How to clean weed seeds

The Straw Bale Methodology for Cleaning Weed Seeds Out of a Combine

In this video we describe how to deep-clean your combine from weed seeds with the use of straw bales.

W e often see weeds visible above a cash crop canopy, particularly in soybean fields. Sometimes these weeds are solitary specimens, while other times they are distributed in patches or even rows. Farmers have told us that these weed species are new to their fields and may have been carried into the fields by a combine. It is a plausible scenario: combines have been documented to spread weed seeds from infested fields to new fields. Weed seeds can survive in debris on a combine across seasons.

Most people think that weed seeds are hidden somewhere in the combine and that is almost impossible to remove, even during a thorough cleaning-up. This is not true. It is both crucial and possible to deep-clean the combine before moving to another field, as well as at the end of the season.

A soybean combine works by cutting off both soybeans and weeds near ground level and bringing the material into the header. All the material then feeds into the threshing cylinder. While grain is collected in a bin, straw and chaff are dropped behind the combine as it moves along the field.

Moving from the rear of the combine to the header, straw chopper knives, walker cranks, and straw walkers can allow residue to accumulate. Weed seeds get stuck in the straw chopper and chaff spreader as well as in the unloading auger. To reach many of those parts, the different access gates on the sides of the combine should be opened. Cylinder and concave are composed of many parts where weed seeds easily hide. Since they are difficult to access they should be cleaned with compressed air whenever possible.

Sieves, tailing return chains, drives, tank auger, and transmission are also important parts that must be considered in the cleaning process.

Plant residues containing weed seeds can be removed by opening the stone trapdoor.

Start cleaning a combine from the top and from the header to the rear, following the normal circulation of the material. Certain parts are better cleaned with an air compressor, while others could be done with a leaf blower. Cleaning the grain bin and augers as well as the moisture sensor is essential to prevent wagon and truck contamination with weed seeds.

After the combine is cleaned with a blower or compressed air, let the fans work until no more residue is coming out the back. A tarp could be helpful to see when that happens.

The last step is to introduce hay through the header and a combination of hay and wood pellets to the grain bin. Be sure to take the bale pieces apart and feed them into the machine from either the feeding house opening or the header. Depending on how big the combine is, it will take from two to three bales to clean it. With the engine, fans, and all threshing components at normal operating speed and the header turned on, carefully feed bales from the sides of the header to the middle. To clean the grain bin, be sure the auger is not running, mix 25 pounds of wood pellets with half a bale, and introduce the mixture into the grain tank auger. Then start operating the auger to clean it. Straw fed into a combine after harvest, as opposed to straw as part of the harvest (grain + straw + chaff), moves around the combine more freely to reach those spots containing hidden weed seeds.

Once the bales have entered the machine, watch the rear of the combine to see when no more material comes out. When that happens, a final, cosmetic cleaning step with the help of a blower may be necessary to remove a few large pieces of straw which might be stuck in different parts of the combine.

Results From Three Combines (pdf)

Prior to storing combines at the end of the season, three previously cleaned combines were tested for weed seed retention. Initially combines were run until no residue fell on the tarp used to collect the weed seeds, then straw bales and wood chips were fed through the combine in an attempt to catch and remove any remaining weed seed.

Research has shown the straw bale cleaning method to be effective.

After running this test from a first combine, weed seeds were identified and counted. Over 3,000 Palmer amaranth seeds along with other weed seeds were collected. A second combine cleaning resulted in more than 1,700,000 Palmer amaranth seeds collected in total over 3,5 million weed seeds were removed from this cleaning. The third combine received a thorough cleaning and resulted in no weed seed retention.

Combines have been designed for harvesting crops, separating grains from stems and pods, and cleaning the grain of unwanted material. Unfortunately, they are not designed for weed seed self-cleaning. Consequently, the machine must be carefully cleaned, keeping in mind where weed seeds can hide. The time it takes to deep-clean a combine to remove weed seeds could range from minutes to hours, depending on how often the combine is cleaned and how weedy the fields are. Remember that prevention is the key to managing weed seed dispersal, and combine cleaning is a major part of prevention.

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Combine Cleaning: Quick Guide To Removing Resistant Weed Seeds (Among Other Things)

By: Meaghan Anderson, Iowa State University Extension; Kevin Jarek, University of Wisconsin-Madison Extension; Angie Johnson, North Dakota State University Extension; Wayne Ohnesorg, University of Nebraska-Lincoln Extension; Mark Hanna, Iowa State University

The front-to-back and top-to-bottom combine clean-outs are significant undertakings and may be necessary for some farmers to complete between fields when producing identity-preserved grains or other specialty crops. All farmers should consider performing this full clean-out after harvest.

Following harvest season, proper clean-out of harvest equipment can remove significant biomaterial and reduce the likelihood of animals nesting in machines, improve function and longevity of parts, and allow for peace of mind when putting equipment away for the season.

You will need:

  • Supplies: shop vacuum, high-pressure air compressor, flathead screwdrivers, and pocket knife. A leaf blower may come in handy, too.
  • Personal protective equipment: protective eyewear, dust mask, hearing protection, and gloves.

Listed below are the steps for a complete top-to-bottom and front-to-back clean-out of all the combine parts, including the head, feeder-house, rock trap, rotor/cylinder/concave, cleaning shoe, tailings/elevators, grain tank, unloading auger, chopper, rear axle, and chassis.

11 Essential Tasks

#1. Prior to leaving the crop field, perform a self-cleaning process with the combine:

  • Run the unloading auger empty for at least one minute.
  • Remove the header from the combine (optional).
  • Open the clean grain and tailings elevator doors, rock trap, and unloading auger sump.
  • Make sure bystanders are at least 50 ft. away from machine.
  • Start the combine and separator, adjust the cleaning shoe fan to full speed for maximum airflow, and alternately open and close the cleaning shoe sieves electronically.
  • Adjust the rotor to full speed for maximum air suction and alternately open and close the concaves.
  • Operate the combine this way for at least two minutes and drive over end rows or rough terrain to dislodge more material.

#2. Thoroughly vacuum the grain tank from top to bottom, including all ledges, steps, lights, sensors, wiring, and around the window to the cab.

  • Vacuum around and inside the bubble-up intake auger. Lower the bubble-up auger if possible to several different positions to access and remove the biomaterial from underneath it.
  • Vacuum all biomaterial from the floor of the cross augers.
  • Attach a smaller flexible hose to the vacuum and remove the biomaterial from the grain tank sump.
  • Use a smaller hose to clean the sump from below using the access door.

#3. Clean the unloading auger by packing 1.5 cubic feet of pine wood chips (0.5 inches long) into the sump. Power-up the unloading auger to scour and remove biomaterial. Then vacuum remaining wood chips and biomaterial from the sump, cross augers, and the exit end of the unloading auger.

#4. Remove the head, lower the feederhouse to the ground, and use compressed air to blow out the interior.

  • Remove biomaterial from all joints, crevices, and feederhouse chains.
  • Shake chains to loosen material. Each area may require repeated blowing and vacuuming.

#5. Raise the feederhouse and lock it in place using the hydraulic cylinder stop. (Figure 4).

  • Open the rock trap door and loosen existing biomaterial. If present, pull down the rubber seal between the feederhouse and the rotor to dislodge additional plant material.
  • Use compressed air and the vacuum to remove dislodged material.

#6. Remove access panels and rotor/cylinder concaves and clean the rotor/cylinder and threshing area. Use compressed air first and then vacuum.

  • Pry out lodged plant material from the front rotor/cylinder section and remove it with the vacuum.
  • Clean the concaves and the remaining rotor/cylinder cage.
  • Use compressed air directed to the back side of the rasp bar sections to remove residue.
  • If concaves were removed, reattach, and vacuum remaining residue from the rotor/cylinder area.

#7. Remove residue from the clean grain augers or shaker pan below the rotor/cylinder.

#8. Clean the chopper by removing the plant material from the rotor.

#9. Open the sieves to their maximum width and remove the covers of the bottom cross augers (if present). Force compressed air through the sieves. Inspect lower cross augers to vacuum any remaining debris before replacing the cross-auger covers.

#10. Clean the elevators by opening the lower doors and shaking the conveyor chains to dislodge any material.

#11. Open and empty the moisture sensor and reassemble.

Header Attachment Clean-Out

Depending upon which type of combine header you have — corn head or a grain platform head — the end-of-season clean-out is crucial to help prevent the spread of potential herbicide-resistant weed seeds and soil pathogens.

Clean corn heads by removing all ears and large residue from the exterior.

  • Raise the snouts and shielding between rows.
  • Next, remove the safety shields.
  • Use the vacuum and compressed air alternately to remove residue around gathering chains, deck plates and snapping rolls.
  • Clean the auger, feed-pan, and other areas at the rear of the head.
  • Replace all covers, snouts, and safety shields.

Clean grain platforms by first removing all large amounts of residue from the exterior.

  • Clean the reel, auger or belt, and the cutter bar areas.
  • Remove auger inspection cover and safety shields for additional inspection and cleaning.
  • Clean the outside and the inside of the crop dividers.
  • Replace all covers and safety shields.

Clean the exterior areas of the combine.

  • Use compressed air to remove residue from the spreader assembly and rear axle.
  • Also remove residue from the combine chassis (ledges behind access panels, above the fuel tank, all standing platforms, cab roof, and around the outside of the feederhouse, including guards and shields).