Florida watermelon growers are reporting problems with squash bug, with young transplants being killed in some situations. They have reported the problem appears to be more severe where they are planting grafted watermelons. This has some potential explanation as grafted plants are on squash rootstock and squash is a more favored and more susceptible plant; however, this has not been noted in the past and is far from proven.
With a mild winter we have the potential to overwinter more insects of all kinds. Squash bugs overwinter as adults and will be entering fields in Georgia now, if they have not done so already. Small plants are more susceptible than larger plants, but squash bugs in large enough numbers can kill mature plants. In watermelon, the damage is difficult to separate from fusarium wilt. If squash bugs are the problem, they should be easy to find. They typically are near the base of the plants and will hide in the hole on plasticulture. Frequently they are clumped within a field and a “spot spray” may be possible.
Squash bugs are not easy to kill. I have conducted two bioassays on this pest in the last few years. Last year, bifenthrin at 6.4 oz/ac worked well on it own. Two years ago, bifenthrin at 6.4 oz/ac was weak, but when tank mixed with Lannate performed well. No other products tested provided good control. If you have an infestation that requires good control, I would suggest use of the tank mix. Try an apply toward the base of the plants on small plants.