I have some leaves that are starting to look very much like the pic you posted. What causes LSF?
Usually LSF is caused by spores entering your grow room. There are certain strains of ganja that seem to be immune to it and are very resilient but in most cases LSF needs to be eradicated and prevented rather then curing as its very hard to get rid of it once its rife.
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 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.
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.
I was looking through some older stuff I have and I found this..
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.
