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Weed Seed Management Prior to and at Harvest

As of Oct. 12, 2021, NASS estimates that 45%, 73%, and 54% of Arkansas, Louisiana, and Mississippi soybean acres had been harvested; thus, information in portions of this article will not apply to those acres. However, the issues discussed herein will apply to future harvests and therefore are worth filing for future reference.

Below are summaries of information in four articles that provide guidance on managing weed seed prior to and at harvest so that they do not contribute to foreign matter (FM) in harvested soybean seed, or exacerbate weed problems in future plantings at the harvest site

The first is an article titled “Got weeds in your beans? You’re not alone” by Naeve, Goplen, and Nicolai at the Univ. of Minnesota. Important points from that article are summarized.

•    Sporadic weed escapes may not affect soybean yield, but they will contribute to deductions at the elevator, lowered quality of product delivered to customers, and future weed problems in the field of their occurrence.

•    Even small escaped weeds will contribute to the weed seedbank.

•    Running weeds that are present in small patches in a field through a combine will result in dispersion of seeds of those weeds over a much larger area than they presently occupy.

•    Weed seed that are harvested with soybean seed contribute significantly to FM in the delivered product, and can result in rejection of the product by the customer.

•    Sanitizing combines between fields can minimize the spread of weeds.

•    Preventing weed seeds from entering the combine is an important component of long-term weed management in commodity crops such as soybean

The second article is titled “How to keep weeds out of the combine at harvest” by Emily Unglesbee, DTN Staff Reporter. In this article, the author provides information from Dr. Jared Goplen, an Extension crops educator at the Univ. of Minnesota. Important points from that article are summarized.

•    Combines are excellent weed seed spreaders.

•    Pre-harvest weed management consists of hand-pulling isolated weeds and mowing accessible areas that have severe weed infestations. Pre-harvest management should be done before weeds [especially those deemed to be herbicide-resistant (HR)] have set seed.

•    During harvest, avoid harvesting areas with severe weed infestations. After harvest, clean combines between fields.

•    Run an empty combine for a short period and/or drive it over bumpy ground to dislodge weed seed after harvest.

•    If possible, blow the combine off, with special attention on the header.

An article titled “Weed seed management at crop harvest” provides the following important points.

•    Weed seed management at harvest is especially critical because many of the weed escapes will be HR.

•    Troublesome weed species that plague soybeans retain over 90% of their seed at soybean harvest. Thus, if these seed are harvested with the soybean crop, they will replenish the weed seedbank.

•    On a combine, the rock trap and rear axle/chopper components are estimated to retain the most FM after harvesting soybean. These two components are estimated to take less than 20 min. to clean, whereas the rotor retains the third most FM and is estimated to take about 45 min. to clean (note: access this article to see a graphic that shows the location of indicated components).

An article titled “Harvest helpline: combine clean-out” by Anderson et al. is from the North Central Extension Agriculture and Natural Resources Academy (NC-ANR Academy), and provides the following important points.

•    As much as 150 pounds of FM (chaff, grain, and weed seed) is retained by a combine following harvest of a field.

•    Diligent effort following harvest of a field can reduce the movement of this FM from one field to another. Appropriate combine clean-out should be a top priority to prevent spread of FM issues, especially seed of HR weeds.

•    Three steps to prevent spreading weed seeds are: 1) remove problem weeds before harvest; 2) consider harvest order to prevent carrying seed of problem weeds to clean fields; and 3) practice good combine clean-out procedures before moving to clean fields.

•    Producers should focus on priority combine areas (see previous cited article) where significant amounts of FM will be retained and subsequently spread to subsequently-harvested fields.

•    A 20-30 minute cleaning process is outlined, and contains 7 cleaning steps that involve the major FM-trapping areas of a combine.

It is important to note the following major points that are associated with weed seed management prior to and at harvest.

•    Pre-harvest weed seed management should involve destruction of weed escapes before seed set, or certainly before weed seed maturity.

•    Mowing dense patches of escaped weeds or not harvesting the crop in these patches is highly recommended to prevent seed maturation or spreading of mature seeds.

•    A combine can be a significant spreader of weed seeds.

•    Combine cleanout is an important part of weed seed management at harvest, and should be practiced as outlined in the above cited article.

•    Failure to adopt good weed seed management practices at harvest could result in a heavily docked or unsaleable product and a worsening of HR weed issues in soybean fields. Either of these occurrences will be costly both now and in the future.

•    The ultimate goal of management of all weed escapes prior to and at harvest is to ensure that the weed seedbank is not replenished and that the harvested product is subject to minimal FM dockage at the point of delivery.

Composed by Larry G. Heatherly, Oct. 2021,