Plant Diseases and Treatment
Cultivation Tips – Common Leaf Diseases
- Why do my plant’s leaves turn upwards?
When leaves turn upwards it is a sign that the plant sheds a lot of water. This is because the lighting system is too close to the plant or because the relative humidity is too low. To correct this problem, place the lighting system higher and prevent the wind from blowing hard on your plants.
- Why do my plant’s leaves turn downwards?
When the leaves turn downwards it means that the nutrient solution is very strong. To correct this problem, dilute the nutrient solution with water that has a correct pH (5,5-6,5), set the lighting system higher and prevent the wind from blowing hard on your plants.
- The lowest large leaves turn yellow.
Do not worry. This is normal. The lower leaves will turn yellow and eventually die as the plant grows and there is not enough light available on the lower leaves. The original leaves will die to allow the new leaves to grow better and absorb as much light as possible.
- There are rusty spots/marks on the leaves.
Turn the leaves upside down and check carefully for pests and insects. If the leaf is free of pests or insects, place the lighting system higher, check the strength of the nutrient solution and the pH, and adjust accordingly if necessary.
- The tips of young leaves of the plant begin to turn yellow.
If the tips of the plant’s new leaves start to turn yellow or lose color, you should check the nutrient solution. In case of a strong nutrient solution, it is recommended to reduce the dosage of the fertilizers you use and especially those that contain a lot of nitrogen, to prevent the problem from spreading to the rest of the plant. If the power of the nutrient solution is correct, then check if the lighting system is very close to the new edges of the plant or if the temperature during the night (when the technical lighting is off) is too low. Indoor Plant Cultivation Tips
What are viruses?
Viruses are infectious, intracellular pathogens that are Submicroscopic particles composed of protein and nucleic acid. Symptoms may be confused with herbicidal or abiotic lesions stress.
Transmitted by injury, insects, parts of plants (seeds, proliferative tissue)
The best way to deal with plant diseases is to prevent them before they start. That’s why it’s important to monitor humidity carefully, air flow and other factors that affect the growing environment. Pythium thrives in liquid terrain. The mildew grows on high humidity and disperses in low humidity. Botrytis loves humid environments, spreads on wet leaves in humid environments.
The prevention of diseases in cannabis plants is done in the following ways:
Maintain a clean and healthy environment
- Maintain proper humidity and temperature
- Treat irrigation water
- Identify and remove diseased plants
- Varieties resistant to plant diseases
- Use disease-free seeds or cuttings
Some pathogens, such as mildew and botrytis thrive in hot, liquid environments with poor air circulation. Contaminated water is the main source of infection for pythium, which produces hydrogen spores
(animal spores). Treatment of irrigation water with ultraviolet radiation, chlorine or other products may prevent it from spreading pathogen as well as Fusarium, which is believed to be responsible for root rot and flower rot.
Root Rotting
What causes root rot? Pythium is a fungus that infects the cannabis plant and causes
rot of the root. Excessive watering causes root rot, affects parts of the roots, then spreads and infects the entire roots causing the death of the plant.
Inappropriate temperatures, either too low or too high, reduce dissolved oxygen levels in the root region.
Maintaining temperatures between 15 and 25 will allow oxygen to be absorbed by the roots.
Bad drainage of your soil will result in water stagnation inside the pot and create root rot.
These are the 3 conditions that are interconnected and cause root rot, and thus create the right conditions for the spores of pythium disease to thrive. The main thing that causes everything is excessive watering. Depending on how serious the problem is, you can add H202 (peroxide hydrogen) with water to kill the bacteria caused by root rot.
If the plant is seriously affected by it, there are only a few things you can do.. cut the diseased roots, add H202, or just chop the plant. To prevent Root Rot, you can add products like SuperThrive that will help protect your plant from root rot and will help treat radical problems.
Botrytis Bud Rot
During the last one or two weeks flowering, you want to rinse your crop 1 ½ to 2 weeks before harvest to flush out all chemical nutrients ingredients that your plant used. If you are an organic cultivator then you can rinse about a week before harvest. Giving them clean water in the last weeks improves the overall quality of your flowers.
Once you start “rinsing” you should check especially for rot in the flowers.
Bud Rot: Occurs when the humidity is high, if you have dense resinous flowers or if there are mold spores in the air. Bud rot looks like a black brown mud that can quickly grasp your plant and to ruin your crop. Mold spores are transmitted by air.
Prevention and control
Removal of any infected or dead part of the plant helps prevent rot of flowers. Reducing humidity and better ventilation of the cultivation area. If you find gray mold, cut off the infected part of the plant well above and below the affected area and move it away from the cultivation area. Reducing the humidity
from 55% to about 40% will do big difference in preventing flower mold. Also, the existence of too large buds can cause them to rot and will could cause rot. It is good to watch the areas of your plant having larger, thicker and denser buds. The use of a dehumidifier for days with high humidity can also help.
Outdoor!
To protect your outdoor cultivation from rotting flowers DO NOT spray the leaves at night, as it will not evaporate because it is night. Water the plants during the day instead of at night. The same goes for foliar spray. Make sure your plants do not get stressed if possible. Frequent observation of your plants can help control and get rid of moldy buds before spores spread to other areas of the plant!
Keep a good circulation of air around the plants. Poor ventilation equals sick plants and a favorite place for mold spores to reproduce! Keep the leaves away from the soil taking care that they DO NOT touch the soil. If your buds have already rotted, the best thing to do is to cut the diseased parts. Move them away from your crop and apply Neem Oil or foliage spray using high pH water. This prevents mold from spreading, and it also kills mold spores.
Powdery Mildew
Powdery mildew is a very common but serious disease for cannabis plants. Powdery mildew can easily be found on the young leaves of a cannabis plant and appears as a white or gray cloudy powder. Once the mildew infects the leaves of a plant, can easily spread to other parts of it, even in flowers thus reducing their quality. Small bumps or blisters on the top of the leaves are a clear sign that you have been infected with mildew. If the infestation is severe, it will smell like rotten vegetation.
When mildew infects your plants, there are limited solutions. Immediately remove visible infected plants and carefully check all the nearby plants to ensure that the mildew did not spread. Inhaling and /or swallowing mildew is dangerous and can lead to dizziness, fatigue, respiratory infections and may even cause severe lung disease.
The most effective way to avoid mildew is prevention. You will most likely see mildew mold on your cannabis plants – during the vegetative stage, in the last few weeks flowering and drying and ripening. Mildew thrives on overwatered and overcrowded plants and in high humidity environments,
so it is important to maintain fresh air circulation.
Οidium spores do not require stagnant water to germinate, only short periods of high humidity. Temporary environmental fluctuations are all the spores need to come alive, stick to the surface of the leaves and begin to absorb energy from the plant.
The prevention of the spread of mildew must include a multi-faceted approach that attacks the fungus.
Avoid extreme temperature fluctuations. Day and night temperatures should not vary more than than about 10°C. The optimum temperature range for production between 22°C and 28°C, but the lower the temperature range, the lower the temperature, the higher the temperature. variation, the less susceptible your crop will be to to mildew infestations.
Use the pH of the leaf surface as a weapon It may be impossible to eliminate mildew spores from the enviroment but at least growers can make life difficult for them. The success of the mildew depends closely on the pH of the of the leaf surface, so increasing or decreasing this value can disrupt its ability to establish itself in the crop.
The application of products containing potassium bicarbonate will increase temporarily increase the pH of the leaf surface, while products containing sulphur will lower it. Although these products are approved for organic production, it is best not to use them on fully flowering plants. If you anticipate problems with mildew, consider use these products as a precautionary measure until the second week of flowering. Beyond this point, the application of these products could negatively affect the final quality of your cannabis. Biofungicides are another organic method of preventing outbreaks of mildew outbreaks.
Products containing Reynoutria sachalinensis use an extract from plant species to activate the natural defensive mechanisms of the plant and produce biochemical substances that fight diseases. This induced disease resistance is not systemic, which means that only the treated area of the plant is protected. However, it is stratified, which means that if sprayed on the top of the leaf surface, the bottom part of the leaf will also be protected.
The growth of new plants is not protected, so the product must be reapplied in a seven to 14 days programme. Although the biofungicides can be a powerful addition to a grower’s disease control toolbox, make sure that the used fungicides -even biological ones- are allowed for your cannabis crop.
Filter out the problem
Most indoor growing spaces do not circulate air between individual rooms, but even the ventilation systems can perpetuate mildew outbreaks by dispersing the spores throughout the growing room. The installation of air filters with a MERV rating of 9 or higher can help capture mould spores and prevent their reintroduction into the growing area. Ask the technician to install these filters in the air management system and be strict about cleaning or replacing them on a set schedule.
With severe infestations, cut your losses, not the leaves When powdery mildew is first detected in a crop, it makes sense to remove the affected leaves. But if not followed by any of the four previous recommendations, it’s unlikely that the outbreak will improve by just by removing the leaves. With intense infestations, leaf removal can actually worsen the problem.
As you cut leaves, your hands are inevitably covered with spores and you keep spreading them on the crop every time you touch a plant. In severe infestations, this activity spreads as many spores as it removes. In addition, if the defoliation is extreme, the mildew will spread to the only part of the plant that remains infected – the flowers.
Maintaining a plant that is severely affected by powdery mildew will endanger the rest of the crop. Sometimes it is best to discard the infected plant rather than provide life support until the the day of harvest.
