One of the most attractive aspects of growing Knockout roses is their resistance to pests and diseases. Gardeners who grow these beautiful roses have an easier time maintaining them because many of the insects that bother other rose bush varieties do not cause problems for Knockouts. You must stay vigilant against two insects, however, because aphids and Japanese beetles tend to enjoy Knockout roses if you give them the opportunity.
Prune the Knockout rose in the late winter or late spring each year to ensure you remove the dead growth. Look for canes that rub against each other and remove these canes because the rubbed areas can attract pests. Try to keep the center area of the Knockout rose bush free of congested growth to reduce the attraction to pests.
Examine the Knockout rose bush once or twice per week to ensure pests do not get a stronghold. If you find aphids on the stems or Japanese beetles on the blossoms, fill the glass jar half-full of warm water and add two to three drops of dish-washing detergent. Manually pick the insects from the stems and drop them into the jar. Continue picking each day to remove the insects as they appear.
Direct a spray of water from the garden hose to areas where insects are congregating. Although some roses are susceptible to water spots, Knockout roses have an inbred ability to withstand water spots so some water on the foliage should not create water spots.
Fertilize your Knockout roses regularly to ensure strong and healthy plants. Mix the fertilizer with water according to package recommendations for the size of your shrub. Pour the fertilizer around the base of the plant every four to six weeks throughout the growing season.