How to treat common citrus problems

We often hear from worried gardeners, in need of advice about pests, diseases and deficiencies that have struck their citrus plants. Did you know, there's a simple secret that can prevent many of these issues? Just feed your trees!

Citrus plants are hungry, hungry, hungry. They have an almost insatiable appetite for nutrients, quickly soaking up all the fertiliser you give them. Well nourished citrus trees are healthy citrus trees; they'll repay you by putting extra energy into fruit production, but also overcoming trace element deficiencies, and sharpening their natural defences against insects and diseases.

How do I keep a citrus happy and healthy?

Add organic matter to the soil

Citrus trees have shallow root systems: this means good drainage and soil that's rich in organic matter is vital. When planting, add Yates Dynamic Lifter Organic Plant Food into the soil, for a supply of rich nutrients that will get all the beneficial soil micro-organisms into top gear. In turn, those happy microbes will feed the citrus for you. Dynamic Lifter is a real winner, once you've seen what it can do, you'll never go back!

Mulch around the base of the tree with organic mulch like bark chips or pea straw (being careful not to let the mulch touch the trunk; always leave a gap around it). Mulch helps retain moisture in the soil, regulates soil temperature, suppresses weeds, and provides a nutrient-rich environment for beneficial microorganisms. All year round, mulching really helps to protect the roots of citrus trees from temperature fluctuations and extreme weather conditions.

Fertilise regularly

Feed your trees regularly through the season. Yates Thrive Citrus & Fruit Granular Plant Food is a complete plant food, that delivers your citrus trees the balanced nutrients they require for healthy growth, and fruit development. Use it regularly, all-year-round for best results. If you have high rainfall in your area, nutrients can leach from the soil more quickly; so you can be more generous with feeding.

Whenever citrus leaves are looking a little yellow or sad, you can give them a pick-me-up of micronutrients. Yates Health Tonic Trace Element Chelates delivers a wide range of micronutrients in small doses, so it's ideal to use when the exact deficiency isn't obvious or can't be diagnosed.

If your tree is carrying small ripening fruit, it's a great time to start feeding with our potassium-rich secret ingredient: Yates Liquid Potash. Adding small but regular doses of Liquid Potash into your feeding schedule will result in bigger, tastier, juicier fruit at harvest time.

Pruning

When your trees have finished fruiting, it’s a good time to prune to prepare them for next year’s growth. To do this, cut back any dead/diseased wood and crossed-over branches, along with any branches growing in towards the centre of the tree. Remove any branches that are hanging low (quite close to the soil) to help lift the canopy.

If there are vertical shoots growing from beneath the graft union (the bumpy bit down at the base of the trunk), trim these back flush with the trunk. These shoots come from the tree's hardy rootstock, but they won’t develop the fruit you're after. Typically, they’re viciously thorny and will eventually take over from the fruit-bearing tree if not removed.

Up higher, give special attention on the areas most heavily congested with branches, to help open up the canopy. This allows for better sunlight penetration and air circulation – making the ideal conditions for fruit development, plus helping to ward off pests and diseases. If you live in a frosty area, wait until the chance of last frost has passed before pruning.

If your tree is a little old and didn’t perform as well this year, it’s worth giving it a hard prune – it'll get a new lease on life! You may not have the best crop for the next couple of years (while the tree grows back), but it'll be worth it in the long run. This method is called ‘skeletonising’ and involves ruthlessly removing most of the growth from the tree, so that you’re left with a single trunk and strong, evenly spaced branches. While removing this much may seem drastic, it really does help to rejuvenate the tree.

Make sure you use a sharp sterile pair of secateurs and/or loppers when pruning. A quick rinse in methylated spirits between each tree pruned will prevent diseases spreading.

After pruning, give your citrus tree a generous drink of seaweed solution to help it recover.

There is one complication to consider when pruning citrus: Lemon Tree Borer. The adult beetles are flying at night from mid-spring to autumn, on the lookout for trees to lay their eggs. The scent of freshly pruned citrus trees attracts them like a magnet, so it’s wise to restrict pruning to between April and August, if you can. Whenever you are pruning, make sure to tidy up and burn the offcuts.

Diagnosis for Citrus Problems

Holes in your citrus tree?

Classic warning symptoms of Lemon Tree Borer infestation are wilting leaves, or dieback of individual branches. If you see 2-3mm round holes in branches, with visible clumps of powdery sawdust (actually, it’s frass – excrement from the borer larvae) it confirms an infestation. This grub pest is a serious challenge for weak or stressed trees. If you find a hole, get a wound guitar string or a length of thin wire, and poke it in firmly as far as you can go. This takes a little time, but it’s very effective. If you have numerous holes then it might be best to remove an entire branch: share a photo with us on Live Chat and we can give you further advice.

If larvae enter the central trunk, it can be fatal to the tree. For this reason, make certain never to scuff the base of trees with your line trimmer; it makes an inviting entry point for adult beetles to lay eggs.

A good solution for protecting fresh pruning cuts is Yates PruneTec, which seals off the wound and forms a physical barrier against larvae boring into the tree.

Black sooty mould on the leaves?

This black, unsightly mould is another problem to watch out for. Sooty moulds are fungi which cover plant leaves, stems and twigs in a black sticky film. The mould itself doesn't feed on the plant, but because it covers the leaf surface, it's blocking light and reducing photosynthesis (essential for plant growth).

In almost all cases, the sooty mould is actually caused by an infestation of insects that secrete honeydew; usually the culprits are aphids, scale or mealybugs. Tackling the insects will remove the source of the honeydew that feeds the sooty mould, which will eventually die off and wash off the foliage. Yates Conqueror Spraying Oil will control most sap-sucking insects on citrus.

Sometimes the insects responsible are hard to spot, but sooty mould on the leaves is a big clue. If you see ants moving up and down the stems, that's a certain indicator of sap sucking insect pests like scale, or aphids.

Regular sprays of Yates Natures Way Organic Citrus, Vegie Ornamental Spray, on both the upper and lower leaf surfaces, is also a great way to keep sucking insects under control. It’s based on a clever combination of natural pyrethrin and vegetable oil. It's BioGro certified for use in organic gardening, so it's ideal for gardeners who prefer organic methods of insect pest control.

Scabby-looking lemons?

Lemon Scab, AKA Verrucosis is a fungal disease that causes raised roughened scabby, warty lesions to form on the outside of the fruit. Although this ruins the zest for cooking purposes, the inside of the fruit and the juice aren't affected. Scab may also be visible on leaves and twigs, but most often it's the fruit that's affected.

It's best to control this disease, because it gradually reduces the vigour of the tree. Damp, cool weather encourages the fungal spores to spread. It’s best to adopt a preventative approach to control verrucosis, with a regular spray program.

Leaves going yellow, but veins staying green?

Iron deficiency is a plant disorder that's quite easy to confuse with manganese deficiency. Iron is needed to produce chlorophyll in plants, so when it's lacking it causes discolouration of leaves. Leaves turn yellow or brown in the margins between the veins, but the veins themselves remain green. Young leaves may develop a bleached appearance.

Iron deficiency arises from a lack of available iron micronutrient in the soil. It's possible for this to be caused by excessive watering, or long periods of rainfall. Most commonly, it's caused by high (alkaline) soil pH, which can severely reduce the availability of iron to the plant. If the problem is persistent, test soil pH and adjust it with Yates Iron Chelate if necessary.

Citrus tree losing leaves?

A citrus tree that's lost a lot of leaves and has dead wood may well be sick. Prune off any dead wood, to encourage new growth. These symptoms can also be caused by dehydration; citrus trees need lots of water! Make certain they get 3-4cms of water each week, from spring until autumn.