Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
Weather conditions have been unfavorable for early transplanted warm season vegetables. We have not had any consistent warming trends to heat the soil under black plastic mulch. As a result, plant losses have been high because transplants have been slow to root into the soil (see previous post http://extension.udel.edu/weeklycropupdate/?p=8993). To make matters worse, we have had temporary flooding in some fields. Previous experience has shown when plastic beds are flooded over the top and planting holes are inundated, plant losses will be severe and replanting will be delayed significantly.
In addition, transplants have tended to be leggier (stretched) due to the overcast conditions. Transplants in small cells do not hold very well for extended periods and may become crowded and root bound. Another problem is diseases in transplant trays during extended wet hardening off periods outside (such as gummy stem blight and Pythium). It is hard to gauge watering when plants have heavy rainfall on trays. Spot watering (edges of trays on wagons or holding areas) is required to limit wetness in the middles. Watch for damping off and apply labeled fungicides as needed.
In seedless watermelons, losses of plants in the field can be problematic, especially where pollenizers died. Replanted pollenizers will flower later and may delay fruit set. To complicate matters, many seedless watermelon growers have switched to co-planted pollenizers (pollenizers planted in the same cell with the seedless variety). Loss of both co-plants will require replacing both seedless and pollenizer. Loss of the seedless in the co-planted cell will require replanting next to the pollinizer with a seedless transplant. Loss of pollenizers in the co-planted cells may necessitate adding pollenizers between plants when replanting is straight pollenizer trays may are available. Another complication is that it may be difficult to tell which plant has died in co-planted cells. Fields with reduced numbers of pollenizers can have fruit set problems, reduced fruit sizes, and increased hollow heart, particularly in the crown set.