Common Problems with Arbequina Olive Trees – Pests, Diseases & Solutions

Even though Arbequina olive trees are known for being hardy and relatively problem-free, they can occasionally face pests or diseases – just like any other plant. Early detection and treatment are key to preventing minor issues from becoming big headaches. In this guide, we’ll go through some common problems you might encounter with your Arbequina olive tree, how to recognize them, and what to do about them. Whether it’s weird spots on the leaves, uninvited insects, or a generally unhappy-looking tree, we’ve got troubleshooting tips to help nurse your olive back to its best.

Yellow Leaves and Leaf Drop

Symptoms: Older leaves on the tree turn yellow and drop off. Sometimes scattered throughout the tree, sometimes more pronounced in certain areas. If it’s just occasional older, inner leaves, and the rest of the tree looks fine, this can be normal aging (olives do shed some older leaves annually). But if you see a lot of yellowing, especially on newer leaves or widespread, it signals an issue.

Possible Causes & Solutions:

• Overwatering or Poor Drainage: One of the top causes of chronic yellow leaves in olives is waterlogged roots. If soil stays too wet, roots can’t get oxygen, leading to yellowing and drop. Solution: Check your soil moisture. If in a pot, ensure drainage holes aren’t blocked. Cut back on watering and let soil dry out some. If the potting soil is old and compacted, consider re-potting with a fresher, grittier mix to improve drainage. For in-ground, if you suspect poor drainage, try to aerate the area or, if feasible, dig around the tree and mix in some coarse material. In severe cases, you might need to replant the tree in a raised spot.
• Underwatering/Drought: Yes, the opposite can also cause yellowing, although usually the leaves will appear dry or wilty before turning yellow. If the tree has been left too dry for too long, it may drop leaves to conserve water. Solution: Resume regular watering. Give a deep soak to the root zone (but don’t drown it all at once if very dry – water, wait, water again to allow absorption). The tree should stop shedding once it’s rehydrated, though very dry leaves won’t green back up – they’ll just fall and new ones will come later.
• Nutrient Deficiency: A lack of certain nutrients can cause yellowing between leaf veins (chlorosis). In olives, iron deficiency is common in alkaline soils – leaves turn yellow but the veins stay green. Nitrogen deficiency can cause overall pale color and slower growth. Solution: If iron chlorosis, consider a foliar spray of chelated iron or soil treatment with iron chelate. Ensure the soil pH isn’t extremely high (if it is, iron locks up; adding soil sulfur can help long-term). For general nutrition, an application of a balanced fertilizer in spring will supply nitrogen and other nutrients. Within a few weeks, new growth should be greener.
• Cold Stress: If a cold spell hits, sometimes leaves will turn gray-green or yellow and fall off weeks later. This is a reaction to cold damage. Often you’ll know if it got unusually cold. Solution: There’s not much to do except wait for new growth. Make sure to water normally and perhaps give a light feeding come spring to help it rebound. Prune out any branch dieback that becomes evident.
• Natural Shedding: If it’s late spring/early summer and you see some interior leaves yellowing, it could just be the tree renewing its foliage. If the overall canopy is fine and it’s just some older leaves dropping, no action needed – it’s natural. Rake them up and discard.

Scale Insects (and Sooty Mold)

Symptoms: Scale are small sap-sucking pests that often look like little brown or gray bumps stuck on leaves, stems, or bark. You might first notice sticky sap (honeydew) on leaves or beneath the tree on surfaces. You may see black sooty mold fungus growing on that sticky residue (it looks like a black charcoal-like coating on leaves or nearby objects). Ants often appear, climbing the tree to harvest the sweet honeydew from scale. Leaves might turn yellow or the tree’s vigor declines if infestation is heavy.

Identification: Common types on olives include black scale and oleander scale, among others. Black scale are about 1/8 inch and dark, often on twigs. If you scratch a scale with a fingernail and it’s soft and moist inside, it’s a live insect (scale have a protective shell). They don’t move (adult females) – they’re stationary under their “scale” covering.

Solution:

• For minor infestations, you can physically remove scale. Wipe branches with a soft cloth or sponge and a mild soapy water solution to dislodge them. Prune off any heavily infested small twigs.
• Use horticultural oil spray. Oil suffocates scale insects. Choose a cool time (not above 85°F, and not during intense sun) to spray to avoid damaging the tree. Thoroughly coat the branches and leaves where scale are present. Follow product instructions – often a couple applications spaced a few weeks apart are needed to catch any newly hatched scales.
• Insecticidal soaps can also work on the crawler stage (the young, mobile stage of scale before they settle and form the scale cover). If you see tiny yellowish specks moving on stems (use a magnifying glass), those are crawlers. Soap sprays can kill those on contact.
• If ants are farming the scale (protecting them for honeydew), control the ants too. Use a sticky barrier on the trunk or ant baits at the base so they don’t thwart your scale control efforts. Ants can actually move scale around, so deterring them helps.
• After scale are gone, the sooty mold will gradually weather off. You can gently wash leaves with water if needed, but once its food (honeydew) is gone, sooty mold will stop spreading and eventually disappear.

Olive trees are fairly tough, so they usually bounce back once scale are controlled. Leaves that turned yellow from heavy scale may fall, but new healthy leaves will grow.

Olive Fruit Fly (if you have fruiting trees)

Symptoms: Small blemishes on olives, premature fruit drop, or olives that, when cut open, have tunnels and maybe a little white maggot inside (ew!). Olive fruit fly is a notorious pest in olive-growing regions. The adult is a small brown fly that lays eggs in the olive, the maggot feeds inside, ruining the fruit.

Identification: If your olives develop soft spots or start dropping early and you cut one open to find a maggot, it’s likely olive fruit fly. This pest is mostly a concern if you intend to harvest and use your olives; an ornamental tree suffering fruit fly doesn’t usually harm the tree itself, just the crop.

Solution:

• Use fruit fly traps. These are often yellow sticky traps combined with a lure that attracts the olive fruit fly. Hang a few in your olive tree in early summer through fall. They help monitor and catch adult flies.
• Some gardeners use GF-120 bait, an organic spinosad bait, which is applied as droplets on the tree. Flies eat it and die. It’s fairly effective if used properly, reducing populations before they lay eggs.
• Clean up all fallen olives! This is crucial. Fallen, infested fruit can harbor larvae that then pupate in soil and emerge next year. Dispose of any fruit (don’t compost unless your compost gets hot enough to kill them). This breaks the life cycle.
• If fruit flies are extremely bad in your area, some resort to completely netting the tree with fine mesh during the fruiting season to physically block the flies. For a smaller tree, this is doable and quite effective, though a bit of a hassle.

If you’re not trying to eat the olives, you might live with some fruit fly damage or simply harvest olives early (green) before flies peak. But generally, managing this pest is about trapping and sanitation.

Fungal Leaf Spots (Peacock Spot and Others)

Symptoms: You may notice dark circular spots on leaves, sometimes with yellow halos. In the case of peacock spot (Cycloconium oleaginum), so named because the spots can have a colorful sheen, these spots occur mostly in cool, wet weather (fall/winter). Leaves might drop if heavily infected. Another disease, Anthracnose, can cause both leaf spots and fruit rot (olives shrivel and get brown rot) especially in wet autumn weather.

Identification: Peacock spot primarily affects leaves – dark blotches on the upper surface. If you hold a leaf up, you might see the spot looks almost blackish. Anthracnose on olives will often manifest as the fruit rotting (soft, brown, with an orangeish spore mass sometimes) and leaves near them may get spots too.

Solution:

• Sanitation: Rake up and destroy fallen leaves that have these spots – they carry spores.
• Pruning for Airflow: As mentioned in pruning guides, maintaining an open canopy lets leaves dry faster after rain, making it less favorable for fungal spores to germinate.
• Fungicide Sprays: In areas prone to these diseases (often regions with rainy winters), preventive sprays of copper-based fungicides in late fall can help protect leaves. Some do a copper spray in fall and again in late winter to reduce overwintering spore load. Copper is organic-compatible and effective against many olive fungi.
• If your tree already has significant spotting, you can spray copper immediately to stop further spread. The damaged leaves may still drop, but new growth in spring should be clean if managed.
• Anthracnose-specific: If fruit are affected, remove all bad fruit. Copper helps here too, but in serious cases, other fungicides (like specific strobilurin fungicides) could be used – usually in commercial settings. For a backyard, focus on removing infected fruit and possibly harvesting a bit earlier before heavy rains set in, if anthracnose is known to strike in late season.

Neither of these diseases usually kills an olive tree – they just make it unsightly and reduce fruit yield. With a little attention, they can be kept at bay.

Olive Knot

Symptoms: Gnarled, tumor-like swellings on twigs, branches, or even the trunk. Often at pruning scars or injury points. These galls are caused by a bacteria (Pseudomonas savastanoi) that infects wounds, especially during wet weather. The galls can range from pea-sized to walnut-sized or larger over time.

Identification: The knobs are distinctive, rough and wart-like. If you see these forming after a wet winter or spring, suspect olive knot.

Solution:

• Prune Out Knots: The best approach is to prune off affected twigs or branches about 6-8 inches below the gall (the bacteria extends beyond the visible gall). Do this in dry weather to avoid spreading bacteria via wet tools. Burn or dispose of the prunings (don’t just toss under the tree).
• Disinfect Tools: After each cut in infected wood, sterilize your pruners in bleach solution or alcohol to prevent spreading the bacteria to other parts of the tree or other trees.
• Protect Wounds: If your region has olive knot issues, consider using a wound paste or spraying a copper fungicide/bactericide on pruning cuts, especially during the rainy season, to prevent infection.
• Unfortunately, if large limbs or the trunk have huge galls, it can be challenging. You might end up just managing it (cutting off new galls each year). Severe cases can weaken a tree over time.
• Prevention: The saying “prune after the rain” (meaning wait until after the rainy season for major pruning) is apt here. Bacteria are most active in cool, wet conditions. Pruning in summer or during a dry period in winter helps avoid new infections. Also avoid injuring the tree (e.g., banging with tools, etc.).

Again, olive knot seldom kills outright, but it can make branches die beyond the gall and overall reduce tree vigor if widespread. Good hygiene and pruning practices keep it in check.

General Decline (When Your Olive Tree Just Looks Unhappy)

Sometimes an olive tree might just not be thriving and it’s not obvious why (no clear pests, watering seems right, etc.). Here are a few additional things to consider:

• Soil Salt Buildup (in pots): If using tap water or heavy fertilization, salts can accumulate in pot soil, causing leaf burn or poor growth. Remedy: flush the soil occasionally by watering heavily to leach salts (ensure great drainage). Or repot with fresh mix every couple of years.
• Rootbound (in pots): If growth has stalled and you see roots matted at the surface or through drain holes, it may simply need a bigger pot or root pruning and fresh soil.
• Extreme pH or Mineral Imbalances: Though olives tolerate a range, extremely alkaline soil might lock out nutrients (iron, zinc). Conversely, extremely acidic soil isn’t olive’s favorite either. A soil test can guide if you suspect a chronic soil issue. Adjust pH gradually if needed or consider growing in a large raised bed or pot with tailor-made soil in extreme cases.
• Lack of Sunlight: If an olive tree is planted in too much shade, it will grow spindly, with sparse foliage and little to no fruit. It might get more pest issues too due to reduced vigor. Solution: if possible, move it to sun or prune surrounding vegetation. If it’s a big tree in place, you can’t exactly move it easily, but you might accept it as an ornamental (with fewer leaves) or try to open the area around it.
• Frost Damage: A late frost can kill spring buds or new shoots, leading to a sparse look in summer. The tree often recovers by pushing new buds later, but might be delayed. If you suspect a cold snap did it, just give supportive care (watering, light feeding) and wait for it to refoliate.
• Compacted Soil (in-ground): If an olive is in a lawn or area that gets heavy foot traffic or just very compact soil, roots can struggle. Consider aerating around the tree, applying a light topdressing of compost, and mulching to improve soil structure over time.

Integrated Care

Maintaining a healthy Arbequina olive tree is mostly about preventive care and observation:

• Keep it clean: Remove fallen diseased leaves and dropped fruit.
• Balance water and feed: A strong tree can resist pests better.
• Prune smartly: Remove trouble spots and keep the canopy airy.
• Use organic or mild treatments at first sign: It’s easier to knock out a few scale insects or treat a couple leaf spots early than to rescue a heavily infested tree later.

Remember, most problems have a solution, and olives are forgiving plants. If your tree is hit with something, don’t despair. Even if it loses a lot of leaves or has a bad pest year, with appropriate action it can rebound. They have an ancient heritage of resilience – some olive trees live hundreds of years through all kinds of adversity!

Lastly, not every leaf blemish or bug requires a chemical intervention. Often a quick hose-down or a bit of pruning is enough. Reserve stronger treatments (chemical pesticides or fungicides) for serious issues, and even then, try targeted approaches like traps or horticultural oils first.

By regularly inspecting your olive tree (perhaps when you water or prune, take a closer look at leaves and branches), you’ll catch things early. Think of it as getting to know your tree’s “normal” so you can tell when something is off. Soon you’ll gain the confidence that you can tackle whatever challenge comes up, and your Arbequina will continue to grace your garden with its beauty (and delicious olives) for years to come.