Garden Detective

White ooze may mean doom for lemon tree

Garden Detective: What’s wrong with this lemon tree? A severe fungal disease may mean its demise.
Garden Detective: What’s wrong with this lemon tree? A severe fungal disease may mean its demise.

Experts tackle readers’ garden questions.

Q: Help! I think this mold or fungus is killing my lemon tree. Any ideas?

Stan Wallin, Sacramento

Master gardener Alice Yee: How long has this problem been going on? Fungal diseases take a while to kill a plant. Was there poor drainage in the area? Was the tree pruned regularly? Watered and fertilized regularly?

First of all, I would check if the tree is still alive. Is there any new growth or green leaves? I would cut off a branch and see if there is a green layer on the outside perimeter of the cut, which is the living cambium layer. If there is a cambium layer, the tree is still alive. If there is no green, then the tree is gone.

Fungal diseases kill by clogging the vascular system of the plant, so you will see dieback in the leaves on one side of the plant initially. Citrus trees require good drainage, good aeration (pruning out excessive branches and leaves), regular watering, and fertilizing. Citrus trees like acidic pH soil.

Due to our severe drought for the past several years, this may have stressed out the tree to a point that the fungal disease became a secondary problem since the tree became weakened. Healthy trees are able to wall off fungal diseases to prevent the fungus from entering into the vascular system.

From looking at your photos, it looks severe. If it was only affecting one part of the tree, hopefully the other side is healthy enough to withstand the fungus.

Alice Yee is a UC Cooperative Extension master gardener for Sacramento County.

Garden questions?

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