Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
With the first hot days of spring, planting is progressing at a rapid pace. With each new planting season there will be reports of poor stands or stand losses in vegetable crops. The culprits are often soil insects or diseases; however, poor quality seed or plants can also be a source of the problem. You will most commonly see problems with poor quality plants or seeds when there are adverse weather conditions after planting.
Seed Quality Problems
As we progress into the warmer part of the planting season, it is often assumed that late spring and summer plantings will not have stand issues as soil temperatures are warm and seeds should germinate and emerge quickly and plants should root out quickly if there is adequate moisture. With seeds, this is not always the case, especially if seed lots are of low vigor. Signs of low vigor seed will be abnormal appearance in the bag (shriveled, cracked, off color, misshapen), small seedlings that emerge late or do not emerge at all, abnormal growth (twisting, snaking, or corkscrewing), small shriveled cotyledons in beans, small or distorted true leaves, swollen or split hypocotyls or coleptiles, and bleached out seedlings. Another issue affecting seed germination and emergence can be uneven or inadequately applied seed treatments (fungicides and insecticides).
Seed companies do a very good job of producing quality seed and most seed is produced in drier areas where seed diseases are limited. Once seed is harvested it is conditioned, treated, packaged, and stored. As seed is distributed it often goes through several phases of where it is handled and stored in different environments. Larger lots may be broken in to smaller units and then repackaged by resellers. Once seed arrives at the grower it will be stored and handled again, finally making it to the planter or greenhouse for transplant production. In each new storage and handling activity, there is potential to do damage to the seed. Rough handling, high temperatures, and high humidity are particularly damaging to seeds.
Poor quality seed can lead to poor stands even under higher soil temperatures.
Transplant Quality Problems
Poor quality plants can be due to diseases or other pest damage. There are however other causes of quality issues in plants such as being poorly hardened off, overwatered, stressed, over or under fertilized, overgrown or leggy, over mature, or root bound. Chemical phytotoxicity can be another problem. As with seeds, improper plant handing can lead to quality problems including overcrowding in greenhouse and holding areas, rough handing of trays, and storing in light limited conditions for extended periods. Breaking plant stems plants, especially those that with excessive growth, is a common problem in transplanting as is damage to roots when pulling plants out of trays.
When troubleshooting stand losses it is important to consider these issues affecting seed or plant quality.