Monitoring fruitspotting bug damage in macadamias

The damage

About two months after initial nut set there is often a natural thinning of fruit in macadamias. Up to this time most nuts damaged by spotting bug will fall readily. As the nuts mature they will fall less readily and this damage can be the cause of most of the kernel damage found harvest.

Fallen nuts need to be sectioned to determine the cause of fall. Green freshly fallen nuts of some varieties show dark slightly sunken spots on the husk. Cells of the inner husk and soft shell collapse and become discoloured in areas surrounding the feeding points. The kernels may be misshapen and translucent instead of the normal milky white colour.

When the shells are beginning to harden and turn brown, small depressions may develop on the outer surface of the shell or there may be only a pin-point mark at the feeding point. Others again show no sign of injury on the shell though the kernel may be completely or partially affected. In this case damage can only be detected after nuts are shelled.

Monitoring procedure for green fallen nut

We suggest monitoring for bugs to commence after fruit set and then every two weeks for 10 or so visits.

You can visit more frequently during pressure periods if you wish.

10 marked trees in a ‘hot spot’

"Randomly select 10 trees - of the same variety if possible - in the ‘hot spot’ area. - and then MARK as trees to be returned to each time.

Most blocks have a ""hot spot"" but if yours doesn't just select 20 trees over the block.

We suggest using marked trees to try and avoid a bias for trees with more nut drop as you walk through the blocks.

10 marked trees (more if you wish) in the ‘Rest of block’

As above for the rest of the block

Total of a minimum of 20 trees for the trial block

Count or estimate the total of fresh green fallen nuts PER SQUARE METER under each marked tree.

Rate the number of fresh green fallen nut per square meter as either 0 to 5, 6 to 10, 11 to 20, 20 to 30, 30 to 50, 50+ (just estimate when over 20)

The above values should be converted to a rating. See table at bottom of monitoring sheet.

Examine 10 of the freshly fallen nuts (if there are that many) and record the number with FSB damage:

Cut open the nut and separate the husk, shell and kernel.

Examine each part for damage, with spotting bug damage appearing as a brown lesion on the inside of the husk.

The developing shell may have crinkled areas.

Up to 100 nuts will be examined for the site.

If you notice FSB nymphs or adults make a note of this in "comments" column.