. TROVITA is an early-ripening variety with excellent quality. Vigorous with good cold tolerance; it is a good substitute for Washington Navel.

PINEAPPLE is early-ripening, medium size, attractive fruit. Not readily available at all nurseries.

DILLER and HAMLIN produce smaller fruit than the Valencia orange with eight to 10 seeds per fruit. The Diller fruit is a little more seedy. Popular, they produce the largest yields of early oranges; good fresh and excellent for juice. They are ideal for home plantings where juice is the main interest. However, the Hamlin orange juice is
normally more pulpy.

"Red" or "blood" oranges, while varying in color are well-adapted and ripen during the same sea son as other sweet oranges. TAROCO, MORO, RUBY and SANGUINELLI are named red or pigmented type blood oranges.

Tangerine-type Fruits:

CLEMENTINE (Algerian Tangerine) ripens
between November and January, is deep orange-colored, loose-skinned, with excellent flavor. It has many seeds when properly cross-pollinated. Yields are irregular. After a tree is 3 or 4 years old, it develops a high resistance to
freezing but fruit is frost-susceptible. Should be planted with other tangerine or tangelo varieties for crosspollination.

The Sour Orange tree can also be used as a pollinizer. Fruit is often dry if left on the tree past minimum maturity or when budded on rough lemon rootstock.

FAIRCHILD is a U.S. Department of Agriculture variety that ripens in November and December. It is of medium size with good quality and flavor. It yields more regularly than Algerian and can be substituted for it. The tree is
dense but smaller than other common tangerine varieties and produces a small tree. It is a medium size fruit with many seeds. It must have other citrus varieties near for cross-pollinatiom in order to produce satisfactorily.

FREMONT also developed and released by the U. S. Department of Agriculture, ripens in December and January with a deep orange color and good flavor. It sets a heavy
crop in alternate years. Responds to cross-pollination. It is an open-type tree.

KINNOW MANDARIN ripens from February through April, bearing yellow-orange colored fruit with excellent flavor. Normally, it sets a very heavy crop, then
fails to bear the following year. Requires fruit thinning in heavy-set years to avoid broken limbs. Trees are frost tolerant in off-crop years but both trees and fruit are subject to frost damage in on-crop years.

Picking time Mature tree for home sizeg (in Variety Consumption diameter)

Sweet oranges Dec.-Mar. 20-24ft
Navel oranges Nov.-Feb, 16-2Oft
Valencia oranges Mar.-May 20-24ft
Grapefruit Nov.-May 20-24ft
Lemon (except dwarf) Sep.-Apr. 22-26ft
TangerinelTangelo/Mandarin Nov.-Apr. 16-2Oft

Grapefruit:

MARSH fruit, normally high in acid, can be eaten after October but flavor is best in April and May. Fruit normally is less likely to be frozen than oranges. Growth is vigorous and it bears consistently. Nearly seedless, it is good for home plantings.

REDELUSH is similar to Marsh except juice sacs are dark pink in fall, fading to a uniform light pink in spring
months.

Limes:

Lines are recommended only for the warmest parts of the Salt River Valley and the Yuma Mesa. They are suitable for protected patios in colder areas.

BEAISS SEEDLESS (Persian) ripens from July through November, but provides some fruit all year. It has a larger fruit than Mexican lime, with a tart but pleasant lime flavor when fully ripe. Very susceptible to frost injury.

MEXICAN (Key) ripens September through October. The fruit is smaller than Bearss with a high acid flavor. Extremely tender to frost.

Lemons:

EUREKA, LISBON AND VILLAFRANCA may be picked green as early as they become juicy. Tree and fruit are quite susceptible to frost injury; recommended only for warmer areas. Size may be controlled with annual February pruning.

Tangelos:

ORLANDO TANGELO ripens from November to January. Fruit is medium size, yellow-orange, with a pleasing flavor. A heavy, regular producer, this tree grows
rapidly and has high tolerance to freezing although fruit is susceptible. May be planted close to the Algerian tangerine for cross-pollination. Leaves normally curl upward.

MINNEOLA TANGELO has fruit generally larger than the Orlando with distinctive pear shape and easy peeling, has a dark orange color when ripe, excellent eating quality. Ripens in January to March. Fruit may freeze in colder areas. Production is lighter than the Orlando, but it responds well to cross-pollination. Other Kinds of Citrus

CALAMONDIN CITRUS, used primarily for landscaping, is well adapted and sets fruit from March to December. Fruit is small with a thin peel, attractive but highly acid and of little edible value. The tree grows upright and is highly tolerant to cold.

KUMQUAT and LIMEQUAT ripen from November through March. Fruit has a very pleasing flavor when fully ripe. The tree size is small. The limequat is extremely frost tolerant, but the kumquat fairly tolerant.

SOUR ORANGE, CLEOPATRA MANDARIN, CHINOTTO, PONKAN, BOUQUET (BOUQUET DE FLEURS), SEVERINA BUXIFOLIA and others fit well into home landscaping. Culture is the same as for other citrus varieties. Trees in this group, except sour orange, generally are smaller than coinmercial varieties and suitable for patio or
container planting.

Care of Young Trees

Regardless of variety, it is best to plant 2-year-old trees, 3-4 feet tall, with a trunk about five-eighths to 1 inch in diameter. Large trees are more difficult to transplant and establish than 2-year-old trees because of the large root ball and
weight.

CHECK ROOTSTOCK VARIETY Most citrus trees are budded on sour orange or a variety of other rootstocks. Sour orange generally is considered best for home
plantings. Because of frost and disease susceptibility, rough lemon rootstock is not recommended. Other rootatocks, which are very acceptable, include the Troyer, Carrizo, Taiwanica and Volkameriana. Troyer & Carrizo rootstocks
may have a slight dwarfing effect but not pronounced. Volkameriana produces strong, fast growing top growth.

When selecting trees, pay special attention to the condition of the root system. The ball should be at least 8 inches across for a 2-year-old tree. If the ball is small in comparison to the top or has been broken, don~t buy it. Trees grown in 2 112- to 5-gallon, plastic-type containers may be somewhat smaller than balled and burlapped trees, but recovery from transplanting has been good. When removing trees from containers, handle the root ball carefully.

PLANTING TIME The best time for planting citrus trees is March or early April after danger of frost has passed.

Fall planting in October or early November is acceptable but consideration must be given to adequate frost protection during the remainder of the winter. Unless you want a hedge effect, space standard trees 12 to 15 feet apart. If youre planting several varieties, two trees may be placed 18 inches apart so that they will develop as a single tree.

The varieties selected should grow at about equal rates. Semi-dwarf types may be spaced 6 to 8 feet. PLANTING Dig a hole at least 2 feet wide and 2 feet deeper than tbe root ball, then refill to the depth of the root ball. In poor soils, it is wise to make the hole larger and backfill with good soil to the desired depth. This hole should be dug at least 3 feet in diameter and 4 feet deep, or as deep as necessary until good drainage is established. When backfill is placed in the hole, irrigate and allow soil to settle thoroughly before planting the tree.

Place the balled tree in the hole without removing the burlap or tar paper. Set the tree so that the top of the root ball is even with the soil level of the yard.
With the tree in place in the planting hole, tar paper should be removed before the hole is filled. Fill in uniformly with good soil, firming it as the hole is filled. Leave a 3- to 4-inch-deep basin to facilitate irrigation. Water thoroughly immediately after planting.

Do not put granulated fertilizer of any kind in the hole during the planting operation, as severe burning may result. Compressed fertilizer "pills" can be used. A mulch of grass clippings, forest mulch or other organic material placed on top of the soil in the basin area, will help conserve moisture.

IRRIGATING YOUNG TREES During the first year, irrigate every seven days in the summer, and once every two to four weeks in the winter. During the second
year, irrigation intervals can be increased to 10-14 days in the summer, and once every three to four weeks in winter.

Maintaining a mulch in the tree basin during the first two to three summers will allow for maximum interval between irrigations without tree stress. Remove mulch in early November to allow full soil exposure to winter sun. Keep basins around young trees grass-free to facilitate irrigation and eliminate root competition. When irrigating, fill
basin slowly.

Do not allow water to stand around trees budded on rough lemon rootstock because of the occurrence of Foot Rot Cummosis Fungus.

PROTECT TREE TRUNKS Young trunks should be whitewashed or wrapped with cardboard to avoid sunburn. Wraps also help prevent lawnmower damage or weed
spray injury to trunks.

PRUNE YOUNG TREES SPARINGLY Remove any sucker growth below the bud union on young trees. Trim off badly placed growth that interferes with other branches.
If limbs are killed by freezing, remove them after spring growth starts. Young trees are not uniform in growth but will become more symmetrical with age. Rapidly growing terminals, particularly noticeable on lemon trees, may be pinched or cut back during the growing season to even-up growth rate.

DONT OVERFERTILIZE Young citrus trees respond readily to fertilizer in most soils, but care should be taken not to give them too much. Overfertilization can cause severe leafburn and rapid defoliation. No fertilizer is needed the first growing season except in very low-fertility soils.

Starting the second year, sprinkle two to four tablespoons of any recommended commercial fetilizer in the tree basin. Water immediately and repeat three more times during the growing season. Apply fertilizer evenly over the tree basin area.
In sandy soils, add commercial fertilizer six to eight times a year to compensate for loss by leaching.

By the third growing season, trees that have made normal growth should receive a total of 1/2 pound of actual nitrogen per tree (see nitrogen chart), in four to six applications. Iron chelate often will help trees maintain maximum growth.

On 4- to 5-year-old trees, nitrogen may be increased to 1 pound of actual nitrogen per year, applied in February, May and July in medium and heavy soils.

IN ARIZONA, DO NOT FERTILIZE CiTRUS ANY LATER THAN AUGUST. Trees in sandy soils respond to more frequent applications. If more mature trees are transplanted into the yard, regard them as young trees from a fertuzer standpoint. Apply small quantities in 4- to 6-week intervals.

FROST Freezing can damage both tree and fruit of all citrus varieties, but some are more sensitive than others.

Older orange and grapefruit trees are quite tolerant to cold, and seldom need to be protected. The fruit, however, is usually damaged when temperatures fall below 26 degrees Fahrenheit for a period of several hours. In the desert areas of Arizona, nighttime temperatures can drop below freezing from mid-November to late March;
most often in January.

During winter, a daily radio frost warning is issued for the benefit of citrus tree owners in Yuma, Maricopa and Pinal counties. PROVIDE FROST PROTECTION In most areas of southern Arizona where citrus is grown, some type of frost protection is necessary from November through March during the first two or three years. Palm fronds give effective protection, but corn stalks also work well. Protect the trunk and main branches of young trees, leaving one-third of the leafy area exposed to sunlight and air. Place four to six fronds or 12-15 corn or sorghum stalks around the tree and tie firmly in place with twine.

Young trees can be successfully protected from frost by running water under the tree during the below-freezing hours, covering them with a large cardboard box, placing a burlap bag over the tree or covering with cloth. Do not use plastic unless you build a frame to keep the plastic away from tree foliage. Plastic does not hold in much heat compared to other materials. Remove heavy cloth coverings after each frost period. Burlap may be left in place for the entire winter. Hanging a light bulb in the branches on cold nights provides additional heat. If a tree is frozen, do not prune frozen parts until new growth emerges in spring. After new growth begins, the exact portions killed by frost can be more clearly seen and pruned off.
Care of Mature Trees

IRRIGATE AS NEEDED

Soil may be considered as a reservoir for water. A thin film of water adheres to soil particles. If particles are large, as with sand, little water is held per cubic foot of soil. As particle size becomes smaller, more particles are present and more water is held. A soil that holds a large amount of water does not need to be irrigated
as frequently, but more water is required per irrigation. Water is lost from the soil by (1) evaporation from the surface, (2) transpiration from the leaves and (3) drainage
below the root zone of the tree. Rate of loss generally depends on the weather. Water loss from the soil under a large, mature 16- to 20-foot-tall tree is about 6 inches in July and 1 inch in January. Thus, average sandy-loan soils that bold about 4 inches of water require irrigation at 14- to 20-day intervals in July. Coarser soils (sandy) require more frequent irrigation.

Supplying water is only part of proper irrigation. All irrigation water in Arizona contains dissolved salts of different kinds, such as table salt (sodium chloride). If irrigation water is applied to only the upper 3 feet of soil where most
of the roots are located, the salt remains in this zone. After several years, this increased amount of salt will injure the tree, causing leaves to turn brown around the edges and fall prematurely. Eventually the tree will die. But, because
the salts are soluble, it is possible to apply excess water to dissolve them and leach them below the root system where subsoil drainage is adequate. This deep leaching is only needed once or twice each season. Sprinkler water should not come in contact with the foliage. Citrus leaves absorb salt directly from water, causing
severe leaf drop.

As a general rule for irrigation of home citrus, apply a deep soaking irrigation of 8-10 inches of water in January to leach salt, then apply normal irrigation in February and March. After March, gradually increase irrigation frequency until summer then irrigate at 2- to 3-week intervals depending on soil type.

As stated before, this pilot schedule may not fit all circumstances. Time each irrigation by the condition of the tree or trees rather than by the calendar. A slight wilting of leaves indicates that a tree does not have enough water, and
irrigation is needed at once. New leaves will show the first signs of water stress.
When trees are watered with a hose, be sure there is a basin around the tree. It should be 3-4 inches deep and extend out from the trunk to the drip line. L~t water run slowly into the basin for several hours or until sufficient penetration is assured.
Do not overwater. This is a common problem where citrus trees are planted in lawn areas. Excess water, particularly light, frequent irrigation, may cause yellow, chlorotic leaves.

Remember that irrigation is one of the most important phases of citrus culture. A tree needs an adequate supply of moisture at all times, including winter months when lawns may be dormant. Much has been said about the danger of irrigating citrus trees during the blooming period.

Excessive blossom shedding can result if the trees are stressed for water prior to bloom. Maintaining an even watering schedule through the bloom period will avoid any undue stress.

FERTILIZE CAREFULLY Citrus trees do not have to be fertilized heavily, but regular applications of nitrogen in one form or another are needed. Usually, nitrogen is the only major nutrient required, though iron often is needed to correct yellowing of the leaves. Potassium and phosphorous generally are adequate in central Arizona soils, but all soils require nitrogen.

On the Yuma Mesa, citrus has responded to phosphate applications. Nitrogen deficiency, showing up as yellow-green leaves, normally develops over a period of two or four years on unfertilized trees but can be quickly corrected with proper fertilization. Pale green leaves are normal in two situations.

A heavy drop of old leaves normally occurs in March and April. Before dropping, nitrogen is removed from these leaves and goes to new ones, leaving old leaves pale green. (Shoots produced on grapefruit during the summer and fall normally turn yellow in the winter, but regain their green color in the spring.)

In southern Arizona, a mature grapefruit tree in good, healthy condition wul need an annual application of 1 pound of actual nitrogen each year. Oranges and other mature citrus will require 2 pounds. Apply half of this in February and the remainder as a split in May/August.

IN ARIZONA, DO NOT FERTILIZE CITRUS ANY LATER THAN AUGUST. Manure may be applied periodically in the fall, but should be supplemented with commercial fertilizer in the spring. On the sandy Yuma Mesa soils, an annual application of two to three pounds of actual nitrogen is needed for mature trees. Nitrogen can be supplied to the soil in the form of animal manures, commercially prepared chemical fertilizers or a
comb mat ion of the two. Commercial fertilizers are generally preferred because research indicates that excessive use of animal manure may induce iron ch loros is in citrus. So, use it sparingly.

WHICH COMMERCIAL FERTILIZER?

Any fertilizer that contains nitrogen may be used. Ammonium sulfate and urea are easily applied, and the nitrogen they contain is readily used by plants But, keep in mind that it is the actual percentage of nitrogen and not the total pounds of material that counts. The chart below lists some of the more commonly used fertilizer and the amount needed to equal one pound of actual nitrogen.

IRON DEFICIENCY This condition is indicated by yellow-green leaves with green veins. As the condition becomes more severe, leaves may turn almost white. Usually, trees will have a few leaves of each type, ranging from normal green to white. Iron chlorosis often is a problem in home yards because nearby plants need frequent irrigation. In some cases it can be corrected by changing the watering schedule to provide longer intervals between irrigations. Frequent irrigation
will make the condition worse, so shallow rooted flowers requiring frequent watering should not be planted in tree basins.

Grapefruit trees normally turn yellow during the winter months but re-green as new leaves appear in the spring. Do not apply iron to correct this "winter chlorosis" condition. To correct iron chlorosis chemically, treat trees with iron sulfate or an iron chelate compound. Place iron sulfate in a shallow circular trench around the tree trunk or broadcast it around the entire tree basin from the trunk to outside the
drip line, and apply 4-6 inches of water. An average-size tree requires 20-30 pounds of iron sulfate.

When using iron chelate, apply according to label directions to the tree basin area and irrigate thoroughly. Trees do not respond to chelate applications in winter but will respond well during April to September. HOW TO APPLY FERTILIZER Apply by broadcasting evenly on the soil beneath the tree. Distribute evenly from
the trunk out to the drip line, just before an irrigation. Water moves nitrogen into the soil where it is absorbed by roots. If irrigation is light, fertilizer may concentrate in the upper root zone and cause damage to roots, and burn leaves.

Applying fertilizer in a few holes or in a trench around the tree is not recommended because this results in a concentration of materials in a small area, which may cause root burn. If barnyard manure is used, apply about 100 pounds per tree every two or three years. Spread evenly under the tree and work into the soil in October or early November.

ACTUAL NITROGEN
(only for mature trees - 5 years or older)
APPROL ANOUNT TO EQUAL 1 LB
FXRTILIZER Z NITROGEN ACTUAL NITROGEN
Calcium Nitrate 15 6 112 lb.
Ammonium Sulfate 21 5 lb.
Ammonium Nitrate 33 3 lb.
Urea 44 2 1/2 lb.

GRASS AND WEED CONTROL Large, old citrus trees have a well-developed root system so the tree grows well despite grass growing in the root zones. In some home plantings, trees are grown in lawns. If enough fertilizer is
applied, growth is satisfactory. A convenient method of weed control in home orchards is to keep the entire basin around young trees freeof weeds
and grass with contact weed killers available from retail nurseries. Avoid spray contact with tree trunks and spray only after regrowth of undesirable grass or weeds has occurred. Follow label directions to avoid overapplication.

GROUND COVER UNDER CITRUS As trees become mature and dense, shade forms under them and Bermuda grass will not survive. Shade-tolerant ground covers such as dichondra or St. Augustine may be substituted. Some dichondra fertilizers are combined with weed-killers. Don't use these within the drip line area of citrus trees.
PRUNE ONLY AS NEEDED Mature citrus trees need little or no pruning, other than the periodic removal of dead wood. Inside shoot growth, which is particularly abundant on navel oranges and lemon varieties, should be thinned out to avoid branch competition inside the tree.

BE SURE TO ELIMINATE ALL SUCKERS ARISING FROM BELOW THE BUD UNION. THEY ARE FROM THE ROOTSTOCK VARIETY AND WILL NOT BEAR EDIBLE FRUIT. When left to develop, they will take over the top portion causing your named citrus variety to be reverted back to an undesired variety.

Although citrus trees ideally should have a skirt of branches hanging all the way to the ground, homeowners may want to cut away this growth for easier yard maintenance. Since citrus trees are very susceptible to sunburn, it will be necessary to white-wash exposed trunks and limbs after pruning. Lemon trees grow more rapidly than other citrus varieties. Moderate pruning --cutting back of very long, vigorous top shoots from 18-24 inches during the spring and summer -- will maintain more moderate top size.

Moving Mature Citrus Trees The larger tree spades are probably the only satisfactory moving device currently available for moving large established citrus trees. Stress on the transplanted tree is reduced if transplanting is done during the cooler, Octoberto- February period. The main advantage of planting these large trees is that they will provide almost instant landscape effect. Before moving, pruning back a portion of the top branch and leaf area will maintain a better balance between roots and top.

Full recovery and regrowth will generally require from several months to a year. Large quantities of water applied in a drip-line-size water basin will be helpful in reducing the transplant shock on mature trees.

HEARVEST FRUIT AT THE RIGHT TIME When and how long you can harvest depends on the variety. It generally is true of all varieties, however, after the fruit becomes edible it continues to improve in eating quality for some time until it reaches maximum flavor. From then on, it begins to deteriorate on the tree, so pick the fruit and use before it reaches this point. Mature fruit remaining on the tree at bloom reduces new crop fruit set slightly.

Citrus fruit does not improve in quality after it's picked. All citrus should be held at temperatures near 50 degrees Fahrenheit if the storage period exceeds one to two weeks. Grapefruit require very specific storage temperatures so they should be left on the tree until used. In many cases, it may be best to pick fruit at its peak of maturity and juice it for more convenient storage. If only a carport or garage storage is available, fruit should be used as quickly as possible after picking. This is
particularly true of late-ripening varieties stored in high temperatures.

Control Insects Wnen Necessary Large citrus trees in Arizona are seldom seriously injured by insects. Thrips, grasshoppers, katydids and orange dog larvae may injure small trees, and soft brown or cottony cushion scale occasionally may attack large ones.

CITRUS THRIPS Thrips are tiny, fastmoving, yellow to brown insects barely visible to the naked eye. They generally appear on new growth in the spring and again in late summer and fall. On young trees, thrips may be noticeable through the summer months. These insects feed on new growth and small, pea-size fruit, causing crinkled, leathery leaves and scarred fruit. Leaf injury is harmful to young trees, but of minor importance on larger ones. Citrus thrips are easily confused with the
flower thrips found in the open citrus bloom, but flower thrips cause no damage.
No effective chemicals available through retail nurseries are currently registered for thrips control on home yard citrus trees. Thrips activity on mature trees does not affect internal fruit quality.

APHIDS They are small, generally black, soft-bodied insects, found clustered on new growth. They may occur at any time of year, but infestations are worse in spring and early summer. No control is generally needed.

GRASSHOPPERS AND KATYDIDS These insects eat large irregular sections out of young tree leaves. They usually appear in the spring and fall. No effective chemicals are available for control.

COTTONY CUSHION SCALE This is a white, waxy insect resembling a tiny inverted seashell. It exudes honeydew, which sticks to fruit and leaves.
These pests usually are kept under control by Vedalia beetles. Call the agricultural agent at your county Cooperative Extension Service for control information if the scales seem to be getting out of hand.

ORANGE DOG It is gray to brown with white markings and is the larval or worm stage of a large swallowtail butterfly. It may be found feeding only on citrus from April through October. The worms feed on all sizes of leaves, but usually do not cause severe damage to large trees. If they are found on young trees and you don't wish to spray, try Bacillus thuringiensis in accordance with label directions. Since only a
few worms are found on trees, hand picking and destroying them periodically is practical.

FUNGUS DISEASES
FOOT ROT GUMMOSIS-This disease is caused by a fungus that attacks the lower trunk and sometimes the roots of susceptible varieties. Gumming, vertical bark
splitting and rotting around the base of the tree usually indicates fungus activity, especially if the bud union is near or below the soil line. Damage from the fungus occurs in the layer between the bark and wood. Sound wood beneath a wound indicates that the problem is caused by the Foot Rot fungus. To prevent the disease, make sure the bud union is at least 4 inches above the soil or mulch level. If the union is buried, uncover it and inspect it for signs of the disease.
Trees on rough lemon rootstock are particularly susceptible. Rough lemon roots may be completely killed without any injury evident above ground. Taiwanica and sour orange rootstocks, however, are highly resistant to this disease. Treatment for Foot Rot requires the fol-lowing steps:

1. Remove soil from around the tree exposing the trunk and upper buttress roots.
2. Cut away diseased bark until clean, unaffected bark tissue is exposed. Paint the exposed cuts with paste made from Bordeaux powder.
3. Ensure the trunk remains dry by mounding a ring of soil around the excavated area. Water will fill up to this dyke, watering the plant but keeps the diseased area dry. When the spread of the disease stops, soil can be returned to the exposed roots and tiunk. Caution: Keen the soil level below the graft union. Maintain the trunk in a dry environment by keeping the inner dyke for the life of the tree.

RIO GRANDE GUMMOSIS-It is confined for the most part to the limbs and crotches of mature grapefruit trees. Gumming occurs with noticeable bark separation but no lateral bark rotting from the point of origin. This symptom separates this disease from the Brown Rot Gummosis. There is no treatment for this disease except removal of dried gum. No attempt should be made to seal the gum in. Gumming may re-occur at intervals for a long period of time. Trees may appear yellow and unhealthy while gumming but seldom die.

HENDERSONULA-This disease usually follows sunburn after a severe freeze or through pruning wounds. The bark sloughs off revealing a black sooty mold. Prevention is the best control for this disease. Whitewash limbs and trunks
following defoliation to prevent sunburn. Apply Bordeaux to all pruning wounds. Maintain an adequate fertility level and do not water stress at any time.

VIRUS-LIKE DISEASES
STUBBORN DISEASE-Orange and grapefruit trees in central Arizona may have what is called "stubborn disease." The disease is especially prevalent in Washington Navel trees, but may occur in Valencias, Sweets and grapefruit. It may appear at any time during the life of the tree, and severity of symptoms varies from year to year. In some instances, only part of the tree shows symptoms, which include multiple small bushy shoots, small leaves, gradual flattening out of the treetop, off-season bloom and early leaf drop in December. The fruit on Navel oranges becomes
coarse, sometimes acorn-shaped, thin-skinned at the navel end and few in number.
No control is known for this disease and no budwood for propagation should be taken from trees with stubborn disease symptoms. Remove trees affected with the disease and replant.

SCALY BAU OR PSOROSIS-Symptoms do not occur until the tree is 10 to 35 years old, even if this virus were present since the tree was budded. First symptoms of scaly bark are usually small flecks of gum which appear on the trunk and main branches. These deposits give way to larger areas of dry scaly bark. As they enlarge, the tree becomes weak, less productive and twigs and limbs die back.
No satisfactory control has been found for the disease, but it can be transmitted from one tree to another only by budwood.

COMMON PROBLEMS
MOTTLED LEAVES-Dark yellow irregular shaped spots on leaves may be caused by too little zinc or manganese or too much salt, boron or lithium. Your local
county extension agent can tell you what the problem is by looking at these leaves.
Mottle caused by excess salt, boron or lithium becomes worse as leaves age, and finally results in the formation of dead areas within the leaves or at the margins or tops. Heavy irrigation to prevent salt accumulation in the soil is the only means of alleviating this condition.

PHYSIOLOGICAL PROBLEMS
LEAF DROP-Citrus trees are evergreen. They shed their leaves gradually, replacing them with new ones throughout the season. Leaf drop normally is heaviest in spring but occurs to some extent all year. LEAF DRYING-High daytime temperatures ccompanied by drying winds occasionally cause heavy leaf drying and drop in October and November. This is called MESOPHYLL COLLAPSE and is most likely to affect leaves that develop during the summer on the northeast side of the tree. Grapefruit trees seem most susceptible to this type of injury.
Nothing can be done about this collapse, but it is seldom a serious problem. In severe cases, small twigs may crack, gum and die back. When one limb or one side of the tree loses its leaves and the trunk seems unaffected, underground trouble is
indicated. This may be gopher damage, disease or even mechanical root injury of some sort.

FRUIT DROP-Only a small percentage of the blossoms on a tree develop into fruit. Although most of these drop soon after petal fall, some fruit will develop to
one-fourth to three-fourths inch in diameter and drop in late May and June.
In most years, this June drop is necessary to thin the crop. If it did not happen, the tree would break down under the load and fruit would be small and inferior.
The amount of June drop depends on variety. Seedless oranges have greater drop than ones with many seeds; tangerines with many seeds have a small amount of drop. Cross-pollination of Tangelo and Tangerine varieties causes many more seeds to develop and thus reduces the drop. With Valencia oranges and grapefruit, a heavy crop of mature fruit reduces the food supply to the young fruit and
this increases the drop. In some years, high (well over 100 degrees F) temperatures in May help induce a heavy drop. Maintaining an even
watering schedule and adequate nutrient level for tree use will minimize small fruit drop in most varieties.

FRUIT ROTS AND SPLITS- Fruit may split and/or drop beginning in August because of
hot dry weather. Fruit split differs among varieties and usually affects only a few fruit. Sunburned fruit are affected more severely.
Navel oranges may turn yellow or orange at the navel end, and drop beginning as early as August. This is caused by a fungus called alternaria or black rot. The infection occurs in early summer and no preventative measure is known.
SUNBURN-Temperatures above 110 degrees Fahrenheit usually burn some leaves and fruit and may damage any exposed bark on young or old trees. Protect any exposed bark areas with tree wraps or white, water based paint. When lower branches or tops of old trees have been pruned, exposed bark usually is sunburned and may be killed. Fungus infection may follow and destroy larger areas. Such trees must be protected by painting trunks and scaffold limbs with whitewash or any white, water based paint. Heavy paper tree protectors or cardboard should be applied to
young trees after planting.