Crop Profile for Citrus in Louisiana

General Production Information

Climatic Zones

New varieties released by the LSU AgCenter (2)

Mandarins

Sweet Oranges

Grapefruit

Acid Citrus

Rootstock Selection

Soil and Site Selection

Cold Considerations

Soil Considerations

Other Considerations

Land Preparation

Spacings

Timing of Planting

Planting

Watering Young Trees

Fertilization

Average Recommendations per Tree*

Young citrus trees may require protection form sunburn, cold or rabbits. Various wraps of aluminum foil, cardboard, plastic, Styrofoam, rope and other materials have been used successfully to protect the trunk. Soil banking is not recommended for commercial orchards in Louisiana because of the possibility of foot rot. Before using wraps, spray a fungicide on the trunk to control Phytophthora. In the summer, loosen wraps to allow air circulation.

For the first four years in the life of a citrus grove, little, if any, spraying is required. Insect problems may need attention, however. Caterpillars, scale and mites may cause serious defoliation. Because leaves are involved in food manufacturing, any damage can result in a tree that is stunted and is less cold hardy. Inspect trees regularly for insect and disease infestations before the pests have built up to serious levels.

Aside from citrus scab, fungal diseases are not much of a concern in young groves. This disease causes distortion and malformation of foliage and tender shoots (as well as fruit) of grapefruit, temples, satsumas and lemons. However, round oranges or tangerines are not attacked.

During the early years of a citrus grove, weed competition affects tree growth more than any other pest. Weeds compete much more seriously with young trees than they do with older trees. Older trees have a deeper and more extensive root system and quite often shade out much of the competing vegetation. Young trees, however, have a poorly defined root system, and weeds compete heavily for moisture and nutrients. Tree growth can be reduced an estimated 50 to 60 percent by competing vegetation in a young orchard.

Weed control is an integral part of citrus, and its neglect can be costly. It is the one cultural practice most often neglected by producers. Producers should have good working knowledge of the science of weed control to achieve consistently satisfactory results.

Pruning is not a major task in young orchards. Sprouts on the trunks should be removed before they are large enough to compete with larger limbs. During the first year, the young grove should be walked every two to three months from early spring through fall for sprout removal. Later, the intervals between inspections may be lengthened. In the fourth year, a single inspection will suffice.

Developing permanent scaffold limbs on young citrus trees is the most important phase of pruning. Scaffold branches should be developed 2¹/₂ to 3 feet from the ground to allow herbicide applications or mowing. This selected height also increases air circulation in the orchard, thereby reducing the incidence of disease problems.

Allowing scaffold branches to grow at this height for the first three years requires no special pruning techniques other than heading the tree at that height and selecting permanent branches at that level. The citrus grower need not be concerned with special training of these scaffold branches for the first three years.

In the fourth year, just before the bearing period, examine the trees for weak limbs. Also look for limbs that may lie across and rub against others. Remove these branches to strengthen the bearing framework. The objective is to construct a well-shaped head with evenly spaced scaffold limbs and space for branches to develop properly without excessive competition from other branches.

Small pruning wounds do not need special treatment. However, any limb larger than 2¹/₂ inches in diameter should be painted with commercial wound dressing or paint. All limbs should be cut flush with adjacent trunks to eliminate stubs.

Nitrogen has the greatest effect on citrus yield. Nitrogen deficiency can be recognized by the uniform loss of chlorophyll and a yellowing of the leaves. Unlike other yellowing related deficiencies, nitrogen deficiency is characterized by the loss of green color and the uniform yellowing of the leaves. It is most clearly marked on the fruit-bearing twigs. Fruits are generally small and have a thick, leathery skin.

Heavily producing trees can tolerate large quantities of nitrogen without suffering any injurious effects if they are also supplied with phosphorus and potassium. Nitrogen is particularly important during blossom time. Within certain limits, the number of flowers formed is directly related to the nitrogen status of the tree. During flowering there is a large translocation of nitrogen from the leaves to the flowers.

If leaves are damaged or nutritionally weak, fruit production is usually affected. The most common form of nitrogenous fertilizer used is ammonium sulfate. Ammonium nitrate is also used and has some advantages. It involves less loss of nitrogen associated with the acid effect of ammonium sulfate. Furthermore, by increasing nitrate and decreasing ammonium forms of nitrogen, the concentration of potash, calcium, and magnesium is increased in the leaves. The amount of nitrogen applied during the year varies according to age and productivity of the tree.

Phosphorus is also critical to maintaining citrus production. Phosphate deficiency is indicated by small, blue-green, lusterless leaves. Under conditions of acute deficiency, leaves show blue-green to bronze-brown discolorations and irregular necrotic spots. The formation of new shoots is restricted. The leaves are easily shed, and portions of the twigs may die.

Phosphate excess seldom occurs on heavy soils because of their high powers of fixation. Superphosphate (0-20-0) is the fertilizer most often used when phosphorus is needed.

Potassium levels are usually maintained by adding a complete fertilizer, but murate (potassium chloride) of potash may be used.

In contrast to most other nutrient deficiencies, initial potassium deficiency is indicated by the fruits remaining small while the leaves show no external symptoms. The advanced stage of potassium deficiency is denoted by a thickening and puckering of the leaves, the disappearance of chlorophyll in the inner vein areas, and the appearance of necrotic spots. Premature leaf fall and shoot die-back occur with severe deficiencies.

Frequently observed symptoms of trace element deficiencies in citrus varieties have led to the conclusion that fertilizer formulae should contain trace elements. Generally, in the case of trace elements, it is advisable to wait until the deficiency of the element is established by visual symptoms or by leaf analysis before treating.

In some instances and in some soils, young citrus trees may show deficiency symptoms as a result of trace element deficiencies. In such instances, the leaves should be diagnosed by an appropriate expert and the proper recommendation made. Applying trace elements to correct minor element deficiencies requires special expertise.

The timing of fertilizer applications must be adjusted, as far as possible, to the growth rhythm of the trees. In most cases, an application is made in late winter (February) before the blossoming and in summer (June) when the summer shoots are formed. For best results, fertilizers are applied 20 to 40 days before the onset of the first growth in late March or early April.

Drip or trickle irrigation allows the precise application of water in the immediate vicinity of plant roots. In addition, it simplifies procedures, reduces labor requirements, and minimizes distribution and evaporative loss. Less of the total soil area is fully wetted than with sprinkler and furrow systems. This reduces significantly the amount of water required. Automatic control of the irrigation system using time clocks or moisture sensors and automatic valves is simple and relatively inexpensive.

Water is carried to individual trees through a carefully planned pipeline system. Each line should be planned for a specific orchard considering size, shape, slope, and tree spacing. Plan the system to provide reasonably uniform pressure at all emitters, to require minimum material, and to achieve maximum operating convenience.

The heart of any irrigation system is the pump. A main pipeline carries water from the pump to the plant rows. A filter, or system of filters, must be installed on the main lines. One option may involve the installation of a fertilizer injector upstream from the filter. If a fertilizer unit is used, an antisiphon unit consisting of a check valve and vacuum breaker will prevent backflow of water and fertilizer material back into the well.

A lateral pipeline containing the emitters is placed along each row of trees. In larger systems, the orchard may be divided into blocks of 10 to 20 acres. The laterals for each block are connected to a header pipeline or manifold. A globe-type valve with pressure gauge installed on the manifold side of the valve allows precise control of pressure in all blocks. Laterals should be on the contour, or perpendicular to the slope, when the slope is too steep to maintain a more uniform pressure at the emitters.

Water is released by drip emitters attached to laterals and located near each tree. Numerous emitters are on the market. Usually each emitter applies one or two gallons each hour, but the rate should never exceed the percolation and infiltration rate of the soil. Some drip emitters can be installed underground, but it is easier to adjust and clean clogged emitters when they are on the surface. Emitter selection is important since satisfactory performance is essential to the success of every drip irrigation system.

Mature citrus trees may not need irrigating frequently in Louisiana. A critical period for irrigation is during fruit maturity. A water shortage can mean severe losses of fruit caused by splitting and premature fruit shedding. The expense involved in installing a drip irrigation system in citrus can often be reclaimed in one season by increased yields.

Generally when freeze injury occurs, cell membranes are damaged by freezing and thawing. Tender tissues in citrus include new buds, flowers, and small fruit. The most cold-hardy part of the tree is the dormant wood. If a citrus tree is gradually exposed to lower temperatures, a process called "hardening" occurs. There is a decrease in the freezing point of the plant tissues. Citrus trees are evergreen and never become fully dormant, as do trees that lose their leaves (deciduous). Trees that are slightly dormant (pre-conditioned by gradual cold) are less likely to be damaged by cold.

The best way to reduce cold damage is to maintain healthy trees. Use cultural practices that induce and maintain dormancy in winter. These methods include no late summer or fall fertilization or pruning. Vigorous trees may recover from cold injury. Weak trees that show disease, insect damage, or nutritional deficiencies are the most severely damaged and the slowest to recover.

Physical means used to prevent cold injury in large commercial groves include heaters (Diesel fuel, charcoal), wind machines to eliminate temperature inversions, and petroleum-impregnated charcoal blocks. To protect a single tree, some home gardeners have constructed frames over trees and enclosed the tree in one or two layers of translucent plastic.

In some cases, extreme measures are needed on the few occasions that it is severely cold and the days are cloudy. Incandescent light bulbs can raise the temperature in the frame a few degrees. Fresh air is a must for such frames, and air temperature within should not be allowed to go above 85 to 90° F. Venting should be provided to maintain a constant supply of fresh air to control the temperature.

1. Clean cultivation, done mechanically or by herbicides before freeze susceptible periods, is recommended. Grass, weeds, and straw mulches prevent heat from entering the soil during the day, so less energy is stored for release at night.
2. Using tree wraps of plastic, rubber, Styrofoam, aluminum foil or rope will help prevent cold damage to roots and trunks. This must be done before the first killing freeze. To prevent foot rot, treat trunks with a neutral copper spray or fungicide before wrapping. Although tree tops may be lost during freezes, a tree can recover if its trunk and root system are intact. Remove wraps in the spring to prevent Phytophthora foot rot.
3. Several days before a cold front, the soil beneath citrus trees can be irrigated. Moisture acts as a buffer. If this is done at the time the front arrives, evaporation may occur and result in lower temperatures near the tree. In Louisiana, this practice is risky because of intermittent warm periods in winter that may result in new growth. The new growth can be damaged by subsequent cold.
4. Prune trees in late spring to maximize tree growth and hardening before winter. Make cuts at branch crotches, leaving no stubs, and treat large cuts with wound dressing. Leave good leaf canopies to cut wind speed through citrus trees and reduce the rate of cooling. Leaves radiate heat to each other. Outer leaves may be lost to a freeze, but complete loss of inner leaves is averted when a thick canopy exists.
5. Apply fertilizer to citrus trees in late January or early February as previously recommended with a subsequent application of nitrogen only when good soil moisture exists and no later than late June. Late summer or fall applications of fertilizer stimulate new growth which is easily killed by cold. Some evidence exists that navel orange trees receiving complete fertilizer are less susceptible to late winter freezes than are trees receiving only nitrogen as fertilizer or no fertilizer at all. Also, trees limed to a soil pH of 6.5 suffer more damage than unlimed trees with a pH of 6.0.
6. Oil sprays used to control insects and mites decrease cold tolerance. Do not use them later than August 15.
7. Scaffold branch irrigation– a new way to modify temperature in citrus by low-volume irrigation. 360° Super Spray irrigation heads are placed on poly tubing risers within the tree canopy.

Much of the labor activities of the citrus industry in Louisiana are done by hand. Pruning limbs and suckers is a tedious process performed with pruning shears and occasionally hand saws for larger limbs.

One of the most important hand operations within the industry is an obvious one: harvesting. Satsumas must be clipped with hand shears and not pulled as the fruit can be damaged and rendered unfit for market. Other citrus varieties are generally hand-pulled.

Irrigation in almost all cases is fixed and in no need of transportation. When spraying pesticides, operators are properly fitted with the appropriate personal protective equipment (PPE), and laborers in the orchard do not return until the restricted entry interval (REI) has expired.

Common injuries within the citrus industry are those common to many farming operations. Minor cuts, bruises, abrasions, and insect stings (wasps, caterpillars) are common. Punctures from thorns can occur. Occasionally a worker will slip and fall due to loose footing in soft soil, a hole, etc. Almost all of these minor injuries are treated on-site with materials found in a first-aid kit. Often, first-aid kits are affixed to equipment in the field for easy access.

MITES

Citrus rust mite, (Phyllicoptruta oleivora)

The citrus rust mite is small (about .01 in. long) and cannot be recognized with the unaided eye. Under 10x magnification, they appear as lemon-yellow, wedged-shaped objects, but distinct features cannot be seen. Rust mites can be seen more easily on green leaves and fruits than on ripe fruits. A heavily-infested leaf appears to be fuzzy or dusty. Eggs of whiteflies are often mistaken for rust mites. The life cycle requires only about a week in summer, which accounts for the rapid build-up often noted.

Rust mites infest leaves, fruit and tender green shoots, causing rusty-colored fruit. Heavily-infested leaves lose their gloss and dark-green color and may drop prematurely. Heavy infestations may develop on the leaves just before bloom and cause severe injury to young fruits soon after they are set. Rust mites seem to prefer exposed locations and are numerous in the tops of trees. They are more numerous on fruit from spring until late summer. Inspect the fruits and underside of leaves with a magnifying glass.

Melanose, a fungus, causes blemishes on citrus often confused with rust mite injury. Lesions caused by melanose are darker, more rounded, and raised with a sandpapery feel. Scab, another fungus, causes spots that are usually rougher, larger, more irregular and lighter in color than rust mite injury.

The six-spotted mite is about 0.02 in. long, pale grayish-yellow in color, and lays a round, yellowish-white egg. It usually has four or six dark spots arranged in two rows on the body. With 10x magnification, the spots are barely visible on the adult mites, and few or none can be seen on the young. Mites and eggs are found in colonies, often covered with webbing, and located only on the upper surface of the leaf. Feeding causes yellow or chlorotic areas, usually along the veins, and results in leaf drop. These mites are usually most numerous March through May, but may build up in January and February after a cold December. Although grapefruit varieties are preferred, they can be found on other types of citrus.

Texas citrus mite, (Eutetranychus banksi)

The adult female of the Texas citrus mite is about 0.02 in. long and has a shiny body with conspicuous hairs. The color varies from tan to brownish-green with dark brown to greenish spots or bars near the lateral margins. The adult male, which has longer legs than the female, also has a smaller triangular-shaped body. The female lays flat, disc-shaped eggs along the midrib and near the lateral margins of the leaves. The eggs vary in color from light yellow when laid to tan and green as they mature, turning to reddish brown just before hatching. Newly-hatched mites are light yellow to tan with pale legs. Populations are usually heavier on the upper leaf surface. Injury to leaves is caused by the mites sucking out the juices giving foliage the classic mottled appearance. Injury may cause leaf drop. Mites are most numerous May through July, but most injurious October through February due to dry weather.

Citrus red mite, (Panonychus citri)

The adult female of the citrus red mite is about 0.02 in. long, rose to deep purple in color with prominent light-colored hairs. Eggs are round and reddish in color. Both eggs and mites are usually found on the upper surface of leaves, but often occur on the under surface and on green twigs. Eggs laid on leaves are most abundant along the midrib and petiole. The life cycle is short, and there may be 12 to 15 generations per year. The mites are most numerous May through July, but most injurious October through February because of dry weather. Leaf injury is similar to that of the Texas citrus mite.

The adult female Florida red scale is circular, less than ¹/₁₀ in., and dark reddish-brown in color with a conspicuous lighter colored center. She lays bright yellow eggs under her armor that produce bright, lemon-yellow, oval-shaped crawlers. There are usually four generations per year. These insects feed on leaves and fruits, preferring exposed surfaces. Their feeding results in yellow areas on leaves and fruit which may often be followed by heavy leaf and fruit drop. The denuded braches may be killed the following fall and winter. Make sure to inspect groves at regular intervals from May through October.

Yellow scale, (Aoniiella citrina)

Yellow scale can be distinguished from Florida red scale by the lighter color of its armor and the shape of the body. The adult female is circular, yellow to light orange in color, and noticeably flatter than other armored scales on citrus in Florida. The body, which can be seen through the semi-transparent armor, is lemon-yellow and kidney-shaped. No eggs are found, as the females give birth to living young. Feeding damage is very similar to Florida red scale.

Glover scale, (Lepidosaphes gloverii)

Glover scale and purple scale are very similar in appearance and habits, but Glover scale is longer and narrower. These scales feed on leaves, fruit, and wood, and are often overlooked because they are found primarily on the inside of the tree and on the wood. They like shady areas such as the under surface of leaves and collect especially at the midrib and base. Yellow, chlorotic areas on the leaf result in defoliation and subsequent twig death. Infestations on the fruit near the stem end cause fruit loss, as well as green spots, which cannot be removed in the coloring room. Grove inspections should be made prior to post-bloom and summer spray periods.

The female purple scale lays grayish-colored eggs in a sac-like enclosure under her armor, while Glover scale eggs are pink and found in two rows. Crawlers of both scales are oval and have an off-white color with a posterior brown tip. Peaks of young stages occur in March-April, June-July, and September-October.

The adult female black scale is nearly circular, hemispherical, and dark-brown to almost black, with two lateral ridges and a longitudinal ridge forming a pattern on the back resembling the letter "H". She lays approximately 2000 eggs in a cavity under her body. The eggs are oval and pink in color changing to reddish-orange before hatching. The light brown, flat, oval, crawlers travel about considerably before settling on twigs or leaves and to some extent on fruit. Later the young move from leaves or fruit to small twigs, particularly stems that hold fruit. There are usually two or three generations a year. Black scales excrete large quantities of honeydew.

Brown soft scale, (Coccus hesperidum)

Brown soft scale is oval and flat, and light brown in color. No eggs are laid as pale yellow crawlers are born alive. Young female and male scales are similar in shape and color, but smaller than adult females. These scales infest young twigs and often gather along the midrib of the leaf. They are highly parasitized by tiny wasp-like insects and rarely become abundant except on young trees, either in newly-planted groves or in a nursery, where ants feed on honeydew and drive away the parasites. Like black scales, brown scales excrete large amounts of honeydew.

The body of the female cottony cushion scale is bright orange, red, yellow, or brown, but its most distinguishing feature is the elongated, fluted, white cottony egg sac that is attached to its body. The female usually occurs on twigs, and the egg sac contains from 600 to 800 red eggs. It may become two to three times as long as the body of the female, resulting in an overall length of almost ¹/₂ inch. Eggs hatch in a few days during warm weather, but take up to 2 months to hatch in winter. Crawlers are red with black legs and antennae. Second-instar nymphs settle on twigs and leaves, usually along leaf veins. The third instar moves to branches and trunks. All three instars are covered with a thick, whitish, cottony secretion, which disappears after the insect molts. The minute, red, winged male is rarely seen; the loose cottony cocoons from which males emerge, however, may be detected in secluded places on the tree or ground. Cottony cushion scale usually has three generations a year; unlike most other scales, it retains its legs and its mobility throughout its life.

Feeding can result in defoliation and dieback of twigs and small branches when infestations are extremely heavy. Feeding also reduces the yield of citrus trees. Like soft scales, cotton cushion scale excretes honeydew, which is often accompanied by sooty mold growth and ants.

Chaff scale forms a light brown nearly round armor, which is slightly smaller than that of a mature female Florida red scale. The eggs and crawlers are purple. This scale infests leaves, wood, and fruit causing green spots, which lower the grade. Tangerines and early varieties of oranges must be de-greened due to Chaff scale damage. Heavy infestations are most likely to develop during late summer and through the winter.

Citrus snow scale gets its name from the white color of male scales. Female scales are brown to blackish with a lengthwise roof-like ridge. They are very difficult to see against the tree bark. Scales are largely confined to the trunk, limbs, and twigs.

Florida wax scale is a soft scale that appears white to pinkish-white when not stained by sooty mold or other foreign matter. The adult female is ¹/₈ inch or less in length, oval in general outline but presenting an angular appearance due to dome-shaped masses of wax on the back. The pale-brown crawlers collect on the lower leaf surface along the midrib. Young larvae are star-shaped. This scale is highly parasitized.

Green peach aphid, (Myzus persiae)

Aphid infestations are usually found on new growth flushes. Aphids suck sap from leaves and stems, resulting in curled, distorted leaves which can retard tree growth and cause fruit and blossom shed. In addition, aphids produce large amounts of honeydew that promote growth of sooty mold, which may reduce photosynthesis. Aphids are also associated with the transmission of plant diseases. Low to moderate infestations of aphids can be considered beneficial to the citrus ecosystem by providing food early in the season for natural enemies, such as lacewings and ladybeetles.

Three aphid species, the spirea aphid, the green peach aphid, and the cotton or melon aphid are the most common aphids on citrus in Louisiana. The black citrus aphid may also be found occasionally.
Aphids reproduce asexually with females giving birth to young nymphs. Within a week of their birth, the females mature sexually and are themselves capable of producing offspring. This rapid rate of reproduction can result in large infestations developing in a very short time. Many generations per year can occur on citrus before the winged aphids migrate to their alternate hosts during the winter. Fortunately, natural mortality factors, especially predators and parasites, are usually highly effective in limiting aphid populations.

Cloudy-winged white fly, (Dialeurodes citrifolia)

Adult cloudy-winged whiteflies differ from other whiteflies by the darkened area in the middle of each wing, which gives the wings a cloudy appearance, and by the fact that the wings are held in a flatter position than those of the citrus whitefly. Fresh-laid eggs of the cloudy-winged whitefly are yellow, but soon turn black and have a network of ridges. Eggs are commonly laid on young leaves. Nymphs and pupae are very similar to those of the citrus whitefly. Populations of this whitefly are often mixed with the citrus whitefly within an orchard.

Citrus white fly, (Dialeurodes citri)

The citrus whitefly lays smooth, shiny pale-yellow eggs. Eggs usually hatch in one to three weeks and the crawlers move about for several hours before settling. The larvae are oval, thin and translucent, which makes them difficult to see on green leaves. The nymphs require three to four weeks before pupating and another two to four weeks before emerging as adults. Pupae are similar to nymphs but are thicker and have distinct eyespots.
Adults live an average of two weeks during which time the female lays an average of 150 eggs. Citrus whiteflies have been observed to develop high populations during growth flush periods, but generally occur in low numbers.

Wooly white fly, (Aleurothrixus floccusus)

Adults are yellowish-white and seldom fly. Woolly whitefly eggs are laid in a circle on the underside of mature leaves, with the female at rest in the center. The eggs are brown and sausage-shaped. The first instars are light green; subsequent instars are brown. Pupae are covered with waxy white filaments, giving a woolly appearance. Copious amounts of honeydew often are associated with colonies of this species.

The adult female citrus mealybug is wingless and appears to have been rolled in flour (hence the name). It grows to ¹/₁₀ in. long and 0.06 in. wide. A fringe of small waxy filaments protrudes from the periphery. The adult male is small, but with its wings and tail filaments, it appears to be ²/₁₀ in. long.

Eggs are oblong, yellow, and are enmeshed in a dense, fluffy, white ovisac.

The tiny crawler is oval and yellow, with red eyes. The antennae are rather distinct. Female nymphs resemble the larger adult females. Male nymphs are narrower and often occur in a loose cocoon.

Citrus mealybugs are often confused with cottony-cushion scale. They also excrete large amounts of honeydew in which sooty mold fungus develops. They may get into crevices in the bark on the limbs and trunk and in such sheltered places as the angle between the petiole of the leaf and stem. Mealybugs often collect around the stem end and under the calyx of the fruit and cause fruit drop. Another favorite place for mealybugs is the sheltered area formed by clusters of two or more fruits, particularly grapefruit. Controls should be applied before mealybugs have settled under the fruit calyx.

The orange dog caterpillar is often a pest of citrus trees. Two or three may defoliate a young tree in a few days. They are most important on young trees and nursery stock. The caterpillar is dark brown with light yellow patches, growing to a length of up to 2 inches. The front part of the body is enlarged and when not feeding, the caterpillar pulls the head back into these large segments and causes the whole front of the body to resemble the head of a dog – hence the name. The orange dog can push out a fold of skin at the back of the head, which forms two long, red, horn-like projections. This organ gives off a strong odor, which repels natural enemies. The adult is a large, yellow and black butterfly.

The broad-winged katydid lays its eggs along the margin of the leaf and there are several generations a year. Other kinds of katydids occur in citrus groves, but only the broad-winged katydid is of any economic importance. They sometimes feed on the rind of growing oranges, causing large, smooth sunken areas to develop on the fruit. Occasionally they cause severe defoliation of young trees.

The eastern lubber grasshopper can cause injury to citrus fruit and foliage. Eggs are laid in the ground. After hatching, young nymphs may migrate to the cover crop and trees in the grove. Injury is most important on young trees. In some instances they have completely defoliated newly set trees. There is only one generation per year, and they can be seen during spring and summer near low, marshy land.

The Fuller’s rose beetle is gray-brown and ¹/₄ to ¹/₃ in. long. The citrus root weevil is blue-green and ¹/₂ to ³/₄ in. long. Both can occur in sufficient numbers to cause severe injury to both roots and foliage of citrus varieties. Injury from these pests has been noted most commonly along the Florida east coast. Growers should become familiar with both the larval and adult stages of these insects.

Injury by the larval stage is by far more serious than injury by the adult stage. The legless white larvae of both species eat canal-like channels in the roots. This injury is usually more prevalent on the underside of lateral roots although primary roots may be girdled near the main trunk root. Adult injury to leaves typically appears as notches cut out along the leaf margin. Adults may also be seen on small fruits.

The pink scavenger caterpillar is a small caterpillar with a deep wine-red abdomen, brownish head and black mouth parts. It has a dark brown area just behind the head. Its diet consists mainly of dead insects and decayed areas of fruit. However, it has been known to feed on the rind of sound fruit causing a reduction in grade. Several may be present during heavy infestations of mealybugs or scale.

Melancose has become the major disease problem the last several years. Several applications of copper are employed to control this disease. The first application is made before bloom with another one made after bloom when fruit are pea size. Only 20% of the growers used copper to control this disease this past year.

Symptoms: Melanose affects the leaves, shoots and fruit. It forms numerous, dark brown dots or spots on the leaves, young shoots and fruit. These spots are at first sunken, but later become raised so that the russeted area has a rough, sandpaper feel. The spots may be irregularly scattered on the surface of the fruit or they can run in streaks (tear stains). Like scab, melanose infection occurs only on the young, tender growth. The fruit becomes progressively resistant with age. However, the same fungus that causes melanose can infect the ripe fruit after harvest. It is one of the two most common causes of the very destructive fruit decay known as stem-end rot. Control of melanose, therefore, helps to reduce the losses from stem-end rot. Prune and burn the dead wood. This practice eliminates much of the source of infection.

Symptoms: Scab is primarily a disease of satsuma, orange, tangerine, grapefruit, lemon, sour orange and trifoliata orange root stock. It does not affect the sweet orange. Scab affects fruit leaves and young shoots, causing irregular, raised, corky, scabby, wart-like outgrowths. Severely scabbed leaves and fruits become misshapen and distorted. The rind of scabbed fruit is thick and puffy.

Symptoms: The sooty mold fungus (Capnodium citri) is not a parasitic organism. It does not penetrate the tissue of the plant but grows superficially on the honeydew excretions of white flies, aphids, mealy bugs and scale insects. Sooty mold causes a certain degree of injury, when its growth is very thick, by preventing the sunlight from reaching the leaf and by making the fruit black and unattractive. Fruit covered with sooty mold is smaller and does not color well.

Green Mold, Blue Mold (Penicillium sp.)

Symptoms: The fungus enters the fruit through injuries to the skin. Decay appears as a softened water-soaked area that is easily punctured by pressure. Later white mycelium appears on the surface and soon a mass of powdery olive-green (green mold) or blue spores (blue mold).

Symptoms: Lesions appear as soft water-soaked spots on fruit at points where injury has occurred and may increase to involve the entire fruit. White fungal growth develops on the surface of the infected fruit. A strong sour odor is present.

Symptoms: Foot rot is the most frequently encountered disease on the trunks of citrus trees in Louisiana. Members of this genus also cause brown rot on the fruit.

Foot rot produces motile spores which usually invade the trunk at the bud union. Wet conditions during the spring of the year favor fruit rot development. Initial symptoms include water soaking of bark that appears as a dark spot on the trunk. At first the bark may appear firm, but with age it becomes cracked and may eventually shred. Gumming often accompanies advanced stages of foot rot. Maintaining adequate drainage in orchards helps to reduce disease incidence.

Establishing a weed management program involves a consideration of plant species growing as weeds and competing in the rooting zone of trees. Indigenous or introduced ground cover species in row middles, while also competitive, can play a positive role in grove management. Inputs into management decisions include: 1) the identification of native and introduced species, 2) a knowledge of their relative level of competitiveness/ interference with trees and other cultural practices, 3) an understanding of their impact on pest and disease management strategies, and 4) an informed selection of efficacious, cost-effective, and environmentally compatible management options. Integrated Weed/Vegetation Management (IVM) stresses the integration of control/suppression methods with other grove practices. It involves the selection, integration, and implementation of effective vegetation management strategies in light of economic, ecological, and environmental consequences. The adoption of practices consistent with IVM will reduce seed reservoirs and vegetatively produced plant parts substantially, making management programs more efficient and cost-effective over time.

All vegetation species are not equally competitive with citrus trees. Grasses, especially sod-forming species are more aggressive competitors than most broadleaf species. Vines in tree canopies can become very competitive for sunlight. Mowed grass can be very competitive due to the moisture demands of vigorous re-growth. Relatively sparse weed growth on poor sandy soils may be more harmful than that on heavier soils with greater moisture and nutrient reserves to be shared between trees and weeds. Large numbers of seeds representing numerous vegetation species reside in the surface soil layers in which tree roots are established. From these seed reservoirs, each species has periods of emergence ensuring weed cover for most of the citrus growing season. With time and appropriate sanitary and suppression methods, weed reservoirs can be greatly reduced. However, one season or year of reduced weed management can all but eliminate benefits accrued over time. From a practical and economical standpoint, the total elimination of weed seed and plant parts is neither economically practical nor desirable.

Vegetation species are considered economic pests if they reduce the growth, health and survival of young trees, or the time to come into bearing and ultimately fruit production. Eventually, trees are deprived of whatever portion of resources that vegetation utilizes. The more competitive the vegetation, the more adversely it alters tree physiology, growth, fruit yield and quality. The attainment of early crop production requires controlling the growth of weed competitors. Weeds alter economic status by competing with trees, particularly young trees, for water, nutrients and even light in the case of climbing vines, which can easily cover trees if left uncontrolled. Weeds also have various effects on tree performance, referred to as interference, including reduced efficacy of low volume irrigation systems, interception of soil-applied pesticides, lowered grove temperatures during freeze conditions and some yet to be clearly defined effects on insect and mite populations, disease incidence, and mammal activity.

Cultural methods include: 1) exclusion and sanitation practices to minimize species introduction, establishment, and spread, 2) modification of other grove practices which may promote the establishment and spread of vegetation, i.e., off-target irrigation and fertilizer applications, 3) early shading of grove floor surface by tree canopies, and 4) leguminous cover crops which can supply nitrogen and require less maintenance after establishment.

Cultivation in row middles kills annual weeds efficiently and economically by severing the stems from the roots. Each crop of weeds must be killed in order to prevent competition with the trees and production of seeds. Each cultivation also brings seeds to the soil surface, where they can germinate and the number of cultivations required should be determined by the number of flushes of weed emergence. Cultivation at proper time intervals can theoretically be used to ultimately kill deep-rooted perennial weeds by exhaustion of their underground food reserves. Although infrequent cultivation provides temporary control, it spreads and invigorates perennials by increasing the number of buried seeds and by widely distributing rhizome and stolon cuttings, tubers, and bulbs. The result of infrequent tillage is the establishment of solid stands of resistant species which can greatly impact tree growth. Constant cultivation also results in the destruction of citrus fibrous roots which normally would grow in the undisturbed portion of the soil.

Generally speaking, all weed species listed as susceptible on the herbicide product label will be controlled by that herbicide at the appropriate rate, time of application and stage of growth. Environmental and plant conditions before, during and following the application are also important including moisture in the form of rainfall and/or irrigation. Poor control can sometimes be expected from postemergence applications to weeds under stress conditions due to poor uptake and translocation of applied herbicides. Assuming that the appropriate herbicide or herbicide mixtures are selected for the weed species present, failures in the program will usually be due to one of the above factors or to the actual application including calibration and/or equipment design and operation.

Herbicides may be classified as foliar or soil-applied. Foliar applied materials may have systemic or contact activity. Soil applied preemergence herbicides are absorbed through weed root systems, being most effective during germination and early seedling growth stages. Systemic herbicides are those that are absorbed by either roots or above-ground plant parts and are translocated throughout the plant. Contact herbicides act as desiccants, damaging or killing all plant parts actually sprayed with little if any translocation. For the control of well-established perennial weeds, a postemergence herbicide with systemic metabolic activity should be used with preemergence soil residual products.

Timing and frequency of application are the keys to good vegetation management. Increased application frequency of lower rates of soil residual herbicides is more effective in young groves where vegetation presence is greater due to more exposure of the grove floor to sunlight and where a greater herbicide safety factor is required.

Biological control of economically important species in groves is not widely observed except in Texas for milkweed vine, Morrenia odorata, for which the commercial mycoherbicide DeVine was developed. However, where species are being stressed by native insects or pathogens in groves, such events should be noted and if possible exploited. Soil applications of fungicides for the control of Phytophthora should be scheduled not to coincide with DeVine applications as they may affect its efficacy.

1. Citrus Research Station, Port Sulphur, LA
   - Roysell Constantin and Wayne Bourgeois (985) 564-2467
2. Plaquemines Parish Extension Office, Braithwaite, LA
   -Alan Vaughn (504) 682-0081
3. LSU AgCenter, Baton Rouge, LA
   - Citrus insects - Boris Castro (225-578-2180)

1. Crop Protection Reference. 2002. C&P Press. New York. 2391 pp.
2. Insects and Mites of Louisiana Citrus. 2000. LSU extension publication 1261
3. Louisiana Commercial Citrus Production. 1994. LSU extension publication 2456
4. Louisiana Citrus Disease Spray Schedule. 2001. LSU extension publication
5. 2002 Louisiana Citrus Spray Schedule. 2002. LSU extension publication

Document prepared by: Matt Shipp, Extension Associate, LSU AgCenter