# horticultural oil as a preventive measure?



## ceriano (Oct 6, 2021)

I planted several trees and shrubs this past fall and planning to add a few more this week. Should I spray them with horticultural oil just as a preventive measure? I have boxwoods, Yew, Japanese maples, azaleas, several conifers, magnolias and a few crape myrtles.


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## corneliani (Apr 2, 2019)

Here's a good bookmark I saved from Cornell University on this topic: http://ccenassau.org/resources/-horticultural-oils-as-insecticides
You'll see that oils are more contact herbicides, used to envelop insects and restrict their oxygen. The 'preventative' application is actually an app for overwintering eggs, etc... but even then the efficacy of oils is limited by their duration (they wash off & evaporate with time).

If you're not against using synthetics, a systemic is the better option as it acts as a vaccine, entering the plant through the roots and making its way up and into the foliage. Depending on which insect you're after Imidacloprid and/or Dinotefuran are your two most-used options. 
I picked this up for my aphid issue since Dominion 2L has almost doubled in price recently: https://chemicalwarehouse.com/products/imidashot-df

Zylam is better if you're targeting bigger/biting insects or heavy outbreaks but more expensive for sure: https://www.domyown.com/zylam-liquid-systemic-insecticide-p-3868.html

Here's a quick side-by-side and options that I came across: https://savehemlocksnc.org/wp-content/uploads/2021/03/Chemical-Product-Comparison-Charts_Oct-2020.pdf


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## ceriano (Oct 6, 2021)

corneliani said:


> Here's a good bookmark I saved from Cornell University on this topic: http://ccenassau.org/resources/-horticultural-oils-as-insecticides
> You'll see that oils are more contact herbicides, used to envelop insects and restrict their oxygen. The 'preventative' application is actually an app for overwintering eggs, etc... but even then the efficacy of oils is limited by their duration (they wash off & evaporate with time).
> 
> If you're not against using synthetics, a systemic is the better option as it acts as a vaccine, entering the plant through the roots and making its way up and into the foliage. Depending on which insect you're after Imidacloprid and/or Dinotefuran are your two most-used options.
> ...


super helpful thanks a bunch! is it ok to use synthetic on newly planted trees and shrubs or could it cause root damage?
Also should I apply fungicide to boxwoods to prevent blight?


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## corneliani (Apr 2, 2019)

I highly doubt it causes any root damage - or any damage for that matter - but I don't know for sure. If you consider that most ornamentals are sprayed & treated with every kind of treatment possible from the seedling stage, i'd personally feel more than comfortable with it. It essentially acts as a vaccine of sorts, entering the plant and affecting any insects that nibble on it. For that matter, our pets are treated with some of these same chemicals to protect them against biting insects as well (see Advantus, a chewable imidacloprid tablet for dogs).

My question to you is why are you considering ANY kind of insecticide? Have you had to deal with issues before and you're being proactive in treatment? I've gone for years without any insecticides on any ornamental - we're that family that does yard work for fun :shock: - and have only needed to apply them after getting hit with Crepe Myrtle aphids that seem to be getting worse & worse each year. It seems to have affected our Azaleas, and possibly even the hydrangeas too. This may be a factor of our new home location (we're in a wooded neighborhood now, whereas previously lived in a manicured/sterile subdivision) and I'm wondering if our surroundings are leading to these pests being more prevalent. Either way, no harm no foul I guess with applying systemics preventatively just that it may not be 100% necessary. Until it is :lol:


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## ceriano (Oct 6, 2021)

corneliani said:


> I highly doubt it causes any root damage - or any damage for that matter - but I don't know for sure. If you consider that most ornamentals are sprayed & treated with every kind of treatment possible from the seedling stage, i'd personally feel more than comfortable with it. It essentially acts as a vaccine of sorts, entering the plant and affecting any insects that nibble on it. For that matter, our pets are treated with some of these same chemicals to protect them against biting insects as well (see Advantus, a chewable imidacloprid tablet for dogs).
> 
> My question to you is why are you considering ANY kind of insecticide? Have you had to deal with issues before and you're being proactive in treatment? I've gone for years without any insecticides on any ornamental - we're that family that does yard work for fun :shock: - and have only needed to apply them after getting hit with Crepe Myrtle aphids that seem to be getting worse & worse each year. It seems to have affected our Azaleas, and possibly even the hydrangeas too. This may be a factor of our new home location (we're in a wooded neighborhood now, whereas previously lived in a manicured/sterile subdivision) and I'm wondering if our surroundings are leading to these pests being more prevalent. Either way, no harm no foul I guess with applying systemics preventatively just that it may not be 100% necessary. Until it is :lol:


Never had any huge infestation per se except the Yoshino cherry. Seems like everything in the yards gets them.
This is the first time I'm planning boxwoods, just trying to be extra cautious. I did lose one of my satsuki azaleas last year to black spot.


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## bernstem (Jan 16, 2018)

I have a lot of shrubs and perennials. The only plantings that get any spray are the roses.


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## Deadlawn (Sep 8, 2020)

ceriano said:


> Never had any huge infestation per se except the Yoshino cherry. Seems like everything in the yards gets them.
> This is the first time I'm planning boxwoods, just trying to be extra cautious. I did lose one of my satsuki azaleas last year to black spot.


I would not treat a problem that doesn't exist yet. Keep in mind that systemic pesticides can be very harmful to pollinators and a cause of bee colony collapse syndrome as the systemic pesticides cause the bees to become disoriented.

Horticultural oil is much, much safer, but I still would not bother unless you notice a problem.


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## ceriano (Oct 6, 2021)

corneliani said:


> Here's a good bookmark I saved from Cornell University on this topic: http://ccenassau.org/resources/-horticultural-oils-as-insecticides
> You'll see that oils are more contact herbicides, used to envelop insects and restrict their oxygen. The 'preventative' application is actually an app for overwintering eggs, etc... but even then the efficacy of oils is limited by their duration (they wash off & evaporate with time).
> 
> If you're not against using synthetics, a systemic is the better option as it acts as a vaccine, entering the plant through the roots and making its way up and into the foliage. Depending on which insect you're after Imidacloprid and/or Dinotefuran are your two most-used options.
> ...


Do you know any good systemic fungicide too? I planted a few yoshino cherries, they are prone to fungus. Seems everything in the garden gets them.


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