Neem / Hort Oil Possibly Dangerous?

Messages
1,408
Likes
1,356
Location
Bethlehem, PA
USDA Zone
6b
#2
My mineral oil (dormant spray) used to make my juniper turn lime green. It would always bounce back eventually, I'm assuming the rain rinsed it clean and it could breathe again
 

just.wing.it

Imperial Masterpiece
Messages
8,282
Likes
9,979
Location
Blips and Chitz (Northern MD, 6b...ish)
USDA Zone
6B
#3
My mineral oil (dormant spray) used to make my juniper turn lime green. It would always bounce back eventually, I'm assuming the rain rinsed it clean and it could breathe again
That's interesting...I know juni's do depend heavily on their foliage....
I'll keep a closer eye on mine...
 
Messages
877
Likes
742
Location
Nashville TN
USDA Zone
7a
#5
I have never used it because I am afraid of it.
I traditionally have taken the natural approach to any treatments, but the thought of putting a viscous lipid on leaves has always made me worry that it would interrupt or interfere with the breathing of stomata, or even potentially their opening/closing

other than this potentially skewed logic, I have nothing to support my not using it...this is an interesting topic.

67159542-DB0F-4E73-A119-E30F88615372.jpeg
 
Messages
448
Likes
695
Location
Minnesota
USDA Zone
4b
#7
One of the more knowledgeable members of the MBS warned about the potential phototoxicity of neem, and advised everyone to wash it off 10 minutes after spraying (the idea being that it will have time to kill all the critters before you wash it away. She claimed to have lost at least one tree (I think it was juniper).

I was skeptical, and did some research, and from what I can tell (mostly from freaked out stoners who scorched their crop under hot lights), there is a legitimate concern about the effects of neem on leaves in heat/sun. It's mitigated by spraying at night, so the oil is dry before the sun hits it.

If I cared more, I might experiment on some of the weeds in the sunny places of my yard. Spray one patch at sundown, another the next day at noon, and check on them both at 5pm.
 
Messages
1,338
Likes
1,855
Location
Netherlands
#9
Depens solely on how you use the stuff.
I have seen the cannabis growers ruin their plants by using more soap than water or oil while making the emulsion. They washed away the cuticulum and their plants dried out.
I have also seen plants respond very bad to rapeseed oil, but that was mainly because of other solvents being used (like naphta). Some tropicals just can't handle oils at all (like miracle berry and eucalyptus).

When dosed and used correct, I have used neem and other oil based insecticides on the following without damage:
Scots pine, magnolia, citrus, mugo, junipers, beech, oak, cannabis, coca, grapevine, and cherry. There might be some more that I forgot.

The key I think, is to use 1ML soap to 2-6 ML oil and 1000ML tapwater (never deionized). You want those soap particles to form mycelles so they can not mess with the cuticulum, so always use the oil in excess. Whatever isn't captured by the soap, will just float on top in the spray bottle, so if you have eyes, it's easy not to use that part. Spray at night only, and preferably not on foliage that hasn't hardened off.
 

0soyoung

Imperial Masterpiece
Messages
5,217
Likes
7,850
Location
Anacortes, WA (AHS heat zone 1)
USDA Zone
8b
#11
When dosed and used correct, I have used neem and other oil based insecticides on the following without damage:
Scots pine, magnolia, citrus, mugo, junipers, beech, oak, cannabis, coca, grapevine, and cherry.
Add azalea, tsuga, mugo pines to this list.

I've been reading and have taken note that NEEM seems to be effective against root aphids and also is a systemic when applied as a root drench (same strength as for a foliar spray).

btw, I've not had any problems applying it in daylight and making no effort to wash it off.
 
Messages
527
Likes
672
Location
Northwest CT
USDA Zone
5b
#12
I have used it on many of the species listed above with no ill effects either... I also make a point of spraying it in the evening (same as I do with all horticultural treatments), most pollinators and beneficial bugs like wasps won’t be affected. I also avoid “leaf burn” that way, I was taught young by a family member while gardening to never spray treatments during the full strength of the sun.
 
Messages
182
Likes
214
Location
Yakima Wa
USDA Zone
6b
#13
This is a very timely discussion. This spring I started using NEEM oil for the first time (my neighborhood has a chronic aphid problem), and not long after my second application a ~5yo Wisteria started behaving very strangely: Vigorous growth with lots of new shoots and a bunch of flower buds, but also lots of leaves yellowing and falling off?!?! I did some some online research but could find nothing that fit the symptoms.
20180628_071711.jpg

After reading these posts I remembered I applied the NEEM oil in full sun during the hottest part of the day (oops! I really should know better but I was being impulsive). It looks like none of the growth that appeared after the application is affected, so I will keep an eye on it but suspect I have found the cause. Thanks for the posts!
 
Messages
1,338
Likes
1,855
Location
Netherlands
#14
Wisteria doesn't show a response like that to Neem around here. And it also doesn't get affected by aphids. I have treated it to hopefully combat other creatures like the wood lice that keep chewing off roots. I can't say I saw anything happen to it after treatment.
Have you used straight neem oil with soap, or some commercially available mixture? That might shine some light on the cause of the problem.
 
Messages
182
Likes
214
Location
Yakima Wa
USDA Zone
6b
#15
I used a commercial mix (from Costco). My other wisteria (about 50' away) has shown none of the same symptoms. The affected one is near my kids organic garden which has had lots of pest problems this year (mostly slugs and aphids) hence the NEEM treatments. The only differences between them are the placement (about 50' apart), that the unaffected one gets some shade in the afternoon, and it is in a pot (the affected one is in a pond strainer).

Not to hijack the discussion, but feel free to pass on any Wisteria advice you care to share as I don't have much experience with Wisteria. I am interpreting it being only about 5 years old and this is the second year it has flowered as a sign I am doing something right (but more likely just dumb luck). I am finding their hardy nature and fast growth allow for lots of low risk opportunities to try things out (mostly stupid things). I have already learned they are quick to indicate poor wiring technique (I could be the poster-child for bad wiring, but that is a totally different discussion).
 

GrimLore

Imperial Masterpiece
Messages
8,502
Likes
7,321
Location
South East PA
USDA Zone
6b
#16
Not to hijack the discussion, but feel free to pass on any Wisteria advice you care to share as I don't have much experience with Wisteria.
Here they grow like weeds as they should and are very difficult to kill. I suspect to much TLC is the problem and not uncommon.

They do fine in Humic soil potted as they do growing in ditches in shady areas often spreading 40 foot and growing another 30+ foot up trees and buildings - they like damp and cool. That applies to both potted and wild or landscape. Insects are of little concern if grown naturally...

Just my 2 pennies :)

Grimmy
 
Messages
1,624
Likes
1,062
Location
Downstate New York, Zone 6b
USDA Zone
6b
#17
Have you ever seen a negative effect from Neem Oil or Horticultural Oil, on your foliage?
I have not...
I have, on some of my plants, but I would have to check notes on concentration, species of plants, and time of year/day sprayed. But yes, I have killed foliage with it.
 
Messages
254
Likes
96
Location
Western Long Island, NY
USDA Zone
7B
#18
Hort Oil and Neem are two separate trade names for two different products. Hort Oil, from my own knowledge and professional use, active ingredient is either mineral oil or petroleum oil and also veg oils; though I have no experience with the latter or have seen it in the trade (I think it is out of favor). Hort oil can be mixed from the concentrate as either a dormant oil or summer oil. Dormant oil is MUCH heavier and applied when plant is dormant or just showing life and little to no worry in damaging the foliage or flowers. Generally this is a early season application, with various theories on timing from before buds break to when buds are just starting to break. Summer oil is much lighter and often sprayed as a follow up to the dormant oil later in season when heat pressure is down and plants will be in dormancy within a month or two. If you miss the dormant oil timing you can mix as summer oil in early spring as long as you do before heat of summer.

There are a few warnings with applying Hort oil. Do not spray blue foliage as it can turn the plant green/damage waxy outer layer, do not spray above 85F and do not spray flowers. For summer oils we focus on underside of leaf as there is much less worry for leaf burn due to application and the trunk. Dormant oil sprays are THICK and will damage plant material if applied improperly.

Neem is more a general purpose pesticide that would be good to use between hort oil applications, following the same precautions. I've only applied neem a few times personally.

I would not spray maples with either product, except MAYBE in dormancy. But still I would not at all. I have heard that both can be damaging to Junipers.

Both are excellent material for insect, fungal and disease control. Hort oil relies on suffocation properties whereas neem has toxicity to its target pests. They're either organic or low impact which is an added bonus.

Often times damage is as a result of not enough time between applications. Plant stromata and other plant functions will work fine under normal application rates and timing They do have a half life and eventually break down, but too close of a schedule between applications and you will damage the plant.

Note: the convenience of Bonsai being in pots leads me to think moving the plant out of direct sun the day of application and short period after should greatly minimize any potential damage.
 
Messages
32
Likes
27
USDA Zone
7b
#19
I accidentally killed a natal plum and a european olive with horticultural oil.

I think I may have used it at the wrong concentration though. I thought I had ready to spray stuff but it may have actually needed dilution. I also may have used it at the wrong time of year, at the time I didn't realize it's a bad idea to spray in the middle of the summer. It was probably user error but it's left me nervous about using hort oil since then anyway.

I have also had a bad experience spraying it on a landscape camellia. For the camellia I definitely used the correct concentration. The camellia was already pretty weak because of wax scale though (reason I was spraying it.) I'm not sure if it's demise was because it was already too far gone from the scale before I sprayed for the horticultural oil to help or if the horticultural oil was the final nail in the coffin. :-/

If I try using it again in the future I'll probably wash it off right after spraying or else only use it in the winter.
 
Messages
254
Likes
96
Location
Western Long Island, NY
USDA Zone
7B
#20
Sounds like you lost the Camellia to scale. These are time tested and well used proven material. If hort oil was regularly killing plants it wouldn’t be used by industry professionals.
 

Similar threads

Top Bottom