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Jeremy from Opelika, Alabama writes

Will Onslaught Fastcap kill Fungus Gnat larve in potted plants and kill spider mites on potted trees by soil spraying only?

If spider mites are on potted conifer and Japanese Maples. By just spraying the soil will it kill the spider mites on the trees? If so how? If not. What will? And will it kill Fungus Gnat larvae in potted plants? If not. What will? I have a problem with both right now and I think the Fungus Gnats are in every pot because we had so much rain in Alabama this year. Spider mites has killed several Japanese Maples this late fall/winter in the garage. I have a home online nursery over 300 Potted Rare plants and trees of ALL KINDS! Tell me what to do and use and how often please?


Onslaught FastCap Spider and Scorpion Insecticide is labeled to control both fungus gnats and spider mites.  It would only be applied as a foliar application though, it is not a systemic so would not be absorb by the roots/leaves to kill those that feed on the plants.  Bifen IT would actually be a better option for drenching the soil to kill the fungus gnat larvae, it is known for being super gentle on plants. Though typically you can just try out the soil for a brief time to kill off the larvae there.  With no moisture they cannot survive.  Avid would be a good option for spraying the plants fo spider mites and it will be absorbed as it is a translaminar systemic (which means the foliar absorbs).  There is no systemic that can be applied to the roots for this pest.

Answer last updated on: 03/18/2020

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