In the 1970s, circles began to mysteriously appear overnight in European crop fields.
Standing crops were flattened in perfect circles or in almost artistic designs. News organizations covered and sensationalized these strange happenings with the implication that extraterrestrial beings were somehow responsible.
Each new circle was accompanied with news reporters standing in the field interviewing local residents, of which some were sure they had experienced strange noises or sights that could not be explained by normal means. The excitement and/or hysteria rose and many were convinced that aliens from another planet were preparing to invade earth.
The mystery continued several months until a local prankster was confronted by his wife about the high mileage on their car and his late night hours. She was suspicious he was having an extramarital affair. So, in order to save his marriage, he had to confess the circle making was concocted and carried out as a joke by a bar room buddy and himself. His confession was not as sensational and was not covered by the news media.
As we travel across the Delta, it is apparent we also have spots in our many of our cotton and soybean fields. But instead of the spots being flattened, they seem to be taller than the crops and getting taller each day. Unfortunately, these are not a result of a prankster and there is no mystery as to how they got there.
These are spots of pigweeds. They are the result of a single pigweed surviving and going to seed location last year. This may not be as exciting as spots caused by potential aliens, but they are causing us plenty of grief. The spots range from the size of a pickup to the size of a small house. There may be several thousand pigweeds in each of these spots and although they are the offspring of a single female plant, the level of resistance and susceptibility to glyphosate may vary among individuals within a given spot.
Susceptible plants are showing typical glyphosate symptoms two days after spraying. Resistant plants show no symptoms and will withstand future glyphosate applications with no effects.
Control of the pigweeds in these spots is critical, but not easy. There are no herbicides that can be sprayed over the top of cotton that will kill these weeds. Staple or Envoke may kill some pigweeds in cotton, but approximately 70 percent of our pigweed populations are resistant to the ALS herbicides.
Therefore, hand hoeing is the only effective means of removing these spots from cotton. Flexstar and Blazer are somewhat effective on pigweed over the top of soybeans if the weeds are not more than 2 inches tall. Once they reach 4 to 6 inches, hand hoeing is required in soybeans as well.
Personally, I never imagined we would have to resort to hand hoeing again and there are as many reasons not to hand chop these fields as there are fields. Hoe crews are difficult to find in some areas and expensive in all areas. Some complain that the weeds re-grow after they are chopped. However, if left to produce seed, the problem will be much larger next year.
There are numerous examples of how spots in one year turn into a jungle when seed are scattered with a combine. Spots in the fields are often noticed, but mistaken for application skips. The combine scatters the seed, and after the first glyphosate application is made the following year, it is apparent the weeds were resistant and there was no way to manage the situation.
A little extra effort to remove the spots this year will go a long way toward preventing a total wreck next year. Hoe crews should be instructed to chop the weeds just below the soil surface. Pigweeds have adventitious buds near the soil surface that will produce re-growth if the top is removed. There are no buds below the soil surface and cutting below the bud line will result in death of the plant. I have already seen some hoe crews in fields because it is much easier to chop the weeds while they are small.
There is still a great deal we do not understand about the inheritance and mechanisms of resistance. However, we do know that resistant female plants are capable of producing hundreds of thousands of seed and may be pollinated by many different male plants. Theoretically, it is possible for the individual pigweeds in a spot to not only possess different levels of resistance, but also have different mechanisms for resistance.
Some may produce excessive amounts of the enzyme that glyphosate affects, while others may not translocate the glyphosate throughout the plant. Scientists throughout the South are working as diligently as possible, but pigweed resistance and spread seems to be outpacing our efforts.
I don’t mean to sound “doom and gloom,” because we have a lot of very clean fields and pretty crops. There is no perfect herbicide program that will provide 100 percent control of weeds in all situations. When a single pigweed is noticed 200 yards out in the field, is it worth going out there and taking care of it this year before seed are produced or shall we wait and manage spots next year? When spots are noted this year, is it worth the effort to remove them or hope to control a solid field of resistant pigweed next year? Hopefully, it will be the former rather than the latter in both situations.
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