The insects listed in this section are generalist feeders for which citrus is not a preferred host. They are therefore only sporadic problems in Florida citrus. While these pests do not require routine treatment in all groves, periodic outbreaks can potentially have dramatic impacts on tree health or productivity. When these insects are detected at a damaging level, treatment is required. Some pests may migrate into citrus from adjacent field or forage crops when these are harvested. Given that the distribution of these insects is rarely uniform, some monitoring effort should be directed toward delineating the boundaries of an infestation prior to any chemical application so that treatment can be limited to affected blocks only. Benefits of "spot" applications, or restricting treatments to affected areas only, are twofold: (1) direct monetary savings realized through reduced labor and material costs, and (2) the preservation of unsprayed refuges for beneficial arthropods, which ensures rapid recovery of natural enemy populations and accelerates the post-treatment restoration of biological control. Frequent monitoring (especially during growth flushes), proper identification, and timely application of the appropriate control measures are all essential to reducing the impact of these pests. If insecticide treatment is needed, select in priority a product that is also efficient in controlling Asian citrus psyllid (ACP) in order to include the treatment for these erratic pests in your ACP program and reduce insecticide applications.
Plant bugs are Heteropteran insects that feed on a wide variety of plants and occasionally migrate into citrus in large numbers when adjacent field crops are harvested. The most important species affecting citrus are the citron bug (Leptoglossus gonagra), the leaf-footed plant bugs (L. phyllopus and L. zonatus), and the southern green stink bug (Nezara viridula). They may also develop on decaying undergrowth within the grove. Under normal conditions, plant bugs are rarely numerous enough to be any cause for concern. However, in large numbers, they tend to aggregate and move into trees during the fruit ripening period. In this period, they can cause substantial direct damage by puncturing the peel to suck juice. Pathogens enter through the puncture wound, producing a surrounding sunken area of necrotic tissue. If damage is done early enough, fruit will fall before harvest. Thin-skinned varieties such as Hamlin are especially vulnerable, as well as fruits destined for the fresh market. Timely weed control can avert plant bug problems, whereas mowing or herbicide treatment of infested weeds may exacerbate a problem. In such a case, insecticidal control may be necessary. If possible, spot treatments of infested areas are always preferable in the interest of conserving natural enemies.
The adult of the orange dog is the giant swallowtail butterfly (Papilio cresphontes). Orange-dog eggs are large, round, semitranslucent, orange, and easily recognized on the expanding terminals where they are typically laid. The developing larvae are shiny brown and white, resembling bird droppings, and they feed preferentially on the new leaves. Under normal conditions, populations are low, and the damage is sufficiently dispersed that there is little cause for concern. However, especially in the fall, situations can arise wherein large numbers of butterflies deposit numerous eggs on very young trees that then suffer severe damage from developing larvae. As with most caterpillars feeding on fruits, damage can only be averted by chemical treatment if the problem is detected early (i.e., when most of the larvae are still in early stages of development). When larvae reach later instars, they are more resistant to insecticides, and most feeding damage will have already occurred. Careful monitoring of young groves early in flush cycles is necessary for timely detection and treatment. For all caterpillar issues, Bacillus thuringensis (Bt) based materials provide effective control with the added advantage of being listed by OMRI, the Organic Materials Review Institute, as not affecting beneficial species.
Grasshoppers, Crickets, and Katydids
These insects rarely require chemical control, because they are only a problem sporadically and in specific circumstances. Grasshoppers, primarily the eastern lubber grasshopper (Romalea microptera) and the American locust (Schistocera americana), can cause serious damage to growth flushes and may also damage fruit, especially in its early stages. The broad-winged katydid (Microcentum rhombifolium), the restless bush cricket (Hapithus agitator), and the jumping bush cricket (Orocharis luteolira) may also attack citrus. However, these insects typically do not spend their entire life cycles on citrus and are usually only a problem if they enter groves in large numbers. Adjacent pastures, hay fields, and fallow lands can be significant sources of these insects, as can weedy swales and row middles. Timely weed control and regular mowing of the surrounding vegetation can often avoid this problem.
The Asian cockroach (Blattella asahinai) is very similar in appearance to the German cockroach (Blattella germanica), although their habits are quite different. The Asian cockroach flies readily and rarely invades dwellings, in contrast to its German cousin. First detected in Lakeland in 1986, the Asian cockroach quickly spread throughout the state and is now present in most citrus-growing areas. They feed primarily on decaying vegetation and largely inhabit moist litter under trees. However, they can also climb into the canopy, especially at night, where they feed on tender flush, giving it a ragged appearance. Insecticide applications, if deemed necessary, should be directed at the soil under the canopy where the population resides and takes refuge.
While fire ants (Solenopsis invicta) are largely predaceous and may attack pests such as citrus leafminer larvae or newly hatched root weevil larvae, some situations can favor a high density of fire ants and lead to direct damage to citrus. For example, trunk wraps applied to very young trees can provide a protected environment for fire ants to attack tender young bark. Density of fire ants can also dramatically increase on soil mounted to protect young trees from frost. Fire ant damage to trunks of young trees produces sap flows that are collected by the ants. Girdling and death of the tree may result from direct effects of ant feeding or foot rot caused by infection of Phytophthora. Leaf buds may also be damaged by feeding. High densities of fire ant mounds can create problems for grove workers during maintenance of irrigation systems and for fruit pickers at harvest. Long-term control is best obtained with food baits, although soil applications of contact insecticides or even foliar applications of oil may provide temporary relief sometimes needed during harvest. Trying to eradicate fire ants completely from a citrus grove is not a desirable or reasonable objective. Only treat mounds directly adjacent to citrus trunk where ants can cause direct issues.
Eastern Subterranean Termite
The eastern subterranean termite (Reticulitermes flavipes) is a native inhabitant of forests throughout the eastern United States, where it plays a major role in the decomposition cycle of wood into soil. Subterranean termites feed on seasoned wood, especially pines, and are major pests of wooden structures throughout their range. Only rarely do they attack living trees. This habit is poorly documented in the literature. Nevertheless, they can become serious pests of citrus in groves where pine woods had supported large termite populations. They persist on buried remnants of the original wood but will also girdle and kill young citrus. Populations in groves have been estimated at 5 million individuals and may range over thousands of square yards. Termites are most prone to attack citrus in the summer when rising water tables force them to abandon other food sources, but attack may occur in any season. Attack commences below the soil line and thus may escape detection until tree death. The termites chew bark and cambium, generally above the scaffold roots and down to bare wood around the trunk. Lesions are characteristically clean and free of gumming. Feeding may advance above the soil line below the bark, in covered galleries, or under tree wraps. Rapid tree decline once girdling is 90% or more complete is characterized by shock bloom, interveinal chlorosis, loss of foliage, and death. Attack is usually limited to trees 5 or fewer inches in diameter.
Control consists of avoiding the problem, first by meticulous removal of wood residues from new grove sites, and then by creating physical or chemical barriers around trees. Eventually, the problem will usually subside due to tree growth beyond the susceptible stage or natural attrition of the colony through lack of sufficient food supply. The following recommended practices can be employed to avoid most losses:
- Remove as much wood as possible when preparing a new grove site, particularly on pine land.
- Scout suspected infested areas by looking for signs of girdling and inspecting tree crowns below the soil line for lesions and termite activity.
- Do not use tree wraps in infested areas.
- Wash soil from crowns, exposing scaffold roots to discourage termites from preferred attack site.
- Create a chemical barrier directly around the tree crown, preferably with a granular insecticide. This practice will give a maximum of 3 months protection.
Caribbean Fruit Fly
The Caribbean fruit fly, Anastrepha suspensa, is a pest of many tropical and subtropical fruits of south and central Florida. The Caribfly is about ¼ inch long with a yellow and brown body and black markings on the wings. Eggs are laid singly under the surface of the peel on ripe or overripe fruit and hatch in 2–3 days. Larvae feed for 10–14 days and develop in decaying fruit. Larvae develop into pupae, and the adults emerge later to complete the cycle.
Caribfly does not pose a direct threat to Florida citrus production, but the management of this pest may be necessary to export fruit to certain domestic and foreign markets. For export fruit, fly-free zones may be created to produce fruit for export. The primary requirements are (1) the designated area and a buffer zone must be maintained free of preferred hosts such as loquat, rose apple, guava, and Surinam cherry, and (2) routine trap surveys must be conducted to monitor any Caribfly movement into the area and document absence. When populations are sufficiently high on the survey traps, bait sprays are used to reduce fly numbers. In addition, postharvest protocols may be implemented to assure that fruit arrives at its destination free of live flies.
Growers and others interested in participating in the Caribfly program must contact the Florida Department of Agriculture and Consumer Services, Division of Plant Industry, Caribbean Fruit Fly Protocol, 3501-0-03 South US #1, Ft. Pierce, FL 34982-6666; phone (772) 468-4092.
Thrips are small, elongate insects in the order Thysanoptera, varying in size from less than 0.2 mm to over 2.0 mm in length. They are easily overlooked because of their minute size. The life cycle of a thrips species consists of an egg, two larval feeding stages, a nonfeeding prepupal stage, a nonfeeding pupal stage, and feeding adults. About 14–18 days are required to complete development from egg to adult in some Frankliniella species.
Flower thrips, Frankliniella bispinosa and F. kelliae, have been identified as causing injury to developing flowers of navel and Valencia oranges. Crop loss on other citrus varieties has not been evaluated to date. F. bispinosa is the prevalent species throughout the citrus-growing areas of the state, while F. kelliae occurs on citrus from Vero Beach and Hardee County in the north to Dade County in the south. Thrips feeding results in cellular evacuation 1–5 cells deep and subsequent necrosis that can result in abortion of the flower or small fruitlet. Adult populations of these two species migrate as “aerial plankton” prior to and during the regular flowering cycle between January and April each year. Both species have very wide host ranges and utilize flowers and pollen of many plants as food sources. High populations of these thrips can cause economic loss in navel or Valencia orange by reducing fruit set. Both thrips species insert eggs singly into all floral parts.
Examine orange blocks during flowering at least twice each week to identify periods when high populations of thrips (i.e., Frankliniella spp.) are migrating into the trees. The number of thrips per citrus flower that causes economic loss has not been determined. Adult thrips are about 1 mm long and yellow to straw-colored. Dark banding along the upper surface of the abdominal segments may be evident on some adult specimens. Larvae are white or yellow. Thrips are capable of entering buds as soon as individual petals begin to separate. Examine individual flowers at random with a 5–10x magnification and observe their numbers. Residual activity of insecticides is very short (i.e., 3–7 days). Timing of one insecticide application to protect the major flowering period between maximum bud swell and full bloom should be considered when thrips are abundant. This is best achieved by treating the block at maximum bud swell or onset of full bloom. Delay will allow thrips to enter the opening flowers and reduce exposure to the insecticide. Treatment recommendations (Table 1) are based on the need for chemical control to optimize fruit set for the fresh market. The recommended insecticides are toxic to honeybees, which are also active around citrus blooms.
Orchid thrips (Chaetanaphothrips orchidii and Danothrips trifasciatus) and greenhouse thrips (Heliothrips haemorrhoidalis) cause rind-blemish problems on developing fruit (i.e., ring spotting or irregular russeting), on immature and mature clustered fruit, or where a leaf or twig is in direct contact with a fruit. For all these species, economic loss has been restricted to fruits directed to the fresh market, mainly red grapefruit and satsuma.
Orchid thrips females are yellow to straw-colored with distinctive dark banding on the wings. Larvae are white or yellow with distinctive minute spines present on the upper surface of the eighth abdominal segment. Adult female greenhouse thrips are black, while the larval and pupal stages are white. All stages of the greenhouse thrips are occasionally found on fruit. Orchid thrips is the most commonly found species associated with damaged grapefruit and occurs throughout the year. D. trifasciatus is usually present in lower numbers than other orchid thrips. Examine interior clusters of red grapefruit at random with a 5–10x magnification beginning the first week of May or just as clustered fruit begin to touch for presence of orchid and greenhouse thrips larvae and adult females. Either wash suspected infested fruit individually in a bucket containing 80% alcohol and record the grove location to verify pest thrips or collect three or more samples of 20 clustered fruit at random from each 10-acre red grapefruit block. Each of the 20 interior-canopy red grapefruit should be immediately washed in a bucket containing about one pint of 80% alcohol. Fruit should be collected at random with not more than 4 fruit taken per tree and a minimum of 5 trees per sample. The presence of 20 or more adult or larval thrips warrants an insecticide treatment. If more than 5 thrips are found, the area should be resampled in a week. One or two insecticide applications (Table 1) between May and July may be required to prevent rind blemish damage on red or white grapefruit varieties. Thrips scouting samples should be collected at random with not more than 4 fruit taken per tree and a minimum of 5 trees per sample. The presence of 20 or more adult or larval thrips warrants an insecticide treatment. If more than 5 thrips are found, the area should be resampled in a week. One or two insecticide applications between May and July may be required to prevent rind blemish damage on red or white grapefruit varieties.
Chilli thrips (Scirtothrips dorsalis) is an increasingly common pest in screenhouse citrus production—e.g., in CUPS (see chapter 21) and nurseries. Chilli thrips are approximately 1/3rd the size of flower thrips and can enter through most screens currently used to exclude insect pests. Chilli thrips cause feeding damage to leaves that reduces photosynthetic capacity and rind damage to fresh fruit similar to fruit damage caused by broad mite. Management of this pest is currently under evaluation.
Recommended Chemical Controls
READ THE LABEL.
See Table 1.
Rates for pesticides are given as the maximum amount required to treat mature citrus trees unless otherwise noted. To treat smaller trees with commercial application equipment including handguns, mix the per-acre rate for mature trees in 250 gallons of water. Calibrate and arrange nozzles to deliver thorough distribution and treat as many acres as this volume of spray allows.
Table 1. Recommended chemical controls for chewing pests.