What is in this article?:
- Weed issues continue to challenge California no-till farming
- Battling weeds early
- No-till farming is about improving the resource base and remaining competitive.
- With no-till, 90 percent of weed seeds are in the top 2 inches of soil. With conventional tillage, 10 percent to 12 percent are in the top 2 inches.
- Costs for weed control in conventional and conservation systems pencil out about the same – 20 percent to 30 percent of production costs.
Battling weeds early
But he warned it is important to keep neighboring weeds out of the seed bank early, pointing out pigweed and horseweed bordering the field and likely to seed it if left unattended.
He said weeds in the sunflower family thrive in no-till environments. “They drift in on the wind and like shallow, undisturbed conditions.” Those pesky seeds can come from plants that include fleabane and mare’s tail.
Hembree sounded a special warning against herbicide resistant Palmer amaranth. “Fleabane and this other stuff are nothing compared to that,” he said.
When making a transition to no-till, he said, it might be wise to use a specialized “flip-over plow” that buries seeds like nightshade, purslane and pigweed.
Sprays for weed control must be timely, Hembree said, and growers need to be aware that herbicides can “get tied up” in crop residue. He cited the example of use of Staple after cotton, which left a residue that harmed the following tomatoes.
“That was devastating,” he said.
Literature provided by Shrestha and others also noted that the crop residue can make it more challengng to use pre-emergent herbicides.
Transplants, notably for tomatoes, have a head start on weed pressures, Hembree said. And subsurface drip also lowers weed pressures because there is less moisture at the surface than when flood irrigation is used.
Dan Munk, UC farm advisor for soils and water and cotton for Fresno County, said the research center is changing some of its irrigation practices along with surrounding farmers.
Many of them are moving to subsurface drip irrigation for tomatoes, burying the drip at 8 to 12 inches and using it for six to eight years. One grower told Munk he has used the same drip tape for 17 years.
Munk said drip is less variable in applying water than furrow irrigation. He cited a graph showing that in cotton a furrow system applied more water to one end of a 300 foot bed than another, varying from depths of 4.5 inches to 2.5 inches.
“There is less surface evaporation from subsurface drip, and uniformity with drip is well over 90 percent, compared to 75 or 80 percent with surface irrigation,” he said, adding, “Were also looking backward in time to overhead linear systems and the center pivot.”
Munk and Mitchell conceded there have been particular challenges to getting good cotton yields out of no-till systems with or without cover crops. Munk said some of that has to do with season length in California and weather – such as happened this year – when planting is delayed by cool conditions.
An added challenge: There has been a move by many from Acala to Pima cotton, which takes still longer to mature.
Mitchell said researchers have learned of the need to plant cotton “into moisture.”
“Cotton enjoys a long season, and we try to plant as early as possible,” Munk said.
He said tomato growers are learning they can do deficit irrigation at the end of the season as roots tap deeper into the soil. “In cotton, it’s no different, and it’s a slightly deeper rooting plant,” Munk said. “Some of our best yields are coming off moderately stressed cotton.”