Dicamba and dust

October 2017

The major herbicidal chemicals used by US farmers haven't really changed very much over the decades. Various forms of 'dicamba', first introduced in 1967, and 'glyphosate', first introduced in 1974 , feature in America's agricultural landscape as much today as they did a quarter of a century ago.

Both these herbicides have a low acute toxicity to animals (you'd need to eat an awful lot before you'd drop dead). However, their properties, modes of action and applications are very different.

Dicamba selectively kills broad-leafed weeds, but not grasses. In 1994, 90% of the 27.6 million pounds of dicamba formulation used in US fields was applied to maize.

Glyphosate kills all plant life. Until the late 1990s, glyphosate was used to clear the ground before a crop was planted, and in 1995 27.6 million pounds of glyphosate-based weedkiller was used in US fields. Since then, usage has increased some fifteen-fold due to widespread planting of GM glyphosate-tolerant soya and later several other similarly-engineered major crops.

In a bizarre twist of fate, glyphosate's popularity has led to a "battle between farmers" and even a farmer's murder, caused by dicamba.

Two problems have emerged which the biotech and agrichemical industries are desperate to solve.

The first is safety.

Glyphosate rose to prominence with a 'safe as salt' tag [1]. Now, it's erstwhile squeaky-clean image is becoming increasingly tarnished [2], and consumer concern has reached a pitch were foods sporting ‘glyphosate-free' label are appearing on the market [3]. This is inconvenient for the biotech and agri-chemical industries who have a huge stake in supplying GM glyphosate-tolerant seed and the glyphosate formulations to spray on them.

Dicamba is a 'phenoxy' herbicide related to 2,4-D and other ingredients of the infamous 'Agent Orange' defoliant used in Vietnam with horrific, ongoing, consequences. It has many well-established harmful effects on mammals including neurotoxicity, mutagenicity, non-Hodgkin’s lymphoma (a blood cell cancer), and reproductive disruption. Despite this, dicamba has stood the test of time: regulators and farmers are well aware of the risks they have to control when this herbicide is used.

A shift from GM glyphosate-tolerant soya to GM dicamba-tolerant soya is a neat way to keep the GM money-spinner going while taking the heat off the herbicide now causing controversy, even if the alternative on offer isn't any safer.

The second problem is weeds. Or, to be more specific, pigweed.

'Pigweed' refers to several related species of amaranth. Some of these are grown as a green vegetable or grain crop, but the weedy ones that US farmers dread are waterhemp and Palmer amaranth. These two weeds can grow to 10 feet tall blocking out the sunlight from the plants around them and making the crop tough to harvest. They produce up to 600,000 seeds per plant, which can be dispersed by many typical farming events and activities such as irrigation, flooding, manuring, footwear, tyres and tools. The seeds have multiple dormancy mechanisms and can germinate new plants over several years. Pigweed grows aggressively and thrives on the hot, dry, high-nutrient conditions typical of many US agricultural areas, especially in no-till production systems which often use glyphosate with GM glyphosate-tolerant crops.

These super-weeds are broad-leaved plants easily controlled by glyphosate, and very easily kept at bay within a GM glyphosate-tolerant crop. At least they used to be.

Like all good weeds, pigweed adapts quickly to its environment. So much so that after a few years of inevitable drenching with glyphosate, the erstwhile killer spray is now being shrugged off.

What better way to keep a GM money-spinner going than to create a new version of the crop able to tolerate a different herbicide to zap pigweed: GM dicamba-tolerant soya.

The war of the farmers has unfolded because the biotech industry, over-zealous in rushing 'Xtend', its new GM dicamba-tolerant soya trick, to market, failed to wait for the US regulators to approve the use of dicamba on it. Since the GM crop isn't much use without the herbicide, farmers faced with a pigweed problem have been resorting to illegal spraying of their precious novel crop [4]. What happens next is dicamba blowing in the wind, and a neighbour's old-fashioned soya starts to shrivel up.

Last year saw mounting farmer complaints of injury to their crops from dicamba spray-drift in eight States. Just half-way through this year, things have been worse: Arkansas has had at least 242 complaints of potential dicamba misuse spanning 19 counties, and a class-action lawsuit has been filed there against Monsanto (producer of the GM soya) and BASF Corporation (manufacturer of dicamba).

Spray-drift is, of course, nothing new. But, in the old days, farmers "just talked it out. The one that had the damage would say, hey, I think you might have gotten me the other day. The one that did it would say, Man, I'm sorry. Let me know, and I'll pay for that." (NPR interview). Somehow, in the case of dicamba and Xtend, talking doesn't seem to work. So much so that one Arkansas farmer intent on killing his weeds with dicamba reportedly shot and killed his complaining neighbour too.

In response to the problems of 2016, the agri-chemical industry rushed out a solution for 2017: it reformulated dicamba so it can't blow around so easily, plus it made a requirement for all dicamba applicators to take and pass an exam covering essential knowledge such as spray-nozzles, wind, buffer zones, and temperature inversions.

Clearly, neither the extra education and certificates nor the improved chemistry have helped.

An Arkansas Extension Weed Scientist, who has been investigating the problem in the field, concluded that either the new-formulation 'heavy' dicamba has a residual volatility it isn't meant to have, or more likely, the dicamba droplets are moving around on dust particles.

In June, the Arkansas Plant Board proposed an emergency, 120-day ban on the use of dicamba in the State.

One grain production manager said of dicamba and GM "It's fracturing the agricultural community. You either have to choose to be on the side of using the product or on the side of being damaged by the product".


Using a GM/ herbicide package to 'solve' a problem created by a GM/herbicide package in the first place?

Promoting a herbicide with known health effects to replace a herbicide whose health effects are only now, four decades on, becoming obvious?

A farming community so fractured it can only unite when suing the biotech industry?

Or, is this dicamba fiasco a cynical ruse by the biotech industry to force all soya-growers to convert to the latest GM seed it's put on the market?

Isn't it about time the biotech industry was prevented from introducing crops which farmers can't actually use, and from 'solving' problems with more of the same and from locking us into a never-ending loop of the same old toxins, ever-increasing in our food and field?

There are other ways, already identified by the European Parliament, all of which avoid chemicals, GMOs and corporate monopolies.


[1] GLYPHOSATE: SAFE AS SALT? - GMFS Archive, February 2009
[4] SPOTLIGHT ON SPRAY-DRIFT - September 2016

·         Charles M. Benbrook, 2016, Trends in glyphosate herbicide use in the United States and globally, Environmental Sciences Europe
·         Caroline Cox, 1994, Dicamba, Journal of Pesticide Reform 14:1
·         Maria Mergel, Dicamba, Toxipedia 2011
·         Dr. Mark Schonbeck, Virginia Association for Biological Farming, Weed Profile: Pigweeds (Amaranthus spp.), eXtension
·         Marianne McCune, a Pesticide, A Pigweed And A Farmer's Murder, transcript,, 14.06.17
·         Tom Barber, Extension Weed Scientist, Damage reports from dicamba pouring in over the last 2 weeks,, 12.06.17
·         Chris Hickey, Arkansas Plant Board approves dicamba ban, transcript, UALR Public Radio, 23.06.17
·         Arkansas farmers sue over crop damage blamed on herbicide,, 14.06.17
·         Dan Charles, Arkansas tries to stop an epidemic of herbicide damage, WBUR News, 23.06.17

Photo: Creative Commons

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