Description
Garden symphylans, Scutigerella immaculata, are small (1/4”) centipede-like soil arthropods common in agricultural soils. They have 15 body segments and 11 to 12 pairs of legs. They are slender, elongated and white with prominent antennae. They feed on decaying organic matter, young roots and sprouting seeds, causing stunting in crops. In hotspots they can kill susceptible plants. The root damage makes plants more susceptible pathogens.
Target Crops
Host crops include solanaceous crops, brassicas, leafy greens, cucurbits, beets and onions. Broccoli, cabbage and cauliflower are also susceptible. Beans and potatoes are rarely damaged, even under high populations. Within a crop, susceptibility is often related to the developmental stage of the crop, young transplants and seedlings being the most vulnerable.
Symphylans are generally associated with heavier soils that are high in clay content and have good soil structure. They do not thrive in compact or sandy soil because these soils do not provide them with adequate tunnels for their movement (Symphylans cannot make their own burrows). It is ironic that these pests are such a problem on farms that practice good soil management—maintaining soil with good tilth, high organic matter and low compaction.
Life Cycle
In the western US, eggs, adults and immature garden symphylans can be found together in the soil throughout the year. Most eggs are laid in the spring and fall in clusters in the soil. Eggs are pearly white and spherical with hexagonal shaped ridges. Eggs incubate for about 25 to 40 days between 50 to 70°F but reduces to 12 days above 77°F. As the immatures molt, they add on body segments and pairs of legs until they reach adulthood. Total time from egg to mature adult (seventh instar) is about 5 months at 50° F, 3 months at 70°F and less than two months above 77°F. Unlike other adult insects which do not molt, adult garden symphylans may molt more than 40 times during their lifetime.
In mild climates with sufficient soil moisture, they can produce up to three to four generations per year and live up to five years. As the soil warms up and dries out over the summer, symphylans tend to move deeper into the soil.
Beneficial Insect Control
Numerous organisms prey and parasitize symphylans in the field including true centipedes, predatory mites, predaceous ground beetles and various fungi, however little is known about their ability to reduce symphylan numbers. There is currently no research as to which biological control agents are effective, however beneficial nematodes and predatory mites may be options in the future.
Insecticide Options
- Azadiractin or neem oils act as insect growth regulators, antifeedants and ovipositional deterrents. These include AzaGuard and Molt-X.
- Mycoinsecticides containing entomopathogenic fungal spores. These include Botanigard, Mycotrol,NoFly and PFR 97. M-52 OD used as a drench is especially good for pests in the soil.
Cultural Control Tips
- Tillage is the oldest control tactic and one of the most effective, physically crushing symphylans and reducing populations.
- Crop rotation. Populations decrease significantly in potato crops, allowing subsequent cultivation of susceptible crops in rotation. Potato roots and leaves have much higher concentrations of alkaloids that are toxic to symphylans than tubers. This has been called the ‘potato effect’.
- Monitor with potato baits placed under pots.
Sources
Symphylans IPM UCCE North Bay Specialty Crops
Symphylans: Soil Pest Management Options ATTRA
The Creepy Crawlers Underground – Symphylan Control OSU
Typical symphylan damage: Some rows of peppers are severely stunted, while adjacent rows have both healthy and stunted plants-ATTRA
Eggplant damaged by Symphylans-ATTRA
Undamaged eggplant of the same age in the same field-ATTRA