Science into Practice: Desiccants for raspberry spawn control

Summer-fruiting raspberries contain both floricanes (fruiting) and primocanes (spawn).

Excessive and uncontrolled spawn production can lead to increases in disease levels and impede access to berries by pickers, reducing picking speeds. The problem is worse under Spanish tunnels where conditions favour more vigorous growth. For years the industry could rely on sodium monochloroacetate for spawn control but, due to EU pesticide harmonisation, a replacement was required from 2008. HDC project SF 73 screened alternative desiccants over three seasons, aiming to secure a SOLA for the most promising.

Assessments were made of spawn die-back, fruiting cane quality, signs of phytotoxicity and yield and berry weights for each treatment under tunnels with a very vigorous variety Glen Ample and outdoors on the variety Octavia. In every year Shark (carfentrazone-ethyl) provided better spawn control than even the industry standard. Having proved to be the most effective candidate desiccant, the HDC secured a specific off-label approval (SOLA 2008/0551) for Shark for use in protected and outdoor raspberries, blackberries and rubus hybrids.

The over-use of Shark will weaken emerging spawn suggesting that a crop that is growing weakly, or in a difficult growing season, should receive one application of Shark, not two. Where plantations are very weak, no application should be made at all. Many raspberry varieties now being planted including Tulameen, Glen Doll and Malling Juno are less vigorous than Glen Ample and are more likely to be damaged by repeated treatments. Growers should seek advice from a qualified agronomist before using Shark and for how many applications.


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