How to Manage Pests
Pests in Gardens and Landscapes
Psyllids (Hemiptera: Psylloidea) are small insects that suck plant juices. The adults resemble miniature cicadas and are sometimes called jumping plantlice. Over 160 psyllid species occur on native or introduced landscape plants in California. Several psyllid species are pests of crops such as citrus, olive, pear, potato, and tomato. Each kind of psyllid feeds on only one plant species or closely related group of plants. Most psyllids native to California are relatively uncommon and rarely become pests. Generally psyllids that have become pests are exotic species inadvertently introduced from other countries. Exotic species make up about 11% of the psyllid species in California.
IDENTIFICATION AND LIFE CYCLE
Adult females lay eggs that hatch and develop through about five instars (nymphal growth stages) before maturing into winged adults. Psyllids become abundant in spring when temperatures warm and host plants produce new growth flushes. Most psyllid species require only a few weeks during warm weather to complete development from egg to adult. Development and reproduction stop or greatly slow during cool weather, and in some species hot weather can suppress their populations. Most species have about 3 to 5 generations a year, but some species may only have one generation a year.
Adults hold their wings rooflike over their bodies and are 1/12 to 1/5 inch long, similar in size to large winged aphids. They have strong jumping legs and short antennae. Nymphs are flattened and less active than adults. Don’t confuse psyllid adults with similar looking but harmless psocids. Psocids feed on fungi, including sooty mold growing on psyllid honeydew. Mature psyllids commonly jump when disturbed, while psocids run or fly away. Psocids have a more narrow “neck” or separation between the head and the thorax and have chewing mouthparts, whereas psyllids have tubular, sucking mouthparts.
Nymphs of many psyllid species secrete wax filaments or form covers, often called “lerps,” composed of wax and solidified honeydew. These covers can aid in identification of psyllid species in the field. Because several hundred species of psyllids occur just on acacia and eucalyptus trees in Australia, exotic, new psyllid species are likely to be introduced into California where these Australian plants have been introduced for landscaping. Take unfamiliar psyllids to your county agricultural commissioner or local University of California (UC) Cooperative Extension office for identification.
Over 140 species of psyllids are considered native to California. They do not appear to harm their hosts and do not warrant control in gardens or landscapes. Certain species can be temporarily abundant; but their populations soon decline naturally, as many are heavily attacked by their natural enemies, including parasitic wasps. Common native psyllids include:
About 18 psyllid species introduced accidentally from other countries can be pests in gardens and landscapes, including psyllids recently introduced on citrus, olive, pittosporum, and rosewood tree or tipu (see Table 1). Earlier invasive species include psyllids infesting acacia, eugenia, eucalyptus, Grecian laurel or sweet bay, pear, pepper tree, and potato. Certain species are now under good biological control, and biological control programs are being developed for new pests like the Asian citrus psyllid. Psyllids are beneficial in some situations. The melaleuca psyllid, Boreioglycaspis melaleucae, for example, has been deliberately introduced from Australia into Florida to help control paperbark tree, Melaleuca quiquenervia, which is a serious invasive weed tree.
Psyllids suck plant juices and excrete sticky honeydew on which blackish sooty mold grows. Some species secrete pale or white wax masses, pellets or strands, or coverings called lerps. High psyllid populations reduce plant growth or cause terminals to distort, discolor, become galled, or die back. Certain species, such as the olive and tipu psyllids, can cause premature leaf drop. The eugenia and peppertree psyllids cause leaves to develop a pit around the spot where each nymph settles and feeds. Excessive honeydew excretion and wax secretions can also damage plants or property below the infested foliage.
Pear psyllid, Psylla pyricola, injects a plant toxin that blackens and “burns” pear foliage and fruit skins. The potato, or tomato psyllid, Bactericera cockerelli, occasionally causes infested potato to develop yellow, severely distorted, dwarfed leaves and shoots. The adult vectors (introduces during its feeding) the bacterial pathogen causing “zebra chip” disease, which causes fried potatoes to develop prominent black stripes. The Asian citrus psyllid, Diaphorina citri, damages citrus directly by feeding on new leaf growth (flush) and is a vector of the bacterium Candidatus Liberibacter asiaticus that can result in the lethal and incurable citrus disease huanglongbing.
Most psyllids on landscape trees and shrubs do not need to be managed to protect plant health. Species warranting control action include Asian citrus psyllid and, in certain situations, other invasive psyllid species that cause intolerable damage (see Table 1). When taking control actions use an integrated program incorporating appropriate plant care and certain insecticides, preferably less-persistent products that provide adequate control and help conserve natural enemies.
Exclude Foreign Pests
Many of our worst pests were introduced from other states or countries. To prevent new pest introductions during planting and travel:
Take any unfamiliar pests to the local county agricultural commissioner or UC Cooperative Extension office for identification or telephone the California Department of Food and Agriculture (CDFA) Exotic Pest Hotline at 1-800-491-1899. Be sure you put pests in a sealed bag or bottle before transporting them.
Most psyllid damage is aesthetic. Tolerance for aesthetic damage varies with people’s attitude and knowledge and the situation, such as the location and species of plants and psyllids. Except for adults, such as the Asian citrus psyllid, that vector plant pathogens most psyllid damage is caused by feeding nymphs. Determine the level of damage you are willing to tolerate and monitor psyllid abundance on susceptible plants on a regular basis. Initiate control actions before psyllid abundance or damage approach the level that you previously found to be intolerable.
To help you decide whether and when to take control action, monitor psyllids by using sticky traps to capture adults, beat or shake foliage to dislodge adults so they can be counted, and inspect susceptible plant parts for eggs, nymphs, and adults. Regular monitoring helps you determine whether natural enemies are becoming more abundant and may provide the needed levels of biological control or the most effective time to take action, if management with pesticides is warranted.
In addition to monitoring psyllids, observe the seasonal growth of plants. Periodically examine plants for the presence and relative abundance of new growing tips, which typically are softer, somewhat differently colored, and undersized in comparison with older tissue. You may discover an annual cycle to psyllid abundance; population increases typically coincide with new plant growth. Conversely, the presence of large numbers of psyllid adults may not be a cause for concern when there is no longer any new flush of growth for egg laying, as the season is ending. The same number of adults observed when a plant is weak or growing poorly might warrant closer attention.
Hang yellow, sticky-coated traps in host plants as an efficient way to monitor the presence and relative abundance of adult psyllids and certain psyllid parasites and predators. Adults of many types of insects are attracted to the yellow color and become stuck to the trap. A significant increase in the number of psyllids in traps can indicate it is time to make a foliar spray of contact insecticide or to shear prune plant terminals (such as with eugenia) to remove psyllid-infested tips while still conserving parasites as discussed below.
Inspect traps once each week and count (or estimate) and record the number of adult psyllids and their natural enemies. If insects are abundant, you can estimate their numbers by using five range categories: no psyllids, 1 to 10, 11 to 25, 26 to 100, or more than 100 psyllids per trap. Count and record the psyllids separately from the natural enemies. Following each count, scrape off all the insects and debris or replace traps if they are too fouled. Periodic cleaning or replacing of traps is essential to keep the surface sticky and make it easier to identify and count newly trapped insects.
Beat or shake sampling
Adult psyllids, certain natural enemies, and other easily dislodged insects can be detected and counted by shaking or tapping infested terminals to knock insects onto a collecting surface underneath foliage.
Hold a light-colored plastic tray, framed cloth, or clipboard with a white sheet of paper beneath foliage or place a small cloth on the ground beneath low-hanging branches. To dislodge insects onto the collecting surface, shake or beat the branch a fixed number of times, such as once or twice. A typical program may sample from four locations per plant, one branch from each cardinal direction. Do this once each week during the time of year when psyllids can be a problem, generally spring to midsummer for most species. Monitor about the same time of day, preferably early morning when temperatures are cooler, which makes adults less active and easier to count. In most situations you can ignore any dislodged immature psyllids. Adults are the egg-laying stage and the seasonal cycle of the adult populations, highs and lows, indicates when the damaging nymphal stages are likely to become more or less abundant.
To suppress populations of phloem-sucking insects, such as psyllids, provide appropriate irrigation and do not apply nitrogen fertilizer to established woody plants, unless foliage appearance or plant growth is unsatisfactory because of a confirmed nutrient deficiency. Be aware that foliar symptoms of nutrient deficiency are often caused by poor root health and improper soil conditions, such as waterlogged soil from inadequate drainage and frequent irrigation, alkaline (high pH) soil, and root infection by fungal pathogens. Adding fertilizer will not remedy these problems.
For plants adapted to summer rainfall, consider irrigating them during summer and fall. For eucalyptus, drought stress increases damage from both lerp psyllids and longhorned borers. For established plants, apply water beneath the outer canopy, not near trunks. Avoid frequent, shallow watering that is often used for lawns. A general recommendation is to irrigate established trees infrequently (possibly once a month during drought periods) but with sufficient amounts so that the water penetrates deeply into soil (perhaps about 1 foot or more below the surface). Waterlogging (soggy soil), especially near the trunk, favors root and crown diseases. The specific amount and frequency of water needed varies greatly depending on the site conditions and plant species.
Minimize shearing or clipping of terminals. Shearing stimulates new growth, which is preferred by psyllids for feeding and egg laying. Prune by cutting plants just above branch crotches and nodes instead of shearing off terminals. An exception is eugenia and other shrubs that are sheared several times each year to provide a smooth, dense canopy surface for ornamental purposes, such as formal hedging or topiary pruning. Well-timed shearing can suppress eugenia psyllid populations.
Avoid planting problem-prone plants and consider replacing them with pest-resistant species and cultivars that are well adapted to local conditions. See the examples below for the acacia, eucalyptus, and peppertree psyllids.
Parasites and predators biologically control many native and certain introduced psyllid species. Important natural enemies of psyllids include lady beetles, lacewing larvae, predaceous bugs, and tiny parasitic wasps. Psyllids under moderate to good biological control include the bluegum psyllid and, especially in coastal regions, the redgum lerp psyllid. The acacia, eugenia, and peppertree psyllids are under good biocontrol in warmer locations but are sporadically abundant in coastal regions (Table 1). Introduced parasites have also reduced the abundance of lemongum psyllid and spottedgum lerp psyllid and in some coastal locations this biological control may keep these pests from becoming an intolerable problem. In most situations these species warrant no management except to conserve natural enemies.
Species-Specific Management Methods
A purplish predatory bug and a small black lady beetle generally provide good biological control of acacia psyllid (Table 1). However in San Francisco Bay coastal locations, these predators may not become effective until June or July. Tolerate psyllids for several weeks when they are temporarily abundant, typically during April and May, and conserve natural enemies until predators provide control. Alternatively, temporarily reduce high populations by thoroughly covering new outer and upper canopy acacia growth with a nonresidual or short-residual insecticide as discussed below. To entirely eliminate the problem, replace susceptible plants. See Pests of Landscape Trees and Shrubs for Acacia and Albizia species that are not preferred by acacia psyllid.
Buy citrus and other Rutaceae family plants only from reputable local nurseries to avoid introducing into new areas this psyllid or the citrus-killing pathogen that causes huanglongbing (HLB) disease, also called citrus greening disease. In locations not known to be infested with Asian citrus psyllid, inspect your citrus trees once a month whenever tiny new leaves (feather flush growth) are present during warm weather, especially in the spring and fall. Slowly walk around each tree and examine new flush growth. Look for twisted leaves, waxy deposits, honeydew, sooty mold, and adult psyllids. Distinguish psyllids from aphids, scales, whiteflies, and certain other insects that can also cause honeydew and sooty mold.
If you think citrus psyllids are present, use a hand lens to examine succulent leaf tips for tiny yellow eggs, psyllid nymphs with waxy tubules, and psyllid adults. If you think you have found this psyllid in uninfested locations, immediately contact the CDFA Exotic Pest Hotline at 1-800-491-1899.
In certain areas the CDFA may apply insecticides to residential host plants to control this psyllid. In known infestation areas, consider applying insecticide yourself or hiring a pest control company to control this psyllid and help protect citrus from the psyllid-vectored huanglongbing disease. In citrus, if applying systemic insecticide to soil as discussed below, make the application during summer or early fall when roots are active and plants are not blooming or about to bloom. A parasitic wasp, Tamarixia radiata, from Pakistan has been released and established in California and is spreading. This natural enemy can help to control Asian citrus psyllid, if Argentine ants and other invasive ants are selectively controlled as discussed in Pest Notes: Ants. These pest ants harvest honeydew from Asian citrus psyllid nymphs and protect them from natural enemies. See Pest Notes: Asian Citrus Psyllid for more information.
In regions with summer drought consider providing eucalyptus trees with supplemental water during summer and fall as described above in Cultural Control. Drought-stressed eucalyptus are more susceptible to psyllids and Phoracantha species longhorned borers. Apply water beneath the outer canopy infrequently but with sufficient amounts so that the water penetrates deeply into the soil. For example, about once per month water trees slowly through drip emitters that run continuously for several days.
Avoid fertilizing eucalyptus because this increases tree susceptibility to psyllids. Use slow-release nutrient formulations if other plants near eucalyptus trees require fertilization. When planting trees choose species that are well adapted to local conditions, including tolerance for the prevailing moisture conditions. Consult Pest Notes: Eucalyptus Redgum Lerp Psyllid for more information on Eucalyptus species’ relative susceptibility to leaf-chewing beetles, longhorned borers, and psyllids; and consider planting species that are not susceptible to these pests.
In cooler areas near the California coast, eugenia psyllid parasite populations may not increase quickly enough to provide satisfactory control during the spring. Where pruning or other control methods are planned, inspect plants regularly for new growth beginning in late winter. Also consider regular monitoring for adult psyllids, especially when managing many eugenia plants.
Regular shearing of terminals reduces eugenia psyllid abundance and is the only way to eliminate damaged foliage, aside from waiting for old leaves to drop. No pesticide or other treatment will restore pitted foliage to a healthy appearance. Prune terminals after maximum spring growth appears or about 3 weeks after the first peak in adult psyllid density, as determined using methods described above in Monitoring. Consider shearing eugenia tips at about 3-week intervals throughout the period of new plant growth or as long as adult psyllids are abundant. Leave eugenia clippings as mulch near the shrubs for at least 3 weeks to allow parasites within psyllid nymphs to complete their development and emerge. Eugenia psyllid eggs and nymphs on the cut foliage will die.
Avoid frequent irrigation near olive tree trunks and provide good soil drainage to improve tree health and resistance to pests. Prune off or thin interior limbs in hot locations to increase psyllid exposure to heat and increase air circulation, which suppresses its populations. Natural enemies are being investigated for potential introduction. Where psyllid populations were intolerable the previous year and insecticide use is planned, target the first generation, typically present March to April. Olive psyllids are more difficult to control during their second generation (May to June), when most of their waxy excrement and damage occurs.
Peppertree psyllids are often satisfactorily controlled by an introduced parasitic wasp, Tamarixia schina. No additional control is required in many situations. Peppertree psyllid produces relatively little honeydew and its distortion of foliage can be easily overlooked on the finely divided leaves of pepper trees, especially on branches above eye level.
To improve pepper tree health and its ability to tolerate psyllids, provide adequate soil drainage and remove irrigated landscape near trunks. These practices are more important methods of improving pepper tree health than applying pesticides. Pepper trees are adapted to well drained, sandy soil and summer drought. Planting trees in heavy clay soils and in lawns and other summer-watered landscapes promotes root diseases and causes trees to decline and die.
In cooler locations, where biological control is less effective, consider growing alternative species if psyllids cannot be tolerated. Australian willow myrtle or peppermint tree, Agonis flexuosa; desert willow, Pittosporum phillyraeoides; and Australian willow, Geijera parviflora, are relatively drought-tolerant and have a weeping appearance that resembles the pepper tree; but they are not affected by the peppertree psyllid. Avoid planting Peruvian pepper, Schinus terebinthifolius; it is invasive in natural areas of California where it forms dense thickets and displaces native plants.
Where psyllids or their damage are intolerable and insecticides will be applied, the most appropriate product will depend on the situation. The recommended products may include nonresidual, contact insecticides; short-residual, translaminar insecticides; and long-lasting, systemic insecticides. Apply insecticide only to psyllid host plants and in situations where psyllids and their damage cannot be tolerated. Completely read and follow the product label instructions for the safe and effective use of the insecticide.
Insecticides Most Compatible with Integrated Pest Management (IPM)
Nonresidual contact insecticides and certain short-residual products have the least adverse effect on bee and natural enemy populations. If psyllids were intolerable the previous year, the best time to spray these products is when young psyllid nymphs are present and before psyllids have become too abundant or produced excessive waxiness or other damage. Thoroughly spray infested parts, such as succulent terminals and the underside of leaves. More than one application per season is generally needed during the times when psyllids are most active.
These products can control psyllids where infested plant parts can be thoroughly sprayed. Nonresidual, contact insecticides have low toxicity to people, pets, and pollinators. They have little adverse impact on biological pest control, because they do not leave toxic residues that would kill natural enemies migrating in after their application. Nonresidual contact insecticides include azadirachtin (AzaMax, Safer Brand BioNeem), neem oil (Green Light Neem, Schultz Garden Safe Brand Neem), insecticidal soap (Safer), and narrow-range oil (Bonide Horticultural Oil, Monterey Horticultural Oil).
Unless plants are too tall to achieve adequate coverage and avoid excessive drift of spray, these products are an especially good choice on acacia, eugenia, pepper tree, and other hosts with natural enemies that may not provide biological control until later in the season or are only partially effective at that location. Spraying nonpersistent insecticides early in the season before natural enemies build up and migrate from nearby unsprayed plants is compatible with late-season biological control. Monitor after the application. If natural enemies become abundant, avoid spraying again.Spinosad
Spinosad is a fermentation product of a naturally occurring bacterium. This insecticide (Captain Jack’s Deadbug Brew, Conserve, Monterey Garden Insect Spray) persists about 1 week. It has translaminar activity (is absorbed short distances into plant tissue) so it can better reach psyllid nymphs in leaf and shoot crevices and pits in comparison with the products above. Spinosad can be toxic to certain natural enemies (e.g., predatory mites, syrphid fly larvae) and bees when sprayed and for about 1 day afterward; do not apply spinosad to plants that are flowering.
Insecticides More Toxic to Psyllids and Beneficial Insects
Systemic neonicotinoids are the most practical insecticides for psyllids infesting large plants and where the more IPM-compatible products are inadequate. Neonicotinoids such as dinotefuran (Safari) and imidacloprid (Bayer Advanced Tree & Shrub Insect Control, Merit) are absorbed by one plant part (e.g., roots or trunks) and moved (trans- located) to other plant parts. Some products can be sprayed onto plant foliage, but drenching or injecting soil, or for woody species injecting or spraying trunks (if the product is labeled for these application methods), minimizes environmental contamination and may be more effective than spraying foliage. Trunk application of systemic insecticide can provide relatively rapid control. With soil application, there is a longer time delay between application and insecticide action.
Neonicotinoids have low, moderate, or severe adverse impact on natural enemies and pollinators, varying with the product, situation, and the species and life stage of invertebrate. Neonicotinoid insecticides can translocate to flowers and poison natural enemies and pollinators that feed on nectar and pollen. Delay systemic insecticide application until after plants have completed their seasonal flowering, unless the product label directs otherwise. Where other plants grow near treated plants, those other plants may also take up some of the soil-applied insecticide or become contaminated with insecticide spray drift. Delay soil application or foliar spraying of systemics when possible until the nearby plants are also done flowering.
To avoid tree injury and potential spread of pathogens on contaminated tools, use a soil application or trunk spray whenever possible instead of injecting or implanting trees with insecticide. Injecting or implanting trunks or roots injures trees, and it is difficult to repeatedly place insecticide at the proper depth. If injecting or implanting multiple trees, prevent the potential spread of pathogens on contaminated tools. Before moving to work on each new tree, scrub any plant sap from tools or equipment that penetrate trees and disinfect them with a registered disinfectant (e.g., bleach). Avoid methods that cause large wounds, such as implants placed in holes drilled in trunks. Do not implant or inject roots or trunks more than once a year.
Insecticides to Avoid
Carbamates (such as carbaryl), the systemic organophosphate acephate (Lilly Miller Ready-to-Use Systemic, Orthene), nonsystemic organophosphates (malathion), and pyrethroids (fluvalinate, permethrin) also can be applied. Except for infestations of the Asian citrus psyllid, these insecticides are not recommended. These materials are highly toxic to natural enemies and pollinators and can cause outbreaks of spider mites or other pests. Because their use in landscapes and gardens can run or wash off into storm drains and contaminate municipal wastewater, these insecticides are being found in surface water and are adversely affecting nontarget, aquatic organisms.
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Pest Notes: Psyllids
Authors: J. N. Kabashima, UC Cooperative Extension, Orange and Los Angeles Counties; T. D. Paine, Entomology, UC Riverside; K. M. Daane, UC Berkeley, and S. H. Dreistadt, UC Statewide IPM Program, Davis.
Produced by University of California Statewide IPM Program
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