There are a number of good reasons for almond growers to add botanical oils to their mite control programs, but the fact that they are very effective at controlling mites is the most important one. Independent field trials have shown that botanical oils are just as effective as conventional miticides at controlling Pacific spider mites in almonds for up to three weeks post treatment. And while botanical oils kill adult mites on contact as do conventional pesticides, the oils are two to three times more active against mite eggs. The resulting disruption of the mites’ lifecycle provides effective control for three weeks after spraying, even though botanical oils volatilize quickly and have little acute residual activity.
Extensive webbing indicates a severe mite infestation on an almond tree.
Oils Make Good Partner with Beneficials
In large-scale trials conducted by ag retailer Wilbur Ellis in orchards of almonds, cherries, nectarines and apricots, Ecotrol, an insecticide/miticide comprised of rosemary and peppermint oils, provided 95% to 100% knockdown of mite populations. An extra benefit – and an important one – was that beneficial insects returned to the field almost immediately. Beneficials are particularly important in mite programs, with natural predators such as sixspotted thrips providing a core level of control. Miticides are used on an as-needed basis. Broad-spectrum insecticides should be avoided if mite predators are to be preserved.
Research conducted by Dr. David James at Washington State University showed that some botanical oils not only allow early return of beneficials, they actually attract them back to the field.
“Plants give off certain essential oils when they are under attack by feeding pests in order to attract beneficial predators,” says Steve Bessette, vice president of the botanicals division at Keyplex. “We don’t invent the botanical oils – we just extract them from Mother Nature. The reason botanical oils have the activity they do is that the plant has evolved to the point where it actually knows the best way to protect itself. We are just taking that and spraying it topically.”
Studies comparing the effect of botanical oils on certain beneficial insects and two-spotted spider mites found that beneficial insects are 2½ to 3 times more tolerant of the oils than are the mites.
“It does make sense in terms of the crop expressing what it knows will protect it,” Bessette says. “The formulated botanical insecticide oils have a much greater impact on feeding pests than they will on beneficials.”
Moreover, because of the shorter acute residual effects, botanical oils are softer on bees during flowering season. If applied in the evening, when bees are not present, the oil volatilizes and is nearly gone the next morning when bees return.
Flexibility in Mite Control
The Wilbur Ellis field study showed no difference in the level of spider mite control with Ecotrol compared to conventional miticides – even systemic chemistries – 27 days post treatment. The high level of immediate knockdown combined with the oil’s activity on the eggs provided excellent control of mites. This is good news for organic growers, since Ecotrol is also OMRI-listed. But it’s good news for conventional growers as well, since it provides another chemistry to rotate into their mite control programs – one with additional benefits of zero pre-harvest interval (PHI), zero worker reentry (REI) interval, and zero maximum residue levels (MRL).
“A good way to fit botanical oils into a mite control program is to put down a couple of applications early to kill the eggs and suppress populations,” Bessette says. “Put down another one just prior to harvest. Because there’s zero PHI, REI or MRLs, botanical oils can clean up the field without disrupting harvest or delaying shipping. If utilized during heavy pest pressure in the middle of the season, it’s been shown that addition of botanicals such as those in Ecotrol in the spray tank can enhance performance of conventionals while mitigating resistance.”
Because of the long history of safe use of essential oils such as rosemary and mint in the flavor and fragrance industries, the ingredients in products such as Ecotrol are classified as GRAS (Generally Regarded As Safe) by the FDA, and therefore exempted from registration by EPA.
“That EPA exemption is very attractive to growers,” Bessette says. “Even states which have very strict regulations such as New York and California have allowed the federal exemption into their own statutes.”
Oils Valuable for Resistance Management
An additional benefit of botanical oils is their different mode of action. Bessette says rosemary oil alone has 20 pure compounds within it. One primary active ingredient targets octopamine, a nerve receptor that only insects have, which is why it is so safe for humans.
“We are finding other compounds are acting as enzyme inhibitors,” Bessette says. “Using oils really help with resistance management, because it’s next to impossible for an insect to develop resistance to a chemistry with 15 or 20 different compounds inside.
The effective use of essential oils as an applied product is made possible through formulation with the right emulsifiers and solvents to ensure good spreading, contact and penetration into the insect cuticle.
“Botanicals are not usually systemics that go into a plant,” Bessette says. “Without contact with the insect, you don’t get kill. The formulation with botanical oils is as important as the active ingredient itself.”