I think the damage was so bad this year for a couple reasons. First of all we really didn't have a winter this year, so there were no hard freezes to knock their populations down. Secondly, it was very wet year, which resulted in lots of new tender growth. So the leaf miners started the season at full strength, and were then treated to a huge supply of food. Of course, I'm sure I see a lot citrus leaf miners because I have a lot of citrus trees. There are also many many citrus trees planted in our neighborhood that experience regular leaf miner damage. So how should I fight them? Even if I had an effective treatment to wipe them out at my house, my trees would soon be re-colonized by invaders from my neighbors' yards. Clearly, this will be war of attrition.
Local expert Yvonne Gibbs says that she just plucks the affected leaves off of her trees, and that she is able to effective control the leaf miners in her yard that way. I wish I could do the same, but it has become so bad that if I plucked off every damaged leaf, the trees would almost be bare! I was talking with Mary Cummings (owner of RCW nursery) after the miracle fruit tasting we had there, and I asked her how she dealt with leaf miners. Their stock of citrus trees looked fantastic and healthy, and I mistakenly assumed that a nursery would have to use some nasty chemicals to keep the trees free of blemishes and looking good for sale. I was wrong! She told me that RCW uses an organic control method they learned from Randy Lemmon, that they use the same products they're selling at the nursery, and that they had not seen any bad leaf miner problems since they had implemented the program.
Randy Lemmon's program consists of alternating sprays of spinosad and neem oil, both of which are organic, every 7-10 days. Once the infestation is under control, he recommends dropping back to spraying every 10-14 days to prevent re-infestation. Spinosad is easy to find at local nurseries and big box stores in low concentrations (0.5% spinosad), but you can also buy one quart Conserve SC (11% spinosad) online for $150. The only containers of neem oil I could find locally were the little 8-ounce containers that cost $10 ($1.25 per ounce). Lucky for me, Mary special ordered a one gallon container of 100% neem oil for me ($0.75 per ounce), which should last over three years. She said she should also special order Conserve SC, but I decided to stick with the Fertilome spray for now.
So beginning September 1st until October 14th, I sprayed the trees every Sunday night, alternating between spinosad and neem oil. My strategy is to try to knock the leaf miners back a bit before we go into winter, spray all the trees with a good dormant oil in January, and then resume the spinosad/neem spray regimen in the spring in order to drive as many out of my yard as possible. I took care to only spray at dusk so as not to harm the bees, and did my best to really cover the trees well, especially the undersides of the leaves. I found that it took approximately 2 gallons to adequately cover everything, including the trees in the greenhouse. I read that spraying neem oil in hot weather could cause in leaf curling, and even though I sprayed at dusk when it had cooled off a bit, I still noticed some leaves with minor curling. Oh well, I haven't noticed any other ill effects from the spraying thus far, and I'd much rather have some slightly curled leaves than leaves damaged by miners. Other than that the results so far have been very encouraging, and I am very optimistic that with continued diligence, my trees can look as good as Mary's and Yvonne's.