Spinosad: The First Selective, Broad-Spectrum Insecticide

What do you want out of an insecticide? If you could design an insecticide with the best possible features, for use on your farm, around your family, what characteristics would you give it? First of all, you would probably want it to be something that was very effective on your worst pest problem(s). You might wish for something that was effective on many different pests and registered on most or all of your crops, so you didn’t have to buy as many chemicals. At the same time, if you are wise, you wouldn’t want it to kill any of the beneficial insects or animals (like your family dog or cat) that might come in contact with the spray. Because you, a family member or employee will be making the applications, you probably would want something that was safe for the handler, in case you were accidentally exposed to it. You probably would expect it not to leave a toxic residue on the food that you produce, and never to leach into the groundwater that your family and neighbors drink. You might wish for something that had no pre-harvest restriction so that it didn’t complicate picking schedules and marketing, but yet lasted for a relatively long time so you didn’t have to keep reapplying it. And at the same time, didn’t accumulate in animals further up the food chain (like eagles or humans). Something that was easily applied with the equipment that you already have. Finally, something that was as cheap as water so that you might be able to make some profit on what you are selling.

Well, as we all know, there is no perfect insecticide. However, some of the newer products on the market are getting closer to meeting all or most of the characteristics on your wish list.

Many of you know me and have heard me talk before. I talk about IPM and using alternative methods like, resistant varieties, hot-water seed treatment, rotation, water management, trap crops, natural and biological controls, sanitation and prevention, mechanical and cultural controls, action thresholds, selective materials, resistance management, and as a last resort, using chemical pesticides in a judicious manner. But let’s climb back into the real world and admit that most of us, including many organic growers, use pesticides to varying degrees. Webster’s defines a pesticide as “an agent used to destroy a pest” and agent, as “something that produces or is capable of producing an effect.” So some of our alternative controls may be considered pesticides in the broadest context of the word, which helps comfort me in what I am about to do. At the request of our moderator, I volunteered to tell you about some of the attributes of spinosad, the active ingredient in the new product SpinTor®, which may come as close as anything on the market at this time at meeting your high expectations for a pesticide. However, because of its list of attributes, it leaves me in the uncomfortable position of sounding more like a salesman, than someone who’s job it is to minimize the use of pesticides, but I promise that after this I’ll go back to talking about IPM and alternative controls.

Spinosad, the active ingredient in SpinTor®, is a new microbial insecticide that is derived from a species of Actinomycetes bacteria; Saccharopolyspora spinosa, discovered in soil samples. It is a fermented product, much like the more familiar Bacillus thuringiensis materials we have become familiar with over the years, but lasts over twice as long as the best B.t. on the market. It will provide a full week of protection for most pests on the label. It will also move through the leaf cuticle to reach leafminer larvae.

Spinosad has a broad-spectrum of activity against many of the worst vegetable pests including; the Colorado potato beetle, diamondback moth, cabbage looper, imported cabbageworms, European corn borer, fall armyworm, corn earworm, hornworms, thrips, and leafminers. Perhaps the most amazing part, is that this product works on many different types of insects (caterpillars, flies, thrips and beetles) but spares most beneficials such as lady beetles, predacious fly larvae (hover flies and midges), most parasitic wasps, lacewings, spiders, predatory mites and bugs. Which means that you may need to spray less often if you use this type of selective material, because the natural enemies will be preserved and should help moderate pest populations later in the season. It is toxic to bees when wet, but is relatively safe for them once it dries, so it should be used when pollinators are not actively foraging.

Another interesting feature of this material is that it is strongest against some of the pests that are traditionally some of the hardest to kill or very prone to resistance, such as the diamondback moth, Colorado potato beetle larvae, fall armyworm, European corn borer, and beet armyworm. That means that although this product is extremely pricy to purchase by the quart or gallon, it is economical on a per acre basis, at least for these pests, because it is effective at extremely low rates (1.5-4.5 ounces/acre).

Spinosad is registered on sweet corn, fruiting vegetables (tomato, pepper, eggplant, tomatillo, pepino and ground cherry), major and minor cole crops, leafy greens (including but not limited to rhubarb, celery, fennel, parsley, etc.) and “tuberous vegetables” (potatoes, sweet potatoes, yams, Jerusalem and Chinese artichokes, cassava, chayote root, ginger and turmeric.

This insecticide has extremely low toxicity to mammals (LD5O oral and dermal> 5,000 mg/kg), birds, and many aquatic invertebrates, is moderately to slightly toxic to fish, but is highly toxic to marine mollusks (shellfish). In the environment, its solubility is low (above pH 5), tends to bind to soil particles/organic matter, does not persist in the soil, and ultimately breaks down to CO2 and H20, so it is unlikely to leach to groundwater. It is a general use product and was registered under EPA’s fast-track reduced-risk program. So, in most states it does not require posting of pesticide warnings after applications. It has only a 4-hour reentry interval (REI) for worker protection and a one day-to-harvest (dh) restriction, so it won’t disrupt harvesting schedules.

Spinosad is both a nerve poison and a stomach poison, so it kills pests that it contacts and those that consume it on the foliage they eat. It has a novel mode of action which will help prevent cross-resistance with organophosphates and carbamates (which are acetylcholinesterase inhibitors), and even B.t. products which are also stomach poisons, but work differently than spinosad. Spinosad overstimulates nerve cells by prolonging electrical impulses across synapses by acting like acetylcholine (but attaching at some novel action site as yet unidentified). Thus, acetylcholinesterase does not stop the impulse and nerve stimulation, as is supposed to happen. This in turn over-activates receptor sites in muscles producing contractions, tremors and paralysis from which the insect does not recover. Feeding stops within minutes and death occurs within 48 hours. To help prevent resistance to spinosad, the SpinTor ®label restricts use of the product to two or three consecutive applications or a maximum of three times in 21-30 days, depending upon the crop, and no more than 29 ounces per crop each year. The label also does not allow SpinTor® to be used in the greenhouse or under shade structures.

The company suggests using a silicon adjuvant (e.g. Dynamic®) to enhance performance on certain crops like cole crops and sweet corn. Researchers suggest that contact exposure is extremely important for managing the Colorado potato beetle. Applications to control potato beetle should be made in the middle of a sunny day if possible, so that the insects are up on the plant and exposed to the spray. The use of drop nozzles and adequate water will help deliver the material to the underside of leaves where beetles prefer to feed.

What are the implications for use of spinosad in IPM programs? For important crops like tomatoes, peppers, eggplant, cole crops or leafy greens you can control almost all the major insects pests in New England with just spinosad, and another “soft” insecticide like B.t., or a growth hormone (e.g. Confirm®). This should allow for the survival of more beneficials and result in fewer sprays over the long run. Insect pests that would not be controlled on these crops with such soft materials include the cabbage and pepper maggots, black cutworm, aphids (the natural enemies should control these most of the time), flea beetles and stink bugs (although there is evidence in some studies of reduced incidence), and a few other oddities or minor pests that are rarely encountered. On sweet corn, spinosad will control both European corn borer and fall armyworm. It also offers the opportunity to control at least low to moderate levels of corn earworm with an environmentally friendly material.

If used wisely, the cost of SpinTor® applications can be kept very low. Strategies for low-rate use on various crops and for specific pests will be discussed. Also, low-rate and other efficacy research results from Connecticut and around the nation will be presented.

By: T. Jude Boucher, Cooperative Extension System, 24 Hyde Aye, Vernon, CT 06066, (860) 875-3331, jude.boucher@uconn.edu. 1999, Reviewed 2012.

Published: Proceedings. 1999. New England Vegetable and Berry Growers Conference and Trade Show, Sturbridge, MA. p. 318-320.

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