Spider mites on lemon trees

Asked January 19, 2021, 10:57 AM EST

Hello! I recently (a few months ago) adopted a few Meyer lemon trees. They are potted and have been living indoors for a few months while the weather drops. I noticed that one of them had some holes showing up in the leaves. Then holes started appearing in the other one. Doing some research, I suspect these are caused by spider mites. I confess, I got a bit freaked out and took them outside to spray them both with neem oil. Was that the right move? Are there any other steps I can take to make sure the spider mites are gone and won’t come back? Any help you can provide would be greatly appreciated!

Washington County Oregon

1 Response

Thank you for the images because they reveal that the missing leaf tissue in the first 2 pictures are due to insects.

The damage to the single leaf with neatly 25% missing is due to feeding by a caterpillar whereas most of the damage on the 3 leaves is due to root weevils.

The good news, though, is that both kinds of damage occurred quite a while ago.. The reason? The edge of the holes is dry and gray. If this damage was on-going, the edge of the wound would be green and moist.

That said, the caterpillar damage probably occurred while the tree was outdoors. But keep an eye out for more damage as is shown in the 2nd image. (see root weevil damage in the 2nd image at this link - https://www.oregonlive.com/life-and-culture/erry-2018/09/c12841c6e8501/how-to-combat-root-weevils-id....

Unfortunately, root weevil larvae (youngsters) live in the soil. Thus, some may be in the potting mix. Don't disturb the potting mix to look for them; instead, keep an eye out for fresh damage along about May or later. when the adults will be active.

See this article about root weevils and the damage they do: "Root Weevils" - https://extension.colostate.edu/topic-areas/insects/root-weevils-5-551/

Obvious damage by spider mites is shown in the final image - the bleached leaves with minimal green remaining. Please keep these leaves until they naturally drop because, even though you may consider them ugly, they do have some green on them which will help support the plant until it again goes outdoors.

Keep a watch on the trees, especially while they are still indoors, becasue the mites are likely to build up to damaging populations again. The first indication will be a faint webbing on the underside of a leaf, or multiple, leaves. The sooner you recognize an infestation, then act, the better.

When you see the signs of mites, take the plant outdoors on a mild day and thoroughly spritz off the leaves by aiming at the undersides. Repeat as needed.

If you think you need stronger treatment, spray the leaf undersides with insecticidal soap, diluted according to label directions. Reserve neem for other, more troublesome, problems.

I see that you have the trees very close to a window as that's generally beneficial for citrus. But, be aware that, if the temperatures is predicted for freezing or worse, move the trees away from the window until temperatures rise to safe levels. (Yes, subtropical plants such as citrus can be damaged during a cold night when they are close to a window.)

I have mixed thoughts about the dish with water sitting on the heat register in the floor. Citrus can survive without the extra humidity but they will suffer if they also receive blasts of heat from the furnace.

You might lie to review "Growing citrus indoors" - https://extension.umn.edu/house-plants/growing-citrus-indoors.

If you have other questions, please ask when you reply to this email.