|dc.description.abstract||A study was performed to develop a generic pest monitoring system for sampling the
main table grape pests in vineyards in the Hex River Valley, Western Cape Province
of South Africa. The presence of phytophagous and predatory mites on cover crop
plants was also investigated as this may contribute to biological control of the
phytophagous mites in vines. Life table studies for Epichoristodes acerbella
(Walker), an important phytosanitary pest, were conducted to determine whether or
not this pest was sensitive to high temperatures. Information gained from the latter
can also be used for breeding purposes in the possible future development of a sterile
insect technique (SIT) programme to control this pest.
The sampling system consisted of inspecting 20 plots of five vines per plot per one to
two hectares. The top fork of each of the five vines per plot was examined for
Planococcus ficus (Signoret) to a distance of within 30 cm of the stem, as well as the
distal 15 cm of one cane per vine for the presence of P. ficus and damage caused by
Phlyctinus callosus Boh. One bunch per vine was examined for insect damage or
presence, and one leaf per vine for the presence of leaf infesting arthropods, such as
Tetranychus urticae Koch, P. ficus and Frankliniella occidentalis (Pergande).
Corrugated cardboard bands, tied around the stem of one vine per plot, were used to
monitor activity of P. callosus. Blue sticky traps, at a density of four to five traps per
one to two hectares, were used to monitor activity of F. occidentalis. Pheromone
traps, at a density of one trap per one to two hectares, were used to monitor activity of
P. ficus, E. acerbella and Helicoverpa armigera (Hübner). All the above-mentioned
inspections were done at two-weekly intervals, except traps for E. acerbella and H.
armigera, which were inspected weekly. In each of the rows in which the sample
plots were situated, one leaf of each of the cover crop plant species was examined for
the presence of phytophagous mites and their predators. The abundance and
distribution of cover crop plants were determined using a co-ordinate sampling
system. Cover crop sampling was done at monthly intervals.
The current threshold for P. ficus is 2% stem infestation, which is reached when more
than 65 males per pheromone trap are recorded. Counting mealybugs on the sticky
pads in the pheromone traps is time consuming. However, the number of grid blocks
on the sticky pad with males present can be counted. When P. ficus males are found in 27 blocks on the sticky pad, stem inspections should commence. Due to the spatial
association between P. ficus bunch and stem infestation, stem infestation could give
an indication of where bunch infestation could be expected.
The use of blue sticky traps for predicting halo spot damage, caused by F.
occidentalis, is not recommended. The presence of thrips on the vine leaves could not
give an indication of where to expect bunch damage, since thrips on the leaves and
halo spot damage were not spatially associated. A suitable sampling method for F.
occidentalis still needs to be developed. The monitoring system described here can
only provide information on the infestation status of the vineyard.
For E. acerbella, H. armigera and P. callosus, the traps and cardboard bands could be
used to identify vineyards where these pests are present and therefore, where
phytosanitary problems may arise. The presence of P. callosus under the bands was
spatially associated with P. callosus damage and could be used as an indicator of the
latter. The presence of drosophilid flies in the bunches could not be used as an
indicator of the presence of E. acerbella in the bunches. If 5% bunch damage is used
as an economic threshold for E. acerbella and P. callosus, there will be a good chance
of not under spraying if control measures are applied at 1% bunch damage.
Epichoristodes acerbella favoured more moderate constant temperatures, with
constant temperatures of 28°C and above being unfavourable for development.
The economic threshold for Tetranychus urticae Koch is six mites per leaf, or if
presence-absence sampling is used, 11 to 29% leaf infestation. Three important
predatory mites, that kept T. urticae under control, were found in the Hex River
Valley, namely Euseius addoensis (Van der Merwe & Ryke), Neoseiulus californicus
(McGregor) and an undescribed phytoseiid in the genus Typhlodromus. Various
cover crop plants served as hosts for T. urticae and predatory mites. The presence of
these plants created suitable conditions for the survival of these mites and may have
influenced their presence on the vine leaves.
In the case of phytosanitary pests, both field and pack shed inspections can be used to
conclude with a 99% degree of certainty that infestation levels in the pack shed will
be 10% or less, since similar results for both methods were obtained. However, more
than 20 plots will have to be inspected.||en_ZA