Friday, 21 February 2014

Spotted Wing Drosophila (SWD)

By the halfway mark, I had found just two that were not sheltering the tiniest of white worms inside. A little stomach churning when the girls had been feasting just last weekend. A quick Google, revealed that this nearly always happens when ripe berries are allowed to sit too long on the cane, or allowed to drop to the soil below and putrefy.

This is the damage caused by the Spotted Wing Drosophila, a pest exotic to Australia and which the Department of Primary Industry (its heirs and successors forever), treats a bit like Mad Cow Disease! The most help to eradicate this pest from my garden came, however, from fellow garden bloggers, eg New Life on a Homestead. There is heaps of more technical information out there on this pest geared toward the commercial fruit grower, eg here, and here, and here.


There are a number of distinguishing features of the SWD for identification
  • They are miniscule.
  • The male SWD has two distinctive spots on the end of each wing.
  • The female SWD’s large, blade-like ovipositor.
  • They have large red eyes.
Both images courtesy of the Organic Growers' School

Prevention and Maintenance
  • Do not leave overripe berries on the vine, and do not let them fall to the ground as this will encourage an infestation. Keep plants picked clean of all ripe fruit every single day. Do not compost unwanted berries. The heat from the compost is not high enough to kill the SWD larvae and they will reemerge the following year. You can seal them in a ziplock bag and leave it out in the sun to kill the worms. Burying and composting are not reliable ways of killing eggs and larvae.
  • Keep plants pruned. Fruit flies like humid, shady environments. Thin plants out and keep sprawling varieties trellised. Burn the prunings instead of composting them.
  • Avoid any puddles or standing water in the garden because SWD seem to be attracted to these areas.
  • Do a ground clean up. SWD larvae can overwinter in the soil and reemerge the following year. Cultivate the soil around plants to expose the larvae to the elements. They don’t survive well in very cold or hot temperatures.
  • Set traps. You can put out a vinegar or yeast-sugar trap. Traps monitor for the arrival of SWD in order to guide spray programs.
  • Harvest in Spring not Autumn. Fruit flies tend to be more of a problem with Autumn crops. Prune them after the Spring harvest so that there isn't an Autumn harvest that would attract the SWD.
  • Both Entrust (Spinosad) and Pyganic (Pyrethrin) are acceptable for organic crop production. Entrust is reported to be most effective. A Spinosad containing product in Australia is Yates' Success Naturalyte, Yates' Nature's Way Fruit Fly Control, and Eco Natra Lure Fruit Fly Bait.

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