Citrus Leaf Miner
Citrus leaf miner is a leaf-eating insect that eats the leaves of the lemon plant and makes tunnels in them. This is found in almost all citrus fruits and other lemons. Other types of insects make tunnels in the bark of citrus and attack the stems, roots, & ornamental plants of lemons. But insect is the only mining worm that attacks most citrus. Citrus leaf miner inset is a big problem in the United States garden. Other mining-type pests target weeds, ornamentals, and crop plants, but citrus leaf miner is the only mining insect that typically affects citrus leaves.
Citrus leaf miner, Phyllocnistis citrella, was not discovered in Imperial County, California, until the year 2000. It quickly spread to neighboring counties and kept moving northward. Citrus leaf miner now infests the vast majority of the United States, the coast up to San Luis Obispo County & the San Joaquin Valley. Citrus leaf miner is indigenous to Asia. It was originally identified as a pest in Australia in the 1940s, and by the 1970s it had spread to other major citrus-growing regions of the world. It arrived in Florida in 1993 and spread westward, invading northern Mexico in the mid-1990s and the United States by the end of the century.
Symptoms Identification of Leafminer
Citrus leaf miners are tiny, light-colored moths. It features silvery and white iridescent forewings with brown and white markings and a unique black patch on each wing. White hind wings and body have long fringe scales. Only citrus leaf miner and similar plants have larvae. The larva leaves a thin dark line of frass inside the serpentine mine under the leaf as it feeds & develops. This visual trait identifies the pest. The larva leaves the mine and goes to the leaf edge in its last stage. It twists the leaf around itself and pupates to become an adult, distorting it. The citrus peel miner, another citrus moth, attacks fruit and stems rather than leaves & no frass trail in its mine. White, crystalline ball-shaped formations cover the peel miner pupa’s silky cocoon. Peelminer pupae hide in bark cracks and crevices on any tree.
Causal Organism of Citrus Leafminer
Phyllocnistis citrella, also known as the citrus leafminer, is a tiny moth that feeds on citrus trees. This pest is native to Southeast Asia but has spread to many citrus-producing regions around the world including Australia, South America, and the United States. The larvae of this moth feed on the leaves of citrus trees, causing them to curl and discolor, making them unmarketable.
Citrus Leaf Miner Life Cycle
Citrus leaf miner has four stages: egg, larva, pupa, and adult moth. Adults survive 1–2 weeks and do not damage plants. Adult moths are rarely observed and spend the day resting on leaf undersides. The female moth releases a sex pheromone that attracts males shortly after hatching. Females lay solitary eggs on host leaf undersides after mating. Egg-laying places on the tree are flush growth leaflets, especially near the midvein. Eggs hatch after one week.
The newly emerging larvae start feeding in the leaf and construct tiny, practically invisible mines. As the larva grows, its serpentine tunnels become more visible. Over 2–3 weeks, larvae molt 4 times. The prepupa larva emerges from the mine and curls the leaf edge. Leaf miners pupate inside curled leaf edges. Pupils endure 1–3 weeks. Insects live for 3–7 weeks. Citrus leaf miner thrives from 70o to 85oF and has 60% relative humidity, but it adapts to most United States climates.
Damage Symptoms of Citrus Leafminer
Citrus leaf miner larvae only thrive in the sensitive, young, shining leaf flush of citrus and kindred species. Unless populations are very large, hardened leaves are immune. The larvae coil and deform freshly sprouting leaves by mining their lower or top surfaces. Mature trees (more than 4 years old) with a dense canopy of older foliage can survive new leaf damage during part of the growing season without affecting growth or fruit supply. Young trees flush year-round and have less mature foliage, supporting greater citrus leaf miner populations. The young trees may shrink.
Young trees with heavy leaf-miner populations rarely perish. In cooler coastal locations of the United States, leafminer populations may remain robust from summer through October. Inland heat suppresses them. Instead of using insecticides to manage citrus leaf miner, let it alone and let its natural enemies feed on and parasitize the larvae in the mines. In other countries with long-standing citrus leaf miner invasions, natural enemies parasitize or consume leafminers, reducing citrus damage after the first year or two. These environmental enemies live by laying eggs in mining insects. As natural enemies multiply, leafminers fall.
Citrus Leaf Miner Control Method and Management
On citrus trees that have reached maturity in a backyard setting, the citrus leaf miner rarely causes substantial harm, and treatment is typically limited to techniques that restrict the growth of succulents and protect their natural predators. Very young trees are more susceptible to damage, hence the use of insecticides may on occasion be warranted. However, the insecticides that are now available for use on trees in backyards are not particularly efficient, and many of the treatments leave residues that are toxic to natural predators, which makes the problem much worse. There are pheromone traps available to use in the search for leafminer moths.
Leafminer Chemical Control
Due to their inability to reach larvae inside mines, several home insecticides fail to control citrus leaf miners. Mature trees rarely need insecticide for leafminer infestations. Insecticides can be given to new foliage when egglaying moths are active or to the soil before new flush growth on young or valuable trees. Azadirachtin and spinosad-based larvae-killing pesticides are harmless for natural enemies. These pesticides may need to be reapplied every 7–14 days due to short-lived residues. Application of Green Light Spinosad is limited to 6 times per season. Imidacloprid (Bayer Advanced Fruit, Citrus, and Vegetable Insect Control) applied to citrus tree bases lasts 1–3 months.
Imidacloprid should only be applied once a year. The imidacloprid applications should be scheduled to protect periods of leaf flushing, such as in the spring and fall. Imidacloprid takes 1–2 weeks to migrate from roots to leaves, so use it when a new flush appears. Avoid imidacloprid one month before or during bloom to preserve bees. Honey bees can avoid imidacloprid in nectar/pollen by removing young tree blossoms before they open. Malathion, carbaryl*, and pyrethroids destroy beneficial insects and can lead to whiteflies, scale insects, and other citrus pests.
Citrus Leaf Miner Control Through Traps
Traps that have been baited with a pheromone can be an effective tool for locating leaf miners, knowing when moths are flying and laying eggs, and calculating the optimal period for applying insecticides. However, they do not capture a large enough portion of the population to be effective as a method of population control. Because only male moths are attracted to the pheromone, only male moths will get caught in the sticky coating of the trap.
Pheromone traps should be hung at a height of approximately shoulder height on citrus trees. Be sure to maintain the trap in accordance with the recommendations provided by the manufacturer, such as the frequency with which the pheromone dispenser should be replaced. Commercial traps designed specifically for citrus leaf miners will only attract citrus leaf miners, but the traps could inadvertently catch other types of insects as well. Identify any moths that have become caught before taking any kind of control measure. Moth traps should be checked for activity once a week. However, the most crucial times to check are in the summer and fall, when there is a flush of citrus growth and the moth population is at its highest.
Leafminer Control Through Cultural Practice
Citrus new growth is a magnet for citrus leafminer moths because of the abundance of fresh leaves. It is important to refrain from cutting live branches more frequently than once a year in order to maintain regular and brief flushing cycles. Once the leaves have reached their full maturity, the pest will no longer be able to mine them. It is not necessary to remove citrus leafminer-damaged leaves from the tree. Because the unharmed portions of the leaves will continue to supply the tree with nutrients. It is important to refrain from using nitrogen fertilizer during the warmer months of the year, such as the summer and fall when leafminer populations are strong and flush growth is likely to suffer serious harm.
Citrus Leaf Miner Biological Controlci
The citrus leaf miner is an insect pest that can be eradicated by a number of parasites and predators, one of which is a type of naturally occurring, nonvenomous wasp belonging to the genus Cirrospilus. The parasites deposit their eggs within the mine, either on top of or within the leafminer larvae themselves. The leafminer larva is eaten by the parasite larva after the parasite egg hatches and hatchlings emerge from the egg. These parasites play an extremely significant role in lowering citrus leaf miner populations.
When it is at all possible, you should avoid spraying citrus with broad-spectrum pesticides and avoid other methods that could disrupt natural enemies. To enhance the activity of native natural enemies, the use of physical restrictions and preventative cultural approaches is essential. You do not need to release parasites since many native parasite species that target other leafminer species will find your citrus plants and attack citrus leaf miner. This means you do not need to release parasites.
Physical Control of Leafminer
On mature trees, vigorous shoots that are known as water sprouts frequently form on the branches and, occasionally, above the graft union on the trunk. These shoots have a strong growth rate and continue to put forth new leaves for an extended period of time. In areas where citrus leaf mining is an issue, you should get rid of any water sprouts that could provide a breeding ground for the moths. Suckers are robust shoots that grow from the trunk below the graft union and should be removed at all times since they originate from the rootstock and do not typically yield fruit that is desirable. Suckers can be identified by their growth from the trunk below the graft union.