How to Manage Pests

UC Pest Management Guidelines

DESCRIPTION OF THE PESTS

California red scale and yellow scale are armored scales that are distributed throughout the citrus-growing regions of the state except in parts of the Coachella Valley where they are under an eradication program. The two species are difficult to distinguish by appearance. Yellow scale, however, is rarely found on mature wood of the tree whereas California red scale can be found on the wood as well as on fruit and leaves. Biologies and management tactics for California red scale and yellow scale are similar, but yellow scale is more easily controlled by natural enemies and, thus, less commonly found.

Female scales have a roundish cover, about the size of the blunt end of a nail. The cover is firmly attached to the leaf, wood, or fruit substrate when the scales are molting or reproducing; they remain under this cover throughout their life. When mature, they produce 100 to 150 crawlers. Crawlers hatch and emerge from under the female cover at a rate of two to three per day. Crawlers move around to find a suitable place to settle and can be spread about by wind, birds, or picking crews. They settle in small depressions on twigs, fruits, or leaves and start feeding; soon after, a circular, waxy cover forms over their body. Midway through the second instar, females and males begin to develop differently. Males form an elongated cover while the female cover remains circular. The female molts twice, developing a concentric ring in the center of the waxy covering each time.

Adult male scales are small, two-winged insects that emerge from the elongated scale covers after four molts. They live about 6 hours and their sole purpose is to mate. The number of male flights, along with the number of generations per year for this insect varies according to the growing region in the state and the weather but is generally about 4 flights per year.

DAMAGE

California red scales attack all aerial parts of the tree including twigs, leaves, branches, and fruit by sucking on the plant tissues with their long, filamentous mouthparts. Yellow scale attacks the plant in the same way, except that it is rarely found infesting twigs. Heavily infested fruit may be downgraded in the packinghouse and, if population levels are high, serious damage can occur to trees. Severe infestations cause leaf yellowing and drop, dieback of twigs and limbs, and occasionally death of the tree. Tree damage is most likely to occur in late summer and early fall when scale populations are highest and moisture stress on the tree is greatest.

MANAGEMENT

Management of California red scale and yellow scale varies according to location in the state and the other pests present in the orchard. Natural enemies can provide good control of California red scale in all regions of California except the Coachella Valley where it is under pesticide eradication. However, biological control tends to be easiest in the coastal areas and some inland districts of southern California because milder weather in these regions allows the overlap of generations, which provides susceptible host stages for parasitism year round.

In the San Joaquin Valley, many red scale and yellow scale populations developed high levels of resistance to organophosphates and carbamates during the 1990s. Growers shifted to using Aphytis releases, oil treatments, or insect growth regulators for scale control. Where biologically based IPM is practiced, yellow scale is easily controlled by parasites and is not currently a problem, whereas California red scale continues to be a key pest. Augmentative releases of Aphytis melinus have been shown to be effective in controlling red scale, but this approach requires that broad-spectrum pesticide use (e.g., acetamiprid-Assail, Danitol-fenpropathrin, or cyfluthrin-Baythroid for the control of pests such as citrus thrips and katydids in spring or citricola scale in summer) be minimized.Avoid multiple applications of these broad-spectrum insecticides using the information in these Guidelines to choose the most selective tactic available. Careful management of these two scales in the San Joaquin Valley may allow them to be managed by resident and augmented natural enemy populations.

Biological Control
The parasitic wasps, Aphytis melinus and A. lingnanensis (coastal areas) and Comperiella bifasciata (San Joaquin Valley), play an important role in controlling California red scale but their effectiveness depends on careful monitoring and use of selective insecticides for other pests. Several insect predators also feed on California red scale including the lady beetles Rhyzobius (Lindorus) lophanthae, Chilocorus orbus, and C. cacti. To enhance the effectiveness of all natural enemies, use pesticides only when their need is indicated by careful monitoring, use the most selective insecticides available, and treat only portions of the orchard where red or yellow scale populations exceed the threshold.

Parasite Releases. Releases of mass-reared Aphytis melinus parasites can be useful in groves with insufficient biological control. Keep in mind that pesticide residues on leaves may have a detrimental effect on released Aphytis parasites. Test for possible toxicity by putting ten to twelve 1-year-old twigs with leaves in a gallon jar with Aphytis parasites for 24 hours and checking their mortality. If more than 35% have died, residues are too high for Aphytis releases. Also, prepare a control jar filled with untreated leaves for comparison of Aphytis vigor.

• In the San Joaquin Valley, recommended release rates are 100,000 parasites per acre per year for orchards undergoing the transition to an integrated pest management program. Begin releases about March 1, making releases of 5,000 to 10,000 parasites per acre every 2 weeks with the objective of releasing 50% of the parasites during the critical spring period, 25% more in summer, and 25% more in fall. Suspend releases when second and third instar scale are not available (normally mid-June to mid-July). Continue releases through mid-November. Concentrate later releases in areas in the block known to have higher red scale densities. Once a grove has moved through the transition period (2 to 4 years), the total number of parasites released per acre may be reduced to 50,000 to 70,000. A suggested release method is to hold the release cup upright and tap it to release a few Aphytis at every sixth tree in every sixth row.
• In southern California where natural Aphytis populations are generally higher, releases are often not necessary or need to be made only infrequently; one to four releases of about 10,000 per acre at 2-week intervals in April and May should be sufficient in these areas. Annual Aphytis releases in southern California are needed in particular on young trees, on grapefruit and lemon trees, and in fall if biological control is not working effectively.

Control ants, particularly the Argentine ant in southern California and the native gray ant in the San Joaquin Valley, because they disrupt red scale parasites. Excessive dust that coats the leaves and fruit, including dust from manure mulches as well as whitewash and kaolin clays interferes with parasitism and should be minimized or delayed until the end of the season when Aphytis has completed its work. In addition, fine, talc-sized particles of ash from nearby brush fires can also disrupt biological control. Watering roads and washing trees can help solve these problems. Heavy fogs, drizzle, or rain can also help by either removing dust and ash particles or causing them to adhere to the leaf surface.

Organically Acceptable Methods
Biological control and organically approved petroleum oil sprays (e.g. PureSpray Green [NR 440]), Aphytis releases, as well as postharvest high pressure washing in the packinghouse are acceptable for use on organically certified citrus.

Resistance
In the San Joaquin Valley, a number of populations of armored scale have been found to be resistant to the organophosphates chlorpyrifos (Lorsban) and methidathion (Supracide) and to the carbamate carbaryl (Sevin). Scales have not developed resistance to oil sprays or insect growth regulators (buprofezin - Applaud), but observations indicate that resistance to pyriproxyfen (Esteem) may be developing. In orchards where resistance is a severe problem, avoid using organophosphates and carbamates, and instead release Aphytis melinus wasps or treat the orchard with buprofezin (Applaud), oil, pyriproxyfen (Esteem), or spirotetramat (Movento).

Selectivity
Oil is the most selective pesticide available for control of armored scale insects. Oil only kills natural enemies that it contacts and slightly suppresses beneficial mite populations. However, the residues do not persist and Aphytis wasps can be released soon after treatments. As with all insecticides, use oil only when needed because oil treatments will eliminate the younger scale instars and thus synchronize development of the scale population. This makes parasitism by Aphytis more difficult, because they prefer to deposit their eggs in third instar scale and after an oil treatment this stage may be absent for a period of time because their life cycle is about twice as fast as that of the red scale.

The insect growth regulators pyriproxyfen (Esteem) and buprofezin (Applaud) are safe for parasitic wasps, predatory mites, spiders, and lacewings but are quite toxic to vedalia beetles, which are needed for cottony cushion scale control. Spirotetramat (Movento) is very safe for parasitic wasps and vedalia beetles but is toxic to predatory mites.

The organophosphate and carbamate insecticides are the least selective insecticides. If adult Aphytis wasps are placed in a jar with leaves that were sprayed in the field with the dilute rate needed for California red scale control, chlorpyrifos (Lorsban) residues are toxic to adult Aphytis for 3 to 6 weeks, methidathion (Supracide) affects adults for 9 weeks, and carbaryl (Sevin) affects adults for 5 months after the treatment.

Monitoring and Treatment Decisions
In the San Joaquin Valley, citrus growers use pheromone traps to monitor male scale during the first (May), second (June-July), and fourth (Sept.-Oct.) flights of male scale. Degree-days are used to estimate when these flights are occurring. Generally, when an average of more than 1,000 scale are trapped during the fourth flight and fruit is infested with scale at harvest, treatment is planned for the next season. The goal is to maintain California red scale populations at levels that do not result in more than 10 scale per fruit at harvest.

Pheromone cards are not reliable predictors of scale populations in Aphytis-release orchards, because Aphytis prefers to parasitize female scales and the male scale numbers can be very high when the female population is low. Pheromone cards are also not reliable predictors of red scale populations when insect growth regulators are used because the males are more sensitive to these insecticides than the females, and so the cards underestimate the scale population.

Weekly pheromone trap monitoring. Select 5 to 6 orchards that have a known population of red scales to monitor every week so that you can determine when flights are occurring and time your sprays.

Put out pheromone traps beginning in March before the 1st flight. Change the sticky cards weekly and the pheromone caps monthly through October. Use two to four pheromone traps per 10-acre block; add two traps for each additional 10 acres.

Pheromone trap monitoring by flight. In the remaining orchards, use pheromone traps to determine areas of heavy scale infestation.

• Hang the traps with a fresh lure just before the predicted 1st, 2nd, and 4th flights: for the first flight this is March 1, for the second flight it is at 1,100 degree-days after the biofix of the first male flight, and the fourth flight at 3,300 degree-days from biofix.
• Use two to four pheromone traps per 10-acre block; add two traps for each additional 10 acres.
• Remove traps at the end of each flight and count scales (or estimate based on counting the scales inside the squares [20%] and multiplying by 5).
• Record results (example form—102 KB, PDF). These traps will tell you which areas of the block have heavy infestations. if the 4th flight is heavy (more than 1,000 scales per card), and fruit is infested with scale at harvest, plan to treat during the next season.

Examining fruit. In all orchards, whether Aphytis wasps are released or not, conduct visual inspections of citrus fruit once a month during August, September, and October. Walk around 20 trees in each quadrant of the block, and record the number of fruit examined along with the numberof fruit with noticeable patches (10 or more) of scales (example form—109 KB, PDF). Calculate the percentage of fruit with more than 10 scale.

Bin counts. At harvest, look at the fruit on the surface of at least 10 bins from areas throughout the block, and count the number of uninfested and scale-infested fruit. Calculate the percentage of fruit with scale. At the same time you can estimate the percentage of citrus thrips, katydid, cutworm, and peelminer-damaged fruit.

Detailed evaluations of parasitism in Aphytis-release blocks. In orchards where biological control agents such as Aphytis and Comperiella wasps are used to control scale, visually monitor all stages of scales on twigs, fruit, and leaves in August, September, and October.

• Collect 10 scale-infested fruit (preferably from different areas of the block). Do not take more than one to two fruit per tree, avoiding trees in the outside rows.

Record the number of second- and third-instar red scales and the number of these that are parasitized (example form—112 KB, PDF). To determine if a scale is parasitized, flip the cover over and search for Aphytis eggs, larvae, and pupae or Comperiella larvae and pupae.

• Calculate the percentage parasitism by dividing the number parasitized by the total number of 2nd and 3rd instar scales examined. If biological control is functioning properly, you should see percent parasitism increase from just a few percent in August to a high percentage in October.

Guidelines for determining when parasitism is at sufficient levels vary growing region, cultivar, and whether or not fruit are sent to a packinghouse that employs high pressure washers to remove scale.

• In the San Joaquin Valley, effective biological control of California red scale and yellow scale is achieved if by mid- to late October more than 70% of the third-instar female scale are parasitized either by Aphytis or Comperiella. A good proportion (50%) of large second-instar females and second-instar males should also be parasitized.
• In interior southern California, if parasitization with Aphytis melinus is poor (e.g., by the end of September, monitoring reveals more than 15 to 20% healthy, unparasitized third-instar female scale), treatment is recommended. If parasitization is good (e.g., by late September to early October there is almost no survivorship of third-instar female scale and parasitism of second-instar male and female scale is greater than 50%), treatment is not required unless infestations by live scale reach 25 to 40% of the fruit. These thresholds can be increased as high pressure washers are used more frequently in citrus packinghouses to remove scale from fruit.
• In coastal areas, biological control of California red scale on oranges is complete and treatments are generally not required. Biological control of California red scale on lemons is substantial, but occasionally a treatment is required to reduce population levels. Maintain a few pheromone traps all year in key areas to determine when red scale flights are occurring and when to apply treatments. In orchards with California red scale populations on scaffold limbs, visually inspect fruit to determine if treatments are necessary, paying special attention to the presence of mature females (which indicates they have escaped parasitism). Generally, if parasitization is adequate, treat only if more than 15% of the fruit is infested. If parasitization is low, reduce the threshold to 10%.

Insecticide treatments. Organophosphates and carbamates. Time organophosphate and carbamate insecticide sprays to treat the crawler stage, which peaks about 555 degree-days (accumulated above a 53°F threshold) or about 1 to 3 weeks after the peak in the male flight. (For assistance in calculating degree-days, see "Degree-days". Optimal treatment timing varies from year to year because of temperature, but usually occurs in May (first generation) or July (second generation).

An even more reliable method of timing organophosphate or carbamate treatments is to monitor for crawlers by wrapping sticky tape around 1-year-old branches (about 0.5 inch diameter) that have both gray and green wood and are infested with live female scales. Always back up pheromone trap count decisions with inspection of twigs, leaves, and fruit for female and immature scale.

Insect growth regulators. Apply pyriproxyfen and buprofezin sprays after crawlers have completely emerged and become white caps because these insect growth regulators will kill the scale when it tries to molt to the next stage. Optimal timing for insect growth regulators is the second generation of scale (June–July) in order to protect vedalia beetle during the time it is controlling cottony cushion scale (Feb.–May).

Lipid synthesis inhibitors. Make a foliar application of the systemic spirotetramat (Movento) between the second male flight (1100 DD after the first male flight) and the third male flight (2200 DD). The systemic action of Movento takes some time, but it is active against all scale stages so precision of treatment timing is not as important as application technique.

Oils. Oils can be effective against California red scale if coverage is thorough. They also have the advantage of being relatively less damaging to natural enemy populations than other insecticides. However, special care must be taken to avoid applying dilute applications of oil at times when it can damage fruit and leaves or reduce populations of natural enemies. Treatments after October 1 carry some risk of increasing frost damage. To avoid phytotoxicity and impact on yield, time oil sprays according to the following guideline:

IMPORTANT LINKS

• Citrus red scale pheromone trap monitoring form (102 KB, PDF)
• Citrus red scale fruit count monitoring form (109 KB, PDF)
• Degree-day calculator
• Degree-day table

PUBLICATION

UC IPM Pest Management Guidelines: Citrus
UC ANR Publication 3441
Insects, Mites, and Snails
E. E. Grafton-Cardwell, Kearney Agricultural Center, Parlier
J. G. Morse, Entomology, UC Riverside
N. V. O‘Connell, UC Cooperative Extension, Tulare County
P. A. Phillips, UC IPM Program, UC Cooperative Extension, Ventura County
C. E. Kallsen, UC Cooperative Extension, Kern County
D. R. Haviland, UC Cooperative Extension, Kern County
Acknowledgments for contributions to Insect, Mites, and Snails:
J. Barcinas, E. S. I., Corona, CA
R. Dunn, Badger Farming County, Exeter, CA
J. Gorden, Pest Management Associates, Exeter, CA
H. Griffiths, E. S. I., Corona, CA
D. Machlitt, Consulting Entomology Services, Moorpark, CA
C. Musgrove, retired entomologist, Riverside, CA
K. Olsen, S & J Ranch, Pinedale, CA
T. Roberts, E. S. I., Corona, CA
J. Stewart, Pest Management Associates, Exeter, CA
P. Washburn, Washburn & Sons Citrus Pest Control, Riverside, CA
K. Godfrey, USDA Biological Control, Sacramento
D. Headrick, California Polytechnic State University, San Luis Obispo
B. Faber, UC Cooperative Extension, Ventura County
J. Kabashima, UC Cooperative Extension, South Coast Research and Extension Center

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