Description of the Pest
In addition to cabbage aphid, the green peach aphid and turnip aphid can also infest cole crops. In the low desert, they are more common than cabbage aphid. However, in coastal areas, turnip aphid is rare and green peach aphid is less common than cabbage aphid.
The green peach aphid adults and nymphs are pale green to yellowish, and some individuals may be pinkish. The frontal tubercles at the base of the antennae are prominent and convergent on adults, which can be winged or wingless. Winged green peach aphids also have a distinct dark patch near the tip of the abdomen, which the wingless adults lack. On adults, the pair of rearward cornicles on the abdomen are markedly swollen or clublike at the tip.
The turnip aphid (also called mustard aphid) is a worldwide pest of cole crops. In California cole crop production, it is most commonly a problem in the low desert. These aphids are dark to olive green and have apparent cornicles, which are shorter than those of the green peach aphid. The waxy coating on the turnip aphid is also much thinner and less apparent than that of the cabbage aphid.
|Cabbage aphid||Green peach aphid||Turnip aphid|
|Thick, waxy coating||No waxy coating||Thin, less apparent waxy coating|
|Dense colonies||More randomly dispersed on plants||More randomly dispersed on plants|
Green peach aphid can stunt seedling growth when abundant, and high numbers sometimes kill young seedlings or transplants. Economic damage is rare on older plants. Green peach aphids tend to feed on older leaves, and rarely enter heads of broccoli, Brussels sprouts, cabbage, or cauliflower.
Turnip aphids feeding on cole crop roots can seriously stunt, and even kill, plants.
In coastal cole crop-growing areas, both green peach and turnip aphids rarely require insecticide application. Because green peach aphids remain mostly on the older, nonmarketed leaves of cole crops, low to moderate numbers can be tolerated on older plants. Apply an insecticide to infested young plants if they show stress from feeding by green peach aphid.
In the low desert, infestations of both turnip aphid and green peach aphid often require insecticide application. Apply insecticide if green peach aphids or turnip aphids are numerous enough to contaminate the marketable heads. Time insecticide application to reduce aphid infestations before they reach the marketable heads. Turnip aphids typically require insecticide application between January and April.
Many general predators and parasitic wasps attack foliage-feeding aphids. Brown or black mummified bodies of aphids indicate the larvae of the parasitic wasps Aphidius matricariae, Aphelinus semiflavus, Diaeretiella rapae, Lysiphlebus testaceipes, or other parasites fed on the inside of the aphids and killed them. Sometimes natural enemies provide adequate biological control, especially in fields where residual, broad-spectrum insecticides are not applied. Consider installing insectary plants to attract natural enemies of aphids.
Remove infested culls and weeds around fields that may harbor aphids that move to crops. Turnip aphid problems tend to recur in the same fields; long-term rotation to other crops (such as lettuce) is advised.
Organically Acceptable Methods
Use primarily biological and cultural controls in an organically certified crop. Sprays of insecticidal soap and other organic insecticides are also registered for aphid control in organic cole crops.
Monitoring and Treatment Decisions
Keep notes on the number of other aphids you see as you monitor for cabbage aphid. Apply insecticide to seedlings if they appear to be stressed by aphids based on monitoring information and observed damage. Older plants can tolerate low to moderate numbers of aphids. An application for cabbage aphid just before heading also controls the other foliar aphids.
|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.|
|(Movento)||4–5 fl oz||24||1|
|MODE-OF-ACTION GROUP NUMBER1: 23|
|(Beleaf 50 SG)||2–2.8 oz||12||0|
|MODE-OF-ACTION GROUP NUMBER1: 29|
|COMMENTS: Thorough spray coverage is essential for optimal control.|
|MODE-OF-ACTION GROUP NUMBER1: 9B|
|COMMENTS: Best used in a tank mix with another insecticide registered for aphids.|
|(Assail 70 WP)||See comments||12||See comments|
|MODE-OF-ACTION GROUP NUMBER1: 4A|
|COMMENTS: For head and stem cole crops, application rate for aphids is 0.8 to 1.7 oz per acre and PHI is 7 days. For leafy cole crops, application rate for aphids is 0.8 to 2.3 oz per acre and PHI is 3 days. This product has potential to leach into groundwater where soils are permeable, particularly where the water table is shallow.|
|(Orthene 97)||8–16 oz||24||14|
|MODE-OF-ACTION GROUP NUMBER1: 1B|
|COMMENTS: Registered for use on Brussels sprouts and cauliflower only.|
|MODE-OF-ACTION: A contact insecticide with smothering and barrier effects.|
|COMMENTS: Provides only partial control. For green peach aphid, label requires that this product be used in a tank mix with a labeled companion insecticide. May be phytotoxic on Brussels sprouts and cabbage. Check with organic certifier to determine which products are organically acceptable.|
|Organic Options (Efficacy research may be lacking on these products)|
|(AzaGuard)#||8 fl oz||4||0|
|MODE-OF-ACTION GROUP NUMBER1: un|
|COMMENTS: Not registered for use on mustard spinach. Rate included is based on tank mix efficacy research. May not significantly reduce aphids as a standalone application. Check with organic certifier to determine which products are organically acceptable.|
|BEAUVERIA BASSIANA STRAIN GHA|
|(Mycotrol ESO)#||0.25–1 qt||4||0|
|MODE-OF-ACTION GROUP NUMBER1: biological (entomopathogenic fungi)|
|COMMENTS: Not registered for use on broccoflower, mizuna, and mustard spinach. More effective on aphid nymphs. When applied to soil, this fungus promotes cabbage growth by increasing nutrient absorption even when moisture is reduced. May not significantly reduce aphids as a standalone application. Check with organic certifier to determine which products are organically acceptable.|
|‡||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 the two intervals is the minimum time that must elapse before harvest.|
|1||Rotate insecticides 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. Mode-of-action group numbers are assigned by IRAC (Insecticide Resistance Action Committee).|
|#||Acceptable for use on organically grown produce.|