February 2019 - 15

Recruiting ants to fight weeds on the farm
By Carolyn Trietsch
Penn State University
Harvester ants that eat weed seeds on the
soil's surface can help farmers manage weeds
on their farms, according to an international
team of researchers, who found that tilling
less to preserve the ants could save farmers
fuel and labor costs, as well as preserve water
and improve soil quality.
" These ants are naturally present in
the fields, " said Barbara Baraibar Padro,
a postdoctoral scholar in plant science at
Penn State University. " They are able to
remove a huge amount of weed seeds from
the system, and if farms till less to preserve
these ants, it can benefit them. "
Tilling a field disturbs the soil and can
destroy ant nests. The researchers wondered
whether tilling had an impact on the
number, size and distribution of ant nests
in the fields, and how these factors could
influence the ant's ability to control weeds.
" Tilled fields might harbor more weeds
because they don't have the pressure from
the ants, " said Baraibar. " If you don't disturb
the soil, you might have more ants. "
The researchers compared the number
and size of ant nests in four tilled fields
and three no-till fields in Spain. They also
marked the locations of different ant nests
using GPS, then analyzed how evenly
spaced apart the nests were in the tilled and
no-till fields. Their paper will appear in the
Biological Control journal in January 2019.
The researchers predicted that tilled fields
would have less ant nests, and that these
nests would be smaller than those in no-till
fields. While they found no differences in
the number of ant nests in tilled and no-till
fields, they did find that tilled fields had
smaller nests than no-till fields. This can
impact weed management because smaller
nests will not consume as many weed seeds
as larger nests.
The researchers also predicted that ant
nest distribution would differ between tilled
and no-till fields. Ants normally compete
with each other and defend territories,
causing an even distribution of ant nests
throughout a no-till field. But tillage could
kill some nests at random and leave some
areas with no ant nests to remove weed
seeds from the surface of the soil.
The researchers found that indeed, notilled
fields had more evenly distributed
ant nests, whereas tilled fields had more
randomly distributed ant nests.
" It was cool that we could see the spatial
difference between the tilled and no-tilled, "
said Baraibar. " There is a lot of variability
between fields, so the idea that we could see
a pattern is exciting. "
Farmers in Spain growing winter cereal
crops like barley till the soil twice a year.
While the fall tilling can help farmers
prepare their fields for planting, the
researchers do not believe that summer
tilling is as beneficial.
" Agronomically, I'm not sure if that tillage
makes that much sense, " said Baraibar.
" You're probably losing a lot of water and
you are burying all the weed seeds, so they
are no longer available to the ants. "
In the dry, semi-arid regions of Spain,
farmers need to preserve water and
maintain soil quality to have a good crop.
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Tilling less can help farmers save water,
improve their soil, and reduce the costs of
fuel and labor, as well as helping the ants
that consume weed seeds. Harvester ants
can also help farmers manage herbicideresistant
weed species such as rigid ryegrass,
a grass that ants may prefer, and with ant
colonies living for years, these benefits are
long-lasting.
" Careful timing of the tillage can preserve
the benefits of weed seed removal that
the harvester ants provide, and also help
with preparing the seed bed or controlling
summer weeds, " said Baraibar. " So, you're
not losing the benefits of tillage, but doing it
at the right time. "
Joel Torra, and Aritz Royo-Esmal,
Messor barbarus ants harvesting and bringing wild oat (Avena fatua) weed seeds to the nest
entrance. Soldier ants (with large red heads) and smaller workers are visible. Photo: Barbara Baraibar
postdoctoral scholars, and Jordi Recasens,
professor, all in the Department of
Horticulture, Botany and Landscaping:
and Carles Comas, associate professor of
mathematics, all at the Universitat de Lleida,
Spain, also worked on this project. The
Spanish National Research and Development
Program and the Department of Agriculture,
Food and Environment of the Catalan
Government, funded this work. VGN
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February 2019

Table of Contents for the Digital Edition of February 2019