Aphids, primarily Green Peach (Myzus persicae)
Green peach aphid overwinters in the egg stage on woody plants in the Prunus species (peach, wild cherry, etc), where nymphs feed in spring. Field vegetable crops are colonized in June by winged females who produce live young (nymphs), resulting in multiple generations of wingless females. Generation time from birth to reproductive adult is 1 to 2 weeks depending on temperature; each female produces 30 to 80 live young. If food quality declines, winged females develop and leave in search of new plants. In fall, both male and female winged aphids develop and return to woody plants to mate and lay eggs.
Winged green peach aphids have a black head and thorax and yellow-green abdomen. Wingless adults and nymphs are usually pale yellow-green including the cornicles (a pair of tubes near the tip of the abdomen) but may be pink. Adults reach 2 mm long. Aphids feed on leaves and excrete a sugary, sticky substance called "honeydew", which fosters growth of black sooty mold fungus. If using plasticulture, this honeydew will be apparent on the plastic. Scout the underside of leaves for aphids as plants establish.
Numerous crop families (including solanaceous crops, cucurbits, brassicas, spinach and chard, and carrot families), as well as broadleaf weeds, support green peach aphid. Feeding on young tissue causes curling, wilting, stunted growth, and contamination of harvested crop. The major damage caused by this aphid is the transmission of many different plant viruses. It is also a pest in greenhouses; see Vegetable Bedding Plants and Greenhouse Tomato for greenhouse management.
Aphids are usually controlled by natural predators and parasites, such as lady beetles, lacewings, spiders, syrphid fly larvae, wasps, and beneficial fungi, unless the populations of these beneficials are disrupted by chemical sprays. Preserve natural enemies by using selective/microbial pesticides for other pests whenever possible. Occasionally green peach aphid (GPA) or, less commonly, melon aphid (MA) and potato aphid (PA) populations build up and require controls. Early-season, broad-spectrum sprays will destroy beneficials and lead to aphid population buildup.
Begin to examine plants in early July for aphids and the presence of beneficial species. Spray only when aphids are increasing and building up to high numbers. Coverage of leaf underside is important. Add a spreader-sticker. Plant crops away from Prunus species. Spray effectiveness may vary depending upon the species present. Reflective plastic mulch may help to repel aphids.
Tarnished Plant Bug (Lygus lineolaris)
In artichoke, bugs may feed on leaves, leaving behind a shothole appearance. More significantly, they may feed at the base of buds and, in extreme cases, cause buds to turn black, rendering them unmarketable. See Lettuce for more information about tarnished plant bug.
Thrips
The piercing-sucking mouthparts of thrips cause twisting and curling of leaves. Occasionally, thrips may also feed on bracts of buds, which can become deformed and thus unmarketable.