Cannabis leaf Septoria vs calcium deficiency

Cannabis leaf Septoria is a fungal disease that affects cannabis plants, as well as plenty of other species including tomatoes, potatoes, parsley, aubergine/egg plant and many others. It often strikes cannabis during early bloom, but it is treatable and tends not to affect the buds. It starts as yellow brown spots before spreading rapidly, yellowing the cannabis leaves before they eventually turn brown and die.

Calcium deficiency is sometimes confused with cannabis leaf Septoria, with certain similarities in the leaf appearance. In this article, both issues are reviewed and the differences highlighted.

What is leaf Septoria?

The small yellow/brown cannabis leaf Septoria spots often have a dark halo. When left untreated, a hole may appear in the position of the original leaf Septoria spot as the plant cells completely die. Cannabis leaf Septoria often starts in early bloom, with spots ranging from around 1mm-5mm in diameter, often on lower leaves initially before spreading up the plant.

As the leaf Septoria spreads the leaves take on a yellow appearance. This turns brown as the leaves die and whither. Cannabis leaf Septoria has the potential to create a great deal of stress for the plant, reducing growth and subsequent yields. The fungus thrives in warm, humid conditions.

How to identify cannabis leaf Septoria?

The conscientious grower tends to check their plants regularly, monitoring overall growth and plant health. Regular leaf checks are the best way to identify cannabis leaf Septoria before it becomes firmly established. Look for small yellow/brown/bronze spots - the starting point of the fungal infection. These can appear on both the upper and under side of the leaves. Unless infected leaves are removed the spots spread up the plant.

In severe cases, the leaves start to yellow and die. This dramatically affects the plants’ ability to reach the full genetic potential contained in the cannabis seeds. Cannabis leaf Septoria can affect plants grown from both autoflower seeds as well as photoperiod feminised seeds.

Difference between cannabis leaf Septoria and calcium deficiency

Calcium deficiency tends not to start with the small yellow/brown spots with the dark halo. Calcium deficiency in cannabis causes a range of biochemical issues, including generally yellow leaves.

Cannabis calcium deficiency will often have the following (serious) implications for your plants, including:

•    Loss of overall growth vigour, leaves may wilt. Calcium is used in many different biochemical pathways. It is vital for overall stress resistance and general health.

•    Nutrient uptake by the roots may be affected. Calcium around the root zone helps organic matter to decay. Overall nutrient absorption may be affected with Calcium deficiency, effectively preventing other minerals from being absorbed. This in turn can cause a series of deficiencies.

•    Reduced yields of cannabis buds. Cannabis requires extra calcium, in addition to other minerals/nutrients, in mid bloom.

•    The leaf spots with Calcium deficiency are different to those caused by cannabis leaf Septoria. Note that Septoria infections start on lower leaves first.

Cannabis growers will be aware that Calcium isn’t the only critical mineral/nutrient required. Many other minerals are essential for healthy growth, if your nutrients are missing key elements, you will see a range of issues. For those seeking more precise information on the damage caused by deficiencies in Nitrogen, Potassium, Phosphorus etc the following guide is vital reading:

Signs of Calcium deficiency in cannabis

Cannabis requires Calcium, alongside a range of other important minerals and nutrients, in order to maintain healthy growth. An absence of Calcium can look confusingly like other deficiencies because the cannabis plant is unable to continue general essential biological functions. The symptoms of Calcium deficiency are wide ranging and may include the following:

•    Cannabis roots may appear brown. Root rot/slime may be threats and the weakened root system may be prone to other infections or pathogens. Nutrient/mineral absorption is compromised, creating secondary issues and reduced growth.

•    Reduced new top growth of your cannabis plant.

•    Growth slows on new blooms and new leaves may curl or show a strained/twisted appearance before dying. Young shoots may show purple or yellow discolouration.

•    Bud production is reduced, especially in severe cases. Emerging buds are small, deformed and rarely reach full potential. Plants are often particularly adversely affected by heat.

•    Large, pale brown spots may form on leaves with Calcium deficiency. However these don’t look the same as cannabis leaf Septoria. With Calcium deficiency the leaf edges are affected and turn brown. Calcium deficiency leads to yellowing of the leaves as the issue increases in seriousness.

•    Branches may be weak and easily broken. The stem of your cannabis plant may rot inside.

It’s worthwhile noting that Calcium deficiency rarely occurs when cannabis plants are grown in reasonable quality soil/compost. That’s because Calcium is generally readily bio-available in most well-prepared soil blends. Instead, Calcium deficiency is perhaps more often seen in hydroponic cannabis grows, where the grower is fully responsible for ensuring that all major (and minor) minerals are present in the added nutrients. Even a small mistake during the creation of the hydroponics nutrients could lead to nutrient deficiencies or overdoses.

How to treat leaf Septoria on cannabis plants?

Prevention is always better than cure, but if you notice the tell-tale signs of cannabis leaf Septoria spots the following tips are essential to prevent spread:

1.Remove and destroy infected leaves/foliage.
If you have caught the cannabis leaf Septoria early simply remove the affected leaves. The infected leaves carry the Septoria fungus, so they need to be removed from your grow area and preferably destroyed. It’s important to add that in severe cases it would be unwise to strip every leaf off a plant in mid/late bloom. In these circumstances, try to avoid complete defoliation and consider some of the other options, below.

2.Reduce moisture/ grow room humidity.
Fungal spores spread and thrive in warm, humid conditions. By reducing humidity, it de-optimises the conditions that fungus thrives in. The passionate grower monitors air temperatures as well as grow room humidity at each stage of plant growth. Decreasing temperature and humidity is a great way to make conditions as unfriendly as possible for cannabis leaf Septoria. Foliar feeding should be discouraged if leaf Septoria is suspected - the regular damping of leaves with a spray increases the odds for leaf Septoria to thrive and spread.

3.Improve air circulation.
Still, stagnant air pockets in your grow room/greenhouse provide the ideal conditions for fungal spores to thrive. Ensure you have adequate levels of air extraction as well as air circulation. Use of clip-on fans above and underneath the plant canopy is a good way to remove dead-spots of stagnant air.

4.Remove weeds & good housekeeping.
Those growing cannabis in a greenhouse or outdoors should note that leaf Septoria is often found on other plant species such as Horse Nettle, Night Shade and many common herbs/vegetables. Good housekeeping is essential for cannabis growers, whether in a greenhouse or indoors. Always strive for the cleanest environment possible.

Remove plant waste immediately, clean and wipe your indoor grow room (or greenhouse) between grows. It only takes a few minutes to wipe down the inside of a grow tent with a disinfectant wipe and vacuum it.

Pro-growers always clean their plant containers, tools etc between each grow to minimise chances of future infections/pests. Cannabis leaf Septoria spores can even be transferred to plants from contaminated netting, garden stakes etc.

If you have suffered from leaf Septoria (or any other pest/disease) it pays to be extra diligent when cleaning your grow area, tools etc for the next grow.

5.Consider a top-dressing of mulch.
Some growers use mulch as a protective barrier between the soil and the plants. The idea is to create a layer above the soil which makes it tougher for any Septoria spores in the ground to spread onto the plant.

6.Neem oil.
Few cannabis growers would consider spraying e.g. copper-based fungicides on their plants. But the natural neem-oil sprays may be useful. Neem oil is a multipurpose material useful for treating a range of cannabis pests and diseases.

Preventing future leaf Septoria infections with indoor cannabis growing

Understanding the fact that cannabis leaf Septoria spreads easily in moist, humid conditions is key knowledge when planning your future grows. If your routine grow room checks indicate regularly high RH (Relative Humidity) then you may want to consider options such as a more powerful extraction fan, a de-humidifier or (in worst case scenarios) avoiding growing in certain seasons, especially the humid months.

Some indoor growers water their plants methodically, allowing the upper soil layers chance to dry a little (making Septoria spore survival more difficult) before watering them. The use of a tensiometer which measures moisture content in soil may be a useful way of allowing you to regulate watering. It’s worth adding that over-watering (and over-feeding) cannabis plants are probably the two biggest mistakes made by cannabis growers, especially less experienced ones.

The use of highly aerated grow containers such as air-pots and fabric sacks is also recommended, providing an oxygen-rich root zone and minimising the chances of cannabis roots sitting in excessively damp conditions where leaf Septoria spores may survive.

Indoor cannabis growers may wish to rotate their plants, e.g. a quarter turn per day. This ensures that no single patch of foliage is forced to endure long periods in areas where air-flow may not be entirely adequate. Of course, it is preferable to have sufficient air-flow through your grow tent supplemented by well-positioned clip-on fans which provide additional air movement.

Preventing future leaf Septoria infections in outdoor/greenhouse cannabis growers

Outdoor/greenhouse cannabis growers may want to try to dry out the soil surface, destroying the fungal spores that may have been sheltering from the previous season. The surface can be raked free of leaves, weeds etc. The soil can be dug over allowing greater aeration and a chance for the upper soil layer to dry. This desiccates and destroys the leaf Septoria spores.

Outdoor/greenhouse growers may also wish to remove as many nearby weeds etc as possible to minimise chances of cannabis leaf Septoria infections. Outdoor growers that have suffered leaf Septoria over a few seasons may wish to select a different grow location. That’s because leaf Septoria spores are tough and can over-winter and thrive the following year if conditions are favourable and Septoria-infected plants are plentiful in a particular area.

Cannabis leaf Septoria FAQ

A typical 1.2m x 1.2m grow tent takes around 10 minutes to vacuum and wipe clean after a grow. This is time well spent - especially if you have seen the damage done by avoidable pests/diseases that pass from one grow to the next. Cannabis leaf Septoria isn’t seen that often, especially if you take the usual precautions. But if you do see the characteristic cannabis leaf Septoria spots it pays to act quickly and assess which areas of your grow you can change to prevent future recurrences.

Is leaf Septoria caused by pests?

No, cannabis leaf Septoria is a fungal infection rather than a pest problem. But some cannabis pests and diseases can look confusingly similar. The following expert guide, with pictures, shows you what the damage caused by the main pests and diseases look like.

Can leaf Septoria spread to other plants?

Yes, leaf Septoria survives and thrives because it spreads from plant to plant in the right conditions. This allows Septoria to infect nearby plants, maintaining sufficient numbers of spores to ensure that it survives and is passed from plant species to species. Cannabis leaf Septoria may not be a regular problem for the average indoor cannabis grower, but it is one which you need to be aware of.

Does leaf Septoria affect the buds?

As the name suggests, cannabis leaf Septoria mainly affects the leaves. If you catch the Septoria infection early you may only have to remove a few lower leaves and adjust grow room conditions (less heat, less moisture, no foliar feeding etc).

There may be no significant loss in yield. But if the Septoria infection is allowed to continue unchallenged it will spread to all leaves and wreak havoc on your cannabis plants. This has a dramatic effect on overall plant vitality, photosynthesis, and many important functions of plant health. Under these conditions yield and quality are invariably affected even if the buds themselves are not the primary victim of the Septoria infection.