Lessons from Blackcurrant Scouting: SCALE

Scale insect pressure increased a lot from the 2024/25 season to the 2025/26 season.  Scouting records when crawlers are present, and this picture changed dramatically from last season to this. 

In 2024/25, crawlers were present in early spring, absent for most of the summer, and appeared again in late January.  In contrast, in 2025/26, crawlers were present in high numbers on many farms for the whole summer.  

There are several theories as to why scale was so bad this year:

1. Lorsban was last used in 2021.  We might wonder if the scale population has been growing since then and has just now reached epic levels, but this does not explain the increase we are seeing from last season to this season (from 2024/25 to 2025/26). 
2. We note from the spray diaries in the 2024 season that winter applications of Ovation and oil tended to be in late August or early September, possibly after the scale had already developed into adults and therefore were not susceptible to an insect growth regulator. 
3. Scale is primarily controlled by parasitism and predation in many perennial cropping systems, especially the wasp parasitoids and stethorus predatory beetles.  Have we inadvertantly disrupted the beneficials from doing their job with other chemical usage?

At present the standard chemical being used for scale control is buprofezin (Ovation).  While this is considered relatively benign to many predators, even some species of ladybird beetles, IPM Technologies mentioned at the February training that buprofezin prevents reproduction of some Stethorus (black ladybird) beetles.  Stethorus and similar beetle predators are very effective predators that used to be quite common in blackcurrant blocks, eating both spider mites and scale crawlers.

Looking back at the industry chemical usage reports, we first used buprofezin on 12% of blocks in 2020 (coinciding with Lannate being phased out). Then in 2021-2022, 40% of blocks used buprofezin. In 2023 our usage went up to 70% of blocks, then back down to 45% in 2024.

We’re concerned that buprofezin, especially used during the growing season, could be reducing a key scale predator in blackcurrant blocks.  We also think that the spring timing and lack of good coverage are two reasons why we are not getting good scale control with our current practice.

Recommendations:

• Switch from August/September winter scale control to May, just after leaf drop, when coverage is more feasible and we’re sure that crawlers have not yet turned into adults.
• Evaluate the efficacy of May application of oil+wetter and cyantraniliprole+wetter on scale crawlers

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