Wednesday, June 18, 2008

Oil is cheap! And Effective!

I'm talking about horticultural oil... the kind that is used to kill soft bodies bugs on plants. Many folks still think of oil as a dormant treatment but for more than 20 years professional landscape managers have been using low rates of highly refined oils (plant and mineral) to control aphids, mites, scale crawlers and other soft bodied insects.

Yesterday, Bucks County's trusty and eagle-eyed Master Gardener coordinator, Betsy-Sue Schneck, spotted discoloration on some plants in the demonstration gardens at our office . Closer examination revealed lots of two-spotted spider mites on the underside of the leaves. A shot of horticultural oil , diluted to a 1 % solution (2.5 tablespoons per gallon) knocked them out in 12 hours. Of course we had to use a sprayer that would direct the spray to the undersides of the leaves where the mites were living. Oil only kills the insect it hits and it has almost no residual activity. In a day or less it has evaporated. But it did the job. Lots of dead mites on those leaves this morning.

So, as summer progresses and aphids, adelgids, mites, mealy bugs, lace bugs, scale crawlers (soft bodied immature stage) begin to damage plants, consider horticultural oil as a treatment option. The benefits: It is cheap! It is easy on beneficial bugs; very low toxicity for the applicator; organically approved, and it works well on certain pests.

Limitations: As I mentioned above, you only kill the bug you spray. Thorough coverage is essential. There is no residual activity so pest populations will rebound and a follow up treatment in 7-10 days is usually necessary. Many insects are not controlled by horticultural oil. Borers, Japanese beetles and bagworms (which have just hatched by the way), to name a few.

As always, read and follow label instructions. Oil can cause plant damage if applied to drought stressed plants and under certain other conditions. Watch those rates... plant safety requires careful measuring. You'll find both plant derived and petroleum based oils available in garden centers.

No comments: