Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
As spring planting season continues at a rapid pace, there are more reports of poor stands or stand losses in vegetable crops. The culprits are often soil insects or diseases; however, lower quality seed or plants can also be a source of the problem. You will most commonly see problems with lower quality plants or seeds when there is a cold period right after planting.
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 because 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 is 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 would 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 (cleaned, lower weight or damaged seed removed), treated, packaged, and stored under proper temperature and humidity. As seed is distributed it often goes through several phases where it is handled and stored in different environments. Larger lots may be broken into 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. 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 transplants 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. 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, especially those with excessive growth, is a common problem in transplanting, as is damage to roots when pulling plants out of trays.
When troubleshooting stand loss or unevenness it is important to consider these issues affecting seed or plant quality.
Reduced bean stand and abnormal growth due to seed quality issues.
Low vigor, dead cotyledons and abnormal unifoliate leaf growth in bean seedling from low quality seed.
Bleached cotyledons and stunted growth in bean seed with quality issues.