Seasonal occurrence, dispersion and pre-harvest control of grain chinch bug

The grain chinch bug (GCB) is endemic to the Western Cape.  It is a pest of wheat and moves into orchards when the wheat is harvested, looking for overwintering sites in the stalk and calyx area of fruit.

The aim of this project was to determine the seasonal occurrence and movement of GCB into fruit orchards and to assess pre-harvest control strategies for this pest.  Six orchards were monitored, four in the Ceres Valley and two in the Witzenberg Valley.  Monitoring took place over three years.  Fruit inspections were conducted in the two orchards in the Ceres Valley.  Preliminary bio-assays were conducted in the laboratory to establish the efficacy of four insecticides using pears which were artificially infested with GCB.

Although good results were achieved in laboratory bio-assays, pre-harvest chemical applications will probably not be a suitable control method.  Since GCB is a phytosanitary pest, sufficient control (100% mortality) cannot be achieved, based on these results.  It is recommended that other control options are investigated.

The results showed that relatively few GCB were caught in the Witzenberg valley where characteristically no wheat is grown.  In the Ceres Valley, migrations into the orchards took place shortly after the wheat was harvested.  When no wheat was planted, the corresponding numbers in bands appeared to be much lower during that season.  Fruit inspections indicated that GCB’s start infesting fruit immediately after they move into the orchards (November) and most likely continue infesting fruit right up until harvest.  A pre-harvest control strategy involving chemical control would therefore not be a feasible option.