Description of the Pest
Armored scales are rarely a problem on avocados in California. If you see high numbers of armored scales on avocados, contact your local agricultural commissioner, as it is quite possibly an exotic species introduced into the state.
Armored scales (family Diaspididae) have a flattened, slightly convex cover that at maturity is about 0.06 inch (3 mm) in diameter. This platelike cover usually can be removed to reveal the actual scale body underneath. Armored scale covers typically have a different colored, slight protuberance (exuviae or "nipple") and concentric rings, which form as each nymphal stage enlarges its cover. Females develop roundish covers. For species with males, their covers are elongate in late instars.
Latania and greedy scale can reliably be distinguished only by an expert. Their covers are gray, tan, or white. Dictyospermum scale has a yellowish brown cover that is somewhat darker than the similar-looking, orange to reddish California red scale cover. California red scale and latania scale occur throughout the plant, with relatively even distribution among fruit, leaves, and wood. Dictyospermum scale infests mostly fruit and leaves. Greedy scale is usually limited to twigs and branches.
Latania scale and greedy scale females lay eggs beneath their cover, from which crawlers hatch. California red scale and dictyospermum scale give live birth to young crawlers. Greedy scale and latania scale reproduce without males, at least in California. Both California red scale and dictyospermum scale produce males, which as immatures develop under elongate covers.
Scales in avocado are usually under good biological control. Latania scale occasionally damages avocado. Large numbers of latania scale on bark can kill twigs, especially on young trees. Unlike many plant-sucking insects, armored scales do not secrete any noticeable liquid. Economic damage is from scale covers on the fruit skin, which appear as tiny dimples or light-colored spots. Feeding may also cause small discolored spots in the skin. Internal fruit quality is not impaired, but infested or spotted fruit may be culled. California red scale is a rare problem, and only on avocado near citrus. Dictyospermum scale and greedy scale occur in avocado only at very low numbers.
Biological control is the primary scale control method in avocados. Conserve natural enemies by minimizing dust and avoiding application of broad-spectrum, persistent insecticides that promote pest flare-ups because they kill natural enemies. If certain areas of a grove have high armored scale numbers, determine whether encrusted fruit can be selectively harvested and sent to a packing house that uses brushes or pressure-washing equipment that can remove scale covers from fruit. In the infrequent event that direct control may be justified, oil spray has little long-term adverse impact on natural enemies. Time any scale treatments to occur soon after most scale crawlers have emerged.
Predatory insects and parasitic wasps control most scales. Armored scale parasites include species of tiny Aphytis and Aspidiotiphagus (family Aphelinidae), and Plagiomerus, Comperiella and Signiphora (family Encyrtidae). Most scale predators feed on both armored and soft scales and often on other pests. Predators include brown and green lacewings, pirate bugs, predaceous mites such as Cheletomimus berlesei and Hemisarcoptes malus, and Karnyothrips species.
Predaceous Coccinellidae include the spotless lady beetle (Cycloneda sanguinea), steelblue lady beetle (Halmus chalybeus), and twicestabbed lady beetle (Chilocorus orbus =C. stigma). As adults, these lady beetles are about 0.16 to 0.2 inch (4–5 mm) long.
- Spotless lady beetle has a black and white head and thorax and orangish wing covers without markings.
- Steelblue lady beetle is metallic bluish.
- Twicestabbed lady beetle is shiny black with two large orangish spots on its wing covers. Its larvae are black to brownish with a yellowish transverse band and are covered with branched spines.
Organically Acceptable Methods
Use biological and cultural controls and some oil sprays on an organically certified crop.
Monitoring and Treatment Decisions
In the rare situation where treatment is warranted, spray oil after the end of maximum crawler emergence. To time an application, monitor scale crawlers by trapping them with transparent tape that is sticky on both sides. Wrap tape traps tightly to encircle each of several twigs near female scales. Replace traps weekly when crawlers are expected. Preserve traps sandwiched between clear plastic and light blue paper, and label papers with the trap date and location. Visually compare crawler abundance in traps among monitoring dates. Treat when it is obvious that more crawlers per trap were caught during previous weeks and catches have definitely declined. If persistent populations of California red scale are present, consider releasing a small number (perhaps 10,000) of Aphytis melinus near the scale infested trees after purchasing them from an insectary.
|Common name||Amount per acre||REI‡||PHI‡|
|(Example trade name)||(hours)||(days)|
|Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honey bees, and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Always read the label of the product being used.|
|A.||NARROW RANGE OIL#||Label rates||4||0|
|MODE OF ACTION: Contact including smothering and barrier effects.|
|COMMENTS: Requires good coverage to be effective. Oil does kill some beneficial wasps and suppresses beneficial mite populations, however the residue does not persist and parasitic wasps can emerge from parasitized scale or be commercially released soon after treatment. Check with certifier to determine which products are organically acceptable.|
|B.||APHYTIS MELINUS#||See comments||NA||NA|
|COMMENTS: For release against California red scale only. Make a single release, or several smaller release at about 2 week intervals, totaling approximately 10,000 parasites per infested site. Time release so that the parasites can attack unmated female scales. Visually monitor scales and release parasites when a significant proportion of the scale population is at or approaching the virgin female stage. Alternatively, monitor using pheromone-baited sticky traps and release parasites at or just before a male flight, which is approximately 800 degree-days after the peak of the previous generation male scales. For more information about obtaining and effectively releasing natural enemies see Natural Enemy Releases for Biological Control of Crop Pests.|
|(Esteem 0.86 EC)||16 fl oz||12||14|
|MODE-OF-ACTION GROUP NUMBER1: 7C|
|‡||Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.|
|#||Certain products are acceptable for organically grown produce.|
|1||Rotate chemicals with a different mode-of-action group number, and do not use products with the same mode-of-action group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a group number of 1B; chemicals with a 1B group number should be alternated with chemicals that have a group number other than 1B. Mode-of-action group numbers are assigned by IRAC (Insecticide Resistance Action Committee).|