Watermelons (Citrullus lanatus) take several months to mature, growing for 90 to 120 days, depending on the variety. They are most susceptible to pest infestations when they are young, but there are several ways to protect the watermelon plants. When the plants are older, only severe infestations require treatment to keep the plants healthy.
Plant watermelons when the soil temperature is at least 70 degrees Fahrenheit. These warm-weather fruits easily become stressed in cooler weather, and planting them too early exacerbates any pest damage because the plants can't easily recover. To get a jump start on the growing season, start seedlings indoors and plant them outdoors when the soil warms.
Install row covers over the watermelon seedlings. Push the U-shaped braces into the ground on either side of the seedling rows, spacing them 1 to 2 feet apart. Lay the row covers over the braces, burying the bottom edges under the mulch or top layer of soil to create a solid barrier against bugs. Row covers allow light and moisture to enter, but not bugs such as peach aphids or cucumber beetles, both of which attack young watermelon plants. Remove the row covers in about three weeks, or whenever you see the plants begin to bloom. The row covers stop helpful insects such as bees from pollinating the flowers.
Lay drip irrigation hoses along each watermelon row. Spread a reflective or plastic mulch around the watermelon plants. These typically come in sheets that you lay around your plants, cutting X-shaped holes or long slits in the sheets when necessary to accommodate the plant stems, using a utility knife. Overlap the mulch sheets by at least 4 inches and press landscape staples every 6 to 8 inches along the edges to hold them in place. Bugs such as the cucumber beetle don't like to cross unnatural surfaces such as reflective and plastic mulches.
Spray a ready-to-use insecticidal soap over young or mature plants if you notice signs of bugs, such as black or white dots on the leaves, chewed edges or stunted growth on the tips of vines. Check underneath the leaves as well -- many bugs like to hide. Cover the leaves and vines thoroughly, including the undersides. Reapply every few days as needed. This organic pest eliminator is safe to spray near where your children play.
Spray a foliar insecticide on mature plants if the insecticidal soap is ineffective. Mix according to the manufacturer's instructions, but start with the smallest recommended amount, such as 2 ounces per gallon of water. Cover the tops and bottoms of the leaves as well as the vines. These chemicals aren't organic, so don't let your kids handle the spray.