What effect are fall army worm pesticides having on non-target organisms like bees, earthworms & butterflies? Let’s investigate..

Thankfully, it is a question that I am frequently asked when using and recommending pesticides which shows that there is a very genuine concern among growers to minimize the impact of our operations on Bees, beneficial insects and Earthworms.

This is an enormous area, and if you will excuse the pun, I could be opening up a ‘can of worms’ here by suggesting that one pesticide is safer than another.

So firstly do not dwell on the specific products below; it is a rough guide to help you understand and manage the risks.

Secondly, there are so many studies involved in toxicology, they may at times conflict in their conclusions. I have summarised the general facts to help to understand the background risks of the products you are applying.

Thirdly, application and use is everything. Applying fall armyworm pesticides at the right time of day, away from Bee hives, using low drift nozzles is as important as the product being applied.

fall army worm insecticide

There is a very genuine concern among growers to minimise the impact of our operations on Bees, beneficial insects and Earthworms.

Below is a list of commonly used products, and how safe they are to Bees in particular. If you are concerned about Lacewings, Hoverflys, Carabids etc, the information is out there too.

    Risk to bees Length of residual toxic effects
Abamectin e.g. as in Voliam Targo HIGH 1-3 days
Acephate e.g. Orthene, Sinophate HIGH 3+ days
Acetamiprid e.g. Aster HIGH Length of toxicity is short, thought to be <1 day. Like Thiacloprid, the cyano group of neonics is a lower risk than thiamethoxam and imidacloprid for example.
Pyrethroids, various e.g. alpha cypermethrin, beta cyfluthrin, deltamethrin, lambda-cyhalothrin

NOTE: Tau-fluvalinate (e.g. Mavrik) is of low-moderate toxicity.

HIGH Varies from a matter of 1 to several days depending on product and formulation, but generally high risk.
Chlorantraniliprole e.g. as in Voliam Targo Very low No known impact
Chlorpyrifos e.g. Dursban HIGH 4-6 days
Dimethoate e.g. Danadim HIGH 3 days
Emamectin benzoate e.g. Prove, Escort HIGH 1 day
Flonicamid e.g. Teppeki Low Possible effect on Honey Bees but no identified risk
Flubendiamide Very low Not identified as a risk to Honey or Bumble Bees
Imidacloprid e.g. Concord YES 1 day max – less for Honey Bees
Indoxacarb e.g. Indox, Merit YES 1 day for Honey Bees, 3 for Bumble Bees
Methoxyfenozide e.g. Runner Low Low – no known identified risk
Novaluron e.g. Rimon Moderate Length of risk is unknown
Pirimicarb e.g. Pirimor Low No known toxicity but reports exist of low mortality in some field studies
Pymetrozine e.g. Chess Low-moderate No risk label on most products but some field studies have shown low mortality.
Pyriproxyfen e.g. Profen Very low Very low risk
Spinetoram e.g. Radiant Moderate A known but moderate risk. Very short lived, likely 2-3 hours risk.
Sulfoxaflor e.g. Transform, Closer Low 2-3 hours. Generally acknowledged as Bee safe.
Thiacloprid e.g. Calypso Low Possible toxicity to Bumble Bees
Thiamethoxam e.g. Engeo Very High 7-14 days – very persistent and to avoid in flowering crops

Simple Steps To Protect Bees

Some basic rules can massively reduce the risk to Bees. Makes sure you know where the hives are located and create a buffer zone around them to avoid direct spray drift.

Spray early morning or late evening when the Bees are not foraging in the crop – for Fall Armyworm you should be spraying at these times of day anyway.

Oil based adjuvants can affect the ability of bees to repel water and can significantly increase mortality, even with fairly benign pesticides. So be aware if using Nufilm or Codicide for example.

Many pesticides contain repellent pheromones designed to keep Bees away from danger. Mixing them with some triazole fungicides such as tebuconazole, propiconazole and cyproconazole for can mask this repellence effect and cause significant Bee mortality.

Take care if there are flowering weeds are present in the crop, even if the crop itself is not flowering.

What About Earthworms?

Natures’ ploughmen as they are often referred can also be impacted by what we spray above ground, but in reality this is to a far lesser extent than above ground species.

Earthworms are usually a great indicator of healthy soil

It is worth understanding the impact of what we are spraying however, and some of the more risky products will surprise you.

Chemical Risk to Earthworms
Acetamiprid High risk, short period of risk
Chlorpyrifos High, with up to 2 weeks risk
Emamectin benzoate Low to Moderate
Flubendiamide Low risk
Lambda cyhalotrhin Low risk
Imidacloprid Very high risk
Lufenuron Low risk
Thiacloprid Low risk
Carbendazim Very high risk
Tebuconazole Low risk
Prothioconazole Low risk
Pendimethalin Moderate toxicity, but low risk at normal application rates
Atrazine Low toxicity, but a reduction in growth rates of worms has been observed in studies.
Cultivations Extremely high risk. Off the scale compared to any of the above!

It is extremely important to understand both the context and origins of this information. Most studies are compiled in a lab, observing earthworms directly exposed to pesticides on filter paper, and measuring acute toxicity.

In the field earthworms are not likely to come into direct contact with the pesticide immediate at or after spraying, and the chemicals are likely to be at an advanced stage of degradation before the worms pull decaying material into their burrows.

Therefore there is a significant difference between laboratory toxicity and the risk of field exposure. For chlorpyrifos which can be persistent for several weeks in the environment there is clearly a risk and this has been measured in field studies. For acetamiprid or lambda cyhalothrin for example the breakdown is very rapid, hence exposure risk is far lower.

Neonicotenoids are in fact the greatest risk by a long way, but the probability of Earthworms coming into contact with them is very very low.

The fungicide Carbendazim however has been acknowledged as posing a high risk, in part due its persistence in decaying plant matter.

Cereal Crops and Nutrients Update

Last week we looked at the effects of the prolonged rains and cool, damp soils on nutrient uptake. As wheat has reached the flag leaf stage over the past week, Magnesium deficiency has become visible in many crops in both The Rift and around Mount Kenya, which is typically in cool, saturated soils. Note that this is even in soils with fairly high magnesium levels, so do not be complacent.

Leaf testing is the best way to verify this, and it can be easily corrected with 2-5 kg/ha of Magnesium Sulphate in 100 litres of water.

Useful references:



Till next time,

Happy farming


About David

David Jones is the Broad Acre Specialist at Crop Nutrition Laboratory Services Ltd. (CROPNUTS). David has a keen interest in soils and no till farming systems where he has undertaken work looking into weed levels and changes in soil structure, and has extensive experience in field trials and in the development of precision farming techniques. In his spare time he enjoys playing rugby.