Pests and Diseases
Keeping Olive Trees is straight forward most of the time, however, like most plants they can be affected by pests and diseases. While for the most part your olive tree will be fine growing in the UK, Olive Tree Pests and Diseases can damage even the strongest Olive Trees. Here are our tips for preventing and treating Olive Tree Pests and Diseases.
An Ounce Of Prevention Is Worth A Pound Of Cure
While this is a bit of an old wife’s tale, it is true that prevention is better than a cure when it comes to pest or disease. If your Olive Tree picks up a nasty pest, you could spend a lot of time (and money) trying to remove all traces. So if your plants in good condition, you should be able to avoid any major problems. To do this, we recommend you follow the tips:
1) Keep your Olive Tree well fed
This isn’t essential but will help prevent disease. Just add a bit of liquid feed or mix in some fish blood and bone to the soil occasionally and there will be plenty of nutrients for you Olive Tree to fight of disease.
2) Keep the soil moist
To keep an Olive Tree healthy, it needs a to have moist soil. This doesn’t mean you need to water frequently as too much water can kill an Olive Tree. Instead, dig a couple of inches into the soil to see if the soil is moist enough. If it’s dry, give it a good water. Just make sure there is enough drainage for the excess water to escape.
3) Prune your olive tree
Although olive trees grow slowly, it is very important to prune. Pinching out young shoots can encourage growth and help the Olive tree to remain strong and healthy. In the late Spring and early Summer, make sure that branches are thinned out to allow light into the centre of the Olive tree however, if pruning is to hard it may hinder fruit/ crop production.
4) Give it some sunshine
Olive Trees love sunlight. The more you can give them, the better! This will not only keep your tree healthy, this will also keep the foliage dry, which will help prevent mildews and fungus building up.
5) Act quickly
If you do spot something, look it up or seek advice. You’ll see some common issues below but if you’re not sure, it’s best to ask someone.
6) Remove diseased fruit
While fruiting in the UK is less likely than it would be in warmer conditions, olives can be grown here. These will attract a variety of pest. If you spot anything out of the ordinary, with your fruit, your best off removing the offending fruit and discarding it. Keeping the height of your tree down by removing the crown can help with this.
Common Olive Tree Pests
Woolly Aphids can be a bit of a problem for Olive Trees and we have seen increased numbers in recent years. The Aphids themselves aren’t too much of a bother to Olive Trees but they do cause damage to the bark as they feed on sap. This can leave your tree open to infection and damage from frost. Fortunately, treating Woolly Aphids is easily done. Just wash the bark with a washing-up liquid & water mixture. This should remove the problem without much fuss. There are also several chemical treatments for Woolly Aphids.
Scale insects feed on the sap on the Olive tree. The scale insects are noticeable themselves which look like orange/brown discs which can be found on the stems or on the leaves of the olive tree. The first signs may be a yellow colouring on the leaf or/and a sticky residue on the leaf or plant. There are lots of easily accessible chemicals which are available to treat scale insects. It may be that to completely remove scale insects using a spray or oil, the process may need to be repeated especially in the egg-hatching period.
Common Olive Tree Disease
Olive Peacock Spot (AKA Olive Leaf Spot. AKA Bird’s Eye Spot)
Olive Peacock Spot is very common and affects the leaves of olive trees around the world from the UK to Australia. It only attacks olive trees and only affects trees through the growing season. It’s quite easy to ‘spot’ as you’ll see small black spots on the top surface of the leaves. This is actually a lesion produced by the fungus. The fungus can be easily spread by the weather and by insects so is near impossible to contain.
Peacock spot can cause significant loss of Olives. Not so much a problem in the UK, but it can ruin an entire yield in Spain. However, in the worst cases, defoliation can occur which can lead to twig death. As a result, Olive Peacock spot can have server effects on an Olive Tree.
The good news is, it is easily treatable. The best way we know of to treat Peacock spot is to spray your Olive Tree with a copper mixture or fungicide. You should do this in November and then again in February. This should be enough to ensure Peacock spot is kept at bay.
Scab disease can cause sooty, dark spots on the leaves, premature leaf loss, aborted blossoms and shrivelled/ scabbed fruit. The most common symptom is purple to dark brown ring spots (with a green centre) on the leaves, followed by yellow and defoliation leaves. Scab disease favours wet weather in the Spring and Summer. There are several ways to control scab disease, some non-chemical approaches include, remove fallen, scab-affected leaves from the bottom of the plant overwinter. Prune out affected shoots and remain a general pruning to encourage a good air circulation which will enhance rapid drying of the foliage after rainfall. There are chemical alternatives to help treat scab disease although these cannot be used on edible crops.
Verticuillium Wilt, Phytophora Root Rot and Honey fungus
Verticuillum Wilt, Phytophora root rot and Honey fungus are sometimes the result of water-logging and poor drainage. Symptoms include wilting, yellow or dying foliage and branch die back. . This is the outcome of a poor root system, as the roots cannot provide the olive tree with the nutrients which are required. Thankfully, this can be easily prevented through good soil drainage, additionally ensure when re-potting or planting an olive tree that the soil used is not infected as this can spread the disease to your olive tree. Also keep an eye on weeds as they can also spread the disease. No chemical controls can be provided to help with root rotting or fungus, the best piece of advice is to ensure there is good drainage.