Organic Tobacco Flea Beetle Management
In addition to questions about organic aphid management in tobacco, I have also received several questions about organic flea beetle management. Most of these questions have been some version of “What organically acceptable insecticides are effective against flea beetles?”
We have conducted a few efficacy trials comparing organically acceptable (OMRI listed) insecticides for tobacco flea beetle. Most of these have been conducted as laboratory or semi-field assays, where we expose field-collected beetles to leaves treated in lab or collected from the field. We use this method because getting reliable data on flea beetle mortality in field trials is difficult.
As I mentioned in a post earlier this week, Arthropod Management Tests (AMTs), a journal published by the Entomological Society of America, is a great first source for pesticide efficacy data. In fact, this is where we published our organic insecticide flea beetle efficacy trial. In this experiment, we measured flea beetle mortality on leaves treated in the lab or in the field with Pyganic 1.4EC, GOS Neem Oil, EcoTec combined with TriTek, Aza-Direct, and Entrust (a standard material that is not registered on tobacco). In lab-only bioassays, all of these materials resulted in high flea beetle mortality.
Lab-only assays do not always approximate field applications. Pyganic 1.4EC, GOS Neem Oil, EcoTec combined with TriTek, and Aza-Direct are all very oily materials and caused contact mortality in the lab. However, when sprayed on plants in the field, these materials were less concentrated on plant surfaces, and only Pyganic and Entrust cause significant flea beetle mortality. For this reason, Pyganic is the only material we currently recommend for flea beetle control in organic tobacco. See our AMT for detailed data tables and experimental methods.
Another important caveat is that we only tested the highest labeled rate of Pyganic 1.4EC, and there is a very large labeled rate range (16-64 fl oz/acre). At the highest labeled rate, this is potentially a very costly application, so growers should be certain that is economically justifiable to treat flea beetles at all! They should carefully scout plants and make sure that beetles exceed the 4/plant threshold for early season populations. This threshold is based on beetle counts not beetle damage! These insecticides are only effective if the target pest is present on plants. A damaged plant does not necessarily mean the insect doing the damage is still present.