What’s new with our weeds

By Mary Edmonds, Rodale Institute Seasonal Research Technician

Rodale Institute is currently in the second year of a series of field trials investigating organic weed management using cover crops. The goal is to examine the efficacy of different pieces of machinery as well as different rolling and planting dates through two field trials; the “supplemental weed management experiment,” and the “soybean establishment experiment.” The experiments are coordinated with Steven Mirsky of United States Department of Agriculture (USDA) who has similar projects running at the USDA Agricultural Research Service (ARS) office in Beltsville Maryland.

Supplemental Weed Management experiment

The Supplemental Weed Management experiment recognizes that a rolled cover crop does not always supply sufficient season-long weed management, and utilizes the Hiniker High Residue Cultivator (HRC) to help control weed populations. The HRC attaches to the back of a tractor, much like a planter would, and has a series of horizontal sweeps attached to vertical shanks. The sweeps travel approximately an inch underneath the soil surface between crop rows and kill weeds by slicing them from their roots while leaving the cover crop mat intact to prevent further weed growth.

Hiniker High Residue Cultivator (HRC)

We are trying to identify what the best timing is when using the HRC in relation to weed-crop competition dynamics and final soybean yields. If cultivation is performed too early, the weeds will be rolled over and not killed. Cultivate too late, and weed crop competition dynamics will have already negatively affected soybean yields. We examine soybean yields and weed population in five different treatments, each with four replications.

  1. Weed Free, hand weeded control plot
  2. No management control plot
  3. HRC at 5&6 weeks after planting
  4. HRC at 6&7 weeks after planting
  5. HRC at 7&8 weeks after planting

Soybean Establishment experiment

The Soybean Establishment experiment investigates a number of different parameters in relation to initial soybean establishment and final soybean yields. The parameters studied include.

• Timing of termination of rye cover crop: Rolling at flowering versus post flowering
• Timing of planting: At rolling versus 10-14 days post rolling
• Efficacy of three different planters when planting into rye: Vacuum planter with and without shark teeth versus finger pick-ups with attachments made for high residue systems.

Terminating the cover crop by rolling at anthesis (flowering) versus soft dough (immature seed) can influence the amount of cover crop regrowth seen in the field. For example, any plant terminated before flowering is more likely to regrow. We also examine planting at rolling versus 10 to 14 days post rolling for both planting dates. Because certain cover crops, like rye and vetch, are allelopathic (meaning they inhibit the growth of other plants), planting at rolling could potentially be detrimental to the establishment of soybeans. Waiting until the allelopathic plant compounds leach through the soil could improve soybean establishment.

Rodale Institute roller-crimper at work followed by the
Pequea planter and, of course, a hard working tech!

Three different planters are also being tested in conjunction with the different rolling and planting dates. The planters, as with the other variables, are analyzed in relation to soybean establishment and final yields. The Monosem planter is our standard vacuum planter which lays seeds down behind it. The Shark Teeth attachment for the Monosem planter cuts through a cover crop mat to plant seeds directly into soil. The Pequea planter uses finger pickups to select and segregate seeds and also has a special modification designed to hold the cover crop mat in place. Each planter is tested in each set of rolling and planting times. There are 17 treatments with four replicas of each, a total of 68 plots!


Before the experiments can even begin, the research plots have to be established for the year. Early in the season research technicians can be seen in shoulder-high fields of cover crop battling with 300-foot-long measuring tapes and using geometry to create identically-sized square plots. The plots need to be laid out in the field while keeping in mind that a tractor needs enough room to turn around and eight rows of crop need to be planted in each plot.

After the plots are established, measurements are taken. This often requires multiple technicians working together and, therefore, very early mornings in the field! Since all the technicians have their own projects, balancing the workload and scheduling group efforts takes creative planning. Tractor and equipment use must also be planned and carefully delegated as there is always much to be done at Rodale Institute.

Immediately before planting or harvest there are baseline measurements to be taken in each plot meaning tractors and planters must be carefully timed. Of course, equipment is also shared across the 333-acre research farm and poses the same availability challenges as the technicians. Once initial measurements are completed and the tractor and farm operations guys are ready to roll and plant, there is literal running to be done from plot to plot in the Weed Management project—guiding haybines and tractors with rollers and planters to the correct plots, and keeping the equipment working in straight lines within the plots. In the Soybean establishment experiment, changing of the types of planters on the tractor can often take longer than the planting itself.

Our Mennonite neighbors the Brubakers remove cover crop by haybine from our cover-crop-free plots.
This requires running in front of this huge machine and pointing them to the correct plots.

In addition to the measurements that directly follow planting and cultivation (moisture, temperature, penetration resistance and biomass), there are weekly counts of soybean emergence in 68 plots, and weekly hand-weeding in control plots. All this takes time, a lot of time. Having other research techs come to help is critical to getting it done, and not passing out in the summer sun.

Weather must also be accounted for and often complicates our experimental plans. Farming is a weather dependant activity—a tractor cannot plant when it is too wet (and this has been a wet spring!), too dry and seeds will not germinate. Seven weeks without rain earlier this summer was not easy on our crops either.

Mid-season observations

Much of the research at Rodale Institute is a learning experience for all of us conducting our experiments. Over consecutive years of running experiments, it becomes obvious what works and what does not. This allows us to cull out time-consuming treatments that do not give worthwhile results so that we can spend that time gathering data that will help you, the farmer. We also develop more precise methods of taking consistent measurements as we see what last years data looks like. Research itself is a field of constant learning and development.

Mid-season observations have been similar to final observations of last year. Terminating rye cover crop at Dough seems to result in the highest soybean establishment rates, as does planting 10-14 days post rolling. The High Residue Cultivator, again, shows the highest level of success in the earliest timing, HRC at 5&6 weeks after planting (though this may be due to drought conditions at 6 weeks after planting). Specific to this July’s seven consecutive weeks without rain, soybeans are suffering severely from drought. Particularly the beans with later planting dates (further into the drought). We look forward to final population and yield data, and to sharing what we have learned.

This material is based upon work supported by the U.S. Department of Agriculture, Agricultural Research Service, under Specific Cooperative Agreement Number 58-1265-9-110. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

2 Responses to “What’s new with our weeds”

  1. John Meyer

    Here in Minnesota, we simply don’t have a long enough growing season to wait for a cover crop to flower in order to roll the cover for termination and plant our corn or soybeans. Our preferred last planting date for corn is May 10. Most of the time, the earliest we can ever get into the field is around April 25… if you get any rainy weather during that period, which is typical, you pretty much HAVE to run whenever the ground will let you.

    So…… what then would you suggest for cover crop species and termination, knowing these restraints.

    What would you think of using a cover crop mix with perennial alfalfa as the primary species, underseeded into soybeans mid-season? Allow the alfalfa mix to grow the season following soybeans and graze it. Then the next season, go in around May 10th with a mower and lay it down, leaving the residue to provide nutrients, ground cover, and thatch for weed suppression. Come in with a good no-till planter, putting in corn in 30 rows, with a 15″ band of herbicide on the row that you can be confident will control competition in the band. Then, when the alfalfa cover starts to come back through the residue enough to NEARLY generate some competition, come back with a specially designed “interrow mower”, again leaving the residue within the row to provide nutrients and suppress regrowth. Any potential weeds in the interrow area will also be controlled automatically by mowing, without the use of herbicide. Mow that inter-row area as needed to control competition from the alfalfa cover until the corn will outcompete it. On the last pass with the inter-row mower, apply another application of contact (no residual) herbicide to the corn row area if needed, apply sidedress N if needed, and apply selected cover crop species to the corn row area to fill it back in.

    Graze the field again after corn harvest. Next season, cut the alfalfa mix again and leave the residue for nutrient supply and as thatch to help control weeds. Fully terminate the alfalfa mixed cover with herbicide, plant soybeans, and interplant alfalfa cover again into the soybeans to start the process all over again.

    One COULD graze it again the year following the corn crop as well, and I do believe that this too would be very beneficial to the following soybean crop. By that time, if the corn interrow area had been underseeded with a grass… like annual ryegrass, for example, or others… the alfalfa should be thinning, and the grasses taking over…. prime to rotate back to the soybean-alfalfa legume type plants again.

    Yes, this requires the addition of animals to the crop operation, and it effectively takes the field out of row crop production 1 out of three years, or more if desired. But I suspect that allowing that perennial to establish for that year and grazing it with livestock will likely provide a significant benefit to the profitability of the cash grain crop in the remaining years.

    John Meyer
    Stewartville, MN


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