Claire Mummery: How to defeat citrus tree borer for a strong fruit harvest

Citrus trees are prone to borer at this time of year. Photo/ Getty Images.

If you grow citrus in your garden, then you may have come across one of the most irritating pests that cause havoc with your lemons. Let’s talk about citrus tree borer and how you can control it in your garden.

Borer grubs are dormant for the next couple of months, so it is the best time to cut out and remove them, otherwise the grub will lay eggs on new cuts, which then bore into your tree’s new growth. Borer can kill citrus trees if left untreated.

If you’ve never seen a borer grub before, they are big, fat, juicy things and can even take up nearly the width of the whole branch in a young tree.

Borer often sneak their way into your trees through an open wound – perhaps a small nick on the lower trunk from a weedeater, which I often see. Prevent this in future by applying a pruning paste any time your trees are wounded.

How you can tell if you’ve got a borer infestation

If you’ve noticed any holes along the branches of your citrus tree, or worse still, mounds of sawdust on the branches and stem, then you likely have an infestation of borer. This, coupled with a weakening tree that generally lacks vigour, means it’s time to take action.

Pruning

You can generally keep your tree alive by removing the dead wood, pruning carefully to remove the borer, and keeping a close eye out for new sawdust trails.

When pruning the borer out of your tree, this is an ideal time to shape and thin, to create better airflow which helps to prevent future pests and diseases thriving in their own cosy microclimate.

Any time you remove infected plants, leaves or branches in the garden, it is vital to either burn or dispose of them carefully to prevent further spread.

Piercing the grub

The totally organic way of dealing with borer is to insert a G string from a guitar down the hole to pierce the grub, however this can take some time (and patience!) and depends on how many borers you have to tackle, along with the size of your tree.

Spraying

There are numerous borer sprays on the market, including ones that use Neem oil. Following this, apply pruning paste over the holes or wounds to protect them from further infestation.

Remember that citrus trees work extremely hard over winter, so remember to feed your tree to support new growth and fruit production.

Over the winter months, it is also a great idea to build up a good mulch around your citrus trees. This improves the soil’s water retention, which is vital for citrus trees with their roots so close to the surface. However, remember to leave a breathing space around the trunk and to mulch right out to the drip line of your trees (where the outer branches are).

Have you ever considered growing a living mulch around your citrus? An ideal living mulch includes comfrey, borage, lemon balm, nasturtiums and parsley, which will also attract beneficial insects and help to keep pests at bay when the warmer weather arrives.

Happy gardening

For more gardening advice, visit growinspired.co.nz and discover Claire Mummery’s online gardening course at www.growinspiredacademy.com