Leaf Spots Near Harvest Please Help!

The image shows what is happening to all my leaves, including the ones around the flowers. The plant itself is well over a meter tall, and about the same width around as well. I have carefully trimmed the plant so it is bursting with many good long flowers. It is right now about 3 - 4 weeks from final harvest, and has long, full buds and colas that are about 10% amber colour at this point.

We have an outdoor hydroponics system 900 mm square, 150 mm deep, with a bamboo frame and bird netting. There is a large nutrient tank with an electric pump fill/drain system which fills and empties the trays every 2 hours. The plant itself is in a large (300 mm diam. x about 300 mm tall) pot of garden soil set down into the hydroponics medium (perlite), with drainage gravel at the bottom of the pot and holes all around. Besides the watering system mentioned above, she has her very own hose/valve split from the main fill hose, which empties the nutrient water into her growing pot itself at the top and drains out into the hydro tray (to help flush out harmful salts buildup) and so through the regular drain and back into the tank.

The pH is perfect at about 6.2. The nutrient levels are ec, ppm = 6440 us/cm, 1800 ppm

We had this spotting problem in the very beginning, but some trace elements (manganese I think) fixed it. It grew amazingly and did not have any problems until now, so close to harvest. Now all the leaves are getting covered with tiny yellow spots, with some darker spots along the veins, and some darker tiny spots along the veins and stems behind.

I would really like to wait the extra few more weeks before harvesting to get the best yield, but I’m not not sure that I can save these leaves and had rather harvest early than risk losing the lot. If need be I can blow down the whole tank and fill with plain water for the final 3 weeks or so.

Any help will be greatly appreciated!

Check for mites on undersides of leaves looks to me like a bug problem


Thanks! :slight_smile: I used a magnifying lens and did not see any mites, so if they are there they must be less than 1/10 mm across because they did not show up under the magnifier. This image is th underside of a leaf – It actually looks like mites in the photo, but in person it simply looks like darker brown spots on the actual leaf/stem and not raised or crawling around like mites, lol. Also the spots on the backside do not correspond to the spots on the front.

lol looks so much like mites? and your ph is fine magnesium is a possible issue but in flower less likely more likely calcium Calcium Deficiencies In Marijuana Plants: How To Find and Fix It

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Yes I’m afraid it does look like mites on the leaves from the images, even though I’m not seeing them on close visual inspection. When I did an image search, unfortunately I have to conclude that the images look more like what I’m seeing than do images of calcium or magnesium deficiency. I will have to get a larger magnifier and take a closer look! We are growing a big tomato plant in the same main tray as the plastic pot with the cannabis plant and using the same nutrient water, but haven’t noticed anything like that on the tomato plant.

If it does turn out to be mites, is there anything that can be done this close to harvest, other than harvesting early? lol

Thanks for the help. :slight_smile:

Mighty wash one of the few products I know can be used in later stages of flower and kills both eggs and adults alike you spray it on with a mister right before lights turn off let it dry off pay attention to under leaves it is non toxic and can be rinsed off later. Cleared them out of my veg room first treatment fighting them in my flower room but have 9 large ladies and would take me gallons and my local hydro shop is out. but would be my first choice it works

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Thank you so much! I will see if that is available in my country. I did find this site with bit of info:


Basically it says that if it’s not too bad when near harvest, just wash with cold water first then later cut, dry, and smoke the little blighters lol :stuck_out_tongue_closed_eyes:

I suppose it is protein, after all… though I’m not sure how that will affect my vegetarian diet :wink:

Thanks again :relaxed:

just to follow up, looking through my photos I found this, which pretty much looks like mites to me :frowning:

Now to deal with them… I appreciate the advice!

For the mites you can try dish soap and water mix. I tried it helped alittle, I think I did not mix with enough soap. Also I was watching you -tube on useing canola oil and water. It’s best to use different kinds each time you spray.

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Spider mites are the herpies of the grow room and if you read up on them you will notice with the extent of leaf damage they have already caused for you they are going to be damn hard to get rid of because they will have laid eggs and have a substantial population going. each adult female lays around 40 eggs a day. Eggs hatch in 3-8 days and most things which kill adults do nothing about eggs some call them the borg they become immune to most insecticides very fast and are relentless once they reach large enough population they will kill a plant overnight worst part they love cannabis.
I have been fighting with them for almost a month cleared them out of my veg room easily but my flower room is haunting me now my goal was to shut it down in next 3 weeks so I have been mostly just trying to keep them at bay. Since I grow perpetual very hard to deal with them when some plants are days from finished and others are weeks my theory is worst case I have lots of bud for oil.


eek now I’m scared :frowning: We figured about 3 - 4 weeks left to harvest, would hate to harvest this early but will if necessary- it’s actually pretty decent already as I know from sampling over the weekend :slight_smile: The plan today is to spray the entire plant good and proper with a 60% alcohol (methylated spirits) solution. The leaf with the damage above is the only one so far that has lesions like that, but I understand what you are saying about how fast they spread so we are taking action now. All the damage occurred over only about a week or so. I refuse to lose this plant, it’s the largest one I’ve ever grown and it’s too close to harvest- I’ll take it down now if that’s what it takes to get rid of them. After that of course we disassemble our hybrid hydro rig and bleach everything.

Thank you very much for this information Donaldj and tlkbear! It has been very helpful and now we know what to look for and some idea what to do about it. I will have to order the Mighty Wash from overseas but will have it for next year’s crop for sure.

The Spider Mites

Use this I found out I had spider mites yesterday morning and went out and bought this, it kill on contact and you can use it up till harvest. And it hlelps the leaves to heal.
I bought mine at Home Depot or at

Amazon. http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=dr+earth+organic+insect+killer&rh=i%3Aaps%2Ck%3Adr+earth+organic+insect+killer

Here are some things you can use and there right in your home.

Hot Pepper Wax,Safer Yard & Garden Insecticide (which can be used right to the day of harvest),GNATROL( used in hydro in the water as well as soil),Doc’s Neem Pest Soap,Safer Sticky Stakes,TR-11000 Pyrethrum. Anything that says dicofol on the back. ( should be used in vegging or early flowering)

GNATROL( used in Hydroponics/Aeroponics in the water as well as soil)
Safer Sticky Stakes
TR-11000 Pyrethrum
Anything that says dicofol on the back. ( should be used in vegging or early flowering)


Hot Pepper Wax,
Safer Yard & Garden Insecticide
Doc’s Neem Pest Soap
Bugzyme Natural Pest Killer
Schultz-Instant Insect Spray
Lady Beetles (Beneficial Insect)
Predatory mite (Beneficial Insect)
Pirate Bugs (Beneficial Insect)
Neem Oil
Neem 2

Tabacco Juice recipe

Take 3 strong ciggeretes soak them over night in water
Boil it for 2 to 3 miniutes, let it cool off and spray the plants 3 to 4 times a week. You can add safer soap if you like to the mixture.
(make absolutly sure you use gloves/face protection while handling and spraying)
Neem oil works very well too!!

Hope this helps


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Thank you garrigan62! The home recipes might work better as I’m not sure what is available here, but will certainly be checking for these things you mentioned.

Tonight I did a full closer inspection all over (it’s a gorgeous huge plant!) and while it is definitely an infestation, it is not to a critical point yet and so far no webs on the leaves or buds. And parts of the plant seem to be definitely hit harder than others, some places hardly at all. I did find some egg clusters however, and also found the little buggers on my tomatoes. :confused:

We sprayed the leaves and flowers top and bottom heavily with a solution of 70% pure ethanol in water, around dusk this evening. This seemed to zap them almost immediately, so if it works we are going to try this for a few days, switch up with some of those things mentioned above and see how it goes. If we can make it another 2 1/2 to 3 weeks that will be great. :slight_smile:

that is something I wouldn’t repeat too many times simply because alcohol is exactly what is used to strip plants trichomes which may cause more damage to your plant’s potentcy and yield.

Yes I thought that was the case as I used to use alcohol to clean out my glass pipes! lol I’ll switch up to something else and hopefully get through this. Thanks!

Great im glad its working out for ya. I have about the same amount of time left be for harvest. I
Checked my crop and couldn’t find any movement. But going to spray again in the morning


Thank you! Good luck to you as well :slight_smile:

Sorry growgirl#, ;
@Donaldj was absolutely correct about the ethanol and I know I didnt tell you to use
But I did make a batch of theTabacco Juice recipe and I added The hotest chili powder I could find ill spray later today.
I will keep you posted


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I actually also have growing a bush of very hot ornamental peppers and a habanaro plant in my garden as well. I will try this too.

I read on another site about using the alcohol… I am curing a cola now that was well sprayed the other day so I should know by tomorrow evening if I’ve damaged it or not. Here’s hopin’ not! Geez I hate it when you make it worse when trying to make it better! lol

And thank you for the updates Will, I am curious to find out how well the pepper spray works.