J. Lerin et I. Badenhausser, INFLUENCE OF THE LEAF CURLING PLUM APHID (BRACHYCAUDUS-HELICHRYSI) ONSTEM DIAMETER, SEED YIELD, AND THEIR RELATIONSHIP, IN SUNFLOWER, Journal of Agricultural Science, 125, 1995, pp. 211-221
The leaf-curling plum aphid (Brachycaudus helichrysi Kalt.) is one of
the main pests of sunflower (Helianthus annuus L.) in Europe. Yield lo
sses were assessed in open field conditions and natural infestations o
ver a 3-year period in Central West France. Plant variability and the
choice of the more vigorous plants by aphids in open field conditions
were two factors interfering with the experiments. To improve their se
nsitivity and to correct for biases without expanding the experimental
design, an analysis of covariance was the best compromise. Field and
cage experiments were conducted between 1985 and 1989 to assess the in
fluence of aphids on the relationship between stem diameter at harvest
and seed yield. As an indicator of plant vigour (size and yield), ste
m diameter at harvest was the best choice, as neither its relationship
with seed yield nor its mean value was affected by aphid infestation.
It was then used as a covariate to study yield losses. Aphid populati
ons were quantified weekly from the beginning to the end of the infest
ations according to the leaf-curling symptom and to the number of aphi
ds per plant. Multivariate analyses followed by cluster analysis ident
ified groups of plants displaying similar infestation dynamics. It was
found that when aphid populations reached > 100 per plant at the budd
ing stage, yield losses occurred. When populations were < 100 aphids p
er plant at the budding stage and then decreased, no yield loss was ob
served. This gives growers ample time to monitor populations and treat
crops.