PLANT DISEASE, vol.97, pp.897-902, 2013 (SCI-Expanded)
Members of the Botryosphaeriaceae family have been associated with
branch cankers of avocado trees (Persea americana) in California.
Canker infections are initiated by spores entering the host plant
through fresh wounds such as pruning wounds. With high-density
planting becoming more common in the California avocado industry,
more intensive pruning may increase the occurrence of branch canker.
The objective of this study was to evaluate the preventive ability of
some commercial fungicides belonging to different chemical families
against fungal pathogens associated with avocado branch canker. Initially,
12 fungicides were tested in vitro for their effect on the inhibition
of mycelial growth of three isolates of Dothiorella iberica and
isolates (five per species) of Neofusicoccum australe, N. luteum, N.
parvum, and Phomopsis sp. Subsequently, azoxystrobin, fludioxonil,
metconazole, and pyraclostrobin, selected because of their low effective concentrations that reduce 50% of mycelial growth (EC50 values),
and myclobutanil, selected for its high EC50 value, were tested in two
field experiments. Azoxystrobin and fludioxonil were used in a premix
with propiconazole and cyprodinil, respectively, in field trials. Significant
differences (P < 0.05) were observed among fungicides in field
trials. Azoxystrobin + propiconazole had the highest percent inhibition
at 52 and 62% (internal lesion length) in trial 1 and trial 2, respectively,
although this level of inhibition was not significantly different from
that of metconazole. A significant correlation (r = 0.51, P < 0.05) was
observed between internal lesion length data in the field experiment
and EC50 data from in vitro fungicide screening. Application of
azoxystrobin + propiconazole and metconazole can play a key role in
protecting Californian avocado against fungi causing avocado branch
canker.