Growing cannabis is an exciting adventure, but let’s be real – it comes with its problems. One common issue you might come across is rust-colored spots on your precious cannabis leaves. These spots can really mess with your plant’s health if not dealt with. But don’t worry, I’ve got you covered! In this guide, we’ll break down what causes these brown spots, how to identify them, and most importantly, how to treat and prevent them.
Overview of rust spots on cannabis leaves
Signs of rust spots on cannabis leaves
Rust spots usually appear as yellow, orange, or brown patches on the leaves. They can vary in size, starting small and then expanding across the leaf. Often, these spots will show up on older leaves first, but they can spread if left untreated. The key thing to remember is to look out for powdery or dusty spots that can easily rub off. This will help you figure out if you’re dealing with rust fungus or some nutrient deficiency.
Why rust spots appear: common causes
Rust spots can show up due to several reasons, ranging from fungal infections to nutrient deficiencies. The most common culprits are rust fungus, magnesium or calcium deficiency, nutrient burn, or even environmental stress. Identifying the root cause is your first step to solving the problem.
How rust spots affect cannabis plant health
Rust spots aren’t just an aesthetic issue; they can have a serious impact on your plant’s health. They weaken the leaves, slow down growth, and ultimately reduce your yield. In severe cases, these spots can spread throughout the plant and affect its overall ability to absorb light and nutrients. So, if you see rust spots, it’s best to treat the issue quickly!
Rust fungus as a common cause
What is rust fungus?
Rust fungus is a parasitic fungus that loves to latch onto your cannabis plants, especially during the flowering stage. It’s known for causing those distinctive yellow or reddish-brown spots. Rust fungus typically spreads via spores and thrives in moist, warm conditions. So, if your grow room is a bit too humid, you might just be creating the perfect environment for this troublesome fungus.
How to identify rust fungus on cannabis leaves
Rust fungus starts off as small yellow or white spots, mostly on the underside of leaves. Over time, these spots turn into orange or brown blisters. One way to identify rust fungus is by rubbing the spots with your fingers. If the spots disappear and leave behind a rusty residue on your fingers, it’s rust fungus. If not, you might be dealing with a deficiency.
How rust fungus spreads and develops
Rust fungus spreads quickly through spores that travel via air or water. It loves a damp environment, so it often targets plants with poor airflow or excess moisture. Once it sets in, it can damage plant tissues, making it difficult for the plant to absorb nutrients and sunlight.
Testing for rust fungus
The finger rub test is the easiest way to check for rust fungus. If the rust spots rub off easily, it’s almost certainly rust fungus. If the spots don’t rub off, then you might be dealing with a nutrient deficiency, which we’ll cover next.
How to treat rust fungus on cannabis
- Prune Infected Leaves: Remove affected leaves carefully to prevent the spores from spreading.
- Disinfect Tools and Grow Area: Clean your pruning tools and the grow area with a mild bleach solution.
- Apply Fungicide: Use a copper-based fungicide to treat the infected plants. Just avoid spraying the buds to prevent an aftertaste.
- Preventive Measures: Apply sulfur dusting or neem oil weekly to prevent the fungus from reappearing.
If the infestation is severe, consider removing the plant entirely to save the rest of your crop.
Nutrient deficiencies leading to rust spots
Overview of magnesium and calcium deficiencies
Magnesium and calcium deficiencies are common causes of rust spots. Your plant needs these nutrients to grow strong, and when it doesn’t get enough, rust spots can appear, especially during the flowering stage. The deficiency could be due to not feeding your plant enough nutrients or because the plant can't absorb the nutrients properly due to a nutrient lockout.
Identifying magnesium deficiency in cannabis
Magnesium deficiency often starts with yellowing between the leaf veins, followed by the development of rust spots. Over time, these spots increase in number and size, moving toward the leaf tips. You might also notice the leaves curling up or the plant looking droopy. Magnesium deficiency usually starts showing symptoms 4 to 6 weeks after it begins.
Identifying calcium deficiency in cannabis
Calcium deficiency shows up as brown spots with a dark outline on the leaves. The leaf tips may also start curling. Unlike magnesium deficiency, the affected leaves won't turn yellow; instead, the veins will remain green. In severe cases, it can stunt the plant's growth, resulting in poor yield quality.
How to fix magnesium or calcium deficiencies
First, identify which nutrient is lacking and increase its intake. If the issue persists, it could be a nutrient lockout. Check the growing medium's pH, which should ideally be between 5.8 to 6.2. If the pH is off, flush the medium with clean water and adjust the pH of your nutrient solution. A balanced Cal-Mag supplement can help prevent future deficiencies.
Understanding nutrient lockout and its impact
Nutrient lockout happens when the plant can't absorb nutrients due to improper pH or an excess of other elements. When this happens, even if you're feeding the plant plenty of magnesium or calcium, it can't use it. To fix this, you need to flush the soil and correct the pH levels to restore proper nutrient uptake.
Preventing nutrient deficiencies in future cannabis crops
Regularly check your plant's pH levels and nutrient balance. Using a Cal-Mag supplement can help maintain a proper ratio of calcium and magnesium. Also, monitor the environment to ensure it's not too cold or damp, as this can affect nutrient absorption.
Other potential pauses of rust spots
Nutrient burn and its symptoms
Nutrient burn occurs when you overfeed your plants, leading to brown or rust-colored spots. It’s more common during the flowering stage when you might be tempted to add extra nutrients. The best way to fix nutrient burn is to flush the soil with plain water to remove excess nutrients, then resume feeding at half the previous dose.
Pest infestations and how they relate to rust spots
While less common, pests like spider mites can cause damage that resembles rust spots. These critters suck the sap from leaves, leaving behind discoloured spots. Regularly inspect your plants for pests and use natural pesticides if necessary.
Environmental stress: temperature and humidity issues
Cannabis plants are sensitive to their environment. High humidity, fluctuating temperatures, or poor air circulation can stress the plant, leading to rust-like spots. Make sure your grow area has proper ventilation, consistent temperatures, and low humidity to avoid this issue.
Preventative measures against rust spots
Optimizing growing conditions
The best way to avoid rust spots is by creating an optimal growing environment. Keep the grow area clean, well-ventilated, and at the right temperature and humidity levels. Make sure that any excess water can evaporate and that your plants are getting an adequate amount of light.
Choosing fungi-resistant cannabis strains
Some cannabis strains are more resistant to fungi like rust and Septoria than others. When choosing seeds, go for strains known for their hardiness. This small step can save you a lot of trouble down the line.
Regular monitoring and adjustments in nutrient routine
Keep a close eye on your plants and regularly check their nutrient intake. Adjust your feeding routine based on your plant's growth stage to ensure they get the right nutrients at the right time.
Using fungicides safely and effectively
Use fungicides like sulfur or neem oil as a preventive measure. Rotate different types of fungicides to avoid immunity buildup in fungi. Always follow the instructions and avoid applying fungicides to buds.
Frequently asked questions
How can I differentiate between rust fungus and nutrient deficiencies?
Rust fungus spots rub off easily and leave a powdery residue. Nutrient deficiencies cause spots that do not rub off and often come with other symptoms like leaf curling.
Should I remove leaves with rust spots?
Yes, remove affected leaves to prevent the spread of rust fungus. Dispose of them away from other plants to avoid contamination.
Can rust spots appear during all stages of growth?
Rust spots are most common during the flowering stage but can appear anytime if the plant is stressed or facing nutrient deficiencies.
Can pests cause rust spots on cannabis leaves?
Yes, pests like spider mites can cause damage that resembles rust spots. Regular checks can help catch and treat pest infestations early.
What is the best way to prevent rust spots in an indoor grow setup?
Maintain optimal growing conditions: clean environment, proper airflow, balanced nutrients, and regular monitoring for early signs of issues.
Conclusion
Rust spots on cannabis leaves can be a real pain, but they’re manageable if you know what to look for and how to treat them. Whether it’s rust fungus, nutrient deficiencies, or environmental stress, identifying the cause is the first step to fixing the problem. By keeping your grow room clean, monitoring your plants regularly, and providing the right nutrients, you can keep those pesky rust spots at bay. Happy growing!
