By Sharon Badilla Arias, ISU M.S. candidate

Weed control under mesotunnels is challenging, especially in organic systems because the use of synthetic chemical herbicides is not allowed. Further, mesotunnels are kept in place almost the entire growing season except during bloom, when the nets can be removed to allow pollinators to visit the flowers. Therefore, we are studying different strategies to optimize the use of living mulches as alternatives for weed control.

Living mulches have multiple uses, but our focus is on weed suppression in the strips between black-plastic rows and yield impacts on acorn squash.

In previous years, my ISU research group tested several living mulches under mesotunnel systems, including a mixture of annual ryegrass (Lolium multiflorum) and red clover (Trifolium pratense) or red clover alone. However, each year the living mulches grew too slowly to suppress weeds.

This year (2020) we tested teff (Eragrostis tef), an ancient cereal grass species that is still used for grain production in the Horn of Africa and the Middle East. At the ISU Horticulture Research Station, we seeded it with a Gandy seeder at either 4 lb/acre or 8 lb/acre, one week before transplanting acorn squash (Table Ace) seedlings, and compared these treatments with bare ground and landscape fabric. Both seeding rates of teff suppressed weed biomass quite effectively. However, teff may have competed with the squash plants for water, nutrients and light, because it also reduced squash marketable yield by 23% and 29%, respectively, compared with landscape fabric.

       

Pictures taken 18 days after squash transplantation. LEFT: Teff is planted in the alleys between plastic-mulched strips. RIGHT: Landscape fabric laid in the alleys.

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Teff has some potential advantages as a living mulch. For one thing, it is relatively affordable at $6.25 per pound (Green Cover Seeds Company). It is also easy to establish (although we provided a bit of sprinkler irrigation to help it germinate and emerge during a dry-weather period). Teff is also resistant to diseases and has very few insect pests. Additionally, there are reports that teff seeds cannot survive Midwest winters, so it should not become a weed. Furthermore, it tolerates traffic and mowing once it’s established.

In 2021, we are planning to add a treatment in which we will mow teff during the bloom period of acorn squash. During this period, we will remove the mesotunnel covers for 2 weeks, to allow bees to pollinate the crop and to make room for mowing. Mowing at mid-season may enable us to reap early-season weed control benefits but slow further growth of the living mulch – hopefully eliminating teff’s drag on squash yield.