Cole Crops XXIII (Leafy Brassicas)

Aphids

Whitney S. Cranshaw

Green Peach Aphid

Cabbage aphid (Brevicoryne brassicae)

Turnip aphid (Lipaphis pseudobrassicae)

Green peach aphid (Myzus persicae)

Identification (and life cycle/seasonal history)

During summer the life cycle of the cabbage-infesting aphids is similar to that of other aphids.  Female aphids give live birth to daughter aphids and no sexual reproduction occurs.  Aphids may mature in less than two weeks under summer temperatures and can produce several young daily for a period of a couple of weeks.  In the absence of natural controls aphid populations increase rapidly.

Cabbage aphids and turnip aphids solely develop on mustard family plants.  Winter is spent on winter annual mustard weeds or surviving crop debris of cole crops.  Green peach aphid has a much wider range of summer hosts and is important on several vegetable crops, including pepper, potato, and lettuce.  Green peach aphid host alternates during the cool season months and winters as an egg stage on various stone fruits, such as peach, apricot, and certain plums.

The three cabbage-infesting aphids can be distinguished, in part, by the way covering on the insect.  Cabbage aphid is blue-gray and covered with fine wax particles.  Wax also covers the body of the turnip aphid, which ranges in shades of brown.  Green peach aphid does not have the powdery wax cover, is smooth bodied and is often straw colored.

Plant Response to Damage

Cabbage aphid feeding on expanding leaves causes twisting and discoloration.  Aphids can also be serious contaminant of marketed heads and is very commonly damaging to Brussels sprouts.

Turnip aphid and green peach aphid are much less damaging to growth of cole crops.  Problems with these species sometimes occur with contamination of produce. 

Management Approaches

Natural Controls

Aphids can be heavily attacked by several natural enemies.  Parasitic wasps are perhaps the most conspicuous of these, causing aphids to swell and stick to plants when dead, a form known as an 'aphid mummy'.  General predators include larvae of syrphid (flower) flies, damsel bugs, and minute pirate bugs.  Green lacewing larvae and lady beetles also feed on aphids, although cabbage aphid is not a preferred host.

Cultural Control

Overwintering crop debris of cole crops should be destroyed to eliminate cabbage aphid winter hosts.

Chemical Control

Plant coverage is critical to aphid control since aphids can locate in folds of developing leaves.  Insecticides with systemic activity can improve coverage and provide better control.  Almost all insecticides used on crucifers suggest use of wetting agents to improve coverage due to the waxy leaves.

Product List for Aphids on Leafy Brassica Crops:

Insecticide	Fl. oz. or oz. product	Preharvest Interval, Remarks
Planting Time Treatments
Admire 2F	10-24 fl. oz./A	12 hour reentry.  Planting time treatment or transplant drench.  Neonicotinoid insecticide (imidacloprid) with systemic activity
Foliar Applications
Provado 1.6F	3.75 fl. oz./A	7 day PHI, 12 hour reentry.  Neonicotinoid insecticide (imidacloprid) with systemic activity
Assail 70WP	0.8-1.2 oz./A	7 day PHI, 12 hour reentry.  Has systemic activity.  Neonicotinoid insecticide (acetamiprid)
Dimethoate	Several formulations	14 day PHI, 48 hour reentry. Organophosphate insecticide (dimethoate) with systemic activity.  Registered use on collards, kale, turnip greens, mustard greens.
Fulfill 50WDG	2.75 oz	7 day PHI, 12 hour reentry.  A specific aphicide (pymetrozine)
Endosulfan (Phaser, Thiodan, Thionex, etc.)	As labeled	21 day PHI, 24 hour reentry.  Labelled for mustard greens and collards only.  Chlorinated hydrocarbon insecticide (endosulfan)
The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality.

Categories:  Cole Crops, Leafy Brassicas, Insects, Aphids

Date: 02/08/2004