Citrus Trees 101: Pests and Diseases

Citrus trees are beautiful, fragrant, and a joy to grow, but like all plants, they’re susceptible to pests and diseases that can threaten their health and fruit production. Recognizing and addressing these issues early is crucial for keeping your trees thriving. Whether you're growing oranges, lemons, or limes, here’s a rundown of the most common pests and diseases that can affect citrus trees and how to manage them effectively.

Common Pests on Citrus Trees

Citrus Weevil

Citrus weevils are beetles that damage citrus trees by feeding on the roots and lower trunk, although they can be found feeding on leaves. The adult weevil leaves small holes in the bark, while the larvae burrow into the tree, causing significant damage to the roots and compromising the tree’s ability to absorb nutrients.

Adults weevils are most active at night and can be hand-picked off trees. It'll be best then to follow up with an insecticidal soil drench to target the larvae, which is best done early in the season. 

Scale Insects

Scale insects are small, oval-shaped pests that attach themselves to branches, stems, and leaves, feeding on the plant’s sap. There are two main types of scales: soft scales, which secrete honeydew, and hard scales, which form protective shells. Both can lead to leaf drop, stunted growth, and even death if left untreated.

Treating scale is a unique process as it's best to scrape off visible scale by hand, with a soft brush, or the back of parring knife. After removing any visible scale, spray the tree with an insecticidal soap or apply a systemic insecticide.

Aphids

Aphids are tiny, soft-bodied insects that often appear in clusters on stems or the underside of leaves that cause leaf curl, yellowing, and distortion. They also produce a sticky substance called honeydew, which can attract ants and promote the growth of sooty mold.

To manage, start by spraying the tree with sharp sprays of water from your house to dislodge the aphids. Then, treat the tree with an insecticidal soap or neem oil to control the spread. If you're up for it, you can use your fingers or a small towel to easily squish and kill aphids! 

Whiteflies

Whiteflies are small, white, flying insects that feed on the underside of citrus leaves. They are another contributor to sooty mold growth on leaves due to their secretion of honeydew, and can transmit diseases like the citrus tristeza virus, which can severely affect tree health.

Using yellow sticky traps can help to to catch adult whiteflies and also help you monitor how bad the infestation is. Apply insecticidal soap or neem oil to target the larvae and nymphs, this prevents them from maturing and reproducing. 

Citrus Leaf Miner

Citrus leaf miners are small, shiny larvae that burrow inside of the leaves of citrus trees, leaving behind distinct winding trails or "mines" that scar the foliage. The damage not only reduces the aesthetic appeal of the tree but also weakens the leaves, making them more susceptible to disease.

The best way to eradicate leaf miners is by pruning and removing infected leaves to prevent the larvae from continuing their damage. Follow up with a horticultural oil or insecticidal soap, and be proactive by treating plants early in the season.

Common Diseases on Citrus Trees

Citrus Canker

Citrus canker is a bacterial disease that causes raised lesions with a greasy appearance on the leaves, stems, and fruit. These lesions eventually lead to defoliation, fruit drop, and decreased fruit quality, severely impacting your citrus harvest.

While there is no treatment or cure for this disease, it'll be best to to prune and destroy infected branches immediately to prevent the spread. Disinfect pruning tools between cuts, and contact your local extension office or a state plant health director. They may recommend you apply a copper-based fungicide. 

Powdery Mildew

Powdery mildew is a fungal disease that manifests as a white, powdery coating on the leaves, stems, and buds. It can stunt growth and reduce fruit production by limiting the tree’s ability to photosynthesize effectively. The best way to get rid of powdery mildew is by pruning off affected branches to reduce the spread and improve air circulation. Apply fungicides as soon as you notice symptoms, especially during damp or humid weather.

Root Rot (Phytophthora)

Root rot is a fungal disease that thrives in waterlogged soil. The disease causes the roots to decay, leading to poor nutrient absorption, wilting, and yellowing leaves. If left untreated, root rot can kill a tree either rapidly or overtime. 

To avoid root rot, ensure your soil is well-draining and avoid overwatering. You can also treat with a fungicide specifically designed for Phytophthora root rot.

Greening (Huanglongbing, HLB)

Huanglongbing (HLB), commonly known as citrus greening, is one of the most devastating diseases for citrus trees. It’s caused by a bacterial infection spread by the Asian citrus psyllid, resulting in yellowing leaves, stunted growth, and bitter, deformed fruit. There is currently no cure for HLB, and infected trees often die within a few years.

To prevent HLB,  control the spread of the Asian citrus psyllid by using insecticides and removing infected trees while implementing strict sanitation practices to prevent the disease from spreading.

Preventative Measures for Pests and Diseases

Preventing pests and diseases before they become major issues is the best approach. Here are some tips to keep your citrus trees healthy:

• Maintain Tree Health: Healthy trees are more resistant to pests and diseases. Regularly fertilize your citrus trees, water them properly, and provide them with enough sunlight.

• Prune & Monitor Regularly: Pruning helps improve air circulation, reduces overcrowding, and removes diseased or damaged branches, which can harbor pests. Regularly inspect your trees for signs of pests or diseases as early detection makes treatment easier and more effective.

• Encourage Beneficial Insects: Natural predators, such as ladybugs, lacewings, and predatory beetles, can help keep harmful pests under control. Marigolds, lavender, sunflowers, and dill are among those that attract the good guys to your garden! 

Conclusion

Citrus trees are resilient, but they are susceptible to a variety of pests and diseases that can interfere with their growth and fruit production. By staying vigilant and practicing proper care and treatment, you can protect your citrus trees and enjoy healthy, bountiful harvests year after year.