The young leaves on my mandarin is wrinkled. The outer layer of leaves are blistered making it look like the slime trail of snails or slug but there're not due to snails or slugs. Sometimes the leaves are blistered in a pattern. These are the pictures of the infected leaves

Leafminer damage. It is not a disease, but a small tunneling insect.

Is there an effective method to control them? I tried to search on the web, but most suggest biological methods which is too expensive and don't know how effective they are.

Got to the top of the page and do a search of this forum for leaf miners. Also try Google, Yahoo, etc.

I am new to citrus and this forum, but I was a pesticide residue chemist for 25 years and although I try to avoid pesticides, I do use them when all else fails.

I read the link I found in the search and I have not yet tried the soap on miners, although I do use soap often on other insects. The problem is trying to kill the moth before the larvae start mining the leaf. Soap works by wetting the insect and causing it to drown, so you have to get the soapy water on the moth to prevent infestation. I will try it on existing infested leaves to see if it can get inside and kill the larvae.

I have used oil and it works with frequent application on any new growth. However, Millet told me on another forum that oil application at this time of year will reduce the plants ability to withstand cold weather, (you may live where cold is not a problem).

I have tried a pesticide called spinosad and it does seem to work. It is a relatively non-toxic pesticide to mammals (several thousand mg/kg if that means anything to you). It is toxic to bees, so try to avoid spraying flowering plants. According to the lable it can only be applied every 6 days and only 6 times per year, so target the primary flushes.

Hi Skeeter, I see you made it onto the forum. I was also a chemical major at the University of Colorado. Welcome to the forum, we are all glad to have you as a member. You can probably still use horticultural oils for another couple weeks, and avoid a hardiness problem. I also recently read an article that claimed the use of horticultural oils also reduces the sugar content of the fruit. Dthong, most commerical growers of citrus do nothing to control citrus leaf miners. Although it does make your tree look bad, it really does not do all that much damage. I know that is not what you want to hear, as I'm sure you want a nice looking tree. Take care. - Millet

Hi Skeeter & welcome to the forum. I use Ultrafine up until the end of August & haven't had a problem. We usually don't get a frost until the middle / end of December here.