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Notes on Strategies for Caterpillar Pests in Greenhouse Peppers

• A. European Corn Borer (ECB)
• Cabbage Looper control

A. European Corn Borer (ECB)

Background

Two strains of ECB exist in Ontario and their egg-laying schedule is as follows:

1-generation strain - peak egg-laying at end of June to mid-August (generally north of London)
2-generation strain (in Essex, Kent, Elgin) - peak egg-laying from end of May/early June to early/mid-July - then from late July to early September

Both strains exist in significant numbers in Lambton, Middlesex, Oxford, Brant, Haldimand-Norfolk, Hamilton-Wentworth and Niagara Counties.

Accumulated degree days or heat units to date indicate that we are in the midst of the 1st peak for the 2-generation strain so growers need to be very vigilant at this time and onwards.

Mating or Action Sites

These are grassy areas or areas of dense vegetation for mating activities which usually begin by 10 p.m., peak at 1 a.m. and end at dawn. The best sites for mating are along waterways or drainage areas and fencerows.

Moths that produce 2nd generation larvae prefer grassy areas with canopy heights of 60-120 cm (2-4 ft). Adults are capable of flying 5-8 km during one evening, with help from winds.

Egg-laying Activities

Warm, calm evenings are best. Egg-laying begins shortly after sundown and ceases by midnight. High winds, thunderstorms and temperatures less than 180C (650F) can delay or stop egg-laying.

Management Strategies

1. Pheromone Traps for Monitoring
   Based on production of kind of sex pheromones (a chemical produced by the female to attract males for mating purposes), ECBs have been divided into Iowa and New York strains. Only the Iowa strain exists in Ontario. Further east towards Quebec, there may be a mixture of both types. Therefore, only pheromone traps for the IOWA strain will be useful to Ontario growers. Both 1- and 2-generation strains are attracted to the same pheromone lures which should be changed regularly, as much as weekly. Note that in the presence of live females, male ECBs are less attracted to pheromone traps, so low counts in such traps can be misleading.
   Pheromone Trap Placement

   • Use small groups of 3 or more traps placed at least 50 ft apart. Single traps are less reliable.
   • Place traps on the edge of a field, grassy area or within a field of soybeans, potato, or corn.
   • Place traps at least 15 cm or 6 in. below the top of the canopy of the vegetation.
   • Cool or windy nights will reduce effectiveness of pheromone traps.
   • Use light traps in conjunction with pheromone traps.

   
   

   2. Light Traps
      Light traps placed at a distance outside of greenhouses and with the protective grill removed, can serve as a monitoring tool as well as a means of reducing populations of both ECB and cabbage looper entering greenhouses. Traps should ideally be inspected and cleaned daily.

   3. Chemical control - Confirm
      Confirm, which is registered for control of ECB in greenhouse peppers, induces premature moulting and subsequent death of caterpillar pests. It is highly specific to moth pests and compatible with biocontrol agents. With regard to Orius, field trials indicate very low mortality after application of the active ingredient in Confirm. Field tests in cotton, using about twice the Confirm label rate, showed that percent survival of Orius nymphs was 80 and 77.5% at 1 and 7 days after its application. Good coverage is necessary to ensure that the fruits, particularly around the calyx or fruit cap, are well covered to provide protection against ECB. Remember that the very young ECB larvae usually enter fruits just under the calyx.

   4. Biological control - Trichogramma species
      Trichogramma wasps comprise one group of potential biocontrol agents for caterpillar pests. Of over 100 species of Trichogramma, a few are commercially available and these include T. brassicae, T. pretiosum, T. evanescens, T. minutum and T. platneri. Of these, T. brassicae and T. evanescens have been successfully used against ECB in field corn. Some points to consider when selecting and using Trichogramma for biocontrol of ECB are as follows:

      • Comparison of several Trichogramma species in the laboratory at Pennsylvania State University showed that T. minutum and T. platneri did not successfully parasitize any ECB eggs, T. pretiosum provided 3.8% parasitism, and T. nubilale 65.5%
      • A commercial greenhouse pepper trial in Ontario (Del Sol's) resulted in 42% and 61% parasitism of sentinel eggs (test eggs of another moth species) by T. brassicae and T. ostriniae respectively, when eggs were located about 3.6 m (12 ft) from point of release of the Trichogramma wasps
      • Comparison of 3 rates of release (100,000, 200,000 and 400,000 per acre) of T. ostriniae (also at Del Sol's) in 2003 did not result in any significant differences in percentage of eggs parasitized
      • In field corn trials, T. brassicae has demonstrated effectiveness against ECB at a rate of 100,000-125,000 per ac
      • In a commercial greenhouse pepper trial in BC, T. brassicae were detected more in the upper canopy than T. pretiosum, whereas the reverse applied for the lower canopy
      • Trichogramma wasps only live about a few days at greenhouse temperatures and it may be best to release a mixture of pupae with different times of emergence for optimum results
      • Generally, the percentage of ECB eggs parasitized is negatively correlated with increase in (a) leaf area or plant size, and (b) distance that eggs are located from the point of release of wasps

    

B. Cabbage Looper control

Cabbage Looper control using the bacterium, Bacillus thuringiensis (Bt) (Dipel, Foray, Bio-Protect)

• Bt is a stomach poison that kills the insect only after the insect has ingested it by feeding on material treated with it.
• The toxins in Bt paralyze the gut causing the insect to stop feeding, usually within an hour. This is followed by a slow poisoning of the insect, resulting in death 1-7 days after ingestion of Bt.
• Because Bt is not systemically transported within the plant, it is very difficult to kill insects that feed within the plant such as by tunneling. Good coverage on both upper and lower leaf surfaces is therefore very important. To assist in coverage, use as fine a droplet size as possible, and apply as uniformly as possible. Addition of a spreader/sticker may improve coverage.
• Bt loses its pathogenicity or ability to kill after about 72 hr of UV irradiation. However, Bt degradation under greenhouse conditions may take a bit longer. Shortening of spray intervals can compensate for the rapid degradation of Bt by sunlight and applications on evenings can help delay breakdown.
• Young stages are usually more easily killed than older ones, so timing of applications as soon after egg-hatch is important.
• Ensure that the pH of the water used for mixing is 6.0-6.5. A high pH will cause breakdown of Bt and reduction of its effectiveness.