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Cover Crops--Pathogen and Weed Associations

There is much interest in and research with cover crops, and much being written about their benefits and positive effects in cropping systems and the environment. However, lest we forget that no agronomic practice is foolproof, the following points are presented.

A recent articled entitled “Isolation of Cultivation-Resistant Oomycetes, First Detected as Amplicon Sequences, from Roots of Herbicide-Terminated Winter Rye” that appeared in an e-Xtra edition of Phytobiomes Journal presents an interesting finding that highlights the need for informed management to reduce the potential of seedling disease risk to a crop that follows a cover crop. Even though the results presented in the above article deal specifically with the pathogenic effects of certain Pythium species on corn following a cereal rye cover crop, they demonstrate that cover crops can influence or affect the fungal population in the soil, and this should be monitored because of the potential impacts of these populations on disease in any crop that follows a cover crop.

 

Dr. Kevin Bradley, Assoc. Prof. (Weed Science) at the Univ. of Missouri, presents a webcast entitled “A Review of the Effects of Various Cover Crop Species on Winter and Summer Annual Weed Emergence” that is posted on the PMN Focus on Soybean website. This is the most inclusive and up-to-date information source that I know of on this subject. The presentation includes results from recent published research that pertains to cover crop suppression of both winter and summer annual weeds. Major points follow.

    Cover crop suppression of winter annual weeds is dependent on both the cover crop species or mixture, time of cover crop establishment, and the weed spectrum present in a given field.

    Effective cover crop establishment in the fall is key to controlling winter weeds.

    All cover crops will provide some level of winter weed suppression, but cereal rye and hairy vetch or their mixture do the best job.

    The big advantage of cover crops in suppression of winter weeds is their control of glyphosate-resistant marestail.

    Cover crop suppression of summer annual weeds is dependent on cover crop species, cover crop biomass, time of cover crop termination, decay rate of cover crop residue, and the weed species that are present in the targeted field.

    Cover crop suppression of weeds is generally better on the smaller-seeded weed species.

A major take-home message from Dr. Bradley’s webcast is that not all cover crops are created equal, and cover crops should be selected based on the intended purpose or gain from their use.

I encourage you to view Dr. Bradley’s presentation in its entirety for his thorough treatment of the title subject.

 

Preliminary (first-year) results from two MSPB-funded projects (01-2016 and 13-2016) indicate that insecticides applied to soybean seed may be necessary to control soil/foliar insect populations that can be associated with cover crops. Subsequent years’ work in these multi-year projects will clarify this dynamic that may result when soybean follows a cover crop.

 

The above three cited cases certainly indicate that using any cover crop preceding any summer crop may not be as innocuous a practice as we would like; i.e., incorporating a cover crop or crops into any production system should be done with the knowledge that the production environment resulting from this practice likely will be altered, and therefore should be monitored for intended results and for potential shifts in pathogens that pose a risk to the summer crop.

 

Composed by Larry G. Heatherly, Apr. 2017, larryheatherly@bellsouth.net