Spinosad. . . A New Organically Acceptable Insecticide

Until Spinosad (pronounced spin-OH-sid) was discovered, the only organically acceptable insecticide was Bacillus Thuringensis (Bt). An insect host had to ingest the Bt bacterium, making the insect host sick and the causing it to die. Bt is very host specific and works only on the caterpillar stages of moths and butterflies. In the past few years a specific variety (Bt, israelensis) was found to infect mosquito larvae and has been used successfully to control mosquitoes developing in stagnant water. With this latter exception, Bt has only been effective by infecting the caterpillars of moths and butterflies. It retains its effectiveness on its substrate for two to three weeks.

In general, Spinosad provides effective control of pests belonging to the following groups: moths and butterflies (caterpillars); flies; mosquitoes, ants, leaf miners and a few thrips. It is also effective against some beetles and members of the grasshopper family if they consume large amounts of foliage. Therefore, it would not be effective on small beetles and only on some larger beetles. For leaf miners the addition of a penetrating surfactant increases the effectiveness of Spinosad. Unfortunately, Spinosad is generally not effective for control of sucking insects such as aphids, whiteflies, most thrips, scale, mites or true bugs (stink bugs, spittle bugs, mealy bugs, lygus bugs, harlequin bugs, cabbage bugs, cicadas, leaf hoppers, tree hoppers, blue sharpshooters, etc.).

Spinosad is a metabolic byproduct of the bacterium Saccharopolyspora spinosa and is listed by the Organic Materials Review Institute (OMRI) as acceptable for use during organic farming and gardening and any use where toxic chemicals are to be avoided. The first large scale use of Spinosad was in the Olive orchards of Lindsey, California where olive fruit flies were infesting the orchards and potentially destroying a one-half billion dollar industry. The fly would lay her eggs on the Olives and within a few days, the eggs hatched and the maggots bored into the fruit. Within a few weeks, the Olives were mushy, filled with excrement and totally useless. Before Spinosad, Olive growers had to use toxic chemicals to control the olive fruit fly. The chemicals they used were not available to homeowners and so the flies gradually migrated north and became established in Santa Clara and San Mateo counties. Harvesting Olives for home use became out of the question and the mess left by falling, rotting Olives was a particular nuisance.

Ten years after Spinosad was discovered it became available for use by homeowners. To ensure that spraying takes place at the proper time, pheromone traps have been made available to catch the first olive fruit flies. The homeowner now hangs several pheromone traps in his Olive trees and as soon as a few olive fruit flies are caught it’s time to spray with Spinosad. Spinosad can also be used to control codling moths (cause wormy apples). The homeowner should place codling moth pheromone traps in Apple and Pear trees to gauge when to spray for this pest. In lieu of the pheromone traps, spraying can begin at petal fall of the flowers. Monterey Chemical Company recommends that spraying continue at 7 to 10 day intervals for at least one month. Spinosad is recommended to be used at the rate of 4 Tablespoonfuls per gallon of water but not more than six times during the growing season. Spinosad can be used up to one day before harvest.

Spinosad loses its toxicity after 8 to 24 hours and so it will be necessary to reapply at 7 day intervals for 5 or 6 weeks after the first olive flies or codling moths are caught on the pheromone traps. Spinosad has a relatively low toxicity for birds and mammals and is slightly to moderately toxic to aquatic organisms. It is toxic to honeybees and lady beetles but after the residues have dried completely, toxicity is considered negligible. Because bees do not fly late in the day or after dark, Spinosad should be sprayed on the Olive, Apple or Pear trees in late afternoon, whenever possible. Spinosad is active by ingestion and contact. Control via ingestion is 5-10 times more effective than by contact. SpinoSpinosadsad works by paralyzing the insect which stops feeding within minutes. These insects may remain on the plant for up to two days.

Wegman’s Nursery received its first shipment of Spinosad during the summer of 2007. Spinosad has been formulated for use by the Monterey Chemical Company under the name Monterey Garden Insect Spray. It is available in pint and one quart sized concentrates as well as in a ready-to-use Hose End Sprayer. Among a few of the garden plants treated effectively with Spinosad are: Corn, Tomato, Cabbage, Kale, Broccoli, Chard (for leaf miners), Melons, Potatoes, Grapes, Cotton and numerous western wildflowers.

Spinosad is easy to use. The concentrate is diluted at the rate of 4 Tablespoons per gallon of water and applied to the tops and bottoms of the plant’s leaf surfaces with a tank sprayer. Using the Hose End Sprayer product is even simpler. The container is attached to the garden hose, the water tuned on and Spinosad sprayed on the leaves of the target plant. We believe that Spinosad represents a new class of insect control products which will meet the needs of a previously unserved gardening group.