• Professor Sprout

Organic Pest Control for Cannabis

We received a growing question from one of our customers about a potential pest problem...

“Hello Professor, The plants are looking great (Okanagan Grape) I am happy, but yesterday I noticed a yellow trail on one of my plants. I am hoping it isn't what I think it is, but I cannot find a definate answer on what to do, I have attached a picture to help illustrate what I see. I think it may be some sort of leafminer but not sure, I see some fungas gnats which I am working on, and I have squeezed along the trail to squish anything potentially inside. I am reluctant to remove the leaves affected because it is still a small plant. Just beginning veg, and for balance I would have to remove the opposite fan leaf.

-Thanks, C”

Our answer to C’s question......


Greetings C, Thanks for the clear pics, that makes it easy to diagnose. Yes that does look like a Leaf Miner trail, but could also potentially be Thrip damage. I would certainly not take the leaf off. The damage is pretty insignificant at this point and taking off the fans at this early stage will really slow things down. Just keep up your inspections daily and squish any bugs you find and you should be perfectly fine.  Certainly no reason to panic. I would also begin to utilize an organic pest control regimen that will target Leaf Miners, Thrips, Spider Mites, Powdery Mildew, and more. Here's how...


Neem oil is a good organic solution and an excellent all-round preventative tool even when you don't have any problems. I use it throughout vegetative growth and early bloom as prevention for multiple forms of insects and fungal infections. If there are signs of insects I spray once every three days for three applications then once per week thereafter.


Cover the soil when spraying as you’ll need to use a few drops of natural dish soap as a surfactant to get it to stick to the leaves and dish soap is not great for your soil.


Do this only when lights are off, and keep a fan going until dry.  Dr Bronner’s Castile Peppermint soap is what I use for the surfactant, and the neem oil is pure organic neem oil that I buy in bulk (in Canada it’s labeled as a beauty product, but it’s the same stuff). Mix one teaspoon of neem oil plus 5 drops of soap in 1 litre of warm water. If you don't want to use dish soap, a great alternative is organic yucca extract, such as the product Wet Betty from Advanced Nutrients.


Note: If you have fungus gnat problems in your soil, you can use the neem oil for that too. In this case use pure neem oil in warm water (1 tsp/L) without the soap. You can certainly use Wet Betty or Yucca extract here if you like though. Shake the piss out of your spray bottle to keep the oil mixed up as you saturate the top layer of soil. Again, apply every third day for three total applications.

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