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Extension > Minnesota Crop News > Pyrethroid resistant soybean aphids: What are your control options?

Monday, July 31, 2017

Pyrethroid resistant soybean aphids: What are your control options?


Bruce Potter (Extension IPM Specialist, U of MN), Robert Koch (Extension Entomologist, U of MN), Phil Glogoza (Extension Educator – Crops, U of MN), Ian MacRae (Extension Entomologist, U of MN), and Janet Knodel (Extension Entomologist, NDSU)

We are receiving an increasing number of reports of pyrethroid insecticide failures for soybean aphid management from northwest and central Minnesota, and northeastern North Dakota this year. However, many areas of Minnesota and North Dakota still have low, non-yield threatening aphid numbers and scouting should continue to determine when to apply insecticides.

In this article, we review the insecticide groups used for soybean aphid control (Table 1) and discuss the potential role of and challenges associated with insecticide mixtures.
We are all familiar with the multistate, researched-based economic threshold of 250 aphids/plant for determining when to apply insecticides for soybean aphid. Waiting until this economic threshold to apply insecticides is KEY for ensuring continued efficacy of current insecticides for soybean aphid. Using the soybean aphid economic threshold for deciding when to apply insecticides will:
  • Prevent unnecessary selection pressure for insecticide resistance; 
  • Save time by reducing the odds of a field needing a second treatment;
  • Mitigate secondary pest problems like spider mites, and perhaps most importantly
  • Reduce production expenses.
Poor insecticide resistance management of a mobile insect like soybean aphid affects not just your farm, but other farmers as well.

Farmers who experience aphid populations above the threshold, those who sprayed too early and now need to re-treat, and those who experienced insecticide failures, face some serious questions. What options do soybean growers have in light of increasing aphid populations, especially when those aphids may be resistant to pyrethroid insecticides?

Here are some general recommendations to improve pest management of soybean aphids:

When applying any insecticide for soybean aphid, spray coverage and canopy penetration are critical.
  • Do not use reduced insecticide rates.
  • Use appropriate spray pressure and spray nozzles (for example. do not use large droplet Engenia or Xtendimax approved nozzles) to treat aphids.
  • Do not skimp on water. At least 15-20 GPA via ground and 3-5 GPA via air.
  • Insecticide applications during windy conditions, temperature inversions, or very hot weather could reduce control.
  • Check insecticide performance 3-5 days after application.
Do NOT retreat a field with the same insecticide group for consecutive applications!
  • If it didn’t work the first time why would it work the second time?
  • If it did work the first time, it might not work the second time.
Insecticide group numbers can be found on the label.

INSECTICIDE GROUPS (TYPES)

Pyrethroids (Group 3A): In light of recent pyrethroid performance issues, it is not advised to apply an insecticide containing only a pyrethroid insecticide(s) in most areas of Minnesota and in northeastern North Dakota.
  • These broad-spectrum insecticides have been widely used for soybean aphid control.
  • Insecticides in this group are not equally effective on soybean aphid.
  • Resistance levels may vary among pyrethroid products and soybean aphid populations.
  • Potential for 7-10 days residual but new growth not protected.
  • If you do use a pyrethroid on soybean aphids use a high labeled rate.
  • Among the pyrethroids, only bifenthrin is labeled for control of spider mites.
  • These insecticides are toxic to beneficial insects and bees.
If a pyrethroid insecticide application may not work well, which insecticides should be considered?

Organophosphates (Group 1): for example, chlorpyrifos (Lorsban and generics)
With the widespread pyrethroid failures, this is one preferred option for first applications in a field or when retreating a field that was previously treated with a pyrethroid insecticide.
  • Chlorpyrifos is still very effective against soybean aphid populations.
  • This insecticide does not have a long residual and volatilization is increased in warm weather. Soybean aphids can recolonization chlorpyrifos treated fields within a few days.
  • This group provides broad-spectrum control of pests
  • Dimethoate, another organophosphate insecticide labeled for soybean aphid, has provided variable and sometimes suboptimal control of soybean aphid in efficacy trials in Minnesota and North Dakota when used alone.
  • Chlorpyrifos and dimethoate have shown good activity on Minnesota populations of two-spotted spider mite. Some populations of spider southwest Minnesota have shown resistance to chlorpyrifos.
  • These insecticides are toxic to beneficial insects and bees.
Neonicotinoids (Group 4A): for example, Belay, Admire Pro, Alias
  • These insecticides are absorbed and translocated short distances within the plant. They may be moved upward for a leaf or two.
  • At high rates, this insecticide group can provide residual activity, but not more than 2-3 weeks.
  • Provide fairly broad-spectrum control for chewing and sucking pests.
  • These insecticides are toxic to some beneficial insects and bees.
Butenolides (Group 4D): Sivanto
  • This is a recently labeled chemistry for soybean aphid. We do not have a large data set for this insecticide on soybean aphid. Data from Minnesota in 2015 showed moderate control of very large soybean aphid populations.
  • Like the related neonicotinoids, this chemistry is translocated short distances within the plant.
  • This insecticide sub-group is only effective on some species of sucking insects.
  • This chemical has relatively low toxicity on honey bees.
  • This is an expensive insecticide (about $17 to $35 per acre for the insecticide alone), so cost is an issue.

INSECTICIDE MIXES

We do not generally recommend premixes or tank mixes of insecticides. From a resistance management perspective, premixes and tank mixes with reduced rates of one or more insecticides should be avoided. However, such mixtures may be necessary when products with single insecticide groups have already been applied to a field.

Pyrethroid premixes (such as Hero)
  • Mixtures of multiple pyrethroids do not make sense when treating a soybean aphid population that is already suspected to be resistant to pyrethroids. All pyrethroid insecticides are in the same insecticide group (Group 3A).
Neonicotinoid premixes (such as Endigo, Leverage)
These premixes would be a preferred option following a chlorpyrifos application.
  • In University research trials, these mixes have provided control of aphids. One of these (Endigo) has been shown to provide control of soybean aphid populations that were potentially resistant to pyrethroids.
  • Based on the lower levels of control observed in northwest and central Minnesota this year, the neonicotinoid portion would need to do most of the control, increasing resistance selection pressure on that group and perhaps control.
  • Watch for increasing spider mite populations after a foliar neonicotinoid application has been applied to field.
  • If you used an insecticide seed treatment, you have already made one neonicotinoid application to the field.
Organophosphate premixes (such as those with chlorpyrifos - Cobalt, Tundra Supreme, Stallion)
  • Our trials have shown the effectiveness of chlorpyrifos-containing premixes (Cobalt) against soybean aphid in recent years.
  • After the application of an organophosphate-pyrethroid premix, the field is protected for up to a few days by the organophosphate; however, the longer residual activity of the pyrethroid will not be effective on surviving or incoming aphids that are resistant to pyrethroids.
  • Though dimethoate alone has provided inconsistent control of soybean aphid, research trials in southwest Minnesota in 2016 suggested that soybean aphid control offered by a pyrethroid was improved with the addition of dimethoate.

For those wanting to mix products, be advised that there may be compatibility issues when tank-mixing insecticides.
  • Test any potential tank mix for compatibility first.
When choosing insecticides, consider the abundance of yield threatening insect pests first. For example, do not base an insecticide choice on non-threatening levels of a secondary pest. However, if dry conditions persist, spider mites could quickly become a real pest concern that will further complicate insecticide selection.

Table 1. Insecticides labeled for soybean aphid control in Minnesota and North Dakota. Not all of these products have been evaluated in University of Minnesota or North Dakota State University trials.



Representative products
Group
Class
Active ingredient
Individual active ingredient
Formulated mixtures
1A
Carbamate
methomyl
Lannate

1B
Organophosphate
acephate
Acephate


Organophosphate
chlorpyrifos
Lorsban Advanced, Chlorpyrifos, Govern, Hatchet, Nufos, Vulcan, Warhawk, Whirlwind, Yuma
Tundra Supreme, Cobalt, Cobalt Advanced, Stallion, Match-Up

Organophosphate
dimethoate
Dimethoate

3A
Synthetic pyrethroid
alpha-cypermethrin
Fastac



beta-cyfluthrin
Baythroid
Leverage


bifenthrin
Tundra, Sniper, Fanfare, Discipline, Brigade, Bifenture
Justice, Match-Up, Tundra Supreme, Brigadier, Swagger, Skyraider, Hero, Steed, Triple Crown


cyfluthrin
Tombstone



deltamethrin
Delta Gold, Batallion



esfenvalerate
Asana XL, Adjourn



gamma-cyhalothrin
Declare, Proaxis
Cobalt


lambda-cyhalothrin
Warrior II, Grizzly Z, LambdaStar, Lambda-Cy, Lamcap, Province, Silencer VC, Taiga Z
Besiege, Cobalt Advanced, Double Take, Endigo, Seeker


permethrin
Arctic



zeta-cypermethrin
Mustang Maxx, Respect
Hero, Steed, Stallion, Triple Crown
4A
Neonicotinoid
acetamiprid

Justice

Neonicotinoid
clothianidin

Belay

Neonicotinoid
imidacloprid
Prey, Admire Pro, ADAMA Alias, Wrangler, Nuprid, Sherpa
Leverage, Brigadier, Swagger, Skyraider, Triple Crown

Neonicotinoid
thiamethoxam

Endigo
4D
Butenolide
Flupyradifurone
Sivanto Prime

28
Anthranilic diamide
Chlorantraniliprole

Besiege


Always read and follow the insecticide label.

Products are mentioned for illustrative purposes only. Their inclusion does not mean endorsement and their absence does not imply disapproval.

© 2017, Regents of the University of Minnesota. All rights reserved.
The University of Minnesota Extension is an equal opportunity educator and employer.

2 comments:

  1. I cover an area in NW Minnesota which includes all of Marshall County, a sliver of Kittson and Roseau Counties as well as eastern Walsh and Grand Forks counties in North Dakota. I have now had to treat every soybean field for soybean aphid. Populations have doubled approximately every 4 days for the last 2 weeks. I have never recommended anything for control except chlorpyrifos and I have never had a control failure. I also have never had subsequent mite problems. Those relying on pyrethroid "guarantees", and mixed them with their 2nd glyphosate application are respraying. I had used 1/2 pint/acre in the past but this year went to a pint. I did do one field at 1/2 pint, a week ago today (Monday), and there is no sign of recolonization after a week. There were well over 1000/plant at treatment.

    ReplyDelete
    Replies
    1. David: Thank you for sharing your experiences and observations. Under favorable weather conditions (which we have had), aphid population growth rates can be very fast like you are seeing. We have also seen situations where folks sprayed below threshold and now have to treat again. The 1/2 pint rate of chlorpyrifos you mention may have worked, but I would encourage you to use a rate within the labeled range for this pest (1 - 2 pints/ac).

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