(AND NEW BAITS FOR MAGGOT CONTROL ON ORGANIC FARMS)

By Jude Boucher, UConn Extension Educator, Commercial Vegetable Crops

Please contact jude.boucher@uconn.edu or (860-875-3331) if you have questions.

 

In the last few years, a couple of organic farms have experienced new invasions of pepper maggots on their farms.  One farm lost 80% of the pepper pods their second year in business.  This year (2013), a well-established organic farm reported their first heavy pepper losses due to maggots.  Maybe the infestation had gone undetected and was building up for a few years, but maybe the flies migrated in from a nearby farm or garden, or arrived in peppers purchased from another farm and thrown on a cull pile.

The pepper maggot is a true fruit fly, about the size of a housefly, but rarely seen in the field, unless you know how to trap for it.  Even the maggots can go undetected for years because they often inhabit the seed head of the fruit and the fruit may be sold before the fly larvae emerge and cause the pods to rot.  Most customers simply core the seed head and throw it away, maggots and all.  Also, you may be culling the pods where the maggots have actually damaged the inner flesh on sidewall of the fruit, without even knowing the damage was caused by maggots inside.  However, chances are, if you are seeing a lot of soft rot in your pepper plantings late in the summer, then you either have pepper maggot or European corn borer problems: and the populations of corn borer have declined significantly in recent years.

When the maggots emerge from pepper, eggplant or horse nettle fruit, they drop to the ground and overwinter just below the surface as pupae.   The adult flies typically start to emerge in early to mid-July, emerge over a two to three week period, and can continue to lay eggs in (sting) fruit until mid- to late August.  Larvae will emerge in 4 to 6 weeks and return to the soil to pupate.  The maggot emergence holes in the fruit allow for infections with soft rot bacteria.  Fruit melting down from soft rot infection are usually noticed from mid-August through September.

We spent years figuring out how to monitor and control this allusive pest.  You can trap the adults 20-feet up in a maple tree using a yellow-sticky card baited with a vial of ammonium hydroxide.   You can also plant a hot cherry pepper plant every 10 to 20 yards in the outside row of your pepper field, especially along tree lines, and check the fruit for stings weekly, starting in early to mid-July.  Full-field insecticide applications would begin within a week of capturing flies or detecting stings on fruit. Usually 2 to 3 applications, at 8 to 10 day intervals, are needed to control the flies throughout their entire flight period.   You can also plant a perimeter row of hot cherry peppers all the way around your pepper field and just spray the cherry pepper trap crop a week after flies are trapped or the fruit stings first occur.

When we worked out the system for perimeter trap cropping with cherry peppers, there were very few effective spray options to treat the trap crop; we had Orthene and dimethoate.   However, in the last few years, Certis has registered two different baits that are OMRI-approved for organic farms and seem to control this pest pretty well.  We tried the liquid GF-120 Fruit Fly bait, together with a perimeter of cherry peppers, in 2011 at the farm that lost 80% of its fruit to the maggots the previous year.  It seemed to work well, but was really tough to apply correctly and even required special spray equipment.

This past year, the same farm tried a solid bait called Seduce, which is registered for peppers and many other crops, but only lists earwigs and cutworms as the target pests for any crop.  Because Seduce contains the same active ingredient (spinosad) as the GF-120 liquid bait, we decided to give it a try for pepper maggots on the same organic farm in Suffield this past season.   Seduce was applied twice about two weeks apart, by simply spreading the round pellets under the pepper plants throughout the field.  What was stunning was that we only found a couple of stings on fruit the whole year, and no flies on traps, or eggs or maggots in the fruit.  Unfortunately, it is difficult to design in a control (untreated) plot for this experiment, because the bait has been shown to be highly attractive to flies (i.e. onion maggots), and may pull them from a wide area to feed on the pellets and ingest a lethal dose of spinosad. So, maybe all the pepper maggot pupae drowned this year before the flies ever emerged, due to all the rain that we had in June, but maybe the Seduce was responsible for the complete control in this field.  As I mentioned earlier, there were other farms that had problems with pepper maggots this past summer, so it’s certainly possible that it was not the water that killed the pest.

The advantages of using Seduce over GF-120 are that it is very easy to apply with a handheld seeder or granular spreader, doesn’t require weekly applications, and because it is not a foliar application it may spare beneficial insects that control aphids and other pests. Foliar applications of spinosad have been shown to kill parasitic wasps and predatory Syrphid flies: both effective aphid and/or corn borer enemies.  Foliar application of non-bait formulations of spinosad  (e.g.  Entrust, SpinTor, Radiant), have no effect on pepper maggot populations because the adult flies do not eat foliage, and therefor do not consume a lethal dose. It is the bait in these new formulations that not only attracts the flies, but cause them to consume a lethal dose of the toxin.

The down side is that Seduce is not yet available in the Northeast, possibly because of low demand for earwig and cutworm control. So if you want to try this product, you will have to call your pesticide supplier prior to the season and ask them to stock a pallet of the bait. Once the supplier is convinced that there is a market for Seduce on onion, cabbage and pepper maggots (and cutworms), they will probably be happy to stock the product in the future.

Note:  It is legal to use a pesticide for a pest that is not on the label as long as the product is registered for the crop (besides, maybe there are cutworms out in your field).