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historic flooding weed seed

Many producers in the area also shifted away from making fall herbicide applications “due to the effectiveness of Xtend, Liberty and Enlist technologies,” Loux adds. “Now, we have to get back to making those applications.”

First, prevent annual weeds from going to seed and entering the soil seedbank. Anything that goes to seed will have to be dealt with in the future.

Ohio: More Fall Applications In The Future

Eventually, farmers disked under many of those fields, which buried viable weed seed. In the following rice crop in 2020, those weed seeds germinated and emerged.

In 2019, agricultural producers reported they were unable to plant crops on nearly 20 million acres, according to USDA figures. It was the highest PPL total in a single year since USDA began tracking prevented planting in 2007. And the 2019 total ran 17.5 million acres higher than what growers reported in the previous year.

Weed scientists offer that outlook after seeing the aftermath of PPL neglect over the last couple of years.

Carl Bell
Emeritus, University of California, San Diego, CA
[email protected]

For most agronomists and weed scientists in the 20 th century, the history of technology in weed control is the history of herbicides. For some it didn’t begin until the introduction of synthetic herbicides in about 1950. In reality, herbicides, in the sense of chemicals used intentionally on a crop for weed control started in the mid 19 th Century. The first herbicides were inorganic salts such as sodium chloride, sodium chlorate, arsenic salts and carbon bisulfide as a fumigant. In addition various oils, inorganic acids like sulfuric acid, and solvents were used as burn-down herbicides. All of these chemicals were used at what today would be unbelievable rates, 600-1000 pounds per acre for sodium chlorate for example. They were toxic and some were extreme fire hazards. This same period also saw advances in weed biology and ecology, which included research into weed seed in the soil, the role of below ground asexual reproduction, plant competition, weed seed movement in animal feces, and other fundamental studies. Much of this foundational biological information is still the best work in the literature today.

There are some likely explanations for this lack of information. One is that, according to Wikipedia, crop production was generally sufficient through the succeeding millennia to meet normal human needs. So even though weeds were present, the available control methods were apparently adequate. The earliest known weed control technology in 8000 BCE was the plow and hand-weeding (which includes hand-pulling, cutting with a knife, hoes and mattocks). It stayed that way for the next 10,000 years until the 18 th Century CE; so there was not much to write about. And why was that? It was because there was an abundance of labor, mostly women and children, to hand-weed [1] . It is not surprising, therefore, that the beginning of the industrial age in Europe was accompanied by improvements in weed control technology; not just because it was an age of invention but also because women and children were being pulled off farms to work in industry. Women and children have apparently always gotten the short end of the stick, but the idea that the only way to get them out of the fields is to put them in factories should make us ashamed.

The discovery of 2,4-D and the chemical synthesis process that allowed for this discovery opened the floodgates for herbicides. By 1969, a scant two decades later, there were 75 modern organic molecule herbicides on the market for use on farms, in industrial settings, in landscapes and elsewhere. According to a genealogy created by Arnold Appleby, Emeritus Professor of Crop Science at Oregon State University, there have been about 80 herbicide discovery companies in the US since the 1950’s. Today there are about 10 active companies in the US due to consolidation and acquisition. The ninth edition of the Herbicide Handbook published by the Weed Science Society of America in 2007 includes more than 200 herbicides presently in use or in development in the US. It is useful to reflect that in 2007 herbicides represented 44% of the total pesticide use in the US and 39% of the world market, while insecticides are 9% and 18% respectively. In developing nations, herbicides are less commonly used. In India, for example, herbicides are only 16% of the pesticide market and in Pakistan only about 5%.

In other parts of the world, where agriculture developed independent of the Mideast, weed control took some interesting forms. In the east, rice was domesticated about the same time as cereal grains in the Mideast. But because it is grown in water, crop production practices were different but weeds were still a problem. By at least 3,000 BCE grass carp were a part of rice production in flooded paddies. This might have been serendipity, some fish got into the paddy because of a monsoon rain or a break in the dikes and the farmers noticed that they ate weeds, and also some insect pests. So putting fish, mostly grass carp but also tilapia and other species, into rice paddies is a common practice from Japan to India. The fish is also an agricultural commodity, so it’s a win-win situation.

Knowing what you’ve seen in your fields before is always a great place to start when thinking about weed management. A few things to keep in mind every year:

Bubba Simmons, Mississippi soybean farmer and soy checkoff farmer-director, emphasizes the 2019 planting season has been challenging. Staying on top of weed control is a priority as the season continues. Mississippi, like much of the United States, has experienced substantial flooding during the spring months.

Knowing which fields you’re going to plant and which you aren’t is important to your success in future seasons. Bradley notes even if you aren’t going to plant in a field this season, you still need to keep weed management in mind. The fewer seeds that reach germination, the better — especially varieties which produce up to a million seeds. If you manage those weeds, when you do decide to plant a field again, you won’t have quite as much recovery to do as you would if you had left it alone. Having a plan to what fields you’re going to plant and what your strategy is for each field is important to success in weed management.

Know What You’re Up Against

Farmers know poor weed control can affect growing seasons for years to come. Kevin Bradley, weed scientist at the University of Missouri, reminds farmers some weeds can produce up to a million seeds. With that level of potential impact — and in a year that has been anything but easy — it is important to remember to address those weeds.

“Weed pressure isn’t usually as strong when we plant in early April,” says Simmons. “Early June planting has made for warmer planting. That has increased the weed pressure and made a time crunch for getting herbicides applied.”

Although farmers are used to thinking on their feet, this season has been especially challenging. Weed management, however, is something farmers face year to year without fail.

“Any time there’s a flood, that creates challenges because it spreads the weed seed significantly,” Simmons explains. Typically planting happens by early April, but this year Simmons couldn’t get seeds into the ground until early June. The late planting significantly impacts the weed presence during the early stage of development for these soybeans.