The dropping of buds as they form may occur if the plant is under some form of stress, such as excessively high temperatures, especially if accompanied by low humidity.
Over watering or rapid changes of temperature are other causes. Large-flowered Tuberhybrida can make difficult houseplants because of the lack of both ventilation and humidity, so bud drop is common when plants are taken indoors for more than a day or two at a time.
Outside, bud drop is not so prevalent, although it will occur in hot, dry conditions. Every effort must be made to keep the humidity high, with pebble trays filled with water or humidifiers in conservatories, or by wetting the floor in the shade house or greenhouse in the morning or early afternoon.
Corky scab (edema)
This condition gives the appearance of a pale brown, cork-like scale on the plant stems and the underside of young leaves. It should not be confused with marking left by mites-corky scab is coarser and covers areas rather than appearing in the form of lines.
The cause is often over potting. When a young plant is over potted, its small root system is unable to cope with the amount of moisture available in the mix. The leaves try their best to transpire this moisture, but there is so much that their cell structures burst, leaving the brown corklike appearance.
In turn, since the plant can now cope with even less moisture because of the damaged leaf cells, the soil becomes even more waterlogged, resulting in the actual drowning of the roots. No oxygen is able to get into the mix, which in turn reduces the plant’s ability to function. If continuously exposed to excess moisture, the roots will rot, causing the plant to die.
Foliar petal is a condition where green, leaf-like petals replace the actual dorsal or guard petal of the flower buds, giving the appearance of a leaf rather than the normal petal. This often happens on the first few buds of the season, with subsequent flowers being normal, and is more prevalent on the paler white and yellow varieties.
The condition is not caused by any pest or disease but is thought to result from overfeeding-particularly with nitrogen-in the early stages of the plant’s growth, although there is no scientific evidence that this is so. Any affected buds should be removed.