Hawthorn/parsley aphid

Aphid populations can build up in celery to densities of several thousand per plant. These pests can inflict three types of damage to celery. First, they stunt plant growth and reduce yield through removal of significant amounts of sap. Next, they transmit virus diseases such as western celery mosaic, celery calico, and cucumber mosaic. Celery yellow spot may be found occasionally. And finally, they contaminate celery produce, particularly fresh market celery, with aphid honeydew and debris; this contamination can lower the crop value.