Description of the Pest
The cotton aphid, also called melon aphid, is a rather small aphid that ranges in color from yellowish green to greenish black. Both winged and wingless forms are produced. The winged individuals are somewhat slender and are not as robust as the wingless form. A mature individual measures about 1/16 inch (1.5 mm) in length. The cotton aphid develops in colonies and prefers the underside of leaves. Unlike other aphids, cotton aphid populations do not diminish with high temperatures; they can also be troublesome late in the season (September and October), particularly in the San Joaquin Valley and in northern California.
Cotton aphid has an extensive host range. Some of the crops it attacks besides pistachio are carrot, cotton, cucurbits, and citrus. Host weeds include milkweed, jimsonweed, pigweed, plantain, and field bindweed.
Damage
Cotton aphids can be a major problem in first-year, newly budded trees. They distort and cause curling of growing leaves, and produce a large amount of honeydew. Clusters become coated with sticky honeydew, creating an environment favorable for the development of a sooty mold.
Management
Biological control can have a significant impact on aphids so be sure to evaluate predator and parasite populations when making treatment decisions.
Biological Control
Naturally-occurring populations of the convergent lady beetle, Hippodamia convergens, may provide effective control in early spring. However, releases of this beetle are not effective because it generally does not remain in the orchard following release. Other general predators, such as lacewing and syrphid larvae, and parasitic wasps, including Lysiphlebus, Aphidius, Diaeretiella, and Aphelinus species, also attack aphids.
Cultural Control
- It is a good practice, where feasible, to control weedy hosts of cotton aphid.
- Preserve habitat for beneficials around the orchard and keep dust down to encourage parasitism and predation.
- Avoid applying too much nitrogen fertilizer.
- Nearby fields infested with cotton aphid should be disced or plowed under as soon as harvest is complete to prevent movement into newly budded pistachio orchards.
Biological and cultural controls and sprays of rosemary oil, insecticidal soaps (potassium salts of fatty acids), and certain oils are acceptable for use in an organically grown crop.
Monitoring and Treatment Decisions
Monitor newly budded pistachio trees for cotton aphid. In most cases biological controls are sufficient to keep aphids at low levels. If unusually large numbers of aphids build up early in the season and appear to be retarding growth, consider applying an insecticide. No threshold has been established.
Pesticides and Natural Enemy Releases
Not all registered pesticides are listed. The following are ranked by their IPM value, with the most effective and least harmful to natural enemies, honey bees, and the environment listed at the top of the table. When choosing a pesticide, consider information related to water and air quality, resistance management, and the pesticide's properties and application timing. Use PestManage to compare summarized management options for different pests in the same crop. Always carefully read the label of the product being used and take all necessary precautions when handling pesticides.
| Rank | Active ingredient | Example trade name | Group | Group Order | MoA 1 | Amount per acre | REI (hours) ‡ | PHI (days) ‡ | Comments | Selectivity 2 | Bees 3 | Predatory mites 4 | Predators 5 | Parasitoids 5 | Residue duration 6 | Leaching(fish) 7 | Adsorbed runoff(fish) 8 | Solution runoff(human) 9 | Leaching(human) 10 | Solution runoff(human) 11 | Last updated 12 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
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Assail 30SG | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
4A |
2.5–9.6 oz | 12 | 14 | — | moderate | — 13 | — 14 | moderate/high | moderate | very low | very low | low | very low | low | 10/2014 | ||
|
|
Admire Pro | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
4A |
3.5–7 oz | 12 | 7 | Review and follow the California neonico... | narrow | moderate | moderate | high | short to moderate | — | — | — | — | — | 10/2014 | ||
|
|
Narrow Range 415 # | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
UNM |
Label rates | 4 | 0 | Narrow range oil. | — | — | — | — | — | very low | low | very low | very low | very low | 10/2014 | ||
|
|
M-Pede # | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
— |
Label rates | 12 | 0 | Insecticidal soap. This material has no... | — | — | — | — | — | low | intermediate | intermediate | very low | low | 10/2014 | ||
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|
Movento | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
23 |
6–9 oz | 24 | 7 | — | narrow | low | low | low | short | low | very low | low | very low | low | 10/2014 |
Legend
- ‡ a b Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without personal protective equipment. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases, the REI exceeds the PHI. The longer of the two intervals is the minimum time that must elapse before harvest.
- # a b Acceptable for use on certified organic crops. Check with your certifier to confirm before application.
- 1 ↩ Group numbers for insecticides and miticides are assigned by the Insecticide Resistance Action Committee (IRAC). Insecticides with unknown modes of action are assigned mode-of-action group numbers (MoAs) that begin with UN. Rotate pesticides 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; insecticides with a 1B group number should be alternated with insecticides that have a group number other than 1B.
- 2 ↩ Range of insect and mite groups affected by a pesticide. Broad means the pesticide affects most groups of insects and mites; narrow means the pesticide affects only a few specific groups.
- 3 ↩ Risk of harm to honey bees. For more information, see Bee Precaution Pesticide Ratings.
- 4 ↩ Risk of harm to predatory mites. Toxicities are generally to western predatory mite, Galendromus occidentalis. Where differences have been measured in toxicity of the pesticide-resistant strain versus the native strain, these are listed as pesticide-resistant strain or native strain.
- 5 a b Risk of harm to parasitoids and general predators. Toxicities are averages of reported effects and should be used only as a general guide. Actual toxicity of a specific insecticide depends on factors including the application rate, environmental conditions, and the life stage and species of a parasitoid or predator.
- 6 ↩ Length of time residue affects natural enemies. Short means hours to days; moderate means days to 2 weeks; and long means many weeks or months.
- 7 ↩ Risk of harm to fish from leaching, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 8 ↩ Risk of harm to fish from adsorbed runoff, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 9 ↩ Risk of harm to fish from solution runoff, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 10 ↩ Risk of harm to humans from leaching, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 11 ↩ Risk of harm to humans from solution runoff, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 12 ↩ Date information was last updated in the UC IPM Pest Management Guidelines.
- 13 ↩ May cause an increase in spider mite numbers.
- 14 ↩ Does not kill adults but sterilizes females.
UC IPM Pest Management Guidelines: Pistachio
UC ANR Publication 3461
R.H. Beede (emeritus), UC Cooperative Extension Kings County
W.J. Bentley (emeritus), UC IPM and Kearney Agricultural Research and Extension Center, Parlier
K.M. Daane, Kearney Agricultural Research and Extension Center, Parlier
D.R. Haviland, UC IPM and UC Cooperative Extension Kern County
Acknowledgement for Contributions to Invertebrates
R.E. Rice, Kearney Agricultural Research and Extension Center, Parlier
