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Rhododendrons and Relatives: timing for dormant oil on azaleas?

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janets412
Pittsburgh, PA

April 2, 2009
6:30 PM

Post #6355269

Many azaleas on my daughter's property in Richmond, Va. Lacebugs are a real problem. I am getting conflicting info from area garden centers about the proper time to spray the azaleas with dormant oil . I have been told Jan., Mar., and now---even though the plants are starting to bud.
Will the spray be effective now? Can it injure a soon-to-bloom plant ?
thanks
luis_pr
Hurst, TX
(Zone 7b)

April 5, 2009
2:36 AM

Post #6365673

I think it is early but here is some information about "the enemy" that should be useful and answer some of the questions...

Most Lace Bugs have two generations per growing season (some can have four). The first generation hatches around May and matures by June. Eggs are laid and hatch around August. Eggs are laid again but they overwinter and hatch the next year. To achieve good control, you have to spray just prior to hatching (or when you discover the infestation) in May and you have to do this more than once, probably about two weeks apart (but check the label directions). There are many weapons at your disposal, dormant oils are just one.

Biologicals: I generally release natural enemies in mid-April. These include lady bugs and lace wings. I purchase these at organic minded stores but Home Depot and Lowe's also sell them in early Spring.

Cultural Controls: Lace bug predators prefer to be in the shade and will not attack as well when the plant is in lots of sun. Thus, try to plant azaleas where they get part shade in the afternoon. You can also spray the underside of leaves with a strong spray of water from a hose as this will control most nymphs and kill them before they return to suck the leaves.

Chemicals: Best control is achieved if you directly spray the insects. Since they like to hide under the leaves, you need to get the underside of the plants well sprayed. Use products like dormant oils, Safer insecticidal soap, spinosad and oils like Green Light. These products are harmful to lace bugs but will still allow beneficial insects to thrive and eat the lace bugs. If your plants is large, it may be best to drench the soil instead. Drenching requires obtaining a small amount of insecticides like Imidacloprid, adding a certain amount of water to dilute it and then pouring the solution onto the soil, near the trunks. For more information, see http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pni7428-1c.html

When applying dormant oils in May, choose a day when humidity is low and when the temperatures are not high (check the label about this). Do not apply when the temperatures are close to or below freezing. Just because they are called dormant does not mean that you have to do it while the plant is dormant.

Dormant oils are used to suffocate the lace bugs. Unless the label directions say otherwise, they should not affect the flower buds. This is a matter of timing. If you apply them too early, there are no lacebugs or nymphs out yet, the oils eventually evaporate and may cause little damage to the lacebugs eggs. If you apply them when too cold, you could harm the plants. If you apply them when too warm, the oil will quickly evaporate and not suffocate the lace bugs. Because the timing is important and because I am unreliable and forgetful, I tend to use systemics instead.

Systemics: I use Ferti-lome Azalea Evergreen Food (it is a fertilizer with a systemic insecticide) and I apply it after my native azaleas have bloomed in mid-to-late April. But you can also use Bayer Advanced Garden Tree & Shrub Insect Control. Systemic insecticides are absorbed, move easily within the plant and last longer than contact sprays (the whole growing season). You basically feed the plant in Spring and forget about it.

Damage: leaves do not need to be removed but you can prune off the worst areas if you cannot stand the sight of the damage. I just let them be.

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