Plant diseases

🌐 🇫🇷 FR · 🇬🇧 EN · 🇩🇪 DE

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Guide to identifying pests, diseases and deficiencies

FR - Access this guide to help you diagnose them by clicking this link.

DE - Access this guide to help you diagnose them by clicking this link.

Protect your plants against disease

Control the temperature/humidity in the greenhouse
Keep the door open during hot periods. Maintain slight ventilation during humid periods to limit the rise in humidity in the greenhouse, because plants transpire, even when the weather is cool outside! During cold periods, you can use a pellet stove and/or plant only winter crops. In general, growth in the greenhouse will be slower during this season.

Nutrient deficiencies cause diseases
Make sure to supplement your system according to the deficiencies observed.

Ecosystem and seeds
A diverse plant ecosystem that includes flowers will naturally tend to be more resilient. Work with controlled seeds and healthy young plants. Heirloom varieties are not suitable for soilless cultivation; choose selected organic varieties instead.

Powdery mildew

Symptoms
A pathogenic fungus with a white powdery appearance on the surface of leaves and flowers. It causes yield losses and affects plant quality.

Solution
Prepare a potassium bicarbonate spray (or sodium bicarbonate if that is easier for you to find). Simply add 5g / L and spray onto the leaves.

• Potassium bicarbonate 0.5% as a spray (5g/l to spray on the leaves)
• Micronized sulphur (avoid if beneficial insects are present)
• Fennel oil (effective only when disease pressure is low),
• Lecithin (e.g. soy)
• Orange essential oil extracts (dehydrates spores, very precise dosage, careful application over the entire plant surface)
• Copper (preventive use only, otherwise limited effectiveness)

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Potassium bicarbonate treatment

If the disease persists after two to three weeks, increase to a concentration of 10g/L.
Do not start with this concentration, as it could burn the plants.

Downy mildew

Symptoms
Appears in cool, humid weather. Initial symptoms include large, angular or blocky yellow areas visible on the upper surface. As the lesions mature, they develop rapidly and turn brown.

Prevention

• Choose resistant varieties (especially for growing conditions during humid spring / autumn periods)
• Aerate and ventilate the greenhouse to limit excess humidity in the air
• Do not plant too densely
• Avoid watering the foliage
• Remove affected parts
• Apply copper-based preparations

Solution
There is no easy cure, so focus on prevention.
Same treatment as for powdery mildew using an alkaline solution.

Root rot (phytophthora, etc)

Symptoms
Phytophthora are parasites that develop in suffocating soils / substrates (excess water, heavy soils). Plants affected by root rot cannot absorb water and nutrients from the soil properly. The roots look brown and are soft. The above-ground parts of the plants seem to suffer from drought. Signs of root rot in plants include stunted growth, wilting and foliage discoloration. If you pull an affected plant out of the ground, you will find that the roots are brown and soft instead of firm and white.

Prevention

• Avoid excess moisture around the roots (growing beds)
• Water preferably in the morning (growing beds)
• Avoid soil splashing onto the plants (growing beds)
• Avoid excess fertilization (growing beds)
• Maintain good hygiene
• Increase fish tank aeration

Solution
There is no easy cure, so focus on prevention.

Stem rots (rhizoctonia, fusarium and pythium)

Symptoms
It is difficult for an untrained eye to distinguish between these different fungi. The different pathogenic fungi have been grouped into this same category because the symptoms and development conditions are almost identical at first glance. Plants generally show partial wilting of the foliage, then total wilting depending on the severity of the contamination. The plants will be very thirsty in the middle of the day and may recover at night. The roots are brown, with limited development, or even dead. In some cases, the vessels inside the roots, stems and leaves turn black. The plants yellow and die.

Prevention

• Avoid overwatering (growing beds)
• Prefer watering in the morning (growing beds)
• Limit root injuries
• Avoid excess nitrogen fertilization (growing beds)
• Remove diseased plants
• Maintain good hygiene
• Incorporate bacteria that are beneficial for plant growth.

Solution
There are few curative solutions that are not dangerous for the environment. Removing the diseased plant to avoid contaminating healthy plants remains the best solution.