Seedsman Blog


Welcome back to Seedsman’s series on common pathogens, where we look at identifying, avoiding, and treating some of the most frequently-occurring problems faced by cannabis growers. In our first article, we investigated powdery mildew, and today, we’re bringing grey mould in for questioning.

Grey Mould aka Bud Rot (Botrytis Cinerea)

What is it?

Grey mould is another fungal pathogen cannabis growers must guard against. A common headache for farmers, this unwelcome nuisance can be found on numerous crops, including vegetables, soft fruits, flowers and shrubs.  Some argue grey mould is a cannabis grower’s biggest threat, and it can destroy an entire crop in a matter of days. If you spot it lurking in your plants, you’ll have to act fast.

What does it look like?

Grey mould is easily seen, although harder to identify in the early stages. It can attack every part of the plant, but is most commonly found on buds during the late stage of flowering. Look out for grey-ish webbing appearing on the leaves. Structures within this webbing contain fuzzy spores, which are then activated and released. Symptoms of grey mould include grey/brown colouring, and dry or lifeless, wilting leaves which may fall apart when touched.

What does it do?

This is a particularly devious adversary, and doesn’t only attack the plant during the growth phase. If plants are not harvested under the proper hygienic conditions, using sanitary practices, grey mould can still appear after harvesting. At this stage, the mould will begin decomposing the buds, and will transmit through the seeds, rendering your yield completely worthless. The grey-ish webbing which appears on the leaves is made up of structures which contain fuzzy spores. These spores are then easily activated, and released, spreading and decimating the plant.

Why does it happen?

As with powdery mildew, grey mould is a sucker for a humid environment (who doesn’t want to get comfy in a nice, warm place?). Higher temperature and moisture are an open invitation for grey mould to crash the party and spoil the fun, so it’s important to keep these levels finely balanced.

How do we stop it?

Again, keeping your environment under control is key to preventing this fungal nuisance from swinging by and putting its feet up. Make sure your humidity levels are under 60%, and keep your gardening practices sanitary at all times. Hopefully, you’re inspecting your crops every day in a bid to outsmart any would-be spoilsports, and should you encounter any signs of Botrytis, begin by immediately pruning off any infected areas completely, taking care to avoid contact with any healthy, uninfected areas of the plant (or surrounding plants).

It should be noted that, as flowers begin to naturally expand through simple growth, this increase in size and density restricts intra-floral ventilation, and increases the risk of mould. Plant infection at this stage can often force cultivators to harvest prematurely in an attempt to mitigate further risk – however, harvesting ahead of schedule can be equally hazardous to your crop. Instead, be diligent in your examination, and take care to prune away any areas which are impeding growth of surrounding plants, and remove any wilting or brown-looking leaves as soon as you notice them, as dead/decaying foliage is an open door to the development of Botrytis.

Sanitise your pruning equipment (with alcohol) before and after use, and ensure the cleanliness of all equipment used to grow, monitor, maintain, and come into contact with your plants – this includes scissors, stakes, labels etc. Don fresh latex gloves before manipulating the plants. After pruning, be thorough in removing any discarded cuttings – do not allow these to lay in the soil beneath the plant. Better yet – manually remove each clipping while you prune, rather than allowing cuttings to fall to the soil, lest they come into contact with healthy buds or flowers, spreading the infection.

Resist the temptation to introduce any chemical sprays to fumigate cannabis plants, as these products do not guarantee that fungus will not ultimately appear, and can be hazardous to health.

Destroy all infected parts of the plant in an area away from the grow, and remain vigilant and frequent in monitoring – after all, good friends look after their best buds.

Next in our series, we’ll take a close look at a different type of threat –  pests, or more specifically, spider mites.

Cultivation information, and media is given for those of our clients who live in countries where cannabis cultivation is decriminalised or legal, or to those that operate within a licensed model. We encourage all readers to be aware of their local laws and to ensure they do not break them.

This post is also available in: French

Duncan Mathers