How to spot and organically control root aphids. A growing pest of greenhouse and garden plants.
Root aphids — aphids that stay at or above the soil line — are from the family Phylloxera, a near-cousin of aphids. They are an escalating problem, especially among indoor growers, and spreading through parts of the country where they haven’t been seen before. They’re hard to spot and unlike small colonies of green and other aphids found on stems and leaves, root aphids are more likely to get out of control. They can multiply quickly, unseen, and sap enough vigor from your plants to kill them.
Because they’re small — about the size of a mite — and often colored to blend with roots and soil, Phylloxera is hard to spot. Often, growers will see the white, waxy material that the aphids secrete, a chalkier type of the honeydew secreted by other aphids. Their bodies are more pear-shaped than oval as are mealybugs. They’re about the same size or slightly smaller than stem-and-leaf aphids with shorter legs and antennae. They come in a variety of colors, including pink, but are mostly white and brown. They’re commonly confused with the larger mealy bugs, because of the white substance they spread. In their winged stage, they can be confused with fungus gnats. Like other aphids, they have small cornicals or “tail pipes” at the end of their abdomen which also distinguishes them from mealybugs.
Because of their size and below-soil habitat they can go unnoticed, even through one or more grow cycles. They can be spotted attached to the sides of grow cups when growers take the trouble to look. Root aphid damage is often mistaken for other problems, especially nutrient deficiencies. Plants that appear to be suffering from magnesium or iron deficiency should be checked carefully for root aphids.
In outdoor gardens, root aphids may be accompanied by ants. Once established in soil or hydroponic systems, root aphids are difficult to completely remove.
Root aphids are surprisingly adaptable and their lifecycle can vary tremendously. They reproduce asexually during the growing season. Eggs over-winter in soil or, in warm seasons, are attached to leaves and stems above the root line where they hatch and fall to the ground. The aphid bores into the root, creating scars that leave plants vulnerable to mildew and disease. As infestations increase, “crawlers” will move up the stem to feed. Once a plant is nearly destroyed, some root aphids will develop wings that enable them to seek new plants to attack. In the fall, winged aphids, now male and female, mate in brush and trees and produce more eggs. Ants are known to carry aphids from exhausted plants to un-colonized ones.
Damage from root aphids is usually visible in a lack of vigor from plants. Withered, curled, and yellow leaves, similar to signs of nutrient deficiencies, appear and plants fail to reach the size of uninfested plants. Fruits and blossoms on aphid infested plants will be small, stunted, and generally less desirable as nutrition is siphoned away from them.
Attacks from root aphids can leave plants vulnerable to root rot, mildew, and disease.
Visible symptoms, like yellowing leaves, often lead growers to consider adding certain minerals, usually magnesium, to their nutrient mixture, often with no result.
In addition to greenhouse and garden perennials, various types of root aphids attack rice crops, the roots of a variety of trees including fir, walnut, and hickory. Root aphids can also cause problems for perennial herbs, including those grown in pots.
Root Aphid Control
Detecting the first signs of root aphids, especially when growing indoors, is crucial to saving your plants vegetating and fruiting abilities. At a certain point, usually sooner rather than later, affected plants and containers should be removed from the grow space completely and destroyed.
Waiting for fruits or flowers to mature in an attempt to save something of a crop is not advised. This only gives root aphids a chance to inoculate themselves into your entire grow area. It’s best to start over, sanitizing all containers and growing equipment that’s been used. Indoor growers should clean their entire grow space.
- Avoid introducing commercial grade soils, including bagged composts, that may contain aphids and their eggs. This is probably the most usual way that aphids have been spread to gardens throughout the country. Buy soil and compost from a reliable, local source, make your own.
- Attract birds who will pick aphid eggs from trees and the ground.
- Several types of parasitic wasps attack aphid eggs. Ladybugs will also predate aphids they find on the surface but not those burrowed in the soil.
- Introduce beneficial nematodes (link below) into soil at the first sign of root aphid infestation or, better, in anticipation of them. Nematodes will attack a number of soil-borne pests yet are harmless to earthworms, pets, and humans. Make sure the soil is moist when applying nematodes.
- Use AzaMax as a preventive treatment to keep aphids from feeding on roots. Because it’s slow acting, AzaMax is not a good choice for treating infestations, but can be effective, over time, for minor infestations.
- Neem oil can help stop aphid infestations from growing, especially as crawlers move up stems.
- Do not use insecticidal soaps to control soil-borne aphids. While they will kill crawlers moving up plant stems, they will do little to stop aphids in the soil and may harm your plants’ roots.
- Pyrethrum-based sprays can be effective if used early enough in the infestation. Water lightly after applying to disperse this chrysanthemum-based botanical into the soil. Reapply every two weeks (eggs in soil may continue hatching) until plants regain vigor and all aphid sign disappears.
- When removing infected plants, be careful not to drop soil or spread aphids into other parts of your garden. Put plants, roots and all, in a bucket, and take away with minimum disturbance. Removal, in conjunction with preventive spraying, may be your most effective form of control.
- Avoid importing soil or other growing medium of unknown origin into your growing space. Many nursery plants, especially those from large, commercial growers, have been found to carry root aphids and their eggs into green houses.
- Use yellow sticky traps across indoor grow spaces to discover signs of root aphids on the move.
- Pay careful attention to your plants. Roots that are visible in grow cups and other hydroponic methods should be periodically inspected. The small, usually white mite stage may be noticeable attached to the sides of grow cups, tanks and trays.
- Beneficial nematodes introduced to hydroponic solutions at the first sign of infestation may slow the spread of root aphids.
- With lights off, saturate the growing medium with a solution of Nuke Em (1 oz/ 31 oz water). Slowly pour near the plant stem into the soil and let stand for at least 1 hour — longer contact times are best. Rinse the media before turning lights back on.
- BotaniGard ES is a highly effective biological insecticide containing Beauveria bassiana, an entomopathogenic fungus that attacks a long-list of troublesome crop pests – even resistant strains! Weekly applications can prevent insect population explosions and provide protection equal to or better than conventional chemical pesticides.
- When treating aphids in various indoor growing mediums, complete and thorough coverage of infected areas is critical to control. Submerge infested grow cups and root balls completely in a pyrethrum concentrate for a half-minute or more, gently swirling roots and medium to insure complete saturation.
- Remove badly infested plants. No orchid, no herb or flowering perennial is worth risking your other plants and the health of your entire grow space in an attempt to wait out harvest on an affected plant.
Dealing with root aphids, indoors or out, is an evolving and ever-changing set of practices. Don’t be tempted to use harsh, chemical treatments if you already have an infestation. A University of Maryland Cooperative Extension study conducted inside two greenhouses with root aphids on gallardia, aster and boltonia perennials found applications of Talstar (bifenthrin) and Marathon (imidacloprid) applied as a soil drench gave poor results. Keeping aphids out of your garden or grow space in the first place is the most effective practice. And with this problem spreading, it is becoming harder and harder to do.
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