Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
There have been plant losses in a number of early planted watermelon fields over the last 10 days even though the fields had every-row rye windbreaks.
Situation 1. Transplants were set during a 4-day period in late April with cloudy and rainy weather. Plants failed to root into the black plastic mulched beds and then when clear sunny weather returned, many plants wilted. Transplant roots of affected plants were dark colored and the base of stems were brown.
This is a common problem in April plantings. Watermelons need soil bed temperatures over 60°F to begin rooting and ideally bed temperatures should be above 65°F to root quickly. In overcast conditions with rain, beds do not reach theses temperatures. Watermelon roots are very sensitive to cold soil conditions and will deteriorate quickly. Cold temperatures at the soil surface will also damage the base of transplant stems, particularly if plants have been set too deep.
Situation 2. Leggy (tall) transplants were set just prior to several days of high winds. Many of these transplants were injured by being whipped around with the wind. The stem base was damaged and water conduction in the stem was impaired.
In this case the issue is with leggy transplants. A more compact transplant will be closer the soil surface where there will be less wind and will not move as much with the wind. In fields with rye windbreaks, wind damage can still occur if the wind gusts are high or the wind direction is down the row.