Download Weed seed predation in semi-arid winter cereals

Persistence of main weeds in dryland cereals despite of high predation by harvester ants (Messor
barbarus L.)
V. Atanackovic1, B. Baraibar1 and P.R. Westerman2
1
Dept. Hortofructicultura, Botànica i Jardineria, ETSEA, Universitat de Lleida, Av. Alcalde Rovira Roure
191, 25198 Lleida, Spain; E-mail: [email protected].
2
Group Crop Health, Faculty of Agricultural and Environmental Sciences, University of Rostock, Satower Str.
48, D-18051 Rostock, Germany
In dryland cereals in NE Spain certain weed species still persist despite of intensive use of herbicides. It seems
that seed predation could contribute as additional weed control. Harvester ants, Messor barbarus, are the main
seed predators and particularly abundant in no-till fields. To maximize natural weed control due to seed
predation, the period of weed seed shed needs to coincide with the activity period of the seed predators.
Two experiments were conducted in no-till cereal fields around Lleida (Catalonia, Spain) to: (i) quantify seed
demand by seed predators over time, and (ii) quantify seed shed of the most important weeds in winter cereals
over time (and determine the maximum). Two g of Lolium multiflorum and 2g of Vicia villosa seeds were
exposed to seed predators on a Petri dish for 48 hours, each month from April to October in 2007. After
exposure, the remaining seeds were weighed and the proportion removed seeds calculated. Dishes were
covered by a mesh to prevent removal of seeds by vertebrates. Seed shed was quantified in three no-till oat and
barley fields (in 2009 and 2010), using 36 seed trap, each consisting of two aluminium trays nailed to the soil
surface. Traps were arranged according to a regular grid in an area with abundant weeds. Traps were emptied
weekly from April to harvest (at the end of June). Seed demand by harvester ants was maximal from April to
the end of June when an average of 78 % of the seeds was removed. The timing of seed shed differed between
weed species such as Capsella bursa-pastoris, Diplotaxis erucoides, Bromus diandrus, Papaver rhoeas,
Galium spurium, Lolium rigidum and Avena sterilis but overlapped with the period of maximum predation.
Because of the overlap between seed shed and high activity of predators we expected that seed losses of all
weed species should be high. However, our results showed that some weeds were able to escape predation,
because 1) they were not preferred, such as B. diandrus, and 2) they shed seeds at harvest and immediately
were covered by crop residues, such as Papaver rhoeas. In addition, some species will escape seed predation
in one year but not in another, such as G. spurium. These results suggest that G. spurium, P. rhoeas and B.
diandrus escaped seed predation and that could explain why those weeds still persist in dryland cereals. In the
future, strategies to prolong seed availability of these weed seeds to predators should be developed to improve
efficacy of weed control.