Delmarva Farmer Columnists
Producing, sourcing quality transplants (March 11, 2014)
Transplant production is underway throughout the region.
Cabbage, tomatoes, peppers, watermelons, cantaloupes, cucumbers, squash, lettuce, and even pole lima beans are commonly transplanted along with many other vegetables.
Producing quality transplants starts with disease free seed, a clean greenhouse and clean planting trays.
Damping off diseases and root rots (such as Pythium) can be a problem where trays are reused, benches are not clean, or trays are placed directly on the floor.
Buy disease indexed seeds when available.
To reduce bacterial seed borne diseases in some crops such as tomatoes, peppers, and cabbages, seeds can be hot water treated.
Chlorine treatment can also be useful on some seeds as a surface treatment but will not kill pathogens inside the seed.
For greenhouse growing areas, clean floors and benches thoroughly of any organic residue.
Use a disinfectant applied to surfaces to kill pathogens.
Choices are: quaternary ammonium products, diluted chlorine bleach, hydrogen dioxide products and pyeroxyacetic acid products.
An important consideration is managing stretch or height of transplants.
The goal is to have a transplant of a size that it can be handled by transplanters without damage and that have reduced susceptibility to wind.
Managing transplant height can be a challenge.
Only one growth regulator, Sumagic, is registered for use as a foliar spray on tomato, pepper, eggplant, groundcherry, pepino and tomatillo transplants.
For other crops alternative methods for height control must be used.
One method that is successful is the use of temperature differential or DIF, the difference between day and night temperatures in the greenhouse.
In most heating programs, a greenhouse will be much warmer in the daytime than nighttime.
The greater this difference, the more potential for stretch.
By reducing the day-night temperature difference, or reversing it, you can greatly reduce stem elongation.
The critical period during a day for height control is the first two to three hours following sunrise.
By lowering the temperature during this 3-hour period plant height in many vegetables can be controlled.
Drop air temperature to 50-55 degrees F for two to three hours starting just before dawn, and then go back to 60-70 degrees.
Vegetables vary in their response to DIF. For example, tomatoes are very responsive, squash is much less responsive.
Managing water can be a tool to control stretch in some vegetables.
After plants have sufficient size, allow plants to go through some stress cycles, allowing plants to approach wilting before watering again.
Be careful not to stress plants so much that they are damaged.
Managing greenhouse fertilizer programs is another tool for controlling height. Most greenhouse media comes with a starter nutrient charge, good for about two weeks.
After that, you need to apply fertilizers, commonly done with a liquid feed program.
Greenhouse fertilizers that are high in ammonium forms of nitrogen will cause more stretch than those with high amounts of nitrate nitrogen sources.
Fertilizers that are high in phosphorus will also tend to lead to stretch.
Exposing plants to outside conditions is used for the hardening off process prior to transplanting. You can also use this for height control during the production period.
Roll out benches that can be moved outside of the greenhouse for a portion of the day or wagons that can be moved into and out of the greenhouse can be used for this.
Many growers choose not to produce their own transplants but contract with greenhouse growers locally or in the south. The majority of these transplants are of high quality and perform well in the field.
However, each year, there are some shipments that have problems with them. The most common problem is transplants shipped before they are ready — without adequate root systems.
These transplants will not perform well in the field, especially in earlier plantings. If possible, they should be placed in a greenhouse to finish growing before use.
Another issue is diseases. Many of our vegetable disease problems including bacterial spot, bacterial speck, bacterial canker, gummy stem blight, bacterial fruit blotch, and tomato spotted wilt virus, impatiens necrotic spot virus, and Alternaria blight can start in the greenhouse and be carried to the field. A number of virus diseases are transmitted by greenhouse insects.
If a disease is suspected on purchased transplants, have it quickly diagnosed and inform the appropriate section of your state Department of Agriculture.
Do not plant diseased plants in the field.
USDA working together for ag industry’s future ... (March 11, 2013)