Organic Farmer October/November 2019


Figure 1. Cover crops, like this rolled cereal rye,

can suppress weeds by preventing light from

reaching the soil and inhibiting weed seedling

emergence. All photos courtesy of Lynn M.


successfully terminated may end up

competing directly with crops resulting

in yield loss. Insufficient cover crop

biomass accumulation may support

weed development by preserving soil

moisture needed for weed growth and

development and by preventing the successful

use of other control tools such as

cultivation or flaming. Make sure that

the cover crop seed you purchase is free

of weedy contaminants to avoid bringing

new problems into a site (the same

holds true for manure and compost).

Weed seed germination and subsequent

seedling destruction in advance of crop

planting (also known as pre-germination

or stale seedbed techniques) can

be useful for reducing the numbers of

weeds that can compete directly with

the crop. The timing of control operations

is crucial as many species can

grow quickly and outpace management

efforts (e.g. Palmer amaranth), especially

when weather events delay entry

into fields. This is a concern as re-rooting/re-sprouting

potential increases

as weeds grow taller and accumulate

biomass. Plants that escape control

measures can directly impact crops by

reducing yields and harvest efficiency;

they also have effects that can span

seasons if they reach reproductive

maturity and propagules enter the


The suppressive effects of the commodities,

themselves, can be maximized by

preparing and planting into as smooth

a seedbed as possible to facilitate

even germination. Seeding depth,

seeding rate and row spacing also play

Continued on Page 40

Figure 2. Weeds, such as bindweed, can move within and between fields on farm equipment.

October/November 2019


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