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9 Effective Steps to Conquer White Spots on Weed Plants with Confidence

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If you're a cannabis grower, you know your plants can suffer from various issues affecting their growth and yield.

Cannabis is an attractive plant for pests, mainly when you grow it in the soil. Pests can range from insects to different species of molds. If you don't treat these weed plants promptly, it could lead to more problems and crop loss.

You might notice white spots appearing on the cannabis leaves at this stage, a symptom that can be triggered by numerous factors such as pests, mold, or nutritional deficiencies.

In this article, we will check the different causes of white spots in weeds, how to solve them quickly and effectively and prevent them from returning your weed plants to health.

Before you can effectively treat white spots on weed plants, it's essential to determine the type of spot and the underlying cause, such as spider mites and whiteflies, and nutritional deficiencies of calcium and magnesium.

Additionally, high humidity and poor air circulation create a favorable environment for the fungal diseases that cause white spots. If the areas are raised and fuzzy, it could be a fungal disease such as powdery mildew.

If the sites are flat and appear on the surface of the leaves, a pest such as spider mites may be infested. If the spots are hollow and appear on the underside of the leaves, there may be a nutrient deficiency. The most important thing is to determine the cause of the white spots on weeds to treat and prevent them effectively. Take a look at the causes and solutions below.


Learn about Causes and Treatments

1. Powdery mildew

Powdery mildew is a white, powdery fungus on cannabis leaves. This fast-growing fungus damages plants and spreads, impacting their overall health.

Powdery mildew develops on the tops of cannabis leaves. The clinical manifestation of the developing powdery plague evolves into a white fuzz covering the entire cannabis plant. The same goes for the base of the cannabis leaf. The powdery mildew enters the cell walls and then extracts nutrients and water. The result is curled, shriveled cannabis leaves that slowly die.

The causes of powdery mildew are:

(1) High humidity

Powdery mildew needs moisture to thrive, but that doesn't necessarily mean it needs water. Having a growing area with high humidity is all that powdery mildew needs to get started. This seems problematic, as young cannabis plants grow best in relatively humid conditions (40% -60% RH). Fortunately, high humidity is usually only a problem when combined with the following cause (low/no airflow).

Growers who live in environments with very high humidity can purchase dehumidifiers or all-in-one HVAC equipment to control humidity in growing areas. This is especially important during flowering when humidity needs to be low enough to prevent the spread of powdery mildew.

(2) Low/No Airflow

White powdery mildew is challenging to colonize in an airy grow room. High humidity will give powdery mildew what it needs to survive, but lack of airflow will allow it to settle in the first place. A small fan moving air around the growing area will prevent most powdery mildew damage.

(3) Poor ventilation

If your growing area has powdery mildew spores, and the air in the ever-increasing room is never exchanged with fresh air, there are many opportunities for the spores to land on your plants and reproduce. This happens most often when cannabis is grown in closed, airless spaces, and no precautions are taken to exchange stale air for fresh air.

(4) Leaf-to-leaf contact

Leaves that touch each other create moisture between them, making them more susceptible to powdery mildew. Untrained bushy/leafy plants with a lot of new vegetative growth are especially prone to this as they often smash their leaves against each other as they try to reach the light.

Powdery mildew can be treated with fungicides or organic solutions like neem oil. Also, you'll want to make sure your cannabis plants have proper airflow and ventilation - even if your grow room has no airflow or ventilation at all, just two fans will significantly reduce the chances of developing powdery mildew while also benefiting the overall health of the plant. So remember to have at least two fans.

2. Pests

Red spiders and thrips are common cannabis pests, both of which cause white spots on weed plants. Learn the differences so you can deal with them better.

Thrips are yellowish-white insects with tiny bodies. They have wings and can fly from one plant to another and cause a trail of white or silvery spots. They tend to be most common indoors, where cannabis grows and reproduces fastest.

These insects can be treated with insecticide, neem oil, or diatomaceous earth, and they are not tricky pests to deal with.

Place yellow sticky traps around your growing area to catch these tiny insects. Use potassium soap or neem oil every two to three days. Be sure not to use neem oil during flowering, as it can negatively affect the flavor of the weed.

The presence of red spiders is more severe than that of thrips. Red spiders spread incredibly quickly once infected, making your plants easily ruined. They will usually show up as white spots on your fan leaves. When you see spider webs, it's a sign that you're in big trouble.

Lower the temperature, boost humidity, and enhance airflow to decelerate growth. Prune infected leaves and discard them safely. Rinse plants to remove any mites. Spray leaves with a safe insecticide or an organic option like peppermint oil, avoiding flower buds to prevent damage.

3. Nutritional deficiencies

White spots may indicate nutritional deficiencies. Common causes include a lack of calcium, magnesium, or zinc. Conversely, insufficient calcium or magnesium can cause white spots on leaves. Use a nutrient solution with the correct mineral amounts to address these deficiencies.

4. Light burning

Excessive light exposure can cause mild burns and white spots on cannabis leaves. To fix this, move the plant away from the light or use shading material to lessen the light it gets.

5. Insufficient light

Too much light can cause white spots, in the same way, that insufficient sunlight can cause white defects in your plants. If your cannabis plants lack natural light or the grow room is poorly lit, they may suffer. To address this, move the plants closer to a light source, but avoid overwhelming them. Proper lighting is essential.

6. Heat stress

Heat stress can cause white spots on weeds, usually at the edges of the leaves. Reduce the temperature in the grow room to reduce heat stress. High temperatures in the cannabis growing space can also cause white spots on the leaves. This can happen if the temperature is consistently above 85 degrees Fahrenheit. To solve this problem, lower the temperature inside the grow room by using a cooling system or ventilation.

7. Excessive fertilisation

Excessive fertilization may cause soil salt accumulation, resulting in white spots on leaves. Be aware of your fertilizer usage and follow the suggested dosage.

8. Use of pesticides

Some pesticides can cause white spots on cannabis plants, especially if the dose is too high. Use pesticides with care and stick to the recommended doses.

9. Genetics

Some varieties of cannabis themselves produce white spots on the leaves, in which case you don't need to deal with them, but you would like to make sure your plants are in nutritious and healthy growing conditions.

10. Environmental stress

Stressful situations such as cannabis transplanting and relocation can cause white spots to appear on weeds. Be patient and give some time for your plants to recover from the stress.

11. Over-watering

Overwatering can also cause white spots to appear on the leaves. This is because overwatering can cause the roots to suffocate, which can lead to nutrient lock-up. To solve this problem, water only when needed and ensure proper drainage.

12. PH imbalance

pH imbalances can lead to white spots on cannabis leaves. High or low water pH levels can cause this issue. To resolve it, use a pH meter to test your water and make necessary adjustments.

13. Soil imbalance

An imbalance in the soil can also cause white spots on cannabis plants. For example, this can happen if the ground is too tight or if there is too much clay. To solve this problem, add organic matter, sand, or perlite to improve the soil.

In short, white spots on cannabis plants can indicate different problems. Identifying the cause of white spots early and taking action can help ensure your plants are healthy and reap a good harvest.

The appearance of white spots is not a good sign, and here are some suggestions on how to prevent cannabis from developing white areas in the grow room.

Prevent White Spots on Your Cannabis Plants

1. Maintain hygiene

Essential to prevent the spread of disease and pests in your grow room is good hygiene. Always disinfect all equipment with a suitable disinfectant before and after use, and keep the room clean and tidy.

2. Use good air circulation

Proper ventilation reduces powdery mildew risk by promoting air circulation and lowering humidity. Keep exhaust fans and air intakes well-maintained, and change air filters routinely.

3. Monitor humidity levels

High humidity levels are conducive to powdery mildew growth, so keep humidity levels at 50% or lower. You can use dehumidifiers, air conditioners, or humidity controllers to maintain the right level.

4. Keep temperatures consistent

Fluctuating temperatures can stress your plants, making them more susceptible to disease and pests. Keeping the temperature inside your grow room consistent will assist your plants in developing healthy and prosperous.

5. Monitor nutrient levels

White spots on plants sometimes indicate a nutrient deficiency. Ensure you give your plants the necessary nutrients and closely monitor their growth and development.

6. Choose drug-resistant cannabis varieties

Some cannabis varieties are more resistant to powdery mildew and other pests than others. Research which strains are more resistant, and then select those for your grow room.

Organic neem oil is a natural pesticide that can help prevent or tackle the spread of powdery mildew and spider mites. Use neem oil sprays regularly to keep your plants healthy and pest-free.

7. Introduce integrated pest management

Integrated Pest Management (IPM) is a pest control approach that combines multiple methods. It involves using natural predators like ladybugs, praying mantises, and natural insecticides to manage pests.

8. Keep your grow room airtight

Make sure your grow room is sealed to prevent pests from entering from the outside. Check all window and door openings and make sure they are closed.

9. Act quickly

When you notice white spots on your plants, respond promptly. If left unaddressed, powdery mildew and spider mites can quickly spread and severely damage your plants.


Act fast if you see white spots on your plants. Powdery mildew and spider mites spread quickly, causing significant harm. Maintain cleanliness, proper airflow, and monitor temperature and humidity for healthy, pest-free plants. If white spots appear, promptly identify and resolve the issue to prevent damage and promote vigorous plants.

Часто задаваемые вопросы

1.What are the little white specks on my weed?

Little white specks on your weed might be a sign of a pest infestation or a fungal disease like powdery mildew. Look closely to determine the cause.

2.Can you get rid of powdery mildew on weed plants?

Yes, you can get rid of powdery mildew on weed plants. Remove infected parts, improve airflow, reduce humidity, and consider using a fungicide.

3.How do you treat white powdery mildew on weed?

To treat white powdery mildew on weed, remove infected parts and improve ventilation. Reduce humidity and use a fungicide if needed.

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