It’s the question that every cannabis grower sometimes asks. ‘What is wrong with my plant?’ Even professional growers can occasionally scratch their head and wonder what has gone wrong with their plant. The good news is that there are plenty of answers and help available. The bad news is that some of the problems can look similar to each other, complicating the diagnosis. Read on to find out more.
Cannabis growers moved indoors for several reasons, including the need to improve quality/security and partly to avoid pests. For many, the environment is much easier to control indoors. In the safety of an indoor grow room cannabis can usually thrive in optimised environmental conditions free from pests and bad weather. But if pests do make it into an indoor grow room they can multiply at an alarming rate. Thats because there are no natural predators. A grow room optimized for plants can also be optimized for pests, meaning extra care is needed.
Many pests are accidentally introduced to a grow room when growers swap plants or cuttings (clones) with each other. Indoor growers that occasionally take their plants outdoors for an hour or two of midday sun often allow pests such as greenfly and whitefly to colonise their plant. All it takes is a couple of insects landing on the plant to infest your indoor grow room.
Spider Mites are small spiders that are often found on the underside of the leaf. They can be one of the most damaging cannabis pests. Spider Mites are almost too small to see. But the wispy webs they build to protect their colonies and eggs are easy to identify. Each generation takes under a week to hatch and start reproducing, so a rapid response is vital. Just like white fly, a harsh water spraying will dislodge them from their safe shelter underneath the leaves. Ladybird insects are a natural predator and are often a preferred solution for organic growers. Spider mites do not cope well in the cold, so a temperature reduction nearer to 20ºC may slow them down while other eradication measures take effect. Some growers find that the less-powerful hand held ‘portable’ vacuum cleaners can suck off the predators and keep spider mite numbers down. However, this technique requires patience/skill and is time consuming even for one plant. A 10% alcohol (ethanol) spray is an effective option. Grow shops do sell chemical remedies, though many cannabis growers feel uncomfortable about using chemicals on their crops. Thats because any residual traces of insecticide on the buds can result in dangerous by-products if the cannabis is later smoked.
Predatory Mites (Phytoseiulus persimilis) are an effective way to treat problem spider mites. They can be bought online, they don’t damage the cannabis plant nor will they bite you! But they do feed on the common spider mite and naturally patrol the underside of leaves looking for them. Heavy infestations of Spider Mite will require a second, or even third treatment. High temperatures of around 30ºC usually favours the reproductive rates of the spider mites. Therefore, when using Predatory Mites, try to keep temperatures on the cool side around 18ºC - 26ºC. Many predatory Mites prefer slightly humidity levels of around 60%, though some can operate well at around 40% humidity. Whenever you use Predatory Mites always carefully monitor the effect on Spider Mite population, and where necessary add more Predatory Mites.
Fungus gnats can be a common pest for indoor growers. Occasionally they are seen by coco-fibre growers. Fungus gnats are usually first noticed when the harmless adults are seen flying around the growroom. The flying adult gnats are a nuisance, but their main threat is the next generation of larvae which they will produce. It’s these larval gnats, feeding in the grow medium, that can damage delicate cannabis roots. Reducing water usage and allowing the top layer of soil to dry can help kill the larvae. Some people use diatomaceous earth in the soil to disrupt the larvae. Others cover the surface of the grow medium to prevent adults laying eggs there. And use of sticky fly paper will control the egg-laying adult gnat population.
Whitefly usually live and breed on the underside of cannabis leaves, feeding on the plant sap. They spread quickly, each white fly can lay 200 eggs at a time. Usually, cannabis growers don’t like to use pesticides or chemicals on their plants. But there are other ways to get rid of white fly. Some growers use a strong water spray to wash/blast them off the underside of the leaves. Lady birds are a natural predator and are used by some growers. Using sticky fly paper isn’t a cure, but many growers feel it is good practice to have a roll of sticky fly paper in their grow room. The sticky fly paper won’t eliminate a pest problem. But it can give you advance warning of the presence of pests. Black fly and greenfly are aphid pests and are often treated in similar ways to whitefly.
Several fungal infections of the cannabis plant can produce brown ‘rust’ colored areas on leaves. Chemicals are effective at controlling fungal infections but are rarely used by the responsible cannabis grower. Rust can find it easier to infect damp leaves. It helps to ensure that ventilation is good and that plants have space to grow, without growing into each other. Most growers will remove the rust-damaged leaves and try to make it through to harvest. If the rust is not severe that should be quite possible. All old leaf material should bealways removed from the grow room. Never leave it inside the grow room because the spores allow the problem to persist.
There are several species of thrips. Regardless of which type you may find in your grow room, they are a serious nuisance. Thrips can reproduce around 10-12 times per year. Mature thrips can survive simply by flying from one plant to another. Thrips are particularly damaging when they appear early in your grow, and can be difficult to eliminate. Thrips are a tiny pest which survive on the sap of your cannabis plants. Thrips can be tiny winged insects (just a few millimetres in size). Thrips can also look like small, pale worms. Frankliniella occidentalis is the main cannabis thrip pest. They are white/yellow flying pests which lay eggs on the plant. These are difficult to spot, look out for small silver marks/dots on the underside of leaves. The thrip eggs produce larvae which give rise to larger critters and finally flying bugs. Many growers routinely use sticky fly paper to catch the adults. Other tips include the use of Neem oil or Potassium soap. Some growers use natural predators such as Orius laevigatus - the common bed bug, which prey on thrips.
Maintaining a clean indoor grow room is a key responsibility for the indoor grower, and it really doesn’t take much effort. Thoroughly clean your grow room between each grow. Remove waste and old leaves/foliage along with any traces of old soil or growing medium. Use a vacuum cleaner to remove any dust and traces of grow medium from the previous grow. Wiping down the surfaces of the grow room or tent only takes a couple of minutes and really helps sanitise the area. Many growers uses a dilute solution of disinfectant, some use diluted Hydrogen Peroxide (often used by hydroponic growers as an additive). Inspect your plants regularly. Look for the first hints of disease or pests. Remember that many pests and diseases are introduced accidentally when plants/cuttings from other growers are brought into your grow room.
Many indoor growers have realised that use of UVB light for around 3 hours per day in the last 2-3 weeks of bloom really helps to increase potency of the buds. Some growers also report that these UVB lights do a great job in making life difficult for pests. Supplemental UVB light replicates the natural UVB light present at high altitudes. For small creatures, UVB is dangerous enough to control their numbers. You can get a UVB supplemental light here from LED By Passion, Dutch Passion’s sister company. Many people also report that UVB kills spores of mold/mildew and is another reason why UVB lights have become one of the most important modern grow room upgrades.
One of the biggest headaches for cannabis growers is when the nutrient regime seems to be causing plant problems. Much of the time, especially for less experienced growers, problems are caused by over-feeding the plants. This is done in a false belief that it will stimulate faster plant growth and bigger harvests. Usually, the opposite is true. Minerals build up in the plant, the leaves turn brown/crispy and the roots die. The best answer is to flush several litres of water through the grow medium. If you have a 5 litre plant container, use 15 litres of water to remove the excess minerals which will have accumulated through over feeding.
Under feeding of cannabis plants is easy to resolve, just slowly increase nutrients as the plant grows. The ideal target is to keep the cannabis plant in the nutrient ‘sweet spot’ where the plant is neither underfed nor over fed. This usually means steadily increasing the nutrient concentration as the plant ages and having the experience to know how the plant is responding. One other tip for less experienced growers is to avoid an over-complicated array of nutrients. Start with the basics, and as you gain experience you can always start to try more advanced mixtures of additives.
This is very difficult to do, since many different deficiencies can look fairly similar. Help from a more experienced grower can be vital. Doing your own online (or book) research is useful, but no guarantee that you will get the right answers. Other factors can complicate the diagnosis. For example, the pH of the grow medium is crucial. If you grow in coco fibre, certain minerals are not bio-available to the cannabis roots unless the pH (acidity of the grow medium) is correct. That means you could have a magnesium deficiency caused by incorrect pH of your nutrient solution. Adding more Magnesium won’t allow the plant to absorb it unless the nutrient solution has a usable pH (usually around pH 5.6-5.8 for coco fibre growers).
Just like pest infestation, prevention is better than cure when it comes to mineral/nutrient issues. Good advice, especially for the less experienced grower is to keep the grow as simple as possible until your skill level rises. Trying to grow in a demanding deep water culture (‘DWC’) hydroponic system requires careful control of pH and E.C. (electrical conductivity, which is a measure of mineral concentration). DWC may be a good option for the experienced grower that doesn’t mind checking their plants a couple of times a day. But less experienced growers will find the demands excessively complicated. If you are new to cannabis growing it can simply be too much to expect yourself to be able to control the preparation of the feed solutions and ‘read’ the plant responses. An easier approach for the less experienced grower would be to grow in a large container of soil, (perhaps 30 litres or more) which would contain many/most of the nutrients required for the complete grow. This simplifies the grow process and the nutrient regime.
It’s worth adding that even professional growers can find difficulties preparing the nutrient solutions. If your pH meter or E.C. meter is not correctly calibrated you will see plant problems very quickly. For less experienced growers, growing organically in soil using organic nutrients from companies like BioTabs is one of the easiest ways to get started.
Growing cuttings/clones from a friend is a great way to cultivate a plant which you know you will enjoy vaping/smoking. A cutting brings and identical genetic copy of the original plant into your grow room. Unfortunately it can also bring pests, disease, fungal infections etc. That’s one of the main reasons that large legal commercial growers are extremely careful about bringing any outside plants into their growrooms. Growing your plants from autoflowering seeds or feminized seeds is one way to guarantee that you don’t import a pest/disease problem. Get them from a cannabis seed company you can trust.
August 2nd 2019