When to spray fruit trees in NZ to prevent codling moth, leaf curl, scale and more
Some fruit trees and berry plants thrive happily without a pest and disease prevention programme, whereas others struggle.
The reasons why can be a mystery, or due to any number of factors: position, neighbouring diseased trees, climate (especially high humidity), or just plain bad luck.
As we get ready to say goodbye to long summer days and hello to cooler autumn mornings, it's timely to consider fruit tree maintenance to ensure the next season's crops are bountiful and beautiful.
Sprays of any sort should be used in conjunction with best growing practices like good pruning hygiene (cleaning your tools), sealing pruning wounds and removing infected fruit and leaves.
And, of course, when you're spraying, take care not to kill or negatively affect beneficial insects like bees, pollinators and natural predators.
The following care calendar to prevent pests and diseases of fruiting plants is intended as a preventative programme. Some plants will grow perfectly well without the need for this care and attention, but others will be susceptible and require year-round intervention to ensure a healthy, attractive and productive fruit tree or bush.
This programme is particularly important if there have been disease or pest problems in previous seasons, to get on top of the infections before they get worse or spread to other trees.
The use of organic control measures is recommended where possible.
What to do: Autumn
When deciduous trees start to enter their dormancy period with the autumn leaf drop, the timing is right to apply a clean-up fungicide.
Copper oxychloride is a good organic option for smothering the fungal spores and bacteria that cause diseases like leaf curl, bacterial blast and leaf spot. Copper sprays are available in various forms, including liquid, powder and ready-to-use products – just choose your preferred method.
Good coverage is required as fungal diseases can be harboured in the rough crevices of the bark, so apply the solution until your trees are dripping wet.
Smothering the diseases will mean there's less chance of reinfection when the tree comes into blossom and leaf next season.
What to do: Winter
Winter brings an extra opportunity to cover any lingering diseases or pests that are over-wintering in or under your deciduous fruit trees and berry plants.
Copper oxychloride or lime sulphur can be used as a coverall fungicidal spray for the likes of leaf curl and botrytis.
Just don't use lime sulphur on apricot trees – they're sensitive to sulphur.
Winter spraying oils, such as neem oil or Yates Conqueror Oil, work by smothering the eggs or larvae of insect pests.
Bugs like cherry aphids and pear blister mites can be controlled by this application, which should be completed a few weeks after you douse them in the copper or lime sulphur.
What to do: Spring
Early spring is often when infections strike fruit trees, thanks to the combination of warmish, wet weather, which promotes rapid spore and bacteria growth, and the soft, fresh growth of blossoms and leaves from the dormant branches.
Diseases such as leaf curl (in peaches and nectarines), black spot (in apples and pears), bacterial blast (mainly in stone fruit) and botrytis (mainly in berries and grapes) accelerate at this time of year.
The good news is, the application of preventative sprays in early spring will usually help you to avoid these diseases altogether.
Applying copper sprays to fruit trees (especially stone fruit) prior to bud burst and again after flowering will help to cover any diseases that are on the tree.
During periods of wet weather, the spray should be applied immediately after rain (rainfall will wash the spray off, removing the shield of protection).
The life cycle of codling moths sees them hibernate in larvae form over winter, inside a cocoon in the crevices of the bark or beneath the tree, then emerge as moths in mid to late spring to lay eggs in the small fruitlets of pip fruit.
Thwart them by scattering neem granules around the base of the tree to the dripline (the area on the ground from the trunk to below the tips of the widest branches) from the start of spring until November or December.
Spraying with neem oil or Yates Success Ultra Insect Control (which is especially effective with codling moths) when the moth activity is high in your traps can help to prevent the fruit being ruined.
Use a trap to monitor the moths so you can time the spray right.
Keep an eye out for black aphids on your cherry trees; they feed on the new growth in spring and early summer. They can easily be killed off with a few spray gun applications of a product like Tui Insect Control for Fruit & Veges. The same applies to leaf-curling aphids in plums, which are easily confused with the fungal disease leaf curl in peaches and nectarines.
What to do: Summer
Summer's generally warmer, drier weather means fewer pest and disease problems than in spring.
But brown rot disease in ripening stone fruit can be a bit of a nightmare for home orchardists, especially in the more humid northern regions, and unfortunately, there are few sprays that can be safely used once the tree is in fruit.
Copper can be applied, but only at a weak rate or you risk burning off the tender growing tips and leaves – less is more in this case.
Berry rot such as botrytis is similar to brown rot in stone fruit, as it affects the ripening fruit. Again, there are few safe sprays to use on the delicate fruit when you're close to harvest time, but Kiwicare Thiram Fungus Control can be applied until seven days before harvest (though remember that the fruit should be washed before eating).
Fire blight in apples, pears and quinces can show up in early summer during warm, wet weather.
Symptoms are a definite blackening of leaves and curling of growing tips into a hook-like form.
This can look similar to trees simply being dry – so get an expert opinion before taking drastic action.
The disease spreads like, well, wildfire, so it should be dealt with immediately.
If a young tree succumbs, it should be removed to prevent the infection of any others. Treatment of more established trees with a chlorine bleach solution to essentially sterilise the tree can be effective in killing the bacteria causing the disease.
Common insect pests such as whiteflies, scale and aphids can ramp up in citrus trees in the summer months.
These should be treated as quickly as possible, as repeat applications are usually necessary to control the pests and interrupt their short life cycles.
Treatment with Tui Insect Control for Fruit & Veges is effective, especially in conjunction with regular (bimonthly) preventative applications of a spraying oil.
- NZ Gardener