Fungal Diseases - Botrytis cinerea
Learning to read your plants is a fantastic skill to have as an orchid grower and one that comes with time and experience. The ability to spot a problem before it becomes a major issue can save you much heartache. We recommend having a brief look at your plants nearly every day to check things are OK. We look for bulb shrivel, marks on the leaves, insect damage, spikes appearing (always a joy), and new root tips to tell you when to re-pot. Each month we will be sharing some snippets of wisdom from the Tuckers experts to help you along your way.
Fungal Diseases - Botrytis cinerea
As orchid growers we need to face the fact that at some point we are likely be faced with pests and diseases appearing in our beloved orchids - try as we might to avoid them. As seasonal changes affect our growing environment, and as we learn more about caring for our orchids, we have the potential for the development of a variety of fungal diseases. Right now we are seeing frequent occurrences of Botrytis cinerea, otherwise known as Grey mold or snow mold; a fungal disease that usually occurs in colder climates and when the air becomes stagnant and damp.
Causes can be many and varied and can include:
- The chief cause is standing air and very high humidity
- Insufficient light reaching plants
- Unbalanced feeding, with too much Nitrogen
- Salt built up by not flushing your Orchids
- Older potting mixes that are starting to decay.
- A too high salt content in cheaper potting mixes as well as potting mixes with too much wooden compounds (above 25%) or compounds that are not fully composted (here we are talking in general as there’s a wide variety of potting materials that orchids are grown in, mimicking their natural growing conditions)
Botrytis loves soft tissue, in particular white flowers are very prone to it…as white is not a colour as such, but is in fact “empty” tissue with no pigments in it. The see-through tissue becomes white only by the refraction of light. You often see Botrytis occurring on these vulnerable white blooms (as pictured) after only one or two nights in which a high humidity condensates below the dew point. It occurs initially as little round, greyish spots, and will eventually darken into black spots over time as the disease develops. This fungal disease does spread quickly in plants and becomes easily resistant against spray chemicals.
- Optimising the overall growing conditions by increasing venting during the day; this is achieved by opening your homes windows (if an indoor plant) or opening the greenhouse roof / top vents, and by leaving a small gap close to the roof overnight (where possible) to allow the excessive humidity to escape. Add a fan to the area to increase air movement
- If possible, start earlier heating to increase the temperature to above the dew point, this will avoid the humidity forming condensation droplets on the plant surfaces. Plants are usually cooler due to their metabolism which is why the condensation forms on them.
- The main aim is to equalise the growing climate by having sufficient heating and venting both during the day and at night, to avoid temperature and humidity spikes in either direction.
- Flush your potting mixes regularly with clean rain water where possible e.g. once monthly, to prevent salt build ups. Mains water usually has a higher PH and a high level of Sodium Carbonate, most orchids like it around 6, too much on Sodium Carbonate will give you brown tips.
- Moist or damp surfaces, not enough light and low air-movement provide an ideal environment for the growth of fungal disease, so we recommend changing your schedule to water in the morning to avoid damp fungal breeding grounds overnight.
- You can treat with FreeFlo Copper as a preventative and to halt spread of the disease through the plant, we have this available in store and online. It is important to note that any plant damage is permanent, so you won’t see an improvement in your existing damaged flowers post-treatment. You may like to consider cutting off heavily damaged flowers, to further minimize infected tissue being around other plants.
- Don’t overdo the spraying, as too many applications of Copper or reapplying treatments in a too short a period, can damage your plants.
- A maximum of 3 applications is recommended; with the 2nd application not earlier than 7 to 10 days after the first application, and then leaving a gap of at least a fortnight before 3rd application.
- You can run another spray cycle several weeks later, if needed.
- To be effective, a treatment with Copper needs to see temperatures around 15C for most of the time.
- Copper itself will stop fungal infections as well as building a protective barrier on the plant surface, so it is good as a preventative measure as well as a treatment.
- Copper was and is still used as Bordeaux broth or Bordeaux mixture in agriculture, vineyards and nurseries. It is s a mixture of copper sulphate and slaked lime invented by French farmers to combat fungal infections and parasitic bacteria. If the preparation is well done, it is a fungicide resistant even to rain because it adheres strongly to the plant. Our Product, FreeFlo Copper, is of course easier to mix and use.
- It is good to keep in mind that Bromeliads don’t stand Copper at all!
As with any fungal disease (and in fact for general plant health), always remember to keep your work environment clean and tidy to prevent spread of disease, keep weeds under control and sterilise your equipment and work bench between plants.