A pond is an attractive and peaceful addition to a garden, especially when it includes plants and fish. Although a pond is usually pest free, it can become infested with tiny black bugs called aphids. The fish in the pond can usually take care of a minor infestation, but other methods may be needed to control large ones.
Black aphids, also called blackfly or waterlily aphids, infest pond plants in the late summer and fall. The females migrate in late fall to nearby cherry (Prunus avium), peach (Prunus persicaria) or other trees of the prunus spp., where they lay their eggs. In the spring, the aphids hatch, mature, and lay more eggs. Several subsequent generations live and reproduce in the trees through the spring and early summer. They are called plum aphids when they are found on trees. In late summer, they migrate back to the pond.
An aphid’s body has a specialized hair-like covering that traps and holds air, so that it can feed underwater. It can also walk across the surface of the water. Aphids reproduce rapidly – each female can lay up to 50 eggs in her lifetime – and can quickly cover an entire plant.
Although black aphids frequently feed on water lilies (Nymphaea spp.), they also attack other pond plants, such as cattails (Typha spp.) and arrowhead plants (Sagittaria spp.). Aphids suck the sap out of the leaves of a plant, which weakens it and makes it susceptible to diseases. They are attracted to new growth and older yellowing foliage. Severe infestations can cause green foliage to turn yellow or brown, and to grow distorted.
A light infestation of aphids can be washed off the leaves into the water, where fish can eat them. If the infestation is large, run water into the pond so that it is overflowing; then wash the aphids off the leaves into the water and out over the edge of the pond. Repeat this process every day or two until the aphids are gone. Drown aphids by covering the leaves with wet newspapers or submerge the plants in a bucket of water overnight.
A light vegetable oil spray effectively controls black aphids and is not toxic to fish. Mix 2 parts vegetable oil to 8 parts water with a dash of dishwashing detergent. Spray infested plants in the evening and rinse them off the next morning. Thoroughly spray Prunus spp. trees infested with black aphids with a mixture of 5 tablespoons Volck oil and 1 gallon of water. Volck oil is not recommend for the treatment of pond plants.
Volck oil is toxic to fish and aquatic animals, as well as people and animals. Keep people and pets out of application area until Volck oil is dry. Avoid getting Volck oil on your skin, or in your eyes or mouth. Do not inhale fumes or spray. Wear long sleeves, long pants, and gloves when applying Volck oil; wash clothes separately from other laundry. Wash any exposed skin with soap and water immediately after spraying Volck oil.
Cherry trees grow in U.S. Department of Agriculture plant hardiness zones 4 through 7, while peach trees grow in zones 5 through 8. Water lilies grow in 4 through 10, cattails in zones 3 through 10, and arrowhead plants in zones 5 through 10.
- Pond Trade Magazine: Water Garden Pests and Water Lily Diseases
- Colorado State University: Water Garden Plants Problems and Solutions
- Fish Channel: Removing Aphids on Pond Plants
- Texas A&M University: Aquatic Aphids
- United States Department of Agriculture: Insects and Other Arthropods That Feed on Aquatic and Wetland Plants
- Missouri Botanical Garden: Nymphaea 'Pygmaea Helvola'
- Missouri Botanical Garden: Typha Latifolia
- Missouri Botanical Garden: Sagittaria Latifolia
- Old Farmer's Almanac: Cherries
- Old Farmer's Almanac: Peaches
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