Fungal Infection in Hydroponically-Cultivated Head Lettuce
In the world of greenhouse lettuce production, one of the most common threats is powdery mildew. This article provides a detailed guide on controlling this fungal disease, focusing on cultural practices, environmental management, and fungicide application.
Cultural and Environmental Control
A proactive approach to managing powdery mildew involves maintaining good air circulation and adequate sunlight. By pruning plants and growing them vertically, you can reduce humidity and leaf wetness favourable to the disease's development [2][3]. Additionally, it's essential to avoid moderate temperatures (60 - 80°F) and shade that favour powdery mildew. Instead, aim to keep the environment less hospitable to the fungus by managing temperature and light conditions [2].
Another strategy is to plant resistant lettuce varieties if they are available [2].
Fungicide Recommendations
When it comes to fungicides, it's crucial to use products specifically labelled for controlling powdery mildew on lettuce. Examples include Neem Oil, Safer Garden Fungicide, Serenade (a biocontrol product), sulfur-based products, such as Cosavet-DF Edge Sulfur, and Monterey Horticultural Oil [1].
Recently, Avelyo has been evaluated for potential control of powdery mildew in greenhouse hydroponic lettuce production, with attention to phytotoxicity, indicating it might be a promising option [1].
Always follow label recommendations for dosage, frequency, and safety when applying fungicides to lettuce, especially in greenhouses, to minimise risks and residues [4].
Summary Table
| Control Measure | Key Details | |------------------------------|----------------------------------------------------| | Environmental conditions | Avoid 60-80°F moderate temps and shade; improve air flow and sunlight via pruning/vertical growth [2][3] | | Resistant varieties | Plant if available to reduce disease risk [2] | | Fungicides | Neem oil, Serenade, Safer 3-in-1, sulfur-based, Avelyo (recent) - all labeled for powdery mildew [1][2][4] | | Fungicide use guidelines | Follow label instructions carefully to ensure crop safety [4] |
Implementing these combined strategies will help manage powdery mildew pressure effectively in greenhouse lettuce production. Always read the label and follow all guidelines when using a fungicide.
It's important to note that products labelled for control of powdery mildew on ornamentals may not be labelled for use on greenhouse vegetables. Older leaves and mature plants are usually affected first and become chlorotic and deformed, limiting plant growth and marketable yield.
Proper greenhouse ventilation to keep humidity levels low is a method for managing powdery mildew. Increased air movement within the plant canopy can also help manage powdery mildew.
Strains of G. cichoracearum can infect over 150 species, including other greenhouse crops in the Asteraceae family. Selecting lettuce varieties less susceptible to powdery mildew can help in its control. Leaf and butterhead lettuce types show more resistance than romaine and crisphead lettuces.
Finally, remember that free water on plant surfaces prevents spore germination and infection for powdery mildew.
[1] Scheckelhoff, B. (2019). Powdery Mildew on Greenhouse Lettuce: Evaluation of Avelyo for Control in Hydroponic Production. [online] Ohio State University Extension. Available at: https://extension.osu.edu/sites/extension/files/2019-08/Powdery_Mildew_on_Greenhouse_Lettuce_Evaluation_of_Avelyo_for_Control_in_Hydroponic_Production_0.pdf [Accessed 21 June 2023].
[2] University of California. (2019). Powdery Mildew on Lettuce. [online] UC Davis. Available at: https://cecentral.ucanr.edu/files/310321.pdf [Accessed 21 June 2023].
[3] University of Florida. (2019). Powdery Mildew Management in Greenhouse Crops. [online] University of Florida. Available at: https://edis.ifas.ufl.edu/pdffiles/PP/PP34500.pdf [Accessed 21 June 2023].
[4] Syngenta. (2018). Lettuce Fungicides: Choosing the Right Tool for the Job. [online] Syngenta. Available at: https://www.syngenta.com/en-us/agriculture/crop-solutions/vegetables/lettuce/lettuce-fungicides.html [Accessed 21 June 2023].