Probably the most common disease for lily growers, botrytis is a fungal disease which affects the stems, leaves and in extreme cases, the flowers and buds of lilies as well. It is not restricted to affecting lilies, it affects a wide variety of other plants and crops as well, such as canola and annual bedding plants.
Botrytis is spread by spores located on the undersides of the leaves, on the ground, and in old garden debris. The spores are spread by wind and rain or water splashing, and are encouraged by damp, wet and humid conditions. Often botrytis starts after frost, hail or other exterior damage is experienced by the plant, or during extended periods of rain and damp weather. Once it starts, and if favorable conditions persist, it moves like wildfire through the lilies. Beginning as a small white or brown spot on a leaf or bud, the spot grows into a larger brown spot with a lighter center, until it engulfs the entire leaf and then the stem and buds, if action is not taken. The damage can be held back or avoided using preventative sprays of chemical or organic nature.
This fungal disease is limited to the plant growth above ground, and does not carry over into the bulb from year to year. How does botrytis affect bulb growth? If the stems are completely affected and totally brown to the tip early in the summer, the bulbs will simply not increase in size, and it will sprout and grow again the next year. Botrytis only affects bulbs if experienced 3 years in a row, under extreme conditions where the stems are totally brown by mid summer. The following year the bulbs will fail to sprout, their quality seriously deteriorated due to the ongoing disease.
To prevent botrytis it is best to remove and burn all garden debris, meaning dead stems and leaves, every season. Spray the ground around your lilies early in spring with a preventative spray such as our Baking Soda recipe, or Bordeaux Copper Spray, a commercial fungicide readily available at most garden centers. Since the chances of botrytis infection increases after damage to the stems or leaves, spray immediately after frost or hail damage has occurred, and every 2 weeks thereafter, until the middle of August, when stems may begin to naturally die down. If you have access to farm chemical sprays, the most recommended product to use for botrytis on your lilies is a systemic product called ROVRAL, and works very well in effectively stopping the spread of botrytis once applied. For those who prefer not to use chemicals, check out our fungal recipe page, or our Botrytis Control page.