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Leaf Septoria (Yellow Leaf Spot) On Cannabis Plants

Cannabis plants, unfortunately, are susceptible to a wide variety of diseases and pests. Leaf septoria is one such disease, and can greatly damage the foliage, development, and yield of your cannabis plant. Learn how to properly treat and prevent leaf septoria from devastating your crop.

Leaf septoria is a harsh plant disease that regularly affects the foliage of a variety of plants, including cannabis.

If not handled properly, leaf septoria can be devastating to plants, destroying foliage, stunting their growth, and ultimately affecting the size and quality of their yields.

In this article we take a close look at cannabis leaf septoria, what it is, and how to treat/prevent this disease from affecting your cannabis crops.

WHAT IS LEAF SEPTORIA?

Leaf septoria, also known as septoria leaf spot or yellow leaf spot, is a plant disease caused by a specific kind of fungus known as Septoria lycopersici.

This fungus usually overwinters on dead foliage or common garden weeds. Fungus spores can also spread onto equipment like garden stakes and netting, before germinating when conditions are right.

Leaf septoria can be an extremely damaging disease, greatly affecting the foliage and growth of a variety of plants, including tomatoes, parsley, and obviously cannabis.

As the name suggests, leaf septoria is characterized by yellow and brown spots forming on both the upper and lower sides of leaves. The spots tend to be circular with dark brown margins and tan or greyish centers. They usually measure between 1.5 to 6.5mm.

Leaf septoria usually affects plants just after they enter the flowering stage and usually forms on lower leaves first. As the disease develops it spreads its way upwards, quickly affecting multiple leaves all across the plant.

Affected leaves will usually turn slightly yellow, then brown, and eventually wither completely. Leaf septoria rarely spreads on to fruit, so it generally won’t affect cannabis flowers.

If left uncontrolled, the disease can destroy a lot of foliage. This ultimately creates a lot of stress for plants and stunts their growth as well as the size of their harvests. Leaf septoria is particularly prevalent in areas affected by extended periods of wet, humid conditions.

HOW TO TREAT LEAF SEPTORIA IN CANNABIS PLANTS

As with most garden pests and disease, early detection is extremely important when dealing with leaf septoria. Make sure to pay close attention to your plants during extended periods of hot and humid weather, as well as during the early stages of the flowering cycle.

Once you’ve identified the disease, make sure you follow the following steps to control it and stop it from spreading:

1. REMOVE INFECTED FOLIAGE

The first step to effectively dealing with leaf septoria is removing infected leaves. If caught early, you can usually prevent the spread of the disease by simply removing all infected lower leaves and burning/destroying them.

However, if the disease has spread to the height of your flowers, you’ll generally want to skip this step. Removing foliage from flowering areas will greatly weaken a plant and reduce the quality of its buds.

2. IMPROVE AIR CIRCULATION

Proper air circulation is extremely important for cannabis plants and plays a big role in the management of pests/diseases.

If you’re growing indoors, improving air circulation can be as simple as adding an extra fan into your room and creating some space between your plants. If you’re working outdoors, however, this might be a bit more difficult.

Pruning is also a great way to help create airflow in and among plants. Try trimming down extremely bushy areas of your plants and avoid having leaves touching or laying on top of each other.

If you’re working outdoors, you may want to try elevating your plants slightly so that they catch a bit more wind. Alternatively, also consider running an electric fan on outdoor plants if possible.

3. AVOID MOISTURE

Moisture is another major player in the spread and germination of fungal spores. Hence, you’ll want to avoid moisture as much as possible.

Avoid overhead watering as this will wet the leaves of your plants and consider watering slightly less regularly in order to give the soil a chance to really dry out. Also water early in the day to allow the soil to dry out during daylight hours.

4. MULCH

Fungal spores often spread into soils where they hang out over the winter until conditions are right for germination.

While you won’t be able to change your growing medium mid-grow, there are some steps you can take to avoid any spores from the ground spreading onto your plants further.

Start by removing any dead foliage and raking the soil to remove any possibly infected vegetation. Next, dry out your soil properly. Finally, apply a thick layer of mulch to the top of your soil then water your plants.

This will help stop the spread of fungal spores from the soil up onto your plants.

5. REMOVE WEEDS

Night shade and horsenettle are common hosts of Septoria lycopersici spores. Hence, make sure you run through your garden and remove any weeds that could possibly host the fungus.

6. KEEP TRACK OF TEMPERATURE AND HUMIDITY

Remember that leaf septoria naturally strikes in hot, wet conditions. Hence, if you’re dealing with an infection, try driving down the humidity and temperature levels in your grow space (where possible).

7. APPLY FUNGICIDES OR NATURAL OILS

If you’re dealing with a minor case of leaf septoria, steps 1-6 might be enough to kill the disease and stop it from spreading any further. However, if you’re dealing with a more serious infection you may need to rely on some heavy-handed fungicides.

Broad spectrum fungicides and disease control sprays will usually do the trick. For extra protection, try opting for a copper-based fungicide. Either way, remember to carefully follow the package instructions when using any kind of disease control agent, and avoid getting any of it on your buds.

If you’re after a more natural alternative, we suggest turning to essential or horticultural oils like neem. Neem oil is commonly used to treat all kinds of garden pests and diseases and can easily be applied to your plants using a mister.

Alternatively, consider trying eucalyptus, rosemary, lemon, and cinnamon oils. Either way, remember that these oils have strong aromas and should never go near your buds to avoid contaminating their aroma/flavour.

Neem oil serves as a completely natural way to protect your cannabis plants against pests.

Leaf septoria, also known as yellow leaf spot, is a fungal disease that can greatly damage cannabis crops. Here's how to deal with leaf septoria on weed plants.

Calcium Deficiency

by Nebula Haze & Sirius Fourside

Problem: Calcium is an important nutrient which helps provide structure to the cannabis plant and helps it withstand stress like from heat. When your plant has a calcium deficiency, the main symptom that you’ll be able to notice is brown or bronze splotches or spots on your leaves.

A cannabis calcium deficiency can sometimes be difficult to diagnose since calcium deficiencies are often accompanied by magnesium, iron, and/or other cannabis deficiencies.

Calcium moves relatively slowly through the plant (it is a semi-mobile nutrient), which means it tends to “stay put” after it’s been given to a leaf. It tends to show up on leaves that are actively growing and getting some amount of light.

Calcium deficiencies most often show up in the following places:

  • Newer growth (upper leaves)
  • Parts of fan leaves that have been exposed to the light

Found near the top of the plant under the light

This lower fan leaf is mostly in the shade, but the calcium deficiency appears near the edges that are getting light. Calcium deficiencies often show up on parts of the leaf that are still actively growing.

Calcium Deficiencies Appear on New or Actively Growing Leaves

Calcium deficiencies tend to appear on newer or growing leaves, which means calcium deficiencies first appear on leaves where there’s rapid vegetative growth.

Some of the most noticeable signs of a calcium deficiency will appear on newer or growing leaves which may display:

  • Dead spots
  • Crinkling
  • Spotting / Mottling
  • Small brown spots
  • Stunted growth
  • Small or distorted new leaves
  • Curled tips
  • Leaf die-off
  • Affected leaves may appear green besides the spots

Here’s a close-up of a calcium deficiency that appeared on leaves towards the top of a cannabis plant grown in coco coir:

Other Symptoms of Calcium Cannabis Deficiency

If a cannabis plant is affected by a calcium deficiency for too long, it may begin to show the following symptoms due to the lack of calcium.

  • Stems become weak or flimsy and may crack easily
  • Stems become hollow or show inner signs of decay
  • Plant does not stand up well to heat
  • Flowers/buds do not develop fully, or development is slow
  • Roots appear weak or under-developed
  • In severe calcium deficiencies, parts of roots may even die off or turn brown
  • Roots are more susceptible to root problems like slimy root rot

Cannabis tends to like high levels of calcium, so it is unusual to feed too much calcium when using normal amounts of nutrients and/or regular soil. There are not many known cases of cannabis calcium toxicity (too much calcium), however too much calcium can cause the plant to lock out other nutrients, so it’s important not to go overboard..

Calcium deficiencies are more likely to appear when…

  • Grower is using filtered or reverse osmisis (RO) water to feed plants – the amount of calcium found in tap water varies, but some tap water has enough calcium to prevent calcium deficiencies
  • PH is Too Low – If grow medium is acidic (below 6.2 pH, Calcium can get locked out even if the Calcium is physically there)
  • Growing cannabis in hydroponics or coco coir without supplementing extra Calcium (it’s recommended to use a Calcium supplement in hydro or coco)
  • When growing in soil that hasn’t been supplemented with calcium (usually from dolomite lime)
  • Too much potassium can also sometimes cause the appearance of a calcium deficiency
  • Outdoors – calcium deficiency is more likely to appear in acidic soil (below 6.2 pH)

Different strains of cannabis tend to have different nutrient problems. Some cannabis strains (or even specific plants) tend to use much higher levels of calcium than others, and so you may see calcium deficiency problems with one plant even when all the other plants (which are getting the same nutrients and environment) aren’t showing any signs of deficiency.

Solution For Calcium Deficiency in Cannabis

Your cannabis plant may show signs of a calcium deficiency if the pH at the roots is too high or too low. That is because when the pH of your root zone is off, your cannabis cannot properly absorb calcium through its roots. Therefore the first step is to ensure that you have the correct pH for your growth medium. Learn more about pH and cannabis.

Please note: After a calcium deficiency is cleared up, the problem (brown spots and unhealthy new leaves) will stop appearing on new growth, usually within a week. Please note that leaves which have been damaged by a calcium deficiency will probably not recover or turn green, so you want to pay attention to new growth for signs of recovery.

  • In soil, calcium is best absorbed by the roots in the 6.2 – 7.0 pH range (in soil, it’s generally recommended to keep the pH between 6.0 – 7.0, but calcium specifically tends to be best absorbed above 6.2)
  • In hydro, calcium is best absorbed by the roots in the 6.2 – 6.5 pH range (in hydro, it’s generally recommended to keep the pH between 5.5 – 6.5, but calcium specifically tends to be best absorbed above 6.2)

If you suspect your growing cannabis plant has a calcium deficiency, flush your system with clean, pH’d water that contains a regular dose of cannabis-friendly nutrients that includes calcium. This will remove any nutrient salts that may be affected the uptake of calcium and help restore pH to the proper levels.

To supplement with extra Calcium… (it’s very rare to give a cannabis plant too much calcium, however, too much calcium can lock out other nutrients so don’t go overboard)

Calcium and magnesium deficiencies often appear together in cannabis. Many growers decide to purchase some sort of Calcium-Magnesium (often called Cal-Mag) supplement for their grow room in case this common deficiency appears.

Listed below are common cannabis Calcium supplements, along with some general information about each one. After supplementing with Cal-Mag and correcting the pH, you should expect to see new healthy growth within a week. Remember, the old leaves will probably not recover, but new growth should be green and healthy.

CaliMagic is Well Suited For Hydro, Coco Coir, or Soil

General Hydroponics CaliMagic is a calcium and magnesium plant nutrient supplement. General application is to mix 1 tsp (5ml) of CaliMagic into each gallon of water. I have used Calimagic several times with great results.

Dolomite Lime – For Soil Growers (Organic)

If you’re looking for a way to supplement calcium in your organic or soil setup, I highly recommend a product called “Dolomite Lime.”

Dolomite is a good source of calcium and magnesium and can be mixed with your soil. The great thing about dolomite is it works slowly over the course of a few months.

Dolomite has a neutral pH of about 7.0 and will help keep soil at the correct neutral pH range which is optimum for cannabis growth.

You can buy Dolomite Lime online, but with shipping, it’s almost always waaaay cheaper to pick up a bag at a home improvement or gardening store such as Lowes, Home Depot, gardening centers, etc. If possible, try to get a finer grade of dolomite compared to something that is more coarse.

How to Use Dolomite Lime for Cannabis: When growing cannabis indoors, add 6-7 teaspoons of fine dolomite lime to each gallon’s worth of soil. So if you’re mixing enough soil to fill a 5 gallon container, you want to add 30-35 teaspoons (about 2/3 cup) of dolomite lime to the mix. Mix the dolomite lime and the dry soil thoroughly, then lightly water it with water that has been pH’ed to 6.5. After getting the soil wet, mix the soil well and wait a day or two to let the soil settle before checking the pH and adding plants. When growing in an outdoor garden, follow the dolomite lime manufacturers instructions.

If you cannot get rid of your calcium deficiency, please consult our 7-Step Cure to 99% of Cannabis Growing Problems

Plant Symptoms

  • Bronze or brown patches
  • Brown or slimy roots
  • Brown or yellow leaf tips/edges
  • Buds dying
  • Buds look odd
  • Bugs are visible
  • Curling or clawing leaves
  • Dark leaves
  • Drooping plant
  • Holes in leaves
  • Mold or powder
  • Pink or purple on leaves
  • Red stems
  • Shiny or smooth leaves
  • Spots or markings
  • Twisted growth
  • Webbing
  • Wilting leaves
  • Yellow between leaf veins
  • Yellow leaves

This page is part of our Plant Doctor series. You can use our tool to filter by symptom and help diagnose your plant.

Calcium deficiencies cause tiny brown spots that appear on new and middle growth. Learn how to fix this problem for good!