Progress of Seedlings in Greenhouses
The 2023 greenhouse season is progressing, and it has been characterized by few warm days and many cool and cloudy days. Nevertheless, most greenhouses have good seed germination and seedling uniformity. Based on the greenhouses that the CTRF has visited, seedlings between farms do vary in size depending on the type of production method being used and when seeding was started.
Preventative applications of the fungicide for the control of Rhizoctonia Damping-off in greenhouses has occurred, and clipping is underway.
Some of the problems that have been reported so far include algae on media surface (float trays) and chilling injury.
Effects of Algae on Seedlings in Trays
Certain algae present on the surface of tray media can affect seedling emergence and establishment. Two situations are usually seen in these cases, one where the seedlings are not able to emerge through the algae and the other being where the seedlings emerge but cannot establish themselves before succumbing to the algae and dying (as shown below).
Cool and cloudy weather conditions are ideal for algae growth, and there are no chemical treatments for algae in tobacco greenhouses. Conditions that are optimum in the greenhouse for rapid seed germination and early seedling growth help seedlings to outpace the algae so that the seedlings become large enough that the algae can no longer affect them. As seedlings grow, the canopy will close over and shade the media surface, therefore, reducing the negative effects of algae. At this time, in some greenhouses, the after-effects that algae can have on young seedlings in trays are evident and are characterized by significant stands reduction and uneven seedling growth.
Chilling Injury
Chilling injury is being observed in some greenhouses. Chilling injury is caused by exposure of the seedlings to a large variation in air temperature, such as when ventilation occurs on a very cool but sunny day or at night when the temperature outside is quite cold and the temperature drops significantly in the greenhouse because the heaters do not have enough capacity to maintain the set temperature.
The initial symptoms of chilling injury are often a bright yellow colour in the growing point of the seedling and upward cupping of the leaves, as shown in the image below.
As the seedlings become larger and the leaves grow out, some leaves become malformed, cupped, and have a distinct yellow/white discoloration. Seedlings do outgrow chilling injury without any ill-effects on the seedlings when transplanted to the field. However, when chilling injury affects the seedling growing point, the plant responds by producing lateral growing points, (suckers), which affects the quality of seedlings.
Clipping Tobacco seedlings in Greenhouses
Currently, clipping of seedlings is taking place in most greenhouses. Be on the lookout for the occurrence of Bacterial Soft Rot (also known as Blackleg), a disease that occurs in both float and dry trays greenhouses during clipping. Bacterial Soft Rot starts when leaf debris fall back onto the seedlings from the clipper, becoming a food source for the bacteria. Factors such as, warm temperatures, high humidity, extended periods of leaf wetness, high nitrogen levels and plant injury (by stress or wounding) contribute to Bacterial Soft Rot spread and outbreaks in greenhouses.
Bacterial Soft Rot infects tobacco seedlings in both dry cell and float trays and has the potential to destroy large numbers of plants in a brief period of time. Initially, the bacteria colonize wounded tissues, organic matter, and debris in trays. Leaves touching the surface of a tray can become infected and the rot can spread through the petioles into the stem of the seedlings.
Infected seedlings transplanted into the field may not become well established and may not survive. There are no control agents registered for control of Bacterial Soft Rot in tobacco greenhouses. Removal of trays with the diseased seedlings from the greenhouse and replacing them with blank trays is the best control in this situation. Other practices for control include trying to keep leaf debris from the clipper out of the beds, not clipping when the leaves are wet, not over-fertilizing, keeping the foliage of the seedlings as dry as possible, and ventilating the greenhouse adequately to keep the humidity level down in the greenhouse.
Tobacco fields Soil fumigation
Soil fumigation in preparation for the season has started. It is important to remember that cooler temperatures and rainy conditions that have been occurring lately may impact the performance or efficacy of the soil fumigants.
When applying fumigants, ensure that the soil temperature and soil moisture are in accordance with the label requirements/recommendations for the specific soil fumigant that is being used. As we get closer to planting season, please note that different soil fumigants may require different time intervals between fumigation and transplanting.
Please follow the label associated with the soil fumigant that was used and refer to the product label for more information.
Post prepared and sent by Canadian Tobacco Research Foundation
Mailing Address: CTRF, P.O. Box 322, Tillsonburg, ON N4G 4H5
Telephone: 519-842-8997
Web Address: http://ctrf1.com