Symptoms of Gray Mold in Phalaenopsis and the Latest Control Methods

Orchid gray mold is also called orchid flower rot. This disease can break out in flower nurseries both in the north and the south. It mainly harms orchids (Orchidaceae), and among them it attacks horticultural treasures such as Phalaenopsis, Cymbidium hybridum and Cymbidium sinense quite severely, seriously affecting the ornamental value of these flowers. The following is a related introduction by Qinong Net on the symptoms and control of gray mold in Phalaenopsis.

Gray mold in Phalaenopsis mainly harms the floral organs, sepals, petals, and pedicels, and sometimes also harms the leaves and stems. In severe cases it causes spots on the flowers and gray mold everywhere, and since Phalaenopsis is an ornamental orchid, this is undoubtedly a devastating disaster.

I. Disease Identification

When Phalaenopsis is infected with gray mold, the affected leaves show brown diseased patches unevenly distributed on the back of the leaves, which affects the photosynthesis of the leaves and causes poor growth of the orchid. When the petals and sepals are infected with the pathogen, water-soaked, semi-transparent small spots appear on the petals and sepals at first, then the lesions turn brown and gradually expand into round patches, and the lesions merge with each other. After the disease develops, the entire flower turns dark brown with pink edges, rots and withers. When the pedicel is harmed by the pathogen, water-soaked small spots appear early on, then gradually develop into dark brown oval lesions, and after about a week the flower dies. Orchids that are harmed early on will have their flowers wither early and buds dry up. Orchids that open early are the most susceptible to gray mold.

II. Patterns of Onset

Diseased residues left in flower pots harbor a large amount of pathogens. When suitable temperature and humidity conditions are met, the pathogen spores will germinate again and become a second source of infection. When the disease occurs, the large number of conidia produced will again spread through airflow, rain, irrigation, or manual handling and touching. When orchids are grown in greenhouses in winter and spring, the temperature and humidity will both meet the conditions for the onset of this disease, with the temperature at around 18 to 25 degrees and the relative humidity at around 90 percent. This will easily trigger gray mold.

III. Control Methods

1. Choosing the Growing Medium

Phalaenopsis has epiphytic roots, which are fleshy aerial roots. Therefore the chosen medium must be air-permeable and have fertilizer-retaining properties. Commonly used media are sphagnum moss, coconut coir, pine bark, and so on. For base fertilizer, use decomposed farmyard manure, which can be slowly absorbed by the roots. What is often used is liquid fertilizer, diluted 1500 to 2000 times. Orchids grown in such a medium are robust and rarely develop the disease.

2. Pay Attention to Orchid Room Cleanliness

The place where orchids are grown should be kept hygienic, and the surrounding dead branches and rotten leaves should be removed as much as possible. When winter comes, the orchids should be moved indoors. Before moving them back, clean the room first, then clear away diseased flowers and leaves and disinfect with limewater, so as to reduce the base number of pathogens as much as possible.

3. Strengthen Management

When growing orchids, management must be strengthened and care must be meticulous, with special attention to indoor temperature changes and timely adjustment, and close attention to the growth of the orchids. Check regularly, and when diseased flowers and leaves are found, measures should be taken in time: wrap the diseased orchid in a plastic bag, take it outdoors together with the pot for disposal, and do not put it back in the greenhouse, so as to reduce pathogen infection. Carry out appropriate wind protection according to weather conditions.

4. Early Stage of Onset

Spray carbendazim over the whole pot to disinfect and sterilize. When placing orchids, do not keep them sealed off; there should be a certain distance between pots to prevent contagion, allow ventilation and light, and prevent water accumulation, which would increase indoor humidity. In daily orchid management, be careful and minimize wounds on the orchids, to prevent pathogens from invading through wounds.

5. Chemical Control

Agents such as carbendazim and chlorothalonil can all treat gray mold and can be bought at ordinary flower shops. When applying them, be careful to use them in rotation to prevent resistance from developing.

The above is the summary compiled by Qinong Net for everyone on the symptoms and control measures of gray mold in Phalaenopsis. It can be seen that because this type of disease is relatively common, the methods of prevention and treatment are fairly mature. Pay attention to observation during daily care, and use medication promptly after onset, and losses can be minimized.