How to Manage Pests
UC Pest Management Guidelines
DESCRIPTION OF THE PEST
Cotton (melon) aphid is a small to medium-sized aphid. It is highly variable in color, ranging from lemon yellow to blackish green in different individuals, often within the same colony. The aphid is commonly lighter in color during the hotter times of the year and darker during cooler periods, but both color forms may be found throughout the year.
Cotton aphid is known to transmit more than 50 viruses, some of which affect carrots. It does not generally build up large populations on carrots but may occasionally cause some feeding injury. Injury is typical of aphid feeding with curled and distorted leaves. If populations are large enough, honeydew accompanied by sooty mold may be produced.
Cotton aphid is attacked by the common aphid predators including green lacewing, lady beetles, and syrphid fly larvae. Several parasites of this aphid are present in California and can provide effective control. Parasitized aphids can be identified by their tan color and bloated appearance.
Carrots planted adjacent to infested cotton or melons are at risk of becoming infested with this aphid, particularly in fall following cotton defoliation or termination of the melon crop. Carrots should be planted a safe distance from both, if possible.
Organically Acceptable Methods
Biological and cultural controls are acceptable for use on organically grown produce.
Monitoring and Treatment Decisions
Monitor fields for aphids weekly during spring and summer by examining the upper and lower surfaces of leaves. Also, look for evidence of predators and parasites and their impact on aphid populations. Treatment not normally required. No thresholds for cotton aphid on carrots have been established. Chemical treatments are not effective in preventing virus transmission and this aphid rarely causes economic damage.
UC IPM Pest Management Guidelines:
E. T. Natwick, UC Cooperative
Extension, Imperial County