Brown, white, yellow or brown spots on cannabis leaves are symptoms of disease. Having noticed these alarming manifestations, it is imperative that the grower pay attention to the health of the plants and take steps to eliminate the effects of stresses on the tree and their consequences.
The reasons for the appearance of stains can be different: attacks of insect pests, viruses, overflow or underfilling, chemical burns, fungal diseases. The sooner the grower takes corrective action, the easier it will be to overcome the disease.
In order to prevent stains on the leaves of hemp, it is important to create optimal growth conditions for the bushes. These relate to temperature for growing marijuana, humidity levels, availability of ventilation, watering frequency, light levels, and day / night cycle. Competent organization of growth conditions will help prevent the development of most of the known diseases, the symptoms of which are the appearance of spots on the leaves.
If spots have already appeared, the first step is to check how the microclimate values correspond to the ideal conditions for a particular cannabis variety and for a particular stage of its life cycle.
An important stage of treatment is diagnosis
To be able to eliminate the causes that led to the onset of the disease, you need to correctly and timely diagnose the problem.
It is necessary to regularly inspect the bushes for insect damage, paying special attention to the inner surface of the leaves. Parasites and pests multiply rapidly and are capable of infecting the entire bush in the shortest possible time. A little later, the disease will manifest itself as yellow or brown dots on the leaves, which will indicate the active development of the disease.
It is possible to determine the defeat of a plant by a fungus at an early stage by carefully examining not only the leaves, but also the base of the stem in the immediate vicinity of the soil. It is this place that is often struck first, since it is located at the maximum distance from light sources.
Dots on leaves for infectious diseases
Brown spots. When the cannabis is infected with mold or mildew, the foliage will develop brown spots with a white or yellowish border. Fungal infections affect bushes with insufficient heat, high humidity and poor ventilation. As the disease develops, the spots on the leaves grow and cover large areas. If a problem is found, the affected areas of the leaves must be removed, and the bushes should be sprayed with fungicidal preparations.
White spots. If white spots appear on the hemp, which resemble crumbled flour, then the plant has undergone a powdery mildew disease. High humidity can also provoke such a problem. However, unlike a fungal infection, powdery mildew can infect cannabis not only in cold weather, but also in warm weather. If such white spots are found on cannabis leaves, fungicides should be applied.
Gray spots. Plaque on gray leaves indicates a disease of the plant with gray rot, in which not only the leaves are affected, but also the branches and stem. Wet areas with a gray bloom gradually grow, turning into a fine black mesh. In this case, a decrease in the level of humidity and an increase in temperature, as well as an improvement in ventilation in the grow box, will help. A more radical method of struggle is spraying with Bordeaux liquid.
Mites and other parasites pose a great danger to cannabis plants, the main of which are spider mites, aphids, whiteflies, and red spiders.
When the bushes are affected by aphids and whiteflies, black spots appear on the leaves. The pores of the plant are clogged, and it becomes difficult for him to “breathe” – the growth and development of the bushes slows down. If you find black spots on cannabis leaves, you need to immediately rub them to remove plaque.
Mites attach to the plant from the back of the leaf and systematically suck out nutrients. On the outside at the puncture site, a small white or yellow dot first appears. If the bushes are affected by infectious and fungal diseases, the spots on the leaves will be much larger. Having noticed small dots-specks, you need to immediately inspect the inner surface of the leaves and take action if parasites are found there.
To combat insects, modern insecticidal preparations will help – they give a good effect, especially if you detect the spread of the pest population at an early stage. It is important to cultivate not only the leaves and stems of the cannabis plant, but also the soil around the plants, as well as the neighboring plants outdoors or the walls of the grow box for indoor growing. It is best to spray in several stages in order to affect the insects that emerged from the larvae after the initial treatment.
Nutrient Deficiency / Excess Symptoms
Leaf spots can also appear as a result of growing errors with the dosage and proportions of fertilizing, as well as with the pH level of the water for irrigation. These factors are related to each other. So, a lack of any trace element in a plant may be due to several reasons:
Underfeeding the plant (the grower does not fertilize with the desired element).
An incorrect pH level can contribute to poor absorption of various micronutrients necessary for normal growth and development.
An excess of some minerals in the bushes can interfere with the absorption of other vital substances. For example, excessive potassium content interferes with calcium absorption.
That is why it is important to give your plants a balanced composition of fertilizers, strictly adhering to the dosage indicated on the package. In this case, you need to monitor the pH level of the water.
Calcium deficiency usually manifests itself in the form of brown or yellowish spots during the active growing season of cannabis. A lack of calcium can lead to soil acidification and the use of improperly treated water (for example, passed through a reverse osmosis filter).
Lack of phosphorus will manifest itself as brown spots on plants that are at the stage of marijuana flowering – it is at this time that the need for this substance in bushes increases. First, the lower, old leaves are affected – before the spots appear, the leaves darken with a metallized shade, the veins turn red.
Overflowing plants or elevated pH levels can cause similar symptoms. If stains appear on the leaves caused by improper feeding and chemical burns, you need to adjust the pH level of the water for irrigation – for cannabis, this figure is 5.5-6.5. After that, the bushes should be spilled with the correct water to clear the soil and roots. Then you should start giving the bushes balanced fertilizers.
Tobacco mosaic virus stains
If you notice dark green spots on the leaves of plants, it is most likely that the tobacco mosaic virus has infected them. The spots can have a brown tint, affecting the leaves in fragments that often fold into patterns and resemble mosaics.
It is impossible to cope with the virus with the help of drugs, so the only way to fight is to remove the affected areas of the leaves or even completely the bushes. The main thing is to avoid contact with healthy plants. This virus can be transmitted through the contact of the leaves, through the tools and hands of the grower.
If you notice spots on cannabis leaves, you don’t need to panic. Whatever the reason, in most cases, the problem can be solved if the cause of the disease is correctly identified and measures are taken to correct the situation.