June 16, 2016
Why do farmers need glyphosate? An answer in 10 weeds

By Brandon Mitchener and Jaden Elsasser

The current political debate around the use of glyphosate in agriculture in Europe is permeated with the simple notions that weed control is optional and that if glyphosate were banned, farmers would just let the weeds grow, because who do they really harm anyway?

Any farmer knows the proper reseponse to that question: Weeds are the enemy! They compete with crops for light and water. Some of them are highly invasive and spread much faster than what the farmer is trying to grow. They can clog up machinery. Some of them are even highly toxic to people and farm animals; if too much of them end up in the harvest, the crop is unusable and might even have to be condemned. Weeds need to be controlled one way or another, and Roundup is the most effective and environmentally friendly way to do it because it kills not just the top of the plant but also the roots, preventing it from growing back.

Weeds are also the enemy for gardeners as well as people who manage railways, rural road intersections, historical monuments and city sidewalks. But whereas we might consider weeds in a private garden or sidewalk a mere nuisance, for farmers they can be devastating.

How so? A picture speaks a 1,000 words, so we’ll not just tell you but show you.

Over the next couple of weeks, we’ll be teaching Weeds 101 in a series of short blog posts and related Tweets and Instagram pictures.

The first weed in our Rogues Gallery of Weeds: Sorghum halepense, also known as Johnson grass. A member of the grass family, it is spreading primarily in Hungary, and it is considered a question of time until it begins to cause problems in Romania, Italy and the Balkans, where the weed is also widespread.Te weed Sorghum halepense.

Sorghum halepense threatens profitable maize production because it is a direct competitor to maize. It can totally suppress crops, resulting in significant hit to a farmer’s yield.

Due to its high level of green mass, sorghum halepense can also block combine harvesters. The green weed mass harvested together with maize or sunflowers will block the sieves and increases losses at harvest.

The good news? It doesn’t have to be this way!

If farmers spray Monsanto’s Roundup or other glyphosate-based weedkillers to the stubble in the field the year before (after harvest), the perennial Sorghum halepense can be fully eliminated to allow healthy maize development and the full achievement of a farm’s theoretical yield potential. Roundup can also be used to prevent resistance to other herbicides that have a different mode of action.

The second weed in our Rogues Gallery is Cirsium arvense, also known as green thistle, which is a deep rooted weed that dries the soil layer where crops take-up moisture.

An image of the weed Cirsium arvense, also known as green thistle.

Cirsium arvense is an aggressively competitive weed species that can overrun any crops. This weed causes significant yield loss for farmers if not controlled and even full loss of crops in heavily infested spots. This weed appears everywhere from agricultural to arable field plantations.  If the green weed parts are not separated from the farmer’s grain, impurities will increase and also elevate grain moisture content by 3-5%, which raises the risk of spoilage of the seed batch. If harvested together with cereals or oilseed rape it can cause the loss of the entire harvest. One practical option to reduce pressure from this weed is the application of glyphosate to stubble after cereal planting and pre-planting in the spring.


The third weed in our Rogues Gallery of weeds is Ambrosia elatior, also known as the common ragweed.

Ambrosia elatior 3

Ambrosia elatior is a very aggressive, highly competitive weed that can overrun any spring planted crop if not controlled. Ambrosia elatior is so competitive that it can completely overrun other weeds, becoming dominant in non-agricultural lands. Ragweed produces a large amount of pollen that causes allergies in the pulmonary tract of humans. It has such a strong allergic potential that it affects 20-30% of the total population where it is present. Ragweed can germinate from spring to autumn. The best way for farmers to eliminate ragweed is by applying Roundup or other glyphosate-based weed killers to the stubble after cereal planting and pre-planting in corn and sunflower crops.


The fourth weed in our Rogues Gallery is Agropyron/Elymus repens, commonly known as couch grass or wheat grass.

Agropyron 3

Couch grass is present in all Europeans countries, arable land, orchards, vineyards and non-agricultural lands. It is an aggressive and very competitive perennial weed, which means it continues to regrow over a few seasons to many seasons. Wherever couch grass is found it quickly becomes the dominant species. In crops with edible parts planted in the soil wounds can occur due to fungal infection and will eventually reduce the quantity and quality of the crop’s production. Couch grass can cause significant yield loss or full loss in heavily infested spots if it is not controlled. One simple solution to reduce couch grass in crops is by applying glyphosate to stubble after cereal planting and pre-planting in the autumn or spring.

Our fifth weed in the Rogues Gallery is Heracleum spp., commonly known as hogweed.

hogweed 2

Hogweed is a dangerous and invasive species that have become very difficult to control throughout Europe. This rapidly spreading weed can be found in pastures, riverbanks, ditches, forests, orchards and non-agricultural areas. They have large leaves that overshadow and overrun pasture grass and other native vegetation. This weed can be especially dangerous for animals and humans. Touching the weed or walking through infested areas allows hogweed sap to get on human skin causing severe rashes and blistering when touched. The best long- term control option is to combine glyphosate with another herbicide compound (Flazasulfuron) and apply before stem lengthening in the spring.

Our sixth weed in the Rogues Gallery is actually two bindweeds with similar nature Calystegia sepium/Convolvulus arvensis.


bindweeds 1

Bindweeds are widespread, aggressive and competitive weeds. The Convovolvulus arvensis (field bindweed) roots can penetrate 2-3 meters into the soil depleting the soils moisture. The biggest damage done by this weed is that it climbs on plants, vegetables and ornamental crops. This inhibits the development of the crop by overgrowing the cultivated plants. To reduce the affects of bindweed farmers can apply glyphosate-based weed killers to the stubble after harvesting the crops early.

Our seventh weed in the Rogues Gallery is Ailanthus altissima, commonly known as tree of heaven.

tree of heaven 1

Tree of heaven is native in China and Taiwan, and was introduced to Europe in the 1700’s as an ornamental plant. The weed’s parts are broadly used in traditional medicine in China and its wood is used to make furniture or cutlery.  This weed produces chemicals in the soil, which can inhibit germination from native plants and root growth of the existing plants and trees. This aggressively invasive species overruns native trees and takes over the entire area.  To help decrease the growth of this weed, farmer’s can apply glyphosate to the stump after cutting.

Our eighth weed in the Rogues Gallery is Phragmites austrialis, also known as common reed.

common reed 2

Common reed is a deep-rooted grass weed that overgrows most crops by blocking their development. This weed can be an important habitat for birds and is used as an industrial base material, but can be considered very difficult to control under arable conditions and in waterways. Common reed produces substances in the soil that suppresses the development of other plant species, allowing it to dominate large areas. Common reed can also be a serious problem in waterways; it grows in high density and can block water movement. To help eliminate common weed, farmers can apply glyphosate to the stubble after harvesting crops early. They could also apply very small amounts of glyphosate in aquatic conditions when there are enough leaf surfaces for the uptake by the weed of the active ingredient.

Our ninth weed in the Rogues Gallery is Asclepias syriace, also known as common milkweed.

common milkweed 1

Common milkweed is a deep-rooted broadleaf weed, and was introduced to Europe as an ornamental and honey plant. Milkweed’s large leaves and profuse roots suppress most plants and crops. This invasive species is mostly widespread on pastures, non-agricultural areas, riverbeds and arable crops. Most compounds will not control this weed, so to reduce common milkweed farmers must apply glyphosate to the stubble after harvesting crops early.

Our tenth and final weed in the Rogues Gallery is Cynodon dactlyon, which is also known as Bermuda grass.

bermuda grass 2

Bermuda grass is a deep-rooted perennial grass, meaning this weed grows back every year, usually increasing in size. This root can penetrate as deep as two metres, although the major part of the root grows in the upper part of the soil where crop roots are found. This competitive species will overrun any cultivated crop. It’s a big problem for maize, as many herbicides cannot control it. To control bermudagrass farmers must apply glyphosate to the stubble after harvesting the crops early.

For more information, see:

Monsanto Europe Media Bank’s Rogues gallery of weeds



    June 20, 2016
    We´d better ask: "Why do farmers WANT TO USE glyphosate?" - expressing much better which is the party the most interested to keep glyphosate for weed control.
    Brandon Mitchener
    June 20, 2016
    Thanks for the feedback. What we hear often, though, is that farmers don't actually regard it as a choice but as a necessity. I don't think "need" and "want" are mutually exclusive; I think in this case they complement one another.


Your email address will not be published. Required fields are marked *