Other Aphids

In addition to the black bean aphid and foxglove aphid, which are discussed separately, about ten other species of aphids are found on celery. Of these, green peach aphid and hawthorn/parsley aphid (also known as the rusty banded aphid) are the most common. These aphid species vary in color (from light green to black), size, and shape. All are soft-bodied insects. They form dense colonies on the undersides of celery leaflets and in some cases on the celery petioles. Winged aphids form under specific conditions of overcrowding or plant stress and disperse to other plants or fields.

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. In some years this aphid may be quite common in celery.

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.

Several parasitic wasps provide natural control of aphids in celery, most notably species in the genera Diaeretiella and Lysiphlebus. In some cases, these parasites can eliminate high densities of aphids over a few weeks. Predators such as lady beetles, syrphid flies and lacewing also attack aphids. Populations of aphid parasites should be preserved by avoiding unnecessary insecticide applications and by providing acceptable habitat for these beneficials.

Destroy crop residue immediately after harvest. Avoid other aphid-favored crops, such as lettuce, in adjacent, upwind fields. Intensify field monitoring for aphids when adjacent fields with aphid-favored crops are harvested.

Biological controls, cultural controls, and insecticidal soaps are acceptable for use on organically grown produce.

Economic thresholds for aphids on celery have not been established. Aphid survival and development are historically greatest during periods with temperatures less than 80°F. On fresh market celery, infestations are more important when the petioles (stalks) start to form, and when the rows begin to close. Infestations tend to be erratic in the field so sample several locations. Sample intermediate age petioles to find the highest populations of aphids. Concentrate on field edges particularly where celery fields border harvested lettuce fields.