Problem Identifier / How to Kill Root Aphids

What are Root Aphids?

A root aphid is a common pest often found in greenhouses, gardens and potted plants. Root aphids feed on different types of plants, damaging the health of the source. Many aphids thrive in the stems and leaves, but the root aphid is different. This insect is found under the surface of the soil. Root aphids attack the plant’s root system, often killing the plant if not identified soon enough.

Identifying Root Aphids

How To Kill Root Aphids
Adult root aphid with nymphs.

Most root aphids belong to the Pemphigus species. Although there are many color variations, most have a brown, yellow, white or whitish coloration. The adults have an appearance that resembles the aphids found on the stems and leaves. The difference is the legs and antennae are shorter, with a pear shape to the body. The majority of root aphids have a cornicle protruding from the tail of the abdomen, similar in appearance to a tail pipe.

The sucking mouthparts are capable of piercing roots, rhizomes and bulbs to extract the sap rich in sugar. Once entering a later lifecycle, the insects produce a waxy white layer. The body remains covered in this layer until this phase is complete. This is the reason a root aphid can be mistaken for a mealybug. The best way to see the actual pests is by examining the roots with a magnifying glass.

Root aphids should not be confused with soil mites including ticks and spiders. The easiest way to tell them apart is soil mites have eight legs, and root aphids have six. They prefer the roots near the soil surface. They are often found where the soil meets the stem of the plant. Prior to transplanting any plant, thoroughly examine the container once the plant has been removed.

Also look at the roots to see if any root aphids are crawling down the sides. The colony will be located close to the roots, near the main stem. Others will be feeding or wandering around the roots. The signature of a root aphid is a chalky white residue. If this residue is present, root aphids are most likely the source. Finding the insects quickly is the best way to save the plant.

Root Aphid Life Cycle

A newborn root aphid is called a nymph. These offspring generally cluster in a specific area of the plant’s root system. The root aphid does not have the same speed of the aphids living above ground because they do not have wings. Root aphids use drainage holes to move from plant to plant. They can also move with water used for irrigation. Root aphids can even be transferred along with equipment or debris.

When soil temperature drops in the fall, winged adults can be seen outside in the soil. Root aphids lay eggs on the residue and stems, enabling a new population to come to life during the spring. These insects are not as common in greenhouses but will appear if the population in the infected container becomes too great. The winged adults are often mistaken for aphids only attacking the tissue and leaves.

This is because they can be seen crawling up the plant stems. When the temperature is warmer, the life cycles of the insects are shortened. The largest numbers are seen during the warmer temperatures of summer and late spring.

What Does Root Aphid Damage Look Like?

Root Aphid Damage Quinoa
Sugarbeet root aphid damage. A colony on roots of quinoa. PHOTO CREDIT Whitney Cranshaw, Colorado State University,

The most common root aphid damage includes:

  • Stunted plant growth
  • Discoloration of the leaves
  • Presence of ants
  • Damaged, or yellowish-brown leaves
  • Damage or wounds to the roots
  • Smaller than normal or wilting leaves
  • White residue with an appearance like fungal growth

When a plant becomes infested with root aphids, the first symptom is often stunted growth. Healthy roots are necessary to absorb moisture and nutrients. The deprivation of these essential elements in addition to root aphids feeding eventually causes the roots to die. The flowers, foliage and stems are deprived of the sustenance required for growth.

As the plant growth stops, the leaves start to wilt. All the soil surrounding the base of the plant often needs to be removed because knots are caused by the root aphid within the roots. This is the result of stress. Some root aphids are often seen moving through the soil since shallower areas provide the best access to the roots.

Another common symptom of a root aphid infestation are ants. Root aphids use the ants to move among the plants, while receiving protection from predators. The ants feed on the natural sugar in the honeydew released by the root aphids.

Plants require nutrients including nitrogen to retain a green coloration from the production of chlorophyll. The plants are deprived of nutrients obtained through the soil due to the damage to the roots. This results in the leaves turning a sickly brownish yellow.

When there is a consistent line of ants around the plants, the soil should be examined for aphid activity within the roots. If the colony is caught early enough, severe root aphid damage can often be stopped. Root aphids can cause considerable damage to both outdoor and indoor plants if not detected quickly. Remaining vigilant, implementing an integrated pest management plan and checking plants on a regular basis is critical for avoiding an infestation.

Conifer Root Aphid Damage
Conifer root aphid damage on a fir. PHOTO CREDIT Eric R. Day, Virginia Polytechnic Institute and State University,

If the infestation is minor, there will not be significant damage to the plants. As the population grows, damage to the roots often leads to disease. Stress to the plants prevents the intake of nutrients resulting in a deficiency obvious in the leaves. During the hottest portions of the day the leaves will begin to wilt.

Due to the slow movements of the insects, the damage is generally restricted to only a few plants. As time passes, the damage will intensify. The best option is examining any plants displaying symptoms. If there is a visible chalky honeydew that is built up on top of and throughout the growing medium, the cause is probably root aphids. This substance will be located on the outside of the roots.

It is important to remember this substance looks a lot like the deposits left behind by mealybugs. The only way to be certain is through a careful examination of the roots. The difference between the two pests can be easily seen with a magnifying glass. Look for a white waxy substance often containing white strands like a fungal growth.

If the infestation progresses too far, there is a good chance the plant will need to be destroyed. Always remember, the destruction of one plant is preferable to losing most of a garden or greenhouse due to a spreading infestation of root aphids. Attempting to save one plant once the damage has progressed to a certain point often results in the loss of all the surrounding plants.

How to Kill Root Aphids Naturally

There are a few answers to the question of how to kill root aphids naturally:

The best options for getting rid of or killing root aphids include:

Using specific predatory insects or species including birds. If the plants are outdoors, birds will often feed on root aphids located above the soil line. Another option is releasing parasitic insects such as ladybugs and parasitic wasps. The insects will destroy aphids crawling above the soil line.

How To Kill Root Aphids
Root aphid.

The beneficial bacteria beauvaria bassiana can be applied as a soil drench. Beauveria bassiana is a fungus pathogenic for insects. In order to be effective, there must be direct contact between the fungal spores and the insects. During the attachment of the spores to the insect cuticle, germination occurs resulting in the fungus growing within the body cavity.

Beneficial nematodes will feed on soil born pests but are harmless to plants and even earth worms. At the first sign of root aphid infestation, you can apply nematodes to moist soil.

Unfortunately, the most effective option if damage has progressed is the complete destruction of the affected plants.

Giving plants time to thrive, produce fruit or flower is not recommended as the root aphids will just be allowed to infest more plants and at a deeper level. We know there are a lot of people who do not want to destroy their plants but sometimes it is what is necessary to save your crops.

When plants are removed, care must be taken to contain both the root aphids and the eggs. Take care not to shake the plant because both root aphids and eggs can fall into healthy plants or the soil. From there, the existing eggs will hatch, and the root aphids will continue to lay even more eggs.

How to Prevent Root Aphids Naturally

There are several answers to how to prevent root aphids naturally. The best way to ensure root aphids do not attack the plants is prevention.

Simple steps such as controlling weeds, watering and basic garden routines can substantially decrease the chance of a root aphid invasion. The soil should be turned during the fall to help prevent pests during the winter months. Other preventative steps include:

  • Beneficial nematodes
  • Do not use commercial compost or soil mixtures when planting. Inspect the soil for adult root aphids, larvae and eggs before use.

Defeat Pests, Mold and Mildew… NATURALLY!

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