Snapdragons remain a popular bedding plant and one of the most popular cut flower crops for growers selling directly to local wholesale and retail florists. While there are several pests and diseases that can adversely impact this crop, some growers have been seeing snapdragon rust in their greenhouses and high tunnels this spring.
Snapdragons by their very nature produce the highest quality flowers when grown under cooler temperatures. Unfortunately, the pathogen that causes snapdragon rust, Puccinia antirrhini is favored by 550F to 700F temperatures, but it is also inhibited by temperatures above 800F. Symptoms of snapdragon rust are very subtle at first. Growers may observe small yellow or chlorotic bumps or swelling on the leaves. The upper leaf surface will develop yellow spots and the lower leaf surface will be lined with concentric rings of reddish-brown pustules that have emerged through the ruptured epidermis.
Wind borne spores, infected cuttings, or plugs can be a source of snapdragon rust in greenhouses and high tunnels. In my area, specialty cut flower growers overwinter snapdragons in their high tunnels. These overwintering snapdragons frequently are the source of infection on many operations. The cool conditions in the high tunnel coupled with the limited management of the crop under row covers creates a petri-dish like environment for Puccinia antirrhini to thrive undetected. As vents are opened in greenhouses and sidewalls are rolled up on high tunnels wind-blown spores can make their way from the infected plants in the high tunnel to the plants in the greenhouse.
Growers that have had a history of snapdragon rust in their operation should consider the following cultural practices:
- Start snapdragons from seed.Puccinia antirrhini can be carried on the seed and on seed pods, but it will not be found in the seed.
- Purchase and use pathogen-free snapdragon cuttings,plugs, or plants in your operation.
- Increase plant and/or pot spacing to encourage more airflow and faster drying times.
- Avoid overhead irrigation and water early in the day to allow for the plants to dry before sunset. *Puccinia antirrhini requires that plants be wet for 6-8 hours for infection to occur.
- Run the greenhouse slightly warmer at 700F for several days and do not allow the night temperature to fall below 600F.
Fungicides can be an effective management tool in preventing snapdragon rust if cultural controls have proven ineffective at your operation.In selecting fungicides please rotate products with different modes of action (different FRAC codes) and consider the re-entry intervals for the fungicide products that will be applied. Also, before purchasing or even deploying a specific fungicide in your operation review the label carefully. Please be aware that some fungicides may injure certain snapdragon cultivars if the higher labeled rates are utilized.
Translaminar fungicidal products may offer the best protection against snapdragon rust in greenhouses and high tunnels. For specific fungicide recommendations please contact your local Extension Educator to determine what is labeled in your state or please contact Penn State Extension Educator, Tom Ford at [email protected].
Source: eGRO Blog (Thomas Ford)