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Cabbage Aphid & Green Peach Aphid
The Cabbage Aphid can cause significant economic loses in broccoli grown in the Willamette Valley (Figure One). The feeding of the aphid on the broccoli plant may reduce yield slightly, but the real damage it causes is contamination. The cabbage aphid contaminates the harvested heads of broccoli. This can result in rejection of entire loads of broccoli by the quality assurance program of broccoli processors. Once the aphids have moved up into the developing broccoli head, it is possible to kill them, but it is no longer possible to remove them as a contaminant.
Authors: Pamela Opfer and Dan McGrath, OSU Dept. of Horticulture
Cabbage Aphid (Brevicoryne brassicae)
Cabbage Aphids (photo by Ken Gray)
How to ID Pest
The cabbage aphid is gray-green with a waxy bloom. It forms dense colonies or clusters on the leaves. The genus of the cabbage aphid is “Brevi” “coryne” which is from Latin and loosely translates as “small pipes”. At the rear end of all aphids, there are two pipes called cornicles. You will need a hand lens to see the cornicles. On most aphids, the cornicles are relatively long and stick out from the body. On the cabbage aphid, the cornicles are markedly short. This helps to identify the cabbage aphid and distinguish it from other aphids that may encounter on broccoli and cauliflower.
Aphids species have similar life cycles. Females produce live offspring though out the entire year without mating. The time between generations is short. The population can increase rapidly. During the summer and fall months, aphids produce winged offspring. These winged aphids blow across the landscape and infest crucifer plantings. When you scout broccoli plantings you will see winged cabbage aphids on the leaves. Underneath the winged females, you often see the beginnings of an aphid cluster, her live young. Adult cabbage aphids overwinter on crops or weeds.
One of the unique behaviors of the cabbage aphid is that when a broccoli, cauliflower, radish, mustard or any plant in the crucifer family bolts and produces flowers, the cabbage aphids move up into the flower stocks. In the fall, you may see flower stocks of mustard plants that are completely covered with aphids. This is why the cabbage aphid is such a problem in broccoli.
Crops Affected & Damage
In general, aphids cause damage by sucking plant sap, which causes heavily infested leaves to curl and stunts plants. If you measure carefully, you can detect some depression in yield do to aphid feeding. But the aphids mostly damage crops by contaminating them. The aphids invade the developing broccoli florets.
Scouting & Risk Assessment
Professional field scouts will cross a broccoli planting and pull leaves from every row. They may examine several hundred leaves per planting. One can get a rough sense of aphid pressure with the 10 x 10 method. Pull 10 broccoli leaves in 10 different spots of the field and record what you observe. You may see when an aphid If aphids populations increase, scout field more often. The critical time to scout is when the broccoli buttons are just beginning to form. If more than twenty percent of the leaves are contaminated by cabbage aphids, an insecticide application may be justified. Apply insecticide before the buttons elongate. The presence of a significant number of aphids at the button stage suggests the need for a two spray program, with one insecticide spray applied at the button stage followed by a second “clean-up” spray about 7 days prior to harvest.
When scouting, do not confuse the green peach aphid (Figure Two) for cabbage aphid. Here is how to tell them apart. The green peach aphid has long cornicles; the cabbage aphid has short cornicles. The green peach aphids are mostly solitary; cabbage aphids form dense clusters or colonies. The cabbage aphids are waxy and grayish; the green peach aphids are green, not waxy.
Green Peach Aphid (Myzus persicae)
Green Peach Aphids (photo by Ken Gray)
Green peach aphids do not crawl up into the developing broccoli florets. They are generally not a significant contaminate of broccoli and generally do not required insecticide for control.
Biological Control: Many parasites and predators attack aphids. Among the more common predators are lady beetles and their larvae, lacewing larvae, and syrphid fly larvae. There are several species of parasitic wasps that produce aphid mummies. Aphid mummies are off colored and bloated like a small balloon. You may see aphid mummies with a hold in the top of the body. This hold is where the mature wasp escapes after the wasp larva has mined out the hollow aphid body. If the proportion of mummies is increasing, or predators appear to be gaining control, and aphid populations are not yet damaging, sprays might be delayed to protect populations of natural enemies. It depends on the crop, however. If the crop is entering the susceptible button stage, be careful. Don’t allow them to crawl up into the develop broccoli florets.
Cultural Control: Where possible, incorporate infested crops immediately after harvest to prevent dispersal. Destroying weed hosts late in the year may help destroy overwintering populations.
Chemical Control: Please consult the PNW Insect Management Handbook for pesticide recommendations.
References & Citations
"Cabbage Aphid Factsheet". Oregon State University. Accessed December 8, 2011. (http://insects.ippc.orst.edu/pdf/reb25.pdf).
"Green Peach Aphid Factsheet". Oregon State University. Accessed December 8, 2011. (http://insects.ippc.orst.edu/pdf/reb23.pdf).
Hollingsworth, Craig S. (Ed.). 2011. Pacific Northwest Insect Management Handbook. Corvallis: Oregon State University.
Natwick, E.T. 2009. "Cole Crops: Cabbage Aphid." University of California Agriculture & Natural Resources. Accessed December 9, 2011. (http://www.ipm.ucdavis.edu/PMG/r108300811.html).
Fresh Market Vegetable Production, Insect management, Integrated Pest Management, Processed Vegetable Production, Cabbage Aphid, Willamette Valley, Broccoli, Cabbage, VegNet