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Weed Suppression Treatment Effects on Tree Seedling Establishment

The photo shows Erin Tapley, PMC technician, and Mollie Herget, study leader, planting woody seedlings into different vegtative treatments.When we hear the word cover crop, we typically think of row crop agriculture.  Annual cover crop species can be used for more than annual cover in rotations with agricultural crops though.  The Elsberry Plant Materials Center in Missouri recently completed an evaluation of annual covers to suppress weeds during the establishment of woody seedlings in comparison to traditional weed suppression practices.

Three commonly produced woody species in the region, ninebark (Physocarpos opulifolius), pin oak (Quercus palustris) and swamp white oak (Quercus bicolor) were used in the study.  All three woody species are native to the Missouri and much of the eastern U.S.  Ninebark is a flowering shrub, while pin oak and swamp white oak are both hardwoods from the red oak and white oak families, respectively.  Seedlings were planted and grown with seven different cool season vegetative treatments that were selected based on their biomass production and ability to suppress weeds.  Annual species used were black oats (Avena strigosa), winter oats (Avena sativa), winter wheat (Triticum aestivum), annual ryegrass (Lolium multiflorum), cereal rye (Secale cereale) and a Brassica mixture consisting of radish, turnip and canola (Brassica spp.).  For comparison, the cool-season native perennial Cuivre River Germplasm Virginia wildrye (Elymus virginicus) released in 2002 by the Elsberry PMC was also included in the study.

All species evaluated provided both short- and long-term weed suppression with minimal to no effect on woody plant growth and survival at the Elsberry Plant Materials Center during the two-year study.  Weed suppression was greatest in plots planted with annual ryegrass or the brassica mix during the first year.  All annual covers matured and scattered their seed, however, none germinated during the second year and most plots had some weeds in them.  There was no effect of the annual covers on woody plant growth during the first year. 

The Virginia wildrye was slower to establish than the annual species but was best for longer-term weed suppression.  Trees and shrubs planted with Virginia wildrye as a cover also had greater growth over the two-year period compared to woody species grown with no vegetative treatment.  Advantages of using perennial vegetation include low maintenance (doesn’t have to be replanted every year), reduced erosion, improved weed control, nutrient cycling and soil improvement.

For sites where weed pressure is high, annual covers may be very useful for suppressing weeds during the establishment year.  But for the longer-term perennial grass covers may be more beneficial.

For more information on results of this study, contact Ron Cordsiemon (, PMC Manager, or Mollie Herget (, Agronomist.