This is an article I've written for the latest Newsletter but it has not been published yet so I thought I might post it up here. There have been a few members with the same problem and some great advice. Here is the article in 'bare bones' form without pictures or anything but contains some good info.
Trouble shooter; Leaf Spot Fungus
As everyone may have seen recently, there have been quite a few members whose plants have been suffering from Leaf Spot Fungus. The problem has been becoming more frequent and only looks set to rise even further unfortunately.
What is Leaf Spot Fungus?
Well, as the name states it is a fungal infection which attacks the leaves. Symptoms of leaf spots vary depending upon the causal agent. Although leaf spots can be caused by air pollutants, insects, bacteria et al., most are a result of infection by pathogenic fungi. Once into the leaf, the fungi continue to grow and leaf tissue is destroyed. Resulting spots vary in size from that of a pin head to spots that encompass the entire leaf. It was OT1 that first brought it to my attention, and you can see it at various stages in certain members grows.
What are the Symptoms?
Below I have included three different pictures of members grows at different stages of infection, so that people know what to look out for. The problem is so much easier to treat if spotted (excuse the pun) early. Each of the following members are happy for their problem to be featured in the hope that it helps another member avoid the problem.
Firstly, here is a picture of Church's Medicine Man grow. This is an example of Leaf Spot Fungus in its early stages:
Next is a picture of Jaygrow's plants and as you can see the Leaf Spot Fungus is at a more advanced stage:
Then this third picture is one of SirBob's plants, a Nirvana Skunk #1, at an even more advanced stage, once the Leaf Spot Fungus has truly set in:
So is there Anything I Can Do If I Discover my Plants Have it?
It seems as though there are a few measures that one can take to eliminate the problem but there is no quick fix unfortunately. How advanced the problem is also affects how to go about tackling it, and how effective each solution will be. Fortunately, I have never had this problem personally and have therefore called on the knowledge of those with more experience than myself in looking for ways to combat Leaf Spot Fungus.
I asked OT1 the following question, being the walking botanical encyclopaedia that he is:
If spotted, what would be your suggestion for eliminating the leaf spot fungus? I'm assuming it has to do with the environment, to prevent others getting it but should they forego plants with the problem or can they tackle it if they catch it early?
This was his answer:
Firstly its not down to the environment as such, the fungus spores are in the air seasonally. Once its replicating in an enclosed environment, i.e. spores are constantly being released into the grow room. The only way environment plays a part is that it’s a sunny warm day every day in the grow room, plus the ideal environment for cannabis is also an ideal environment for the fungus, there are no seasons, under these circumstances the fungus replicates very fast.
I think Citrofresh does work against leaf spot, but its not instant, also you have to understand that Citrofresh only works on the leaf surface, its not systemic, so spores that have already germinated into the leaf tissue before spraying will appear [depending on temperature] as a new rust spot 10 to 14 days after treatment and produce new spores, so repeat spraying is needed.
I don’t know of a systemic fungicide available to home users that is effective against this fungus at this time. Even if there were I’m not sure I would want to use it.
Copper oxides work as a shield killing spores as they germinate on the leaf surface before the hypha can penetrate the surface. Adding seaweed hardens the leaf surface helping to add resistance to fungi and stimulating the plant. Like Citrofresh it does nothing to hypha already living within the plant tissue.
Fungi are some of the most difficult things to eradicate, especially those that live in living tissue, the environment we create for our plants is also an ideal place for the fungi to replicate and once in, a few spots get ignored, next thing you know its ripping through your crop.
This lead me to ask the following question:
So once it's caught hold, there's not much one can do. So I suppose taking a cut from and uninfected area if you can, keep spraying it and get rid of the original mum when possible?
To which OT1 replied with:
With repeat treatment protecting new growth, the new growth should remain healthy, cuttings can be taken from this.
Its like all gardening, hygiene helps, totally removing infected tissue from the area, i.e. cutting back infected leaves to sound tissue or removing leaves that are infected all over, this helps reduce the spore count.
Spraying with BioLife to run off every 5 days until no further infection is seen to work, no doubt about it, this can follow Citrofresh as an initial treatment, but if you spray with Citrofresh after BioLife it will kill the BioLife.
You can’t use BioLife after copper.
Biolife works mainly by populating the leaf surface with tricoderma species, these are plant friendly fungi that predate pathogenic fungi when they try and invade. Unfortunately there is no simple answer, understanding the issue, helps understanding how to deal with it.
Input From Arnold Layne
When discussing this problem, Arnold Layne came up with another good idea for an organic way to tackle the leaf spot fungus.
He took the following knowledge of tackling fungus on humans and applied it to plants and it appears to be totally sound in both theory and practice.
Garlic is amazing at killing of some fungal infections in humans - could it have beneficial use in growing weed? Could it deal with this problem through a regular spray of some garlic solution.
Then he found the following information whilst researching this idea further.
Ah! Now then, here, look at this -
Fungal suppression. Regular use of garlic barrier will assist crops to resist or recover from most of the common fungal diseases. Research worldwide has shown garlic's fungistatic and fungicidal activity against Fusarium oxysporum, Phytophthora spp., Phythium spp., Rhizoctonia solani, Botrytis cinerea, Alternaria brassisicola, Sclerotinia sclerotiorum and numerous other pathogenic fungi.
So it seems that a regular spraying of a garlic solution would help as both a preventative and a mild cure for fungus on the leaf surface. Well deduced Sherlock Layne mate.
OT1 Spotting it in Jaygrow’s Room (pic.7) and his Advice:
Its a leaf spot fungus. I've seen this before, its very very infective.
For future grows the following protocol has been used and proved effective.
The way out is fast growth, i.e. a lot of light, good air exchange, protection with probiotic bacteria and fungi i.e. use BioLife.
To make up BioLife ignore the instructions, bubble a litre of warm water [35c] for an hour, bring the temp back up to 35c stir in a level tea spoon of black treacle and add a gram of inoculant, leave to bubble overnight.
At the same time leave 2 or 3 litres of water to stand overnight to allow chlorine to evaporate, if you can bubble it all the better, mix the two in the morning, spray the plants then water the surplus through the compost. Chuck any excess or use on any other plants you want to inoculate.
Final point when spraying only use the sprayer at low pressure, too high a pressure will burst the membrane of larger fungi strains such as tricoderma. Also do not use internal pumps with venturi valve for added aeration, the water being drawn through the impeller again will shred the fungi.
Then another post later in the same thread…
From what I can see its the same fungus, damage to the leaves will be more rapid and greater with high temperatures, but I've see grows with it in Jan and Feb this year as well. Once the spores are in the room and general area it will tend to reoccur.
Its best to protect your young plants before it shows and repeat spray every week or two until the third week into flowering. Also spray your mums every two weeks if you have any..…
Bish Spotting it/ Practical Application of Advice:
Bish spotted it in one members grow, Steve7876, in a thread I saw and made some good recommendations. A brief overview of the conversation is as follows. Steve noticed that he had a problem with some of his leaves and posted up some pictures in the hope that one of the members would be able to identify the problem and offer some help, hints or tips. Luckily Bish had seen it before and gave him some valuable advice.
From the thread ‘What’s up with my Plants’ in the ‘problem solver’ forum, Here
Cut back infected leaves to healthy growth first, get some Murphy’s Copper & start treatment.
A good wash down of your grow area would help too.
This rust spot fungus is on the increase, but it can be beaten
This was short, sweet and to the point. It says exactly what the problem was and how to deal with it in a no frills, straight to the point manner. Just what was needed in the thread to get it on track.
well I just trashed the offending little shit and trimmed the others right back I guess ill continue with this grow and see what happens as I’m already a month in. I plan on moving ‘em to the flowering room in a week or 2 anyway so ill give the veggie room a good clean and hope that everything goes ok with my second grow.
Cheers for the advise bish I reckon you’re SPOT on
Why don't you just treat them?
I just ordered some copper fungicide should be here within a day or 2
the one that I threw has been in bad shape ever since it sprouted I’m gonna keep the other 7 and treat them
So it looks as though Steve is on his way to tackling the problem. By getting rid of he most affected plant and trimming back the others, he is reducing the spore count. Then by ordering the copper fungicide and cleaning down his grow rooms, he will eventually get on top of the problem. But it may take a bit of time depending on how advanced into the leaf the fungus is on the remaining plants.
It appears that there are both ways of preventing Leaf Spot Fungus and ways of curing it once the problem has been identified. If the problem is spotted early then obviously the job of tackling the problem is made easier but it is not too late even when the problem becomes systemic.
Here’s to a happy and problem free grow.