Gordon Johnson, Extension Vegetable & Fruit Specialist;gcjohn@udel.edu
As watermelon planting season gets into full swing, we are starting to see some issues with transplants, both shipped from the south and grown locally. Problems include:
• Overgrown and past prime transplants. Often plants will already be flowering, they may be stretched or excessively root bound. Transplants kept in shipping units too long are the most likely to exhibit these symptoms. Fortunately, watermelons will regrow and yield well, even from overgrown plants. However, the plants often take longer to produce fruit because plants must recover and start to regrow, which will take 1-2 extra weeks. Existing flowers will abort.
• Wire stemmed transplants or transplants with stem damage. These are transplants where the outer part of the stem has deteriorated and only the inner core remains or that have lesions on the stems. These plants will not perform well and may die. Wire stem or stem damage can be caused by diseases such as Pythium or Rhizoctonia, from secondary infections where cotyledons have dropped off, or from physical injury.
• Mites and/or aphids. Mites and aphid infestations can occur in the greenhouse and be taken out into the field.
• Fungal and bacterial diseases. See prior WCU articles for potential diseases to look out for such as gummy stem blight or bacterial fruit blotch.