10/29/2020

Novel Corn Rootworm Beetle Control Options

Written by Hannah Weber, Pioneer Agronomy Intern; Jake Bates, Alex Woodall, and Nate LeVan, NC Iowa Pioneer Field Agronomists

Key Findings

  • How effective is Steward® EC insecticide in reducing CRW populations? Pioneer conducted trials in several long-term continuous corn fields in north central Iowa.
  • Steward EC is a group 22 insecticide with up to 14 days of residual control, which could provide greater flexibility when treating for CRW adults to suppress populations in corn-on-corn fields.
  • Steward EC insecticide provided control of CRW adults for at least 14 days after treatment at all locations, and for 21 days or more at most locations.

Importance of Integrated Pest Management

  • The best way to manage corn rootworm (CRW) is with an integrated pest management (IPM) system that includes multiple effective control tactics such as:
    • Rotation to a non host crop
    • Planting hybrids with multiple Bt traits for CRW control
    • Applying in-furrow or lay-by insecticides
    • Scouting for and managing CRW adults 
  • Management for extended corn on corn systems (3+ years corn) requires using multiple strategies every season for long-term success and profitability.
  • CRW have shown to be highly adaptive, with rotation-resistant northern CRW (extended diapause variant) and western CRW (adults that lay eggs in soybean fields) as well as some populations that are resistant to Bt traits or insecticides.
  • Single strategy tactics such as ephemeral use of only soil-applied insecticides, or only CRW Bt corn may decrease the length of time that tactic is effective and reduce available options for CRW management.

Adult Corn Rootworm Control

  • Foliar insecticide treatment to control adult CRW, a practice commonly referred to as “beetle bombing,” involves applying an insecticide as CRW beetles begin to emerge in a field.
    • This tactic is used to suppress CRW populations by reducing egg laying, as well as reduce silk feeding by CRW beetles, which can have serious effects on pollination.
    • Timing of foliar treatments has historically been based on GDU accumulation or corn growth stage, typically around VT/R1. 

Photo - CRW eggs and corn ear damaged by silk feeding.

Figure 1. Well-timed insecticide applications for control of CRW beetles can reduce silk feeding in the current crop reduce and eggs laid for the following year’s CRW population.

  • A properly timed insecticide application can be very effective in reducing adult CRW populations (Figure 1).
  • A challenge with using foliar insecticides to reduce egg laying and future CRW root feeding pressure has been timing the application to coincide with the peak emergence of female CRW beetles, which generally emerge later than males.
  • Sticky traps are a useful tool for monitoring adult emergence. Use these in conjunction with corn growth stage and GDU accumulation to determine the best time for treatment (Figure 2).

Photo - Corn rootworm sticky trap one week following an insecticide application.

Treated – 2 beetles/day

Photo - Corn rootworm sticky trap from a non-treated location one week after installation.

Non-treated – 17 beetles/day

Figure 2. Corn rootworm sticky trap one week following an insecticide application (top) compared to a trap from a non-treated check (bottom).

Dealing with Extended CRW Beetle Emergence

  • Recently, the duration of CRW beetle emergence has extended over a wider window than historically “normal” in north-central Iowa, with emergence continuing later into the growing season.
 

“Management for extended corn on corn systems requires using multiple strategies every season for long-term success and profitability."

  • Extended duration of CRW beetle emergence can reduce the effectiveness of a foliar insecticide application, even when properly timed.
  • Many insecticides are available that provide excellent knock-down of high populations of CRW beetles; however, a new product, Steward® EC, offers extended residual control of adult CRW beetles.
    • Steward EC is a group 22 insecticide with up to 14 days of residual control according to the manufacturer.
    • The active ingredient, indoxacarb, works through both contact and ingestion.
  • An insecticide with a longer window of residual control could provide flexibility when treating for CRW adults to suppress populations in corn-on-corn fields.

2020 Pioneer Research Trials

  • In 2020, foliar insecticide trials were conducted in several long-term continuous corn fields in north central Iowa likely to have high CRW beetle emergence (>7.0 beetles/trap/day) to evaluate effectiveness in reducing CRW populations.
  • All trial fields included an area treated with 8 oz/acre of Steward EC insecticide; some also included a non-treated check.
  • The study included both ground and aerial applications.
  • Fields were monitored for CRW adult pressure once every week for up to two weeks prior and six weeks after insecticide application.
  • Trial locations included populations of both northern and western CRW, which were composited in beetle counts.

Results

  • At six trial locations where CRW beetle populations were moderate to high prior to treatment, Steward EC insecticide reduced populations to low levels (avg. 3 or fewer beetles/trap/day) (Figure 3).
  • Among 3 locations where beetle populations were measured through 28 days after treatment, populations remained low at two locations but rebounded after 14 days at one location.

    Figure 3. Corn rootworm beetle populations (beetles/trap/day) at six moderate to high pressure locations following treatment with Steward EC insecticide. (Beetle counts at T0 reflect samples taken within 8 days prior to insecticide application.)

  • Four trial locations included a nontreated check in the field and were sampled 35 days or more after treatment, providing an extended look at CRW population levels following treatment compared to no treatment.
    • At one location, beetle counts were very low throughout the sampling period (data not shown).
    • Two locations had high CRW pressure and one had low to moderate pressure (Figure 4).
  • Insecticide treatment reduced beetle populations relative to the nontreated check throughout the sampling period at all three locations with CRW pressure.
    • Beetle populations remained low for more than 21 days after treatment.
    • Beetle populations rebounded somewhat beyond 28 days after treatment at the two higher-pressure locations but were still lower than the nontreated checks.
    • Minimal rainfall during late July and August of 2020 at many of the trial locations may have helped extend the duration of insecticide residual activity.

Photo -  Corn rootworm beetle populations (beetles/trap/day) with and without insecticide treatment.

Figure 4. Corn rootworm beetle populations (beetles/trap/day) with and without insecticide treatment at three moderate to high pressure locations that included both a treated and nontreated area.

Conclusions

  • Steward EC insecticide provided control of CRW adults for at least 14 days after treatment at all locations, and for 21 days or more at most locations.
  • Results demonstrate that a properly-timed foliar insecticide application can be very effective at reducing adult CRW populations, making it a valuable option to consider as part of an integrated CRW management plan.

Always read and follow product label directions.

Please reach out to your local Pioneer sales representative for more agronomic insights.



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The foregoing is provided for informational use only. Please contact your Pioneer sales professional for information and suggestions specific to your operation. 2020 data are based on average of all comparisons made in over 10 locations through Sept 20, 2020. Multi-year and multi-location is a better predictor of future performance. Do not use these or any other data from a limited number of trials as a significant factor in product selection. Product responses are variable and subject to a variety of environmental, disease, and pest pressures. Individual results may vary.