What’s up about Roundup (Glyphosate)?

 

With the selection of Robert F. Kennedy Jr as Secretary of Health and Human Services, many farmers are wondering how long Roundup (active ingredient glyphosate) will be around. On 298 million acres of USA cropland, 280 million pounds of glyphosate are used annually. Globally, Roundup (glyphosate) has increased 15X since its introduction in 1996 due the use of genetically modified crops which allow its use without killing the main crop. 

The World Health Organization’s International Agency for Research on Cancer (IARC) has ruled glyphosate a carcinogen. The IARC says that glyphosate could cause Parkinson's disease, Alzheimer's disease, autism, and cancer. The USA has not outlawed glyphosate or even definitely said what health risks may or may not be caused by glyphosate use. Many legal and health questions remain about the use of glyphosate.

In agriculture, weed resistance is becoming another problem, especially with glyphosate. Weeds over time genetically change to become resistant to certain herbicides. As of December 2022, there were 515 “unique resistance cases” or weed species resistant to at least one herbicide (in 267 species), a large increase from less than ten cases in 1974. Of those, over 100 species are resistant to two herbicide modes of action, and more than 50 species are resistant to three modes of action. Weeds have evolved resistance to 21 of the 31 known herbicide modes of action and to165 different herbicides. The number of glyphosate-resistant weed species now stands at 56. Hard to control glyphosate resistance weeds include water hemp, marestail, palmer amaranth, horse weed, Italian rye grass, giant and common ragweed, Johnson grass, and many others.

Weeds become resistant to a chemical when it is used multiple times in one year or over several years. Rotating weed spray chemicals keeps weeds from developing resistance. Weed resistance to continuous use of the same herbicide occurs because of the high rate of viable weed seed production. Over time, a few plants become resistant and these survivors produce viable seed. The percentage of herbicide resistant weeds increase greatly and and then makes a huge jump to become more than half the weed population. This is why fields can typically go from adequate control (>90% control) to failure (<50% control) in one year. The worst weeds are also some of the most prolific in producing large numbers of weed seed. Applying the same chemical multiple times with the same mode of action greatly increases the chance for resistant weeds to occur.

The European Union is trying to reduce using certain hazardous pesticides by 50% by 2030. It looks like the USA may be following their lead; however, no target levels or timelines have been set in the USA. A common goal seems to be finding new ways to fight and reduce weed infestations. This may include using physical barriers (mulches, plastic or mechanical weed barriers, etc.). Mechanical ways include cultivators, electric weed zappers, or even drones or small robots that either spray, zap, or physically remove weeds. 

Biological controls include using crop rotation and other plants or living organisms to reduce weed populations. Farmers often switch between growing corn, soybeans, and even wheat or hay crops to help control weeds. Getting crops planted early and forming a canopy of leaves over bare soil effectively reduces many weed populations. Cover crops like cereal rye, barley, wheat, sorghum, Brassicas (radish, rape, kale), buckwheat, sunflower, and even alfalfa and red clover have certain natural chemicals which reduce weed growth. These plants have natural chemicals which cause an allelopathic or negative effect on weed growth. Some suppress weed germination; others suppress weed growth.

There are several ways farmers can reduce the spread of weed resistance seed. The movement of farm equipment (combines, feed equipment) appears to be a major way resistant weed seed is spread. Cleaning tillage and harvest equipment when moving between fields may reduce the movement of weed seeds and slow the spread of resistant populations. Weed management practices like crops resistant to other herbicide modes of action such as glufosinate, HPPD inhibitors, and synthetic auxins (2,4-D and dicamba) offer additional tools to manage glyphosate-resistant weeds. Be aware that many weed populations are also resistant to these modes of action in the USA too. Overreliance on any single herbicide to manage glyphosate-resistant weeds may lead to resistance to that herbicide as well.

While Roundup or glyphosate has been widely used its future is uncertain. In the USA, it will be around for a while, simply because it is used so widely and alternatives need to be developed. Chemical alternatives (herbicide alternatives) to using glyphosate for spraying and killing weeds is another article by itself (coming soon).