Living Heritage
Protect your trees
When pear blight devastated the foothills' orchards, mandarins helped local growers survive. The threat this generation has to keep out is citrus greening — and every backyard grower in the foothills can help.
Placer County's mandarins are a living heritage — and keeping them healthy is a job we all share. The single greatest modern threat to citrus, here and worldwide, is a bacterial disease called Huanglongbing (HLB), or "citrus greening," spread by a tiny insect, the Asian citrus psyllid (ACP). There is no cure — so keeping the pest out is everything, and homeowners are the front line.
The disease and the insect that spreads it
- HLB / citrus greening is an incurable bacterial disease of citrus. It makes fruit small, lopsided, and bitter, and can kill a tree in about five to eight years.
- The Asian citrus psyllid is the carrier — an aphid-sized, mottled-brown insect. It picks up the bacteria feeding on an infected tree and injects them into healthy ones. Controlling the psyllid is the best way to prevent the disease.
How to spot it
The psyllid (ACP): aphid-sized with mottled-brown wings; it feeds head-down at about a 45° angle. The nymphs are tiny and yellowish and leave distinctive white, waxy tubules. Look on the new leaf flush — the tender young growth.
The disease (HLB): blotchy, asymmetrical yellowing — green on one side of a leaf's midrib and yellow on the other; and small, lopsided fruit that stays partly green, tastes bitter, and drops early.
How to protect your trees
For Auburn-area backyard citrus growers:
- Inspect monthly, spring through fall. Check the new flush for eggs, nymphs (those white waxy tubules), adult psyllids, twisted leaves, sticky honeydew, or black sooty mold.
- Buy trees only from local, reputable nurseries. Never accept budwood or plants of unknown origin.
- Control ants around the trunk — ants protect psyllids from the natural predators that would otherwise keep them in check.
- Treat for the psyllid only if you find it (horticultural oils or soaps, or a product your local garden center carries per UC recommendations), and avoid spraying during bloom to protect bees.
- Don't move citrus out of a quarantine area — no plants, budwood, leaves, or clippings. Fruit may be moved only if it's washed and free of stems and leaves.
- Keep trees healthy and well-fed so that anything wrong is easier to spot.
- If HLB is confirmed, infected trees are removed to stop the spread. It's hard, but it protects every other tree in the neighborhood.
Think you've found it? Report it.
If you spot a suspicious insect or symptoms, call the CDFA Exotic Pest Hotline:
You can also contact your county agricultural commissioner. In project areas, state and county survey, trapping, and treatment are typically free to residents.
Learn more
- CDFA — Citrus Pest & Disease Prevention (current California status, quarantine maps, reporting).
- UC IPM — Asian Citrus Psyllid & Huanglongbing (homeowner identification and protection guidance).
- California Citrus Threat — HLB Quarantine (where the disease has been detected).
The mandarin is Placer County's second act — the crop that saved these foothills. Keeping it healthy is how we pass it on.