Your cannabis garden should be green and healthy for proper growth and outcome. If you are spotting brown or bronze spots, then it may cause significant harm to your cannabis. It deteriorates plant health and inhibits photosynthesis, resulting in lower yields. Don’t panic!
It is generally due to nutritional lack, bugs, excessive or insufficient light, or pH imbalance. However, it is easy to fix once you know what is bothering your plant.
This article will help you know how to identify brown spots on cannabis leaves and how to fix them.
How do you diagnose cannabis leaf problems?
Diagnosing brown spots on marijuana leaves can be a bit tough because cannabis problem patterns may look similar. Here is what spot patterns reveal:
- Uniform browning: Do you see a widespread discoloration on many leaves? It may be due to nutrient deficiencies ( potassium, nitrogen, etc), overwatering causing root rot, or light burn from overly light exposure.
- Circular or Target Spots: Are you seeing a bull eye-shaped spot? Then, the plant is dealing with fungal infections like Septoria Leaf Spot. In this situation, fungal spores land on leaves and cause circular patterns.
- Speckled Brown Spots: Scattered brown speckles are a sign of pest infestation. For example, Spider mites love munching on leaves and parts with brown feeding marks. However, the early stages of fungal infections might look like speckled spots.
- Browning Edges: Have you noticed the edges of your cannabis leaves start browning? It may be due to possible reasons, like nutrient deficiencies causing browning along leaf margins. Under watering signals brown crispy leaf edges due to lack of moisture. Strong winds whipping the leaves cause windburn.
If you want to diagnose the spot patterns effectively, always compare both sides of the leaves because spots on one side of the leaf indicate pests feeding the leaf surface. Also, look for the newer spots for a clearer picture.
Common Causes of Brown spots on cannabis leaves
You know what a healthy cannabis plant should look like, right? It should be green, vibrant and lively. It means you are feeding your plant right with proper nutrients, water, pH levels, light, and environmental conditions. But if it develops white or brown spots, there is some issue.
As stated earlier, which reasons cause what kind of brown spots? Having brown spots on your cannabis leaves can cause them to wilt, resulting in reduced buds.
Here are the Specific Brown Spot Causes and Solutions:
1. Nutrient Deficiencies
If you detect cannabis leaves are turning yellow or showing brown spots, it may be due to the most common nutrient issue. So, check your nutrient solution first.
As we have mentioned in earlier cannabis guides- every macro and micronutrient ratio required at every stage of cannabis growth is different. It also applies to the strain variety. So, pay attention to each nutrient proportion.
Here are the common nutrient issues and how to overcome them:
- Nitrogen Deficiency
We know that NPK is very important for plants’ overall health because it helps produce chlorophyll necessary for photosynthesis. It also helps create amino acids, an essential compound during the vegetative phase.
Your plant may have nitrogen deficiency if you notice brown spots, curling, or premature falling. Anything excess is also bad.
How to know? Look for brown spots and dark green leaves appearing to be black. Check nitrogen levels.
- Calcium Deficiency
Calcium is a building block for numerous plant processes, helping plants to develop strong roots, stems, leaves, and branches. It also helps in absorbing potassium.
Being a heavy compound, it moves slowly through plants. Hence, this deficiency generally happens in the vegetative stage when the plant is at its most crucial growing stage.
So, if you see these brown spots in the vegetative stage and weak stems or immature buds, you know the reason- calcium deficiency. It may happen due to low pH or high potassium in the soil, causing calcium lockout.
- Potassium Deficiency
The third essential macronutrient regarding cannabis brown spots is Potassium because potassium is required to maintain healthy roots and root growth.
Your plant will start absorbing essential nutrients via leaves and other parts if it is not in the right amount. Also, potassium resistance may occur when other macronutrients are in excess (nitrogen or calcium).
Solution for Nutrient Deficiency in Cannabis Plant:
The first thing to check when you see brown spots on cannabis leaves is the nutrient solution. The growing media must next be flushed with pH-balanced water that has the right amounts of calcium, potassium, and nitrogen.
You can also buy balanced supplements from trusted cannabis-selling websites. Be attentive during the veggie stage because this time is when the plant is applying its energy and concentration to grow healthy parts. If you see spots, adjust the supplement levels.
If you are skeptical about store-bought chemicals, introduce organic matter in the soil. They will break essential nutrients, making it easy for your plants to absorb.
2. pH Low-level
Low pH affects cannabis the most, irrespective of what growing medium you have chosen- soil, coco coir, or hydroponics. When the pH is below 5.5, it is acidic and may cause various problems, including nutrient lockouts and imbalances in growth.
Check the soil pH and nutrients if you experience brown spots on plants despite using quality and proper supplements.
However, just checking pH isn’t enough, you have to run off nutrient solution. If you find low pH, flush the roots and balance it accordingly by flushing technique. The optimal pH range for soil is 5.5 to 6.0.
3. Light Burn
Lighting in cannabis growing is an important aspect as most growers grow cannabis indoors, where they need to mimic the natural light cycle. Sometimes they go overboard by increasing light panels or choosing extremely high-intensity lights that cause browning of leaves.
Have you noticed cannabis leaves are brown and crisp while touching? Because too much light is soaking up the moisture and inhibiting photosynthesis. Usually, light burn looks like brown spots, yellow tips from above the surface- greener at the bottom.
If you notice a light burn, fix it by reducing the lights or changing the panel. Inspect the plant and light distance as well. Sometimes it’s not the lighting fault, you have kept cannabis close to the panel. An ideal cannabis light is about 50 meters per square foot.
Read- Why Proper Lighting is Crucial for Cannabis?
4. Fungus, Bugs, or Pest Infestation
Yes! The white powdery growth followed by brown spots on the leaves is Powdery Mildew, and the circular brown spots are due to Leaf Septoria. These two are the common culprits of cannabis plants. To combat them, get fungicides available in the market. If you notice this earlier, remove the infected leaves and maintain proper air circulation and humidity ( below 60%).
Lastly, it’s the pests that also cause brown spots. Here are a few common bug attacks that are ruining your cannabis harvest:
- Thrips: These tiny, sap-sucking insects leave behind silvery streaks on leaves and small black droppings. They may also result in twisted leaves and reduced growth.
- Spider mites: Even smaller than thrips, spider mites create fine webbing on the undersides of leaves and suck out plant juices, causing yellowing and stippling.
- Leafhoppers: These green or brown, sap-sucking insects leave behind white, cast skins and yellowing stippling on leaves. They also jump fast when disturbed.
- Leaf Miners: These tiny moth larvae burrow inside leaves, creating winding white tunnels and causing distorted, stunted growth.
- Broad Mites: These microscopic mites feed on plant cell contents, causing distorted, stunted growth, bronzing of leaves, and sometimes excessive bud hair production.
- Fungus Gnats: These tiny flying insects are primarily a nuisance for adult plants, but their larvae can feed on fungus in the soil and potentially damage young seedlings.
- Bud Rot: This fungal disease thrives in cool, humid conditions and can quickly devastate your buds. It appears as a grayish-brown mold on flowers and leaves, leading to bud rot.
Read- Identifying and Treating Common Cannabis Pests and Diseases
Brown spots appear on cannabis plants when fed on by any of the above insects. To combat them, keep an eye on your plant’s growth. Notice leaves getting dark green, yellow, or white. It must be a pest infestation. To combat this, improve growing conditions, trim leaves, and severe cases, use pesticides or miticides designed to tackle these mites.
5. Poor Air Circulation
How will plants breathe without proper ventilation? Plants are living beings, and they need a suitable environment to flourish.
Overexposure to light may cause heat stress in plants. In this condition, it develops brown spots. If you notice leaf curling and browning, underdeveloped buds, and nutrition-lacking symptoms, ensure proper ventilation and air circulation.
6. Over Watering/ Under watering
As we mentioned earlier, brown spots on cannabis leaves are due to many reasons, and another issue is less watering or too much watering, even if you are using RO-purified water, you may notice brown spots.
Try adjusting the watering schedule, if you are watering less, maybe you are in a place where the weather is humid, and you need to water more and vice versa.
Here’s a table outlining some specific causes and solutions for brown spots on marijuana leaves:
| Cause | Symptoms | Solution |
| Magnesium deficiency | Yellowing between veins followed by brown spots and leaf edges | Supplement with magnesium sulfate (Epsom salts) |
| Calcium deficiency | Distorted new growth, brown spots on edges of older leaves | Supplement with cal/mag solution, Bone meal |
| Overwatering | Wilting leaves, brown spots throughout, soggy soil | Improve drainage and let the soil dry fully between waterings. |
| Light burn | Bleached, brown spots on leaves facing the light source | Raise the light source or decrease light intensity |
| Powdery mildew | White powdery growth on leaves, followed by brown spots | Raise the light source or decrease the light intensity |
Preventive Measures and Tips
Prevention is better than cure. So, preventing problems in your cannabis garden is better than battling them when they arise. Here are preventive measures and tips that will ensure cannabis thrives:
1. Maintain Proper Watering Practices
First, know the soil type. As Sandy soils drain quickly, clay soil retains water for a long time. Always pick the potting mix accordingly.
Next is to take a finger test or buy a moisture meter. It needs watering if it seems dry. Also, as the plant matures, lift your pot, if it’s light then it needs watering. In short, you need to saturate the root zone, so that excess water drains.
2. Provide Adequate Nutrients
Young seedlings have minimum nutrient requirements. So, you can use a nutrient solution or focus on nitrogen supplements at this stage.
Nitrogen (N) promotes leaf growth, Phosphorus (P) encourages root development and flowering and Potassium (K) aids in stress resistance and overall cannabis health. A balanced nutrition of all these is essential at every cannabis growth stage.
As your plants mature, their nutrient needs change. During vegetative growth, prioritize nitrogen for lush foliage. As flowering approaches, gradually increase phosphorus and potassium for optimal bud development. Do not overfeed your plants. Follow the schedules and check for signs of nutrient burn like brown leaf tips and clawing, so flush out excess feeding.
3. Ensure Proper Air Circulation
Use oscillating fans to create equal airflow in the grow space. It helps remove stagnant air leading to fungal diseases. Also, ensure proper ventilation to remove excess moisture and stale air. Control humidity levels and avoid mold growth by installing exhaust fans.
If you are an outdoor cannabis grower, then take advantage of natural air circulation. Place plants strategically to benefit plants from a gentle breeze.
4. Maintain Optimal Temperature and Humidity
Cannabis ideal temperature should be between 20- 26 Degree Celsius: excessive heat stress plants and extreme cold hinder plant growth and development. Consider using AC, heaters, or a ventilation system to adjust temperature accordingly.
Similarly, humidity should be around 60-70% during seedling and young plants. As the plant enters the flowering stage, aim for a low humidity of 40-60% to reduce bud rot risk. Buy a hygrometer and humidifier/ dehumidifier as needed.
5. Inspect Plants Regularly
Regularly inspect your plants. Pay attention to the leaf’s underside too. Your plant will tell you if there is any issue by showing signs of discoloration, distortion, or insect activity. It will help you to perform swift action by isolating infected plants or removing rotten leaves.
Spray insecticides or neem oil spray. Keep your grow area clean and remove any debris that can harbor unwanted guests.
6. Build a Healthy Microbiome
Consider incorporating beneficial microbes like mycorrhizae and beneficial bacteria in your soil. It will help promote plant growth, improve nutrient uptake, and enhance overall plant growth.
Also Read- How to Fix Cannabis Curled Leaves?
Invest in Essential Tools and equipment for Thriving Cannabis
The right tools and techniques empower you to monitor plants’ health and deliver precise care for a bountiful cannabis harvest.
Tools For Growing Healthy Cannabis
- pH Meter: A pH meter helps you measure the alkalinity or acidity of your nutrient solution. An ideal pH range for cannabis should be 6.0-7.0. If you are a beginner, purchase a digital pH meter for automatic calibration for easy readings.
- Electrical Conductivity Meter (EC): EC meters measure the total dissolved solids (TDS) in your nutrient solution, indicating the overall nutrient concentration. Seedlings require a lower EC than flowering plants. A digital EC meter with clear calibration instructions is ideal for beginners.
Tools For Diagnosis and Treatments
- Magnifying Glass: This simple tool allows you to get a close-up look at the undersides of leaves, stems, and buds. It is crucial for identifying early signs of pests, such as spider mites or thrips, which are often too small to see with the naked eye. Invest in a magnifying glass with good magnification (around 10x) and built-in LED lights for better visibility.
- Handheld Microscope (Optional): A handheld microscope can be a valuable asset for detailed examination. It allows you to identify pests and diagnose fungal diseases by examining spores and other microscopic features. Look for a portable microscope with adjustable magnification (up to 60x) and LED illumination for optimal viewing.
- Spray Bottle: A good quality spray bottle is essential for applying various foliar treatments to your plants. It can include organic pest control solutions like neem oil spray, insecticidal soap, or fungicides. Choose a spray bottle with an adjustable nozzle for precise application and to avoid overspraying. Consider a pressurized sprayer for large grow operations.
- Watering Can: While some growers utilize automated watering systems, a simple watering can remains valuable. It reduces the possibility of fungus problems and enables base irrigation. Select a watering can with a comfortable grip and a long spout for easy maneuverability.
- Safety Gear: When handling certain chemicals or fungicides, wearing gloves, eye protection, and a respirator is essential to protect yourself from harmful fumes or irritants.
- Pruning Shears: Sharp pruning shears are necessary for removing dead leaves, and diseased plant parts, or taking clones. Choose shears with a comfortable grip and bypass blades for clean cuts.
- Grow Light Meter (Optional): For growers using artificial lights, a light meter can help ensure your plants receive the optimal light intensity for healthy growth.
Cannabis leaf rusty spots FAQ
1. What is light burn, and how can it be prevented?
When cannabis receives too much light intensity, it gets light burn. Symptoms include bleached white spots that turn brown and crispy leaves. Raise the light source or reduce light intensity to prevent it.
2. How do you treat brown spots on leaves?
Brown spots can have various causes. Nutrient deficiencies (magnesium, potassium, nitrogen), over/underwatering, low pH, light burn, or fungal diseases can all show brown spots. Look for additional signs to diagnose the exact culprit. Treat the underlying cause (adjust nutrients, watering, pH, etc.) or remove infected leaves for diseases.
3. What does magnesium deficiency look like in cannabis?
Magnesium deficiency in cannabis shows distorted new growth and brown spots creeping in from the edges of older leaves. Supplement with magnesium sulfate (Epsom salts) to address it.
4. Why does my cannabis plant have rust spots on the leaves?
Rust spots on the leaves are uncommon in cannabis and usually indicate a fungal disease like rust. However, some nutrient deficiencies can mimic rust spots. Inspect closely and compare with pictures of cannabis rust online. If rusted, isolate the plant and apply a fungicide labeled for cannabis.
Conclusion
We are sure you are a confident grower now as you have resolved brown spots on cannabis leaves. If there is a problem, there is a solution, so be vigilant and don’t get discouraged. See, now you have it!
Happy cannabis gardening!