With proper care, any plant, including hemp, will look attractive outwardly: this is expressed in a healthy and rich color of foliage and inflorescences, as well as in the strength and elasticity of the stem and branches. Any problems associated with the health of a plant cannot but affect its appearance. If the plant is sick, its leaves begin to change color, become stained, deformed and dry. The main thing in this case is to timely and correctly determine the cause of certain violations. This is the only way to help plants restore their previous healthy appearance.
The main causes of cannabis diseases can be roughly divided into 3 groups:
Deficiency or excess of nutrients;
Parasitic organisms, infections and fungi.
Incorrect setting of the internal climatic parameters of the system
Most marijuana strains grow best in temperatures ranging from 18˚ at night to 28˚ during the day. Only a few sativa cannabis varieties prefer temperatures a few degrees higher (20˚ – 30˚). Deviations from these conditions can lead to plant health problems.
An increase in temperature can lead to overheating or thermal burns, while the leaves begin to curl or dry out. This happens especially quickly at high humidity.
With a decrease in the thermometer, a blockage of phosphorus can occur, which outwardly usually manifests itself in a change in the shade of the foliage to purple. Low temperatures, especially when combined with high humidity, can trigger various fungal infections.
It can be difficult to adjust the temperature regime, but it is extremely important to do it. Adjusting the ventilation or changing the lighting fixture to a more suitable one and emitting the required amount of heat will help to solve the problem.
It is imperative to choose the right lighting: it should be strong enough but should not exceed 800 W / m2. Otherwise, the hemp will receive a light burn, which manifests itself in the yellowing and drying of the leaves. This problem is solved by reducing the power of the lamps (in case of an overabundance of light), or by adjusting them over the plants.
Watering and moisture problems
If the plant gets too little or too much liquid, it can cause problems and slower development. Outwardly, the symptoms of underfilling or overflowing cannabis may be slightly similar, however, when overflowing, the tips of the leaves first fade, while from underfilling the foliage begins to sag at the base. Moreover, some leaves may dry out when underfilled.
Deficiency of essential nutrients
Nitrogen is one of the most important macronutrients in the life of cannabis, especially during the growing season. Lack of nitrogen negatively affects the development of the plant – the formation of chlorophyll is hindered, which manifests itself in the loss of the green color of the leaves and their yellowing. In this case, the old lower leaves are the first to suffer. This process is only normal before the marijuana harvest, which signals maturation. In other cases, it is necessary to fertilize with nitrogen fertilizers.
Phosphorus is essential for good flowering. Its deficiency negatively affects the health of plants, their development and productivity. Outwardly, it can be identified by the darkening faded foliage, acquiring a bluish tint, the veins and petioles of the leaves become violet-purple, the stem becomes weakened. In addition, the leaves sometimes begin to curl, and dark necrotic spots may appear on their surface.
Cannabis needs potassium throughout its entire life cycle. Its deficiency is also characterized by a general weakened appearance of both leaves and stem. The bronze tint acquired by the leaves helps to distinguish this problem from others. The leaves begin to curl, their edges turn brown and die off, with the lower leaves being the first to suffer. There is a slowdown in the growth or flowering of cannabis.
Lack of micronutrients
Calcium is extremely important for the structure of cells, it gives hemp tissue strength, stimulates healthy growth. Calcium deficiency appears primarily on young hemp leaves, they curl and die off, irregular yellow-brown spots appear. At the same time, growth slows down or stops significantly.
The first signs of a lack of sulfur appear in the blanching of young leaves and new shoots. Overall growth slows down, the leaves turn yellow, become more fragile and narrow. Unlike magnesium deficiency, which develops from the tips of the leaves, sulfur deficiency starts from the back of the leaf and moves to the middle.
First of all, young leaves react to a lack of manganese – a yellow or brown spotted bloom may appear on them. Sometimes the leaves begin to turn yellow, while their veins remain green. Progressive deficiency of manganese leads to the death of yellowed areas and the curling of leaves inward.
With a copper deficiency, hemp leaves lose their elasticity and look weakened, their color becomes much less saturated, and growth slows down significantly. The tips of the leaves turn gray and die off. Young shoots look underdeveloped, bent and can also die off.
Iron deficiency is identified by whitening foliage and begins with the lower and middle leaves. New leaves appear with necrotic spots and suffer from chlorosis from the base of the leaf. Growth slows down noticeably.
This element plays an important role in the vascular structure of plants, contributes to normal metabolism and general development. Magnesium deficiency can be identified by the yellowness spreading from the leaf veins. The disease spreads from the older lower parts of the plant to the younger upper parts. At the same time, new shoots can acquire a pale green tint.
The painful symptoms of plants are very similar with both a lack and an excess of chlorine. The leaves acquire a bronze tint, turn pale, their edges die off due to burns.
It is not always easy to pinpoint the cause of leaf disease, since with a deficiency or excess of certain substances, the plant may exhibit similar external symptoms. From a lack or excess of one element, the assimilation of other substances can be hampered or blocked. In any case, it is much easier to solve the problem associated with a deficiency of certain substances than in the opposite situation. Therefore, it is better to try to make complementary foods with nutrients smoothly and constantly observe the plants and the changes that occur to them.
Problems caused by fungi and parasites
Most often, fungal infections occur at low temperatures (less than 18 degrees) and high humidity (more than 70%) and weak air circulation.
Fungal diseases include: rhizoctonia, fusarium, powdery mildew, black mold, etc. The external signs of such diseases are manifested in the appearance of white, gray or almost black bloom on the tips of leaves and cones. At the same time, starting from the tips, different parts of the plant begin to discolor, acquiring gray shades. With the development of the disease, individual branches begin to die, dry out and break.
To combat fungi and mold in hemp, there are many different fungicidal agents, with which it is also possible to carry out preventive treatment of plants to protect against diseases. Sometimes it is better to remove the affected plant parts so that the disease does not spread.
Maintaining normal conditions in the greenhouse is also very important for maintaining plant health. Hemp is most at risk of contracting a fungal infection during the flowering stage, so during this period you need to be especially careful to monitor the temperature and humidity, as well as to ensure good air flow to the plants and ventilation of the grow box. Outdoors, bush shaping techniques can be used to better airflow around all parts of the plant.
Most of the pests that infest cannabis settle on the underside of the leaf, less often on other parts of the plant. In this case, convex points and various deformations may appear on the leaves. The most common pests are spider mites, whiteflies, aphids and other insects.
Also slugs are very fond of cannabis, abundantly eating up its foliage. Outwardly manifests itself in numerous uneven holes on leaves of different sizes.