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Armoured Scale - insect pest in kiwifruit

 

Armoured scale is an ongoing pest issue in New Zealand kiwifruit, and populations can slowly build unbeknown to the grower. Export market access can be challenging as many markets, particularly Asian countries, have a zero tolerance for scale.

With a tendency to populate in sheltered areas, scale can be difficult to control. Growers now have fewer chemical options available and narrower spray windows to operate within. It is therefore essential that growers are aware of scale to ensure populations are kept at low levels.

Scale are only mobile once hatched. Referred to as crawlers, the juvenile scale finds a suitable spot to “limpet” onto a plant surface and build a wax protective covering. On reaching the third instar, scale start laying eggs, and the cycle repeats.

With two distinct generations per season, crawler release starts in late October and peaks in December (figure 1). Targeting chemical covers during generation 1 will impact crawler numbers emerging in generation 2. Pre-flower cover spray options are straight forward, however the post flowering period creates challenges. Growers need to determine if spraying is required, the product options, timing, and possible risks.

Growers of conventional Hayward and Gold cultivars rely heavily on | Armoured scale can be difficult to control. pre-flower applications of Movento (spirotetramat). Unable to be used after flowering it is often the only cover spray used. Growers should consider if this provides control right into the second generation and be aware of post flowering spraying windows available to break multiple scale life cycles.

The post flowering period provides some specific windows for both conventional and organic growers. Excel Oil, applied at 1% up to 14 days post fruit set, works through a smothering action. Other studies have shown that oils can also discourage crawler settlement. Oils should be applied before fruit become too sensitive to marking. NB: organic growers must ensure products are Biogro certified.

As fruit develops, second generation control for gold kiwifruit growers is limited due to a high risk of fruit marking. Nevertheless, Plant and Food Research have identified a window to safely use a 1% Excel Oil application in the second and third week of February. The trials showed that during this period Sungold skin is less sensitive to fruitlet marking, and that no significant increase in fruitlet drop occurred.

Hayward growers can safely apply 1% Excel Oil, while being aware of the 14-day PHI, drying conditions, and humidity on the day of application.

Packhouse pest monitoring centres are a great source of data and can potentially identify scale hotspots. Monitoring also identifies populations leading up to harvest, allowing assessment of spraying programmes, if a second or third generation is present and post-harvest control options — these range from Movento through to winter oil applications.

Plant and Food Research showed that Movento applied post-harvest had a detrimental effect to the next season’s scale population. Adding a penetrant such as Kwickin improved the plant uptake. Alternatively using Hywet will improve spread and uptake. Good leaf condition is essential for efficacy. The earlier harvest of gold and earlier picked Hayward crops may provide the opportunity for a post-harvest cover spray. Possible spray residue issues should be considered in blocks or maturity areas yet to be harvested.

 

For further information please contact your Farmlands Technical Advisor.

Article supplied by Dwayne Farrington, Technical Leader - Kiwifruit & Subtropical Crops, Farmlands Co-operative
Source: McKenna. C, Dobson. S, Rogers. P, Herrick.J, McKenzie.C, Tuck. H; Pest Day Presentation Oct 2020.