Proactive early spray programmes key to Psa-V control

A focus on spraying at regular intervals from budbreak onwards will provide ongoing protection of expanding leaves and shoots. Leaves in the first week of emergence and up to three weeks old are most vulnerable to Psa-V infection.

‘Pulses’ of leaf infection observed in previous years may have been due to high numbers of leaves at this vulnerable stage not being suitably protected through significant infection events.

Psa-V inoculum on the edges of leaf spots can reactivate in suitable weather conditions and add to the inoculum load within the canopy. This increases the risk of flower bud infection across the spring period. Hayward and Green14 can be particularly vulnerable to this infection.

A full winter rate copper with a spreader applied immediately prior to budburst is highly recommended to protect breaking buds on all varieties.
A following regular programme of coppers, Actigard™ and, in high-risk situations, KeyStrepto™, should be applied through to flowering.

Ambitious may also help reduce leaf spot and may be applied once there is sufficient leaf in the canopy (see photo). Similarly, Actigard™ also requires sufficient leaf cover at time of application to ensure uptake is sufficient to fully activate the vine. Manufacturer recommendation is to apply Actigard™ two to three weeks after bud burst, when leaf diameter is approximately 25mm.

Many Hort16A canopies will already have sufficient leaf for application of these products. AI nozzles and drift-reducing adjuvants must be used until canopy closure to minimise spray drift. Excellent spray coverage will optimise product efficiency. Use of wetter papers is recommended to check applications.

• Click here to view the Plant & Food Research report on the influence of leaf age.