Mastering Citrus Mealybug Control for Healthy Citrus Trees Naturally

Citrus mealybug is among the worst and most stubborn pests that pose a menace to citrus production allover the world as it has the potential to create massive loss of yield and make the fruits unmarketable even in a single growing period. These are little inconspicuous insects, which will infest leaves, twigs and young fruit, and which will suck sap into the plant tissues rendering it weak and reducing the size and quality of the fruit. Besides the citrus mealybug damage caused by direct feeding, citrus mealybugs excrete honeydew- sweet sticky honeydew liquid, which not only promotes fungus, but also makes orchards vulnerable to future attacks increasing the stressor to citrus trees. 

Citrus mealybug is among the worst and most stubborn pests that pose a menace to citrus production allover the world as it has the potential to create massive loss of yield and make the fruits unmarketable even in a single growing period. These are little inconspicuous insects, which will infest leaves, twigs and young fruit, and which will suck sap into the plant tissues rendering it weak and reducing the size and quality of the fruit. Besides the citrus mealybug damage caused by direct feeding, citrus mealybugs excrete honeydew- sweet sticky honeydew liquid, which not only promotes fungus, but also makes orchards vulnerable to future attacks increasing the stressor to citrus trees. 

Identification, Citrus Mealybug Scientific Name and Life Cycle

One of the Pseudococcidae is the citrus mealybug Pseudococcus citri (Risso). Adult females are oval and are 3-4 mm long and thin and covered with their special secretion; the fluffy is white in colour and secreted with waxy coating which is easily noticed in the field, although they tend to creep in the axils of the leaves, under the bark and in the fruiting clusters. The males are winged and small in body and bear a thin white tail; they barely ever feed, and only exist to mate.

The breeding and citrus mealybug life cycle is short: one female ovulates 300-600 citrus mealybug eggs in a thick, fluffy nest known as the ovisac and usually placed in the crannies of the plants. After a few days, crawlers (nymphs) are produced and start to spread themselves to seek their feeding places. Given ideal conditions, the entire generation life cycle of an egg to adult is between six to ten weeks, which implies that many overlapping generations can be generated within a single growing period. The wingless females are also dependent on the crawlers, wind, ants, birds, and human handling in order to be dispersed to other new branches and trees which is a pivotal fact that must be factored in when a management strategy is being established. In the upcoming sections, we will discuss citrus mealybug treatment.

Symptoms in the Orchard: Spotting Citrus Mealybug Damage Early

How to get rid of citrus mealybugs? The principle of effective management of citrus mealybugs is the care of their timely identification of the issue, yet it is often disregarded until the time when the population has grown to large proportions. The first signs are small groups of white, fluffy insects on new shoots, the underside of leaves, along petioles and these insects love to feed on the crawler. Due to the growth of the infestation, honeydew is observed as an oily layer on the leaf, twigs, and fruit rapidly after which black sooty mold develops that hides foliage and damages photosynthetic functions.

Surface scabbing and discoloration are also evident on fruit because mealybugs tend to feed, injecting saliva, and make produce unsellable despite removal of the insect later. Highly infested leaves roll in, turn yellow and then fall, compromising the capacity of the tree to carry on flowering and fruit set in the following seasons. Twigs can dry up when subjected to extreme stress, and even shrivel. The orchard foragers should pay special attention to the early spring development, and especially to the sheltered, microhabitat (curled leaves, calyces of fruits, crotches of sections) on which the mealybugs cluster; a hand lens is better than the naked eye at identifying the existence of such insects.

Cultural and Physical Practices as the First Line of Defence

Citrus mealybug management on a sustainable basis can be achieved not through the application of pesticides but through the maintenance of orchard hygiene and the physical structure of the orchard that eliminates the places of pest habitation and survival. Opening the tree canopy by pruning enhances airflow and penetration of light to the interior foliage making them less desirable to the mealybugs and more easily monitored. The cutting out of dead wood, sprouts, and low-hanging branches, gets rid of sheltered areas where female mealybugs lay their eggs free.

The citrus mealybug control is very necessary since ants protect the mealybug colonies against natural enemies actively in exchange of honeydew, in effect securing pests against predators. Trees are banded using sticky barriers on the trunks, disrupting the ant highways, thus lowering mealybug cover and enabling useful insects to forage more easily. The control of weeds in the orchard boundaries eradicates other host plants, which may entertain a population of mealybugs in the off-season, lowering carry-over pressure into the subsequent crop season.

Chemical free control of light infestations in nurseries and home gardens can be done by physical removal with a cotton swipe dipped in rubbing alcohol and then gently rinsed with soapy water. Population can be controlled with insecticidal soaps (designed to work with ornaments and specifically with mealybugs) and more than one application every 7-10 days is required since ovisacs defend eggs against penetrapation by the spray. Biological control is the easy answer to how to get rid of citrus mealybugs, which will be discussed in the next section.

Biological Control: Natural Enemies and Beauveria bassiana / Beveria WP

The nature has a lot of weapon against citrus mealybug, it has various parasitoids and predators like parasitoid Leptomastix species, ladybird beetles, etc, that can be bottlenecked down and populations also controlled by preserving them and attracting to the orchard. But chemical insecticides and interference in the Food webs by ants tend to break down these natural control agents and the passage to biological control is an investment and tolerating and belief in the ecological principle.

Beaueveria bassiana (citrus mealybug pesticide) is a commercialized entomopathogenic fungus under the name Beviera WP for citrus mealybug treatment,, which is a more recent addition into the benefits of citrus mealybug biological control. The action of this fungal agent is to generate spores which stick to the cuticle of the mealybug, hatch, and infest the insect leading to its death by draining internal resources- 5-7 days. Beveria WP (best insecticide for mealybugs) should be applied in the form of foliar spray (in accordance with the label instructions on concentration and time interval) on crawler when recently laid eggs are the most susceptible to infection (nymphs).

Timing is important: applications made at the same time as maximum egg hatch result in a maximum contact with crawlers stages, and those made too late are not efficient against adult females since they have a protective waxy layer. Blended with natural predators and cultural management, Beauveria bassiana (citrus mealybug insecticide) is a gentler, slower replacement of the hard insecticides, which perfectly fit into IPM programs where many mortality variables work in concert to maintain populations below the economic control temperature.

Targeted Use of Chemical Insecticides Within IPM

In spite of cultural and biological control efforts using citrus mealybug pesticide, there are times when commercial citrus growers believe it is necessary to invest in the use of chemical insecticides-whose application is usually justified when populations are out of economic thresholds or because the biological control devices are inadequate. The systemic insecticides (like imidacloprid) travel into the plant tissue and penetrate into internal feeding by mealybugs as they provide a prolonged residual performance. Special purpose contact sprays (e.g. horticultural oils, insecticidal soaps) are highly efficient on knock down but must be used extensively and frequently reapplied.

The secret of sustainable chemistry lies in resistance management: mode of action cycling of citrus mealybug insecticides, not applying the same group of insecticides back to back and citrus mealybug management agent recovery. The extreme use of one of the chemistry is subject to resistance evolution, which will make the tool irrelevant in a few seasons. Timing can be used to prevent application during a vulnerable stage of life (crawlers and not egg sacs) to ensure maximum efficacy, and minimum pesticides. Moreover, the application of less toxic sprays to predators and parasitoid keeps the biological citrus mealybug control foundation which is highly significant to healthy orchards in the long run.

Season-Long IPM Plan and Key Takeaways for Farmers

The successful citrus mealybug management calendar superimposes all the tools at the disposal of the growing season. At the beginning of spring (growth flush): search, eliminate by hand or deforest severely infested shoots, and apply horticultural oil in case of light populations. Late spring to summer (crawler emergence stage): release Beauveria bassiana or parasitoids, keep up ant guards, and weekly scan the ant fruit calyces to detect new infestation. Middle to end of the summer (activity) period: persist with biological and cultural techniques; in case of population surpassing the limit, selective insecticides are only to be used in case of unavailability or lack of biocontrols. Fall and winter (dormancy): rake up leaf litter, prune dead wood, and destroy volunteer host plants to decrease overwintering habitats.

Mealybugs: For citrus, a program of sustainable management to reduce the population of this pest was provided:

• Look frequently in the spring and fall; inspect some of the sheltered leaves of the trees and the roe of fruit.
• Clean and wipe off the orchard every year; use a rake on the dead wood, and enhance air circulation.
• Managing ants with trees banded or slick covers laid over trees to disrupt the ant-mealybug mutualism.
• Use Beauveria bassiana or bioinsecticides for citrus mealybug treatment at the heights of crawlers, as per label instructions on time and coverage.
• Use reserved chemistry only in case of threshold conditions; alternating mode of action of insecticides to avoid resistance.

Make a season calendar so every team member is aware of what the management sequence will be as well as be able to implement it repeatedly.

Growers of citrus can sustainably control citrus mealybug pressure by using a combination of early scouting, cultural practices, biological citrus mealybug control, and judicious use of chemistry which will hold profitability of orchard without jeopardizing quality of fruits and environmental steward. Now you know that how to get rid of citrus mealybugs is not a rocket science.

Reference: 

• Chartier FitzGerald, V. C., et al. "Screening of entomopathogenic fungi against citrus mealybug, Plannococcus citri (Hemiptera: Pseudococcidae)." African Entomology 24.2 (2016): 343-351.
• Cloyd, Raymond A., and Nathan J. Herrick. "Are Entomopathogenic Fungal-based Insecticides and Insect Growth Regulator Mixtures Effective Against the Citrus Mealybug, Planococcus citri (Hemiptera: Pseudococcidae), Feeding on Coleus, Solenostemon scutellarioides, Plants under Greenhouse Conditions?." HortScience 58.10 (2023): 1225-1229.