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Controlling Lace Bug

Article by Kevin Quinlan, Supply Chain Manager NIS.

A field day covering the control of Lace bug and Husk Spot was held on the 8th July 2009 at Dick Campbell’s orchard in Alstonville. The following is a brief report on the findings from the day.

The key messages from all speakers were:

  1. Monitor your flowering to see if you have lace bug present.
  2. You will only need to apply a control option if there is lace bug present.
  3. If applying control options, you need to do so in a manner that does not impact upon pollinators, especially bees.

Macadamia Lace bug identification and the damage it causes.

Ruth Huwer & Craig Maddox (NSW DPI)

There is little known about macadamia lace bug which has emerged as a serious pest in some orchards over the last few seasons. Macadamia Lace bug (Ulonemia concave) is a small insect, with adult lace bugs being up to 3-4mm in length (figure 1). These insects are sap suckers. They suck the sap from flower buds, which causes the flowers to desiccate. This insect has the ability to cause crop failure in orchards if it is not managed.

Figure 1. An Macadamia Adult Lace Bug

Figure 1. An Macadamia Adult Lace Bug

Figure 2. Macadamia Lace bug Nymphs.

Figure 2. Macadamia Lace bug Nymphs.

The life cycle of Macadamia lace bug has not been studied in detail, but it is estimated that it is between 12-18 days. Lace bugs have been found to survive at temperatures as low as 5°C, giving them the ability to over winter in cold locations.

The eggs of lace bug are laid in the florets of flowers. These eggs hatch and the nymphs (figure 2) move up and down a flower raceme, feeding on developing flowers. These nymphs are yellowish to brown in colour. As the nymphs progress through their lifecycle stages they shed skins that are attached to flowers. These skins can be found on desiccated flowers that they have fed on, which indicates the cause of the racemes death.

The complete host range of macadamia lace bugs is unknown. Currently there is a university student studying the alternative hosts for lace bugs.
The typical damage that lace bugs cause is the death of florets on flower racemes (figure 3). The loss of significant numbers of flowers can have serious ramifications, with crop losses of up to 90% being observed.

Figure 3.1 Typical damage symptoms caused by macadamia lace

Figure 3.1 Typical damage symptoms caused by macadamia lace

Figure 3.2 Typical damage symptoms caused by macadamia lace

Figure 3.2 Typical damage symptoms caused by macadamia lace

As this pest has a very short life cycle and numbers can build up rapidly, it is crucial to monitor flowers closely to detect if the pest is present. It is also crucial to monitor so that you only spray if there is a problem, as there is a risk of reducing pollination. Spraying at flowering has rarely been used in the past due to the large numbers of pollinators present in orchards, especially bees. This makes it necessary to apply any chemical control at a time that curtails the potential impact upon bees and other pollinators.

You must only spray when bees are not actively foraging. This is usually late afternoon/early night depending upon weather conditions. Currently the only chemical control option registered for lace bug is Endosulfan. Endosulfan has an effective life of approximately 8 hours. This means that if pollinators are not active for 8 hours after application there is a low chance of killing these insects. Trichlorfon (eg Lepidex®) is registered for the control of macadamia flower caterpillar, another flower pest. This chemical has low bee toxicity if applied correctly. It also has a low residual life. The same timing issues for this chemical as those for endosulfan apply.

How do I monitor and when do I spray for lace bug?

Alan Coates, Consultant.

Alan has found that lace bug activity has increased considerably over the last 6 years, with the last couple of seasons having considerably higher levels of activity. Lace bugs feed on flowers and they can also feed on small nutlets. They attack throughout all flower stages. If damage has been found in an orchard previously, then it is likely to occur again. This makes monitoring crucial.

To monitor, look for damaged flowers (figure 5). The most obvious sign of lace bug activity is the death of florets on the end of a raceme but you can also have florets die anywhere on the flower from attack.
It is best to check flowers weekly, as lace bug numbers can build up very quickly. There can be hotspots within orchards and it is important to look to see if there are any of these in your orchard. These can be treated to stop the spread of lace bug and minimise damage across the entire orchard.

Figure 4. Lace bug damaged flowers found during monitoring.

Figure 4. Lace bug damaged flowers found during monitoring.

A control threshold has not yet been developed for lace bug. Research into what levels you should find before applying controls is required. From experience Alan looks for damage to flower racemes and then adds up the number of flower racemes found with damage. He then bases his recommendation upon these counts and also the flowering intensity and flower stage.

As lace bug has a short life cycle and you can have multiple flowerings it may be necessary to apply control options more than once. This makes monitoring very important to ensure you know where the activity is in the orchard and to ensure good control. It is best to apply any control options late afternoon/evening time when the bees are not active in the orchard. If you have bee hives on your farm, talk to your beekeeper about what you are planning to do if you have a lace bug problem.

Monitoring results have found that lace bug is active in orchards from early July to October, so it is important to start monitoring early. This will allow a good picture of what the trend is in your orchard to be picked up. Monitoring may show that there is no lace bug present and so there is no need to spray.