The results of our field studies did not indicate any single practice or material that reduced symphylan populations by an agronomically significant amount. Our laboratory studies indicated some materials had a biological effect on symphylans under laboratory conditions, but whether and how such materials could be used effectively to reduce symphylan populations under field conditions could not be explored within this work. Our choices of practices and materials to study were based upon input from organic growers, consultants and other researchers and we chose those treatments which we thought held the greatest potential for influencing symphylan population numbers. Based primarily on our own studies, but also influenced by the experiences of others, we have drawn the following conclusions:
1. It is very difficult to study the effects of management practices on symphylans because: a. Their unpredictable vertical movement in the soil profile means they commonly disappear from the soil surface layers for several months and then return. b. Their fragility makes direct sampling difficult at the surface and very time consuming and difficult from depths below a few inches; baiting methods allow more rapid assessments of symphylan numbers, but are only developed for the soil surface and only attract symphylans during the actively feeding stages. c. Since they can move up to one foot/day laterally in the soil, plot sizes may need to be quite large. On the other hand, symphylan spatial distribution is typically very non-uniform, so large plots are very difficult to use.
2. In our field studies, none of the management practices that we tried proved to be successful in reducing symphylan numbers in an agronomically meaningful way. This may be because: a. The practices truly did not have a significant biological effect, or b. There may have been some small effect, but it may take more than one season of treatment for any effect to be agronomically meaningful, or c. there may have been effects, but symphylan movement between plots did not allow us to measure the effects.
3. In the Davis trial, while the barley cover crop resulted in significantly lower symphylan numbers shortly after transplanting of the subsequent tomato cash crop (shown consistently by direct core, plant plug and beet bait methods), barley also showed the highest numbers of symphylans in the last sampling before mowing and discing the cover crops. In addition, barley did not seem to help the tomatoes as the season progressed. One possible explanation for this is that somehow the barley stimulated the symphylans to move closer to the soil surface than the other treatments late in the cover crop season and, therefore, the tillage that occurred at this time was more damaging to the symphylan population in the barely plots. Thus, there was a temporary reduction in the surface population of symphylans following spring tillage, but either this reduction was insufficient to reduce damage to the subsequent tomato crop or migration of symphylans from deeper in the soil or ad . acent plots eliminated surface population reduction over course of the tomato growing season.
4. The Santa Cruz trial was hindered by a general lack of symphylan activity in the surface layers of the soil (where sampling is possible) for the almost 12 month duration of the trial, despite the fact that relatively high numbers of symphylans were seen in this soil both before and after the trial. In this trial, there were few statistically significant differences between treatments. However, there was some indication that, compared to a vetch/oat/bell bean mix cover crop with "regular" tillage, the same cover crop mix with an extra tillage (conducted when symphylans were observed near the surface) resulted in fewer symphylans at the soil surface, as did a barley cover crop with only "regular" tillage.
5. Taken together, the results of these two trials lead, first and foremost, to the conclusion stated in #2, above. However, they also indicate that the practice of timing pre-plant tillage to coincide with periods of symphylan presence near the soil surface, may, at least temporarily, reduce symphylan populations to some extent. This appeared to happen in both the barley plots at Davis and the VOB-T plots at Santa Cruz.
6. Our laboratory studies indicated that some organically acceptable materials may have biological activity on symphylans. However, we did not demonstrate any such activity in the field. There are several factors that may cause a material that is effective under certain laboratory conditions to be ineffective in the field. In the case of symphylans, one of these factors is the symphylans' ability to move a number of feet deep in the soil. From our results, neem extracts and products such as Farewell, seem to warrant further study in this area. The mustard seed extract also appeared to have potential although it's effects were not as great as with the other two materials. While it was not demonstrated in this study, the mode of action of the mustard seed extracts might be similar to the demonstrated mode of action of decomposing Brassica crops on various soil bome organisms, which we were not able to demonstrate on symphylans in our "Brassica" treatment in the Davis field study.
7. The workshop we conducted at the Ecological Farming Conference reconfirmed that symphylans are a significant problem for a number of organic growers. Similarly, it reconfirmed that there are many seemingly contradictory growers' experiences with symphylans. During our discussion there were a number of examples of management strategies that appeared to be successful for one individual but not for one or more of the other participants.
