Symphylans: Soil Pest Management Options

Symphylans: ATTRA Soil Pest Management Options A Publication of ATTRA - National Sustainable Agriculture Information Service • 1-800-346-9140 • www.attra.ncat.org By Jon Umble (Oregon Garden symphylans are soil-dwelling, centipede-like creatures that feed on plant roots and can cause State University), extensive crop damage. They cause frequent and often misdiagnosed problems in well managed west- Rex Dufour (NCAT ern soils with good tilth. This soil pest may not be familiar to farmers and agricultural consultants. Agriculture Specialist), This document describes the garden symphylan life cycle and the damage symphylans can cause. It Glenn Fisher (Oregon includes monitoring techniques to determine whether symphylans are present in the soil and sustain- State University), able management options to prevent economic damage. James Fisher (USDA/ARS), Jim Leap (University of California, Santa Cruz), Mark Van Horn (University of California, Davis) arden symphylans (Scutiger- © NCAT 2006 ella immaculata Newport) are Contents Gsmall, white, “centipede-like” soil arthropods, common in many agricultural Damage ............................. 1 production systems in Oregon, Washing- Identification ................... 3 ton, and California (Berry and Robinson, Biology and Ecology ..... 3 1974; Michelbacher, 1935). Life Cycle ........................3 They feed on roots and other subter- Occurrence ...................4 ranean plant parts, causing significant Movement in Soil and crop losses in some cases. Control can be Factors Influencing Population Levels ........ 5 extremely difficult due to symphylans’ A garden symphylan is about the size of this letter ”l.” Sampling ........................... 6 vertical movement in the soil, the com- lexity of sampling, and the lack of sim- Soil Sampling ................7 problem on farms that practice good soil ple, effective control methods (Umble Bait Sampling ...............7 management — maintaining soil with and Fisher, 2003a). Indirect Sampling good tilth, high organic matter, and low Methods .........................8 With the recent spread of organic agri- compaction. Economic Thresholds: culture and better soil management tech- Interpretation of niques, crop damage associated with sym- Sampling Results .........9 Damage phylans has become more commonplace. Management Diagnosing a garden symphylan prob- It is ironic that these pests are such a and Control ....................... 9 lem is sometimes difficult, since damage Tactics to Decrease may be exhibited in a number of forms Populations ................ 10 and garden symphylans are not always Tactics to Reduce Damage to Crops ..... 10 easy to find, even when their damage is References ...................... 14 obvious. Economic damage may result from direct feeding on root and tuber ATTRA - National Sustainable crops and reduced stands of direct- Agriculture Information Service seeded or transplanted crops (Umble is managed by the National Center for Appropriate Tech- and Fisher, 2003a). nology (NCAT) and is funded under a grant from the United However, most commonly, root feed- States Department of Agricul- ing reduces the crop’s ability to take up ture’s Rural Business-Coopera- tive Service. Visit the NCAT Web water and nutrients, which leads to gen- site (www.ncat.org/agri. Soils with high organic matter, good structure, and eral stunting. html) for more informa- reduced disturbance, as in these hand-dug garden tion on our sustainable beds, are ideal habitat for garden symphylans. agriculture projects. �� Root damage may also render plants Eggplant stunted by garden symphylans. Undamaged eggplant of same age in same field. Related ATTRA Publications Sustainable Soil Management Sustainable Management of Soil- Borne Plant Diseases Symphylan damage can be hard to diagnose because it may seem to be from other causes. This photo shows Pursuing Conservation two rows of eggplant, one that is severely stunted and one less so. Neither the rows to the left nor the peppers on Tillage Systems for the right seem to be affected. It is likely that the timing of planting and tillage influences the amount of damage Organic Crop that symphylans cause. Many factors may interact to promote or reduce symphylan damage: conditions when Production the soil is tilled, time after tillage, heat requirements of the crop, irrigation management, size of the plant, etc. Soil Managment: National Organic Program Regulations Typical perplexing symphylan damage: Some rows of peppers (above, left) are severely stunted, while adjacent rows have both healthy and stunted plants. Symphylan damage can be mistaken for skipped seeding or poor seed-to-soil contact, as in these fields of squash (above, right), sweet corn, and tomatoes (below, left and right) Page 2 ATTRA Symphylans: Soil Pest Management Options Certain areas of this squash field are laid to waste by Typical symphylan damage, showing healthy plants symphylans, while other sections thrive. alongside stunted plants and empty areas. more susceptible to some soil-borne pair per body segment) and quick move- plant pathogens. Correct diagnosis of ments. Millipedes are generally slower garden symphylan problems and identi- moving, with two pairs of legs on each fication of appropriate management tac- body segment. arden sym- tics for a given cropping system will gen- phylans are Some Symphyla species feed primarily on erally require the following: not insects, dead or decaying organic matter, play- G but members of the 1.) Sampling to determine whether ing an important role in cycling nutri- garden symphylans are present in ents. Other species, such as the garden class Symphyla damaging numbers symphylan, are serious pests, primarily feeding on living plants. 2.) A general knowledge of management tactics and garden symphylan Several Symphyla species are present in ecology to select the specific tactics the western United States; however, the that will be most effective in a given garden symphylan is the only Symphyla cropping system species that is documented to cause crop damage in the western U.S. Garden Identification symphylans are by far the most common Symphyla species found in agricul- Garden symphylans are not insects, but tural systems. members of the class Symphyla. Species of this class are common soil arthropods If Symphyla are found in an agricul- worldwide. Symphyla are small, whit- tural system at a high density, concen- ish “centipede-like” creatures rang- trated around the roots of plants, they ing from less than 1/8 inch up to about are likely to be garden symphylans. The 5/8 inch (or 1/4 inch for garden sym- pest is not known to vector any plant dis- phylans) (Edwards, 1990). They have 6 eases, although extensive research on the to 12 pairs of legs (depending on age), question has not been conducted. which makes them easy to distinguish from common soil insects (e.g., spring- tails) and diplurans that have only three Garden Symphylan pairs of legs, all on the thorax, or mid- Biology and Ecology dle body segment. Life Cycle Though their color may vary, depending on what they have eaten, garden sym- In the western U.S., eggs, adults, and phylans are generally whiter and smaller immature garden symphylans can be than true centipedes, which are also soil found together throughout most of the arthropods with many pairs of legs (one year. Temperature plays a key role in www.attra.ncat.org ATTRA Page 3 Garden Symphylan eggs Newly emerged (Photo credit: Ralph Berry) symphylans (first instar) Mature adult garden symphylan (Photo credit: Ralph Berry) regulating oviposition (egg laying), and three months at 70°F and less than two the greatest numbers of eggs are usu- months at 77°F. Therefore, it may be ally deposited in the spring and fall possible to have two complete genera- (Berry, 1972). tions a year (Berry, 1972). Interestingly, Eggs are pearly white and spherical with unlike adult insects, which do not molt, hexagonal shaped ridges. Eggs incubate adult garden symphylans may molt more than 40 times (Michelbacher, 1938). nderstand- for about 25 to 40 days, when tempera- tures range from 50° to 70°F, but hatch- ing of ing occurs in about 12 days as tempera- Occurrence garden U tures reach 77°F (Berry, 1972). Understanding of garden symphylan symphylan First instars emerge from the egg with six occurrence and movement is far from occurrence and pairs of legs and six antennal segments, complete. Nonetheless, some general- movement is far their bodies covered with fine hairs. izations can be made both about soils in from complete. Slow movements and a swollen posterior which garden symphylans occur more make first instars appear superficially commonly and about their movement in more like a collembolan than an adult soils. Garden symphylan populations garden symphylan. These first instars, are highly aggregated within fields and however, are rarely found in the root- on a larger scale. ing zone and within days molt to second In Oregon, Washington, and Califor- instars that resemble small adult garden nia, garden symphylans are more com- symphylans (Michelbacher, 1938). mon in the western regions of the states. Each of the six subsequent molts results Within these regions, garden sym- in the addition of a pair of legs and vari- phylans tend to occur in heavier irri- able numbers of body and antennal seg- gated soils, and within these heavier ments. Total time from egg to sexually soils, garden symphylans tend to occur mature adult (seventh instar) is about in “hotspots” of a few square feet to sev- five months at 50°F, decreasing to about eral acres. Even within shovelfuls of Fields often show symphylan damage in the same places over many seasons, as on these two farms. Page 4 ATTRA Symphylans: Soil Pest Management Options Pores, cracks, and holes in the soil allow symphylans to move through a field with relative ease. arden symphylans Gare unable to burrow through the soil. They use pores, seasonal “Hotspots” of garden symphylan infestation show clearly in this aerial view of a broccoli field. cracks and burrows made by soil, garden symphylans often occur in other soil animals, very distinct aggregations. such as earthworms, Garden symphylans are unable to bur- to travel through the row through the soil.

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