# Horticultural Oil and Suceptible Tree Species



## Themadd1 (Dec 17, 2007)

Hi,

I am at a loss. I cant locate my list of suceptible tree species that are damaged by hort oil application.. Does anyone have a reliable list? I have been searching online to no avail. I know many nut species have problems, but I am sure there are more. So far this is what I have listed.

* Black walnut
* Cryptomeria
* Douglas-fir
* Hickories
* Junipers and cedars
* Maples (particularly Japanese and red maple)
* Redbud
* Smoke tree
* Spruce (particularly dwarf Alberta spruce) 

Thanks,

Themadd1


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## BayouTree (Dec 19, 2007)

No list here, but I seem to remember bald cypress being susceptible to damage.


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## windthrown (Dec 19, 2007)

I have found that temperature is a bigger factor in applying agricultural oil than anything else. I spray for mites with it here. Temps should be under 60 degreed for 8-12 hours after application for less or no damage on sensitive plants. Also you can spray some types of conifers when they are dormant, like this time of year in the No. Hem. 

What are you using it for?


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## Ed Roland (Dec 19, 2007)

Spraying at high psi can cause damage as well.


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## Themadd1 (Dec 20, 2007)

Agreed, pretty well versed in the techniques and such. I have been spraying for a while now. I am doing some cover sprays in the early spring. Anyway, thanks for the replies. Still looking for any lists.


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## Ed Roland (Dec 20, 2007)

Of course we know this but perhaps others viewing this thread do not: “Proper timing is critical for success when using oils. Dormant oils should be applied in late March or April before leaves or flowers show signs of breaking dormancy; that is, before "bud break." A common mistake is to apply 'dormant' oil sprays too early (on the first warm day in February or March) before insects are actively respiring and susceptible to the oil's suffocating effects. Wait until as close to bud break as possible before applying oil sprays. For summer use, oils are effective against insects that are "soft and slow." Oils will not control late instar immatures or adult stages. Effective monitoring to discover pest populations in the early instar stage will be necessary for effective control.”

Oil Sensitive Plants
Maples	Dormant
Hickories	Dormant
Black Walnut	Anytime
Cryptomeria	Anytime
Smoketree	Summer
Azaleas (Limited)	Summer

Tendency Toward Sensitivity 
Beech Dormant
Japanese Holly	Dormant/Summer
Redbud Dormant
Savin Junipers	Summer
Photinia sp.	Summer
Spruce Dormant
Douglas-Fir	Dormant

1Taken from Johnson, W.T. 1985. Horticulture Oil. J. of Environmental Horticulture 3:188-191.


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## alanarbor (Dec 20, 2007)

Take into account the product you are applying as well. Many of the "Dormant Oils" contain a large amount of toxic impurities and residues that are resposible for damage. 

Using more highly refined products will result in fewer issues. 

I have never personally had an issue with oil, except with it's removal of the glaucus bloom (Blue color) from from species with that feature. I have heard anecdotally about serious damage to Cryptomeria, however.


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## Themadd1 (Dec 22, 2007)

Thanks for the list you put up. I think I had that one but have no idea which huge pile of research I stuck it in. 

Thanks again,
Themadd1


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## Urban Forester (Jan 8, 2008)

First- look into a product called pure Spray (petro Canada) VERY low unsulfonated residue which is a major culprit when it comes to "burn". Two I've sprayed some of the plants you've listed for 20 years with oil, i.e. spruces, maples, firs, redbuds w/no ill effects. I believe the poster who said temp plays a role. Also rate has alot to do with it. I stay in the 2 to 3% range exclusively. Also VERY important, purge your hose regularly. Oil tends to seperate from the emulsifier and that can lead to problems.


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