Bees and Fungicides: Part Three

Part three: Alternative to fungicides.

Axten Family

Axten Farms near Minton, Saskatchewan began to integrate a number of different cropping systems about 10 years ago including no-till, cover crops, inter-cropping, combination planting, compost teas and controlled traffic farming. The goal is to have high plant diversity and plants growing for as long as possible to help feed soil biology and make the whole system more sustainable and resilient to stress from drought.

For several years the farm has been growing an intercrop of flax and chickpeas, which are seeded in alternate rows, and has eliminated disease and the need for fungicide applications. “Since we started doing flax and chickpeas we’ve only ever had one application of fungicide, and that was in 2016 when it was wet and most guys that year sprayed five or six passes,” says Derek Axten. “By separating the rows of chickpeas, we have basically eliminated the need for fungicides.”

Subterranean clover crop

Axten is now going a step further and planting a subterranean clover crop under the flax and chickpeas, which he believes further helps reduce disease risk. “I think it stops rain bounce and splatter, which helps with disease control,” he says. “I don’t have any data to prove that, but I was out looking after a rain and because the clover covers the ground there is no bare soil, so the rain hits the leaf instead of hitting the ground and it doesn’t splash spores up on the chickpea plants.”

Reduced fungicide use and the inter-crop system has put more money in Axten’s pocket and reduced his overall risk. “We’ll usually be 10 to 15 per cent under the average yield for a chickpea monocrop for the area, but that usually comes with 10 to 15 bushels of flax and $100 per acre less fungicide bill,” says Axten. “We carry a lot less risk.”

Pollinator strips


Axten is also experimenting with pollinator strips to provide habitat for and encourage pollinators like bees, but also as a way to prevent erosion. Most of the farm is in controlled traffic farming, where the equipment always travels on established tramlines, leaving the no-tilled, cropping areas free from compaction. Because Axten initially was worried about possible soil erosion over time on the hills of the tramlines, he decided to use a small Valmar applicator to seed a mix of clovers in the tramlines as he is seeding the crop. “The idea is that every 60 feet we’re going to have two strips, 10 feet apart of clover growing in every crop,” says Axten. “I want those to be there forever, so it gives a bit of a buffer, and provides a pollinator strip every 60 feet. We lose that five per cent of the crop in the tramlines anyway, so we might as well do something that is useful.”

Bees and Fungicides: Part Two

bee on sunflower two aug 2010

Image: Angela Lovell

Part two: What can farmers do to minimize risk of fungicides to bees?

Scott McArt, Many farmers don’t consider the effects that fungicides can have on non-target insects such as bees.  But new research by scientists at Cornell University have found that fungicides can make certain insecticides such as neonicotinoids  – already known to be toxic to bees – much more toxic.

Farmers will often refrain from spraying an insecticide during the day when bees are active because they know it could affect them, but because they don’t think that fungicides will have any effect, they often spray them on a sunny, clear day when the bees are active, says Scott McArt, assistant professor of entomology at Cornell University’s College of Agriculture and Life Sciences, who is leading the research study.“Although the fungicide may not be having a direct affect on the bees because they aren’t necessarily very toxic to bees by themselves, it’s the insidious interactions with the insecticides or pathogens in bees that they need to think about,” he says.

Best practices

McArt suggests a number of best practices that farmers can follow to try and minimize the negative effects of fungicides on bees and other non-target insects.

  • Avoid spraying during the day when bees are out foraging.
  • Avoid certain classes of fungicides such as ergosterol-biosynthesis-inhibitors (EBI) and sterol biosynthesis inhibitors (SBI). “Basically, any fungicide names ending in ‘zol’  are the worst in terms of increasing the toxicity of insecticides, including propiconazole which increases the toxicity of pyrethroid insecticides by 1,000 fold,” says McArt.
  • Avoid all fungicides containing chlorothalonil, which is particularly bad because of its synergism with insecticides and bee diseases such as nosema.

Developing strategies

Researchers are already working on trying to figure out the interactions between different pesticide products and their effect on bees and other insects and develop some guidelines for management practices that can help them manage their pests with less risk to non target insects. They are already working with apple growers to test the effects of different types of fungicides for their synergistic effects and to understand the effect of different spray regimens.”We are looking at things like spray timing, and nozzle technology to reduce drift to try and make applications more targeted to pests and reduce the impact on bees,” says McArt. “We need to get the science into growers’ hands.”

(A version of this story first appeared in Grainews).

Next week in part three of this three-part series we explore an alternative to fungicides.

Fungicides and Bees: Part One

Bee on Phacilia forage two MBFI tour Aug 2017

Image: Angela Lovell

In this three-part series we take a look at the negative health effects of fungicides on bees, what farmers can do to minimize the risks and what other producers are doing as an alternative to using fungicides.

Part one: Fungicides could be having negative health impact on bees.

A team of scientists at Cornell University studying pollinator health were surprised to find that fungicides could be having negative health impacts on wild and managed bee populations.

There has been a lot of research studying the effect of insecticides, such as neonicotinoids, on bee health, but it was largely assumed that fungicides, designed to kill pathogens, had no impact on bees. Although researchers found that fungicides themselves are not necessarily very toxic to bees, they can act synergistically with insecticides to make them much more toxic to bees.

Fungicides and insecticides together are more toxic to bees

Fungicides can do two things, says Scott McArt, assistant professor of entomology at Cornell University’s College of Agriculture and Life Sciences, who led the research. “In our laboratory we have shown that fungicides can synergize with insecticides and causes the detoxification mechanism in the bees to be knocked out so they are unable to detoxify the insecticide as well, and even at low levels the insecticide then becomes much more toxic to the bee,” he says.  In their tests the rate of death of bees increased by a least 25 per cent when they were exposed to fungicides and insecticides as opposed to just insecticides alone.

Secondly, in their analysis of bumblebees in the United States, researchers have found that fungicides interfere with the bee’s gut microbiota. “Just as humans need a good balance of microbiota in our gut for proper function, so do bees,” says McArt. “If the fungicide impacts the microbiota the bee is more susceptible to pathogens, in particular nosema, which is a gut pathogen specific to bumble and honeybees.”

In the team’s analysis of 198 managed bee colonies across New York State they found that each had at least six different detectable pesticides in the hives, and 90 per cent of the residues found were fungicides. Overall, their lab research found that fungicides are the best predictor of range contractions in wild bees. “We are not sure if fungicides are contributing to bee decline, but we know that there is a connection between fungicides and the disappearance of bees from areas where they were previously present,” says McArt.

Chlorothalonil of particular concern

One of the active ingredients in some common fungicides – chlorothalonil – has been shown to be especially harmful because it synergizes particularly well with common insecticides such as neonicotinoids and pyrethroids and makes them five times more toxic to bees. “Laboratory studies have shown that exposure to chlorothalonil makes bees more susceptible to nosema,” says McArt. “Although we have to do further studies to understand why, we know it is disrupting the microbiota so they are not blocking the pathogen.  We are also hypothesizing that it could be killing actual gut cells, so there are less to ward off pathogens and less of an immune response.”

Chlorothalonil is an active ingredient in a number of fungicides registered with the Canadian Pest Management Regulatory Agency. Some of those used for agricultural purposes include Bravo 500® and Daconil® from Syngenta.

In response to an email inquiry to Syngenta asking if someone from the company could comment on this research and make any recommendations for growers, Peter Campbell, Head of Research Collaborations for Syngenta at Jealotts Hill, UK replied.

“This study is a correlative study and the authors themselves within the publication ‘caution against over-interpretation of correlational patterns between pathogens and bee declines that may not be indicative of larger patterns or causal mechanisms.’

“Among other things, this suggests a need for further research investigating the reported correlations to provide greater clarity regarding the presence or absence of a plausible mechanistic pathway of causation.”

“It is also well known that a major factor affecting bumble bee populations and their ranges is habitat, in particular, availability of nesting, foraging and queen over-wintering sites. While habitat was included as a variable in this analysis, the classification used was very broad (e.g. cropped land, forest, agricultural area). The categories used in the study are too broad to capture the specific habitat needs of different bumble bee species in terms of their nesting, feeding and queen over-wintering site preferences, as well as the need for continual availability of food.”

Not just a problem for bees

Research into pollinator health has gained a lot of momentum over the past four or five years as there has been a much broader recognition that declining pollinator populations is a serious issue that could have a huge financial impact on agriculture, not to mention global food security.

The United States typically loses 25 to 40 per cent of managed honeybee colonies every year and the last three years that rate has been between 44 and 54 per cent.  There are 416 wild bee species documented in New York State and 53 are known to have had range contractions over the last few years.

The problem is not just unique to bees. A German paper recently published showed a 75 per cent reduction in total insect biomass in Germany in the past 25 years, not restricted only to bees. “There are likely many causes but we have seen a reduction in insects over the last 30 to 40 years we have never been seen before,” says McArt. “It’s a worrying trend.”

(A version of this story first appeared in Grainews).

Next week in part two of this three-part series we explore what farmers can do to minimize risk of fungicides to bees?