Don’t Let Weeds Go to Seed: Managing
Lambsquarters and Redroot Pigweed in Vegetable Fields
Weed management continues to be one of the
biggest challenges in vegetable production. Two weeds that can become
particularly troublesome are common lambsquarters (Chenopodium album) and
redroot pigweed (Amaranthus retroflexus). Both are fast-growing annual
broadleaf weeds that can compete aggressively with vegetable crops for light,
water, nutrients, and space.
During my field visits this season, I have
seen how quickly these weeds can grow and overtop vegetable crops when they
escape early-season control. Once they become large, management becomes much
more difficult. This makes timing one of the most important components of weed
management.
If They Have Escaped Control, Act Now
Ideally, lambsquarters and redroot pigweed
should be controlled when they are small. However, if they have already become
large in vegetable fields, field edges, headlands, or areas where the crop has
been harvested, the priority should shift to preventing seed production and
reducing additions to the soil weed seedbank.
If these weeds are approaching flowering or
seed development and you have not controlled them yet, mow, cut, hoe, or remove
them as soon as practical—before mature, viable seed is produced. Do not leave
mature weeds standing simply because the vegetable crop is close to harvest or
has already been harvested.
This is especially important because
allowing weeds to produce seed this year can create weed-management problems
for many years to come. Small-seeded weeds such as lambsquarters and pigweed
can persist in the soil seedbank for years, producing new flushes whenever
environmental conditions are favourable.
Don't Wait Until Weeds Are Large
The best approach is still to manage weeds
early and when they are small. Regular scouting is critical, particularly
during the first several weeks after vegetable crops are planted. Depending on
the crop and production system, an integrated weed-management program may
include crop rotation, stale or false seedbeds, cultivation, hoeing, mulches,
cover crops, and appropriately labelled herbicides.
Once lambsquarters and pigweed become
large, they are much more difficult to control and may already have competed
substantially with the vegetable crop. Even when late-season control can no
longer recover lost crop yield, removing or mowing escapes can still be
valuable because it can reduce seed return to the field.
Think About Next Year's Weed Problem
Today
Weed management should not end when the
vegetable crop is harvested. Walk fields after harvest and look closely at
field edges, headlands, missed rows, irrigation areas, and patches where weeds
escaped earlier control. These areas can become important sources of seed for
future infestations.
If lambsquarters or redroot pigweed are
present and have not yet produced mature seed, do not give them the opportunity
to finish their life cycle. Mow or remove them promptly. Where mature seed is
already present, use additional care during mowing, removal, tillage, and other
field operations to avoid unnecessarily spreading seed around the field.
The goal is simple: control weeds early
whenever possible, and when weeds escape, prevent them from going to seed.
Every weed prevented from contributing seed is an investment in reducing future
weed pressure.
I am also including a few photos taken from
different vegetable fields this season to illustrate how aggressive
lambsquarters and redroot pigweed can be under field conditions. Growers work
hard to manage weeds, but during the busy growing season, other time-sensitive
farm operations can take priority, allowing these fast-growing weeds to get
ahead very quickly. The photos highlight how rapidly these weeds can grow and
compete with vegetable crops, reinforcing the importance of timely management
before they mature and produce seed.
Take-Home Message
Lambsquarters and redroot pigweed grow
rapidly and can become highly competitive in vegetable fields. Scout early,
control them while they are small, and never intentionally allow escaped plants
to mature and replenish the weed seedbank. If large plants are still present
and viable seed has not matured, mow or remove them as soon as possible.
Figure 1. Lambsquarters growing along the edge of a vegetable garden.
Figure 5. Uprooted lambsquarters and redroot pigweed showing their extensive root systems, which allow them to compete strongly with vegetable crops for soil moisture and nutrients.
Manphool Fageria, PhD, P.Ag.
Vegetable Specialist | Agricultural Services
Perennia Food and Agriculture Corporation
Email mfageria@perennia.ca
Mobile
902-890-7716
6-28 Aberdeen Street, Kentville, NS B4N 2N1
