Published in Fall 2024
By: Nick Andrews, Navneet Kaur, Cora Bobo-Shisler and Alison Willette, Oregon State University
Many local farmers have struggled to manage garden symphylans (Scutigerella immaculata) over the years. When Jon Umble was studying them at OSU in the early 2000’s he uncovered this poem in a report from Hugh Morrison who conducted detailed investigations on symphlyans while at Oregon State University from 1937-1967. Symphylans feed on plant roots, and in hotspots they can kill susceptible plants, sometimes getting bad enough to force dramatic changes to crop rotations. Some people have even sold badly infested fields or stopped farming because of losses from symphylans.
Symphylans are small, soil-dwelling arthropods that can be pests in gardens and agricultural fields. Insects have three pairs of legs, and centipedes have one pair of legs per body segment, whereas symphylans have 12 pairs of legs as adults. This difference places symphylans in the myriapod subphylum with centipedes and millipedes and in their own class: Symphyla. Some say the damage they cause also sets them apart.
Figure 1. Symphylans are normally easily distinguished from other soil organisms by the number of legs, their antennae, and the short, paired cerci at the end of their body. | Figure 2. Crop damage radiates out as the symphylan colony grows in this squash at Winter Green Farm in Noti, Oregon. Photo by Jon Umble.
In mild climates with sufficient soil moisture, they can produce up to three or four generations per year. Adults are white and roughly 1/4 inch (6 mm) long. Adults lay eggs in clusters in the soil, and they hatch in about two weeks. Nymphs go through seven instars before becoming adults adding a new pair of legs at each molt until they reach maturity. Eggs develop into sexually mature adults in about 80 days, and they can live for up to five years. Their population can increase quickly when soil temperature is above 40◦ F and moisture conditions are optimal.
Recognizing symphylan damage for the first time can be tricky. If your crops are struggling to grow but don’t have any clear signs or symptoms of insect or disease damage on the foliage, dig up some plants to check for symphylans around the roots. If you find symphylans, you’ll have to learn to live with them.
Once you know that you’ve got symphylans, it’s probably worth figuring out where they are on your farm so you can avoid spreading them and do what you can to kill them in hotspots. Thankfully, they are relatively easy to monitor by placing potato baits under pots, then checking the bait and surrounding soil for symphylans a few days later. They are fairly easy to distinguish from other soil organisms (Figure 1). As the soil warms up and dries out over the summer, symphylans tend to move deeper into the profile, so early season monitoring is often most effective. Under irrigated field conditions, later sampling might also be helpful.
Mark your symphylan hotspots on a farm map or keep track of their location in a way that works for you. Knowing where they are will help in the long run. They don’t spread very quickly unless you move the infested soil around with equipment, so you shouldn’t have to monitor them very often. Typically, symphylan damage radiates in roughly circular patterns as the colony expands (Figure 2).
Vegetables and flowers are most susceptible to damage when they have a small root system early in the season and as the plants mature, they can tolerate more root damage. Unfortunately, symphylans thrive in soil with high organic matter content and good soil structure. Aggressive tillage immediately before planting can temporarily kill enough symphylans near the soil surface to help susceptible crops get established. Stale seedbeds for weed control are risky in symphylan hotspots because the delay between tillage and planting gives symphylans time to return to the soil surface to feed on seedlings or transplants.
If you have symphylan hotspots on your farm, avoid spreading infested soil to other areas. Clean off tillage and weed cultivation equipment and work from clean to infested soil. Also, be careful with compost, manure, and crop residue storage and handling. Symphylans can move from infested soil into organic amendments and then spread from field to field or farm to farm that way.
Potato roots and leaves have much higher concentrations of alkaloids that are toxic to symphylans than tubers. Although potato tubers are used as bait to track symphylan populations, Jon Umble’s research at OSU shows that symphylan populations drop significantly after potato crops. Anecdotally, this has reduced damage in many and allowed susceptible crops to be planted until populations increase again. Potato plants reduce symphylan populations within a couple months, suggesting that they could be used as a pest management cover crop on farms that aren’t interested in growing and selling potatoes. Few organically allowed or conventional insecticides are effective against symphylans. Preliminary results suggest that some neem products used as a soil drench might reduce symphylan populations.
The ATTRA article “Symphylans: Soil Pest Management Options”, by Jon Umble and colleagues in Oregon and California gives more in-depth information about symphylan biology, monitoring, and management.
Organic vegetable and flower farmers are looking for more effective symphylan management solutions. This prompted the workshop “Symphylans: In a class of their own” held in Corvallis on February 16, 2024. It was funded by NW Transition to Organic Partnership Program (NW TOPP) that is striving to increase organic adoption in the region through mentorship, technical assistance and wrap-around support for transitioning and existing organic producers. Over 30 participants attended the workshop eager to share their management strategies and weigh in on priorities for future research and Extension efforts. Most of the attendees were farmers and had existing infestations on their farms.
Figure 3. Symphylan workshop attendees share their experiences and management strategies with the group. Photo by Navneet Kaur.
We surveyed attending farmers on their experiences with symphylans and learned that most felt that they had exhausted common management options such as tillage, and were enthusiastic to try more creative solutions. Many farmers shared that they had positive success with using potatoes in rotation with other crops, and the most prominent area of symphylan management interest was on the “potato effect,” which still has a lot of unknowns. There was also a strong interest on topics relating to planting timing and cropping strategies such as intercropping or “trap-crops” to distract the symphylans, and interest in organically approved insecticides. The overwhelming message that we received as hosts was that there is a pressing need for organic farmers to have effective symphylan management options. In some cases, it can make the difference between success and failure for a farm. We are seeking grant funding to continue working on symphylan management with applied research, technical assistance, demonstrations, workshops and updated management guidelines starting in 2025.