On farm fields across Frederick County, the leaves of a pesky weed are already emerging where corn and soybeans will soon be planted.
Marestail, a winter and summer annual weed, has become the bane of growers as it has spread and become resistant to groups of herbicides over time. Farmers have a limited arsenal to destroy the weed before it can outcompete their crops for sunlight and nutrients, and being good stewards of those few chemicals was the focus of a Cooperative Extension lecture series by Maryland, Virginia and Delaware this winter.
“I think what we’re going to see [is] the era of simplified weed management is over,” Michael Flessner told local growers and consultants at the Frederick County extension on Feb. 23.
Cover crops, crop rotation and tillage are approaches farmers are considering as their chemical options dwindle due to resistance.
It took only four growing seasons after RoundUp Ready soybeans were released by Monsanto in 1996 for marestail to develop a confirmed resistance to glyphosate, which is the active ingredient in the herbicide RoundUp. And in the last four to five years, marestail has moved into Frederick County.
“That stuff is wicked. It overwinters and it’s there,” said Drew Haines, a salesman at Eddie Mercer Agri-Services, a seed and chemical company in Frederick County.
Haines grew up in Middletown and started farming right out of high school. He has worked on the Mercer sales team for the past six years, and his clients farm on the west side of U.S. 15.
Already, he can see marestail coming up in their fields.
The plant, a prolific seed producer, can drop 200,000 seeds per plant, whether in a soybean field or along the edge of a road.
For farms that can till their soil, research has found that there is no emergence of marestail if the seeds can be buried 0.2 inches or deeper, Frederick County agriculture extension agent Matt Morris said at the meeting. For everyone else, he emphasized burning down the emerged marestail with an herbicide before planting to give the crop — and not the weed — the best shot at growing.
What continues to be hard about herbicide-tolerant and -resistant weeds is that they look no different from the ones that an herbicide would kill.
Sporadic death in a field — where some of the weeds survive and others shrivel and die after an herbicide is applied — is a good indicator that there are some resistant plants in the field, Morris said. The surviving plants may still be susceptible to another class of herbicides, which is why Flessner recommended applying two or more herbicides together that attack the plant two different ways.
Spraying plants at the appropriate height, correct dosage and time frame before planting is also key to preventing the spread of resistant genes between plants.
“We have to really use the resources we have wisely,” Flessner said.
Misuse has been of particular concern for the staff at Eddie Mercer Agri-Services as reports of crop damage in the Midwest from incorrectly applied Dicamba have surfaced. Dicamba attacks weeds that are resistant to RoundUp, and when used correctly can do a good job, Haines said. But incorrect use of generic versions of the chemical let the herbicide drift in the wind to neighboring fields, causing damage to the crops.
The company’s concern is that further misuse of the chemical will lead to its label being taken away by regulators, and farmers will lose yet another weed-fighting tool.
Another threat potentially even greater than marestail has already invaded some fields in eastern Frederick County.
Palmer amaranth, an invasive weed from the Sonoran Desert in the southwestern U.S., can wreak havoc on cornfields, said Ben Beale, a University of Maryland Extension agent for St. Mary’s County.
The weed does best when corn does its worst, he told the group. Palmer amaranth’s optimal temperature for photosynthesis is 108 degrees Fahrenheit, whereas corn enjoys 80-degree days. It also grows rapidly and can have an extensive root system, making it hard to pull from the ground.
One palmer amaranth plant can drop between 500,000 and 1 million seeds, depending on the circumstances in which it is growing. And because it drops so many seeds, researchers and extension agents cautioned that 100 percent control of the weed in a field is the only way to prevent its spread.
Beale showed a map of a single palmer amaranth plant in a field and another after a combine hit it during harvest. A long line of the weed was now growing in the field after the machine spread its seeds. In his experience in Maryland, Beale said that most of the spreading of palmer amaranth has been done by combines. He recommended pulling any visible plants by hand before harvest and starting with a clean field before planting.
“The critical thing is prevention and catching it early,” Beale said.
credit:fredericknewspost.com