Psa symptoms ramping up

KVH has received many calls from growers reporting an increase of Psa symptoms over the past two to three weeks.

Many Hayward sites now report significant leaf spotting in male and female vines, particularly where spray programmes through autumn, winter, and spring were compromised or blocks are wind exposed or have experienced extremely wet soil conditions.

Reports of flower bud infection vary, both between and within individual blocks. Typically, wetter or wind exposed areas are more affected, with 25-30% flower bud loss estimated in some cases. Overall effect on crops will not be known until pollination is complete. Pre-flower trunk girdles have reduced infection levels on many sites.

More Gold3 sites are also reporting leaf spotting this season. This suggests higher inoculum levels than in past years.

KVH visited some Edgecumbe sites this week and talked with growers who are still seeing active cankers along trunks and leaders in some Gold3 vines. View the photo gallery.

Recent shoot and cane collapse was also not uncommon on Psa challenged sites. Highest infection levels were in a young Gold3 block where strung canes had suffered damage during storms which occurred last autumn (images included in above photo gallery).

Here, for some plants, die-back suggested infection had entered when canes were cut to length during winter, while for others whole scions were collapsing indicating systemic infection within the plant. Scions cut back earlier in the year were starting to produce regrowth which would be restrung this season. Plants put under stress through silting relating to floods were also reporting higher Psa impacts.

In more mature blocks odd canes and shoots were being seen. Often these were associated with older leader cankers some of which showed recent exudate.

Growers are telling KVH that the ability to complete good autumn spray programmes and proactively apply a mixed range of products through early spring has been key to better results. Applying wound protectants to all winter pruning cuts on Gold vines, including all cane ends in younger blocks, was very necessary. KVH is pleased to hear and see that tool hygiene and infection removal was also considered by growers to be necessary “business as usual”.

Overall, the approach of growers is to keep moving through the workload and look forward to warmer temperatures.

Any new or unusual symptoms should continue to be reported to KVH.