The pest status and chemical control of whitegrubs and cutworms in forestry in the Natal Midlands.
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Date
1995
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Abstract
The limited availability of land to forestry and the ensuing emphasis on intensive silviculture,
developed a renewed interest in soil pests in the establishment of plantations. Ten field trials
were planted over three seasons to determine the mortality factors influencing the
establishment of commercial eucalypt and black wattle plantations in the Natal Midlands, and
simultaneously, to investigate the chemical control of the soil pest component. A complex
of indigenous soil pests contribute to an average 22,9 % failure of Acacia mearnsii and
Eucalyptus grandis seedlings from reaching full establishment. This pest complex, which
includes termites, whitegrubs, cutworms, tipulid larvae, wireworms, millipedes and
nematodes, was responsible for an average 12,3 % of the failure of the plantings to establish.
In the absence of termites, in shallow humic soils, whitegrubs followed by cutworms were
the most frequent and economically important pests. Eucalypts are more susceptible than
wattle seedlings to whitegrub damage when planted in marginal sites. Seedlings in the
summer rainfall region were most susceptible to whitegrub damage from December to April;
and to cutworm damage during the first two months after planting. An average of 398
hectares was annually damaged by whitegrubs and cutworms. The total annual loss in
planting costs and the additional costs of blanking over the three year study period were 1,22
and 2,65 million rands respectively.
Existing non-chemical control applicable to woodlot forestry is reported. Chemical control
as one of the options in the management of whitegrubs and cutworms was evaluated. The
controlled release formulations of carbosulfan 10% and chlorpyrifos 10% at 1,0 g active
ingredient/tree (a.i./tree), gamma BRC 0,6% dust at 0,06 g a.i./tree and the synthetic
pyrethroid deltamethrin 5 % SC at 0,025 g a.i./tree were persistent and effective in
controlling whitegrubs, even when applied early in the planting season. Deltamethrin 5 % SC
at 0,025 g a.i./tree was also successful in controlling cutworms.
Description
Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1995.
Keywords
Insect pests--Control., Trees--Diseases and pests., Soil pesticides., Forest insects--Control., Theses--Zoology.