Protecting kiwifruit from Psa in Spring
Psa can be present on the outside and inside of expanding kiwifruit buds in Spring, and rainfall then encourages the multiplication and spread of Psa infection in the orchard.
Best practice is to have good coverage of a winter rate copper in place as spring buds’ break. Then, knowing when and where your earliest buds break in a block should trigger the start of a protective Psa programme.
Young leaf tissue in spring is particularly vulnerable to Psa with research showing that Psa infection of flower buds can occur at a very early stage of vine development (around 4 weeks after budbreak in Gold3).
Developing leaves needs to be protected during this period, so it is an ideal time to make the first ACTIGARD® application, which elicits a natural protectant response in the plant - called Systemic Acquired Resistance (SAR).
Leaf spots typically take 14 days to develop post infection, and these remain an inoculum source of Psa in the orchard. Best practice in Spring, according to KVH guidelines, is to maintain a strong early season Psa spray programme. This will reduce the risk of leaf spots developing and the infection of valuable flower buds.
An early application of ACTIGARD® will take advantage of the systemic nature of the product, as it will move into the vine to protect rapidly expanding growth. The first spray of ACTIGARD® is best applied as soon as leaves reach an average of 25 mm in diameter (i.e. 50 cent piece size).
The addition of copper offers immediate protection, while ACTIGARD® delivers up to 21 days protection, at a time where Psa pressure is usually high.
A second application of ACTIGARD® (plus copper) should be made one to seven days prior to flowering, which will offer protection from Psa over the flowering period.
The KVH Psa risk model can be used to support the timing of ACTIGARD® applications throughout the season. This online decision tool is available for growers to identify the daily risk of Psa infection, based on forecasted weather variables. Growers can then ensure adequate protection is in place prior to a risk event.
A total of four applications of ACTIGARD® can be made per season, which in practice usually means two in the spring (prior to flowering) and two post-harvest (prior to leaf-fall).
- Apply 20 grams of ACTIGARD® per 100 litres of water as a dilute spray (200 g/ha).
- As it can take up to 7 days for ACTIGARD® to fully activate the plant, the addition of copper is recommended to give immediate protection, especially when applied prior to wet weather events.
- To avoid the risk of residues, DO NOT spray female flowers or fruit with ACTIGARD®.
- If vines are under stress, delay application until vines have recovered and are actively growing.
For more information click here to download the latest spring Kiwifruit Technote for ACTIGARD®.