American Crystal Sugar’s pre-pile harvest campaign is scheduled to start on August 12. This early start creates an opportunity to establish a cover crop to reduce the potential of wind and/or water erosion throughout the winter and early spring. Winter rye may seem like the obvious choice as it is nearly foolproof to get established and is the most winter-hardy. Likewise, spring or winter wheat may look like an option too. If you, however, plan to seed spring wheat on this year’s sugar beet acreage (or seed wheat adjacent to this year’s sugar beet fields you plan to establish this cover crop), you may want to read the rest of this article. Three potential pest and disease problems in spring wheat can take advantage of a "green bridge" to overwinter and cause problems next season.
The earlier seeding allows the cover crop to grow much
longer, and thus taller, this fall. The earlier seeding, however, also creates this
green bridge for barley yellow dwarf virus (BYDV), wheat curl mite/wheat streak
mosaic virus (WSMV), and Hessian fly that can wreak havoc on next year’s spring
wheat crop. Wheat is the preferred host, but rye can be a host too. An anecdote
to demonstrate how devastating a green bridge can be can be found here.
To close the green bridge, the cover crop needs to survive
the winter and resume growing next spring.
Both winter rye and winter wheat survive Minnesota’s winters most, if
not all, years. Some of our spring wheat varieties carry the vernalization gene
on chromosome 1A. While these spring wheat varieties do not need a
vernalization period to trigger the transition from vegetative to reproductive
growth like a winter wheat variety, the presence of vrnA1 does impart some
winter hardiness. Consequently, a cover
crop of these varieties can, provided there is some snow cover, survive the
winter in Minnesota.
You have two options to avoid the green bridge. The first option is to use oats instead of
wheat or rye. Oat is not a host for
Hessian fly and readily winterkills, reducing the risk of BYDV or WSMV bridging
across to the next year’s crop. The fact that oats are not a host to Hessian
fly allows you to ignore the so-called fly-free date and seed immediately
following the beet harvest. In addition,
oat can be seeded as deep as 3 - 4”. This improves your odds of establishing the
cover crop successfully.
The second option is to use winter rye and terminate it with
a burndown herbicide before the first killing frost if you plan to seed
immediately following beet harvest. If
you heed the fly-free date of September 15 for Hessian fly, you can opt to not
terminate it in the fall but instead terminate it in the spring using tillage
or a burndown herbicide. When
terminating the winter rye in the spring, you need to give the rye some time to
die and dry down enough for the wheat curl mite to leave the field, potentially
delaying seeding of the spring wheat. In addition, you create the risk that,
despite your best effort, some rye plants survive. In turn, those surviving plants not only could
be a reservoir for wheat curl mite/WSMV or BYDV, but they will eventually contaminate your spring wheat during harvest and increase your dockage at the
elevator.
If you plan to seed soybeans on this year’s sugar beet
acreage (or in adjacent fields), you have the option to let the winter rye
wheat overwinter. It is best to terminate these no later than the boot stage.
This creates a large enough window for an effective spring herbicide burndown
without risking lower yields. The 2022, 2023, and 2024 results of several
on-farm trials doing just that can be found here, here, and here.
(This post was written by Anna Cates, Lindsay Pease, and Jochum Wiersma.)
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