Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
Many vegetable growers in the region have lost significant number of transplants to cold conditions after planting, seed and root maggots tunneling into stems, seedling diseases such as Pythium, wind damage, and wildlife damage over the last 3 weeks. Weather conditions have been suboptimal for warm season vegetables many days this month, limiting root growth, and placing plants under additional stress. There was also a late frost earlier in the week in some areas that injured or killed some transplants.
Growers will need to decide how to deal with plant losses in the field. Replanting with transplants is the best option. However, the base cause of the loss must be known to avoid losses again in the replanting. If losses were strictly due to cold, then the replanting can go ahead without further consideration. If the losses were due to seedling disease affecting roots or stems then appropriate treatment of the area with registered fungicides should be considered before replanting. The same holds true if losses were due to maggot feeding and seed/stem/root maggot flies are still active. Appropriate insecticides should be considered prior to replanting.
If growers do not have spare transplants, they can try to obtain transplants from other growers or commercial transplant operations. Most transplant growers do produce some overage when they grow transplants and limited amounts may be available. The main issue when this occurs is that you will not always have access to the same varieties that you initially decided on for the field affected with the losses. You need to decide if the substitute varieties will suit from a marketing standpoint. Planting varieties that you will have a hard time selling or that do not fit your marketing program will serve no purpose.
Another issue is that many of our transplants such as watermelons come from southern growers. Full trailer loads of plants are shipped north to our region (most economical). To get partial shipments for replacements (if available), growers will still be paying full shipping fees. Most large transplant growers do not grow on speculation – they grow to order. Any available plants will be from overages or orders that were not shipped for some reason. These plants may be of lower quality because they have been held in small trays for longer than desired. Growers seeking replacement plants should contact their plant suppliers, seedsmen, or brokers for assistance in finding plants.
One option for large seeded crops is to direct seed in the holes where transplants died (again making sure that the underlying cause of death is known and dealt with). This works for crops such as cucumbers, squash, muskmelons and watermelons. In watermelons, if losses are scattered, planting holes with pollinizer seed is an option. If seeded watermelons are used as the pollinizer (such as Stargazer, Mickylee, Sangria, etc.) they will grow very quickly from seed and you may only see 5-14 days difference in flowering compared to transplants. If the losses are light, then taping the holes (to prevent weeds from growing) and just letting the plants vine into the missing area is an option. Watermelons have some ability to compensate for stand losses by putting on additional vines and fruits. If soil temperatures are in the 80s then it is also possible to plant seedless watermelon seed directly in the holes with missing plants (plant 2 per hole) using a shorter season variety. While a full yield will not be obtained, there is potential for some yield recovery.
If losses are heavy, then destroying existing plants and growing new transplants for a late planting in the same area is another option. It can take as little as 3-4 weeks this time of year to grow out some transplants so they will be available for a June planting.