Yarb Tales - Aphids
January 18, 2016

The Heritage Herb Garden at the Ozark Folk Center graces the park with visual colors and textures, sweet and pungent aromas, and helps us to interpret the history of the human use of plants.

When you see masses of tiny, black or gray dots on the stem tips and leaves of your plants, it is probable aphids that have invaded and are feeding. Aphids are sap-sucking bugs that cluster on the growing tips and under the leaves of plants in the home, greenhouse and garden. They have soft bodies and are easy to kill. The trick is to spot them early and repeat controls to catch the ones that were missed the first time.

To control aphids, it is important to deter ants that invade the greenhouse and home. Ants nurse and care for aphids in return for honeydew. Ants move aphid populations around; some build shelters for their charges with leaves. They fight off predators and ants have been known to chew the wings off of winged aphids to keep them from leaving the "family".

Boric acid traps can be effective against ants. If we were to try boric acid traps, we would mix the boric acid with a fruit jelly and put it into plastic containers such as those used for dips, cottage cheese and the like. We would cut entrance holes into the lower portion of the container for the ants. The lids would protect the bait from becoming too wet. The sugar in the jelly would attract the ants. Boric acid is toxic to children and pets if eaten.

Suppress ant travel by tying yarn soaked in vegetable oil around plant table legs. Paint a band of sticky, water resistant substance such as Tanglefoot®, sticky fly traps or petroleum jelly mixed with dish soap around each table leg as a barrier.

The essential oil of vetiver does repel ants and does not evaporate quickly. This essential oil is expensive; mix it with a carrier to apply it on surfaces where ants are observed. We combine 1/4 teaspoon of the vetiver oil with 2 tablespoons Murphy Oil Soap® and then add this to 1 gallon of water in a pump sprayer. We spray the foundation of the greenhouse and the line of travel used by ants, shaking the sprayer frequently to keep the oil, soap and water well mixed.

To control aphids indoors during the winter, keep plants as cool as possible. The warmer the greenhouse or sunroom is at night, the faster aphids and other plant pests multiply.

The safest way to kill aphids is to blast the plant with a strong spray of water. Those that are feeding at the time will be washed away and will leave their proboscis embedded in the leaf.  The others will have to walk back up the plant. This control really does help keep the aphid numbers down.
When looking at aphid colonies through a magnifying glass you will often see beige-colored balls that are just a bit bigger than the aphids. This is a good thing! Be of glad heart. Those funny-looking balls are “mummies” for any of several species of parasitic wasps. The mere presence of parasitic wasps can disturb aphid colonies. Alarmed aphids secrete a pheromone that causes colony members to leave or fall off the plant! These beneficial predators enter greenhouses on their own accord and live in gardens that are not sprayed with full-spectrum insecticides.

Parasitic wasps are tiny, only slightly larger than aphids. The wasp inserts an egg into an aphid host. The egg develops into a larva. The larva goes through four stages inside the aphid, finally spinning a cocoon. The young adult emerges from the mummy through a small hole.  

Native ladybeetle adults and larvae make spontaneous appearances in the greenhouse. We see them in the late winter, spring, summer and fall. We relocate the newly introduced Asian ladybeetles that we find in our homes and sheds to the greenhouse.  Each beetle can consume 50 to 60 aphids in a day and also feeds on scale, mealy bug, mites, and other soft-bodied bugs.

Lacewing adults and larvae also feed on aphids. The adult is light green, almost inflorescent with a long fragile body and wings. They can be seen on screen doors, at night, during the summer months. The larvae can only be seen with a magnifying glass. Lacewings, ladybeetles and parasitic wasps are nature’s way of keeping pests in balance. When we observe the presence of beneficial predators, we do not use anything but water sprays to control aphids.

Pruning for pest control is a double-edged sword. Many hundreds of aphids may be pruned away by nipping infested tips. Pruning does stimulate new, tender growth. Tender growth is the food of choice for aphids. When we do prune away pest-invested plant tips, we are sure to keep a watchful eye on the new growth.

Many different agents are effective when used as sprays on aphids because they have soft bodies.  However, because of their sheer numbers and ability to asexually reproduce, it is necessary to repeat sprays to achieve control. Repeat sprays every three days. Concentrate the spray on green- growing tips and under leaves.

Sprays made with essential oils have great potential for insect and disease control. Many highly concentrated plant essences have been shown to repel or kill insects. According to Valerie Ann Worwood in The Complete Book of Essential Oils & Aromatherapy, 4 to 8 drops of essential oil to 1 gallon of water makes a sufficiently strong repellent spray. Ms. Worwood lists the essential oils of spearmint, peppermint, cedar wood, and hyssop to repel aphids.

Soap sprays kill aphids by coating and dissolving the protective wax on the surface of the exoskeleton. A technical bulletin published by Safer®, Inc. explained how effective Safer® Soap sprays can be. The test included ten species of aphids on ten different garden plant species. After three days, a single treatment killed between 90 to 98% of the aphids. Three species of plants were 100% aphid free in three days. The most important thing to remember is to go back in three days to get that remaining live percentage!
Summer or superior oil is lightweight, highly-refined petroleum oil. It is reportedly less harmful to beneficial predators than pests. It kills aphids by suffocation. We had success eliminating aphids from two large lemon verbena plants with Sunspray®. The pots were isolated on separate stands. We sprayed three times, three days apart each time. The plants remained aphid-free for well over a month. Be aware that soap and oil sprays can burn plant leaves. Always use these controls during the cool of the day and never in direct sun. Happy aphid hunting! If I don’t see you in the future, I’ll see you in the pasture!