Over a Half Century of Trying to Solve Weed Management Challenges

2019 Crop Production Clinic Proceedings

Over a Half Century of Trying to Solve Weed Management Challenges January 9, 2019

Ridge Plant Systems

In the early 1960s we were demonstrating the ridge plant system. Ridge planting combines tillage and herbicides to achieve improved weed control in row crops. Crop seed is planted into ridges formed during cultivation and/or ditching of the previous crop. In ridge planting, the planter follows the old row and ridge-clearing sweeps or disks move the surface soil, residue, and much of the weed seed out of the row. Weed seeds are deposited between the rows where, upon germination, they can be controlled with cultivation. Two cultivations generally are used for weed control. The first cultivation loosens the soil and the second rebuilds the ridge.

Advantages of the ridge plant system include:

  1. Improved weed control. In the row, annual weed density can be reduced nearly 80% with ridge plant compared to mulch-till systems. Herbicides are more effective at lower weed densities. Also, any weeds that have germinated or are about to emerge in the ridge at planting time will be cleared away by the planter.
  2. Warmer soil temperature. Residue from the previous crop settles between the ridges, permitting the ridge to warm up sooner.
  3. Better soil moisture. Without preplant tillage, ridge planting preserves soil moisture. Tillage can dry the soil to the depth of the tillage operation.
  4. Volunteer crops reduced. Ridge planting almost eliminates volunteer crops. The seeds, ears, or heads are moved by the planter to the row middle where cultivation or a directed herbicide application can control seeds that germinate. Volunteer crops, especially herbicide-resistant ones, often are the worst weeds in conventionally tilled fields.
  5. Reduced herbicide cost. Band application of herbicides at planting works well with ridge planting because the system reduces weed seeds and clears the row of residue which may intercept herbicides.
  6. Erosion control. If ridge height is maintained and the land does not have more than a 4% slope, erosion will be reduced. With a 4%-7% slope, it may be necessary to ridge plant on the contour.
  7. Controlled traffic pattern. Soil compaction in the row is reduced if all equipment is designed to stay off the ridges.

Disadvantages or inconveniences of the ridge plant system include:

  1. Early weeds, especially with late planted crops. Weeds must be controlled prior to planting. The later a crop is planted, the more likely that weeds may be present. Consider fall or spring burndown herbicides treatments.
  2. Preplant incorporated herbicides inappropriate. The exception is where a ridge cleaning device is used in front of a tiller that incorporates the herbicide after ridge cleaning.
  3. Equipment changes. The planter, cultivator, and ditcher may need to be modified or new equipment may need to be purchased. Planting equipment must have a row-cleaning device to push residue and weed seed to the row middles. The cultivator and ditcher need to be able to operate in crop residue.
  4.  Wheel spacing and tire size adjustment. The wheel spacing of implements and the combine must be adjusted to the row spacing. Also, tire size is limited because large tires may destroy the ridge. An alternative is to use duals with spacers to fit rows if extra load-carrying capacity is needed.
  5.  Limited traffic pattern. All traffic must follow rows.
  6. Works best for continuous row crops. With modification, small grains have been drilled on ridges.

Ecofallow, Ecofarming and No-till Systems

The next major advancements were the ecofallow, ecofarming, or no-till systems of crop production. Ecofallow and ecofarming systems control weeds and manage crop residues throughout a crop rotation with minimum use or tillage so as to reduce soil erosion and production costs while increasing weed control, water infiltration, moisture conservation, and crop yields.

The success of ecofallow, ecofarming or no-till depends on herbicides and the proper application of herbicides used to control weeds.

Herbicides were very limited when the system began in the early 1970s. The 1968 Guide for Chemicals that Control Weeds (EC68-130) included the following for corn and sorghum.

1968 Weed Guide Table

One notes that the few herbicides listed were not effective in controlling grassy weeds.

With ecofallow and ecofarming, we learned that our pesticide application practices needed to be improved. When we spray weeds in corn, soybeans, grain sorghum, wheat, and pastures, the crops as well as the weeds were green. If you did not control a few weeds, it did not look too bad.

When spraying weeds after winter wheat harvest, you could see every weed you did not control. Also, since the weeds you did not control did not have any plant competition, they did well using all the soil water and other plant requirements. They also produced a lot of seed that made weed control in the following crop difficult.

Crop residue distribution with the combine was a major problem. Chaff spreaders were added to the combine and modifications to the straw spreader were made to improve residue distribution.

Planters

Planting into the winter wheat crop residue was a real challenge with the planters when we began the ecofallow and ecofarming program in the early 70s. Field demonstrations were held to help producers modify and make planter adjustments for planting into crop residues.

Weed Resistance to Herbicides

In the 1986 Crop Protection Clinic Proceedings the late Gail A. Wicks, Extension weed specialist, wrote:

“In 1981 Drs. Craig Salhoff and Alex Martin reported finding atrazine-resistant kochia along railroad rights-of-way in Idaho. The area has been treated for 13 years with atrazine. These plants were not killed with 20 lb/A of atrazine while kochia plants from non-atrazine treated adjacent areas were killed with 2 lb/A. They showed that if kochia were resistant to atrazine they were also resistant to other triazines.

At Paxton, Nebraska, a farmer who has repeatedly used atrazine for several years reported that in 1981 and 1982 he was having difficulty killing kochia in a continuous irrigated corn field with atrazine. Seed was collected from these plants and kochia from an area that had not had any atrazine and planted into soil containing atrazine at 2 lb/A in the greenhouse. The kochia from atrazine-treated fields was not injured while kochia taken from non-atrazine treated fields were killed.

In 1983 and 1984 atrazine resistant kochia has been identified at several locations in Nebraska. Several field reports were received in 1984 and 1985 on poor kochia control with atrazine and Bladex. These fields may be along railroads, feed lots, machinery lots or other places where triazine or other herbicides are used as soil sterilants or fields previously treated with atrazine or Bladex.”

In 1996 Roundup Ready soybeans became commercially available. In the 1999 Crop Protection Clinic proceedings, Fred Roeth, Extension weed specialist, in an article on weed control and crop production in Roundup Ready crops:

“Roundup Ready corn and soybean cultivars offer the opportunity to simplify weed control with one or two postemergence Roundup Ultra applications. The theme '32 ounces at 32 days' conveys this convenience. If properly timed, 32 ounces of Roundup Ultra will kill or seriously cripple most weeds. However, proper timing is essential for both good weed control and no yield loss from weed competition. So when is the proper time?”

Weeds resistance to the triazine herbicides in the 1980s and ALS resistant weeds from the 1990s are still present on many farms. With glyphosate controlling these weeds, there was little concern with the triazine and ALS resistance. In Nebraska we have waterhemp populations that have three-stack resistance (triazine + ALS or HPPD + glyphosate). We need to not use the same mode of action or we can lose another mode of action to resistance. We have only eight modes of action.

Not all weeds in a field have the same genetic makeup. This genetic variability allows a weed species to survive diverse environmental and management conditions because at least some individuals live to reproduce each year.

Take-Home Message

Yes, there have been many challenges in controlling weeds. Even with hand weeding barnyardgrass in rice paddies in China, there were problems. The barnyardgrass resisted hand weeding by mimicking rice until it was too late to pull. An effective weed management program must be planned and must include timely application. Its performance needs to be continually checked and followed up with additional control measures if needed.