Coarse grains such as corn and soybeans usually thresh relatively easily, but wet field conditions may slow field drying. With the heavy amounts of rain that have soaked parts of Iowa this September, especially northeast, north-central and eastern Iowa, you should consider adjusting your combine to harvest in wet fields this fall. The following observations and recommendations come from Mark Hanna, Iowa State University Extension ag engineer.

Adjusting rotor speed. Rotor speed should not be increased and concave clearance should not be decreased more than necessary for threshing, but spongy corncobs or damp soybean pods may be more difficult to thresh. Greater rotor speed or reduced concave clearance may be necessary in these conditions.

Evaluate need to adjust. Evaluate the need for combine adjustment by checking for unthreshed corn or soybeans behind the combine and in the grain tank before being overly aggressive with threshing; causing damage to seed coats and increasing the potential for storability problems.

Larger bits of cobs or pods in the cleaning system require more attention to adjustment of airflow and sieve opening sizes in the cleaning shoe. Use an adequate amount of airflow to help fluidize the bed of material and allow pneumatic as well as mechanical separation.

In corn, the head should be operated low enough to gather all ears. Avoid going lower than necessary if a significant amount of soil or sediment is on lower parts of the stalk, as soil adds wear inside the combine and increases cleaning load. If ears hang low, the head will need to be operated low enough for gathering. Soybeans will have to be cut at ground level, regardless.

Clean combines to avoid weed seed contamination across fields

Another step farmers need to consider taking during harvest this fall is to clean your combine—inside and out—this fall to avoid spreading weed seed contamination from one field to the other.

Removing material from inside and outside your combine to avoid moving weed seeds between fields can be a daunting task, says Bob Hartzler, ISU Extension weed management specialist. Typically, combines hold 125 to 150 pounds of grain and biomaterial after the unloading auger has operated “empty” for one minute.

A true clean-out: A true clean-out requires about six hours to remove as much biomaterial as possible. A clean-out process may be necessary to prevent the spread of weeds to new fields. A first line of defense is to avoid harvesting fields with an offending weed species, such as burcucumber or Palmer amaranth, until the end of the season to avoid introducing seeds of new weeds to other fields.

Steps for limited cleaning: While a thorough, top-to-bottom cleaning of the combine is best to avoid the spread of weed seeds between fields, spending 15 to 30 minutes cleaning the combine before moving it out of the field will still remove some biomaterial.

First, allow the combine to do some “self-cleaning” by opening doors at the bottom of the clean grain elevator and unloading auger sump on the clean grain tank. Remove the gathering head if time allows. Then, start up the combine; operating the thresher and separator at full speed. Have the cleaning shoe sieves fully open and the fan adjusted to maximum speed. Make sure no one is within 100 feet of the area to avoid being hit by flying debris. Use the rest of the time available to clean the outside surfaces of the combine, the gathering head, and inside the rock trap. Head removal allows cleaning of the feederhouse and easier access to the rock trap. Remember to close elevator and sump doors when finished.

Removing larger weed seeds (e.g. burr cucumber) will probably be more effective than smaller weed seeds (e.g. Palmer amaranth) with this type of limited cleaning. However, any effort is likely more effective than none.