As a two-for-the-price-of-one bargain, annual cilantro (Coriandrum sativum) is an herb dear to the hearts of thrifty gardeners. Its lacy green leaves imbue salsa, pesto and chimichurri sauce with fragrant, grassy flavor. Its white or pinkish flowers supply the coriander seeds to spice curry powders, barbecue rubs and dessert sauces. The bad news is that green peach and coriander aphid insects occasionally regard cilantro as gourmet dining. Fortunately, several organic aphid-killing options protect the harvest.
Wash Them Away
Although their light-green coloring is an effective camouflage, these aphids reproduce so rapidly that they soon become visible on cilantro's tender new stems and leaves. Stunted shoots and yellow leaves coated with the insects' sticky, transparent waste are an early clue to their presence.
An easy and effective treatment is to set the garden hose spray attachment to jet or sharp spray and blast the cilantro with water. Any aphids that don't drown fall to the ground and have difficulty returning to the plant. To reduce the risk of fungal disease, spray the cilantro early in the day so it dries quickly.
Hit the entire plant, including the backs of the leaves where groups of aphids often feed. Repeat the treatment every two to three days until the pests are eliminated.
When Water Is Scarce
One water-conserving, aphid-killing alternative is to wipe small colonies off the cilantro with a water-dampened cloth. Another is to prune the infested leaves and stems and dispose of them in a sealed plastic bag.
Both methods require daily inspection because aphids are born pregnant and start giving birth to their own pregnant daughters in about a week. Missing just one or two means a swift reinfestation.
To prevent the spread of disease, disinfect pruning tools between cuts with a cloth dipped in rubbing alcohol.
Enlist the Enemies
Entice the beneficial bugs with shallow-throated, nectar- or pollen-heavy flowers such as sweet alyssum (Lobularia maritima), perennial in U.S Department of Agriculture plant hardiness zones 5 through 9, or coreopsis (Coreopsis spp.), hardy in USDA zones 3 though 9, depending on variety. They'll stay to lay eggs that hatch hundreds of voracious aphid-eating babies.
Smother Them With Soap
When cultural controls or friendly bugs aren't enough, organic, ready-to-use insecticidal soap spray suffocates aphids on contact. Safe to use up to the day of harvest, the soap won't harm aphid predators visiting the plants after it dries.
Treat the plants on a dry, windless day with no rain expected for at least 24 hours. Dress appropriately in long pants and a long-sleeved shirt, waterproof gloves, safety goggles and a respiratory mask. To hit all the aphids, spray until the soap runs from all the cilantro's surfaces.
Reapply the soap every two to three days, or at the label's recommended frequency, until the infestation subsides.