Lavender diseases
The main problems in the cultivation of lavender are caused by fungi and fungal-like organisms. The most common Lavender diseases are: phytophthora, gray mold and seedling rot.
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Phytophthorosis
It is one of the most dangerous diseases of lavender and can occur at any stage of the cultivation of this plant. During rooting, the leaves on individual cuttings turn yellow, wilt, turn brown and die.
A brown necrosis spreads from the base of the seedling towards its upper parts. After removing the young plant from the ground, root rot is visible. On older plants, single shoots are stunted in growth, turn yellow, gray, brown and die, and at their base there are browned and dead tissues.
The root system is necrotized and when you knock the plant out of the container with a gentle pull, it breaks down very easily.
The perpetrator of the disease develops in the substrate from which it infects the roots and the base of the shoot. It can survive in the substrate on plant debris for many years, thanks to its spore forms.
Lavender diseases – contaminated water
The most common sources of phytophthora in cultivation are:
- diseased starting material (although initially the plants may not show any disease symptoms);
- medium reused for lavender production, without prior disinfection;
- water for watering or sprinkling seedlings or seedlings, as well as plants planted in production pots.
Usually it is water from nearby watercourses or ponds contaminated with spores of the pathogen. Ideal conditions for the development of phytophthora also prevail in facilities where lavender is grown on flood tables or gutters with a closed circulation of water and fertilizer.
Pathogens can also spread on tools during maintenance work. The perpetrators of phytophthora hibernate in the ground, on plant debris in the form of oospores, chlamydospores or hyphae.
Prevention and protection against Phytophthora
- Decontaminate beds, growing tables, walkways and greenhouse or tunnel structures before starting the production cycle. Only healthy starting material should be used for planting.
- In facilities where lavender is grown, water or nutrient solution should be supplied individually to each plant, or drop by drop, which significantly reduces the risk of disease.
- When symptoms of phytophthora appear, remove infected seedlings, seedlings or older plants; the remaining ones must be thoroughly sprayed with an antifungal agent
Gray mold
Its symptoms may occur on plants at any time, as long as the environmental conditions favor the development of the pathogen (this fungus grows commonly as a saprotroph on dying plant residues and is ubiquitous in horticultural facilities under cover).
Water-soaked, later brown, rot spots appear on the lower leaves of the lavender infested with gray mold and those in the center of the leaf rosette.
Sometimes necrosis begins at the apex of the shoot, and other times – at its base. The tops of young dead shoots bend downwards in a characteristic way. With time, individual shoots and even plants may die.
Lavender diseases – contaminated soil
At high air humidity, a gray dusting coating is visible on the surface of the dead tissues. In the life cycle of the fungus causing gray mold, there is a sack stage and a conidia stage.
On the sclerotia (spore forms of the pathogen composed of hyphae), cup-shaped apotheias are formed, which contain bags with spores. The released bag spores are carried by air currents to neighboring plants and infect them.
A profuse gray bloom is formed on the surface of decayed tissues when the air humidity is high. The released conidial spores are transferred to neighboring plants and infect them at the sites of minor wounds or through undamaged skin.
Conidia spores germinate in a drop of water, and then the hyphae of the fungus penetrates the plant tissues.
After a few days, the first symptoms of the disease appear – in the form of brown watery spots. With a decrease in air humidity, dead tissues become dry.
Sometimes the fungus forms black, shiny sclerotia several millimeters in diameter. It winters in the form of sclerotia or on diseased plants.
Gray mold prevention and protection
- Do not allow too high plant density, especially in the autumn and winter season, when there is insufficient light
- Provide good air exchange around the plants; ventilate rooms where lavender is grown
- Cut and burn diseased plant fragments
- Avoid wetting the leaves when watering the plants
- When symptoms of gray mold are found, spray the plants twice every 7 days using fungicides
Rotting of seedlings
This disease occurs on many plant species during the rooting period of cuttings, including lavender. Then, from the base of the seedling upwards, a dark brown necrosis spreads over the shoot.
Roots turn brown and die. Diseased rooted seedlings or young plants permanently planted have chlorotic leaves and stunted growth, and then die.
Pathogens that cause this disease develop in the medium from which they infect seedlings. Water used for watering or sprinkling seedlings can also be a source of pathogens. On the surface of dead tissue
Pythium forms a delicate white mycelial bloom. In turn, fungi of the genus Fusarium form a white mycelium with orange sporodochia (sporulation clusters) on the surface of dead tissues.
The formed and released spores move with the water in the substrate or with drops of water splashing during watering, as well as with air currents or dust, and infect neighboring seedlings.
In the case of the Rhizoctonia solani pathogen, its mycelium and quasi sclerotia can be transferred on dried substrate particles with air currents or on used and uninfected containers or tools.
This fungus grows best in the top layer of the substrate, to a depth of 5-10 cm, with plenty of air.
Seedlings rot prevention and protection
- Take seedlings only from healthy mother plants
- Root them in a freshly prepared substrate
- Systematically remove and burn diseased seedlings
- Before bringing rooted cuttings or seedlings into the production facility, decontaminate beds, growing tables, walkways and the greenhouse or tunnel structure
- During the production of seedlings, rooting cuttings and after planting them, remove diseased plants immediately after noticing symptoms
