Controlling or Avoiding Leafminer Damage
By Marie Iannotti
If your plant leaves look like someone was doodling squiggly lines, you have leaf miners. Leafminers are the larvae of various beetles, flies, moths and sawflies. The adult lays their eggs on the leaf and the larvae burrow into the
leaf and tunnel through it, feeding and leaving a transparent trail of where they've been. If you look closely, you can often see a dark dot at the end of one of the lines. That's the culprit at work.
Not all leafminers zig zag their way through leaves. If you see a similar whitish transparent blotch, this could also be a leaf miner. Blotchy leafminer damage is often mistaken for some type of disease. The photo here is an okra leaf, but many plants are attacked by leafminers. Columbine is almost guaranteed to have a few. The damage is rarely severe enough to kill the plant, but it is unsightly. And in the case of vegetables grown for their leaves, like spinach, chard and beet greens, leafminers can mean a loss of a crop.
Least Toxic: Insecticides are rarely recommend to control leafminers. Since the damage is mostly cosmetic, the remedy is to remove the affected leaves. This does more than improve the appearance of the plant. It also gets rid of the existing leafminers before they become adults and lay more eggs.
Less Toxic: If you know that a certain plant is susceptible to leafminer every year, you can target the adults before they lay their eggs, by spraying early in the spring with an insecticide such as neem.
Last Resort: There are some systemic Insecticides that are labeled for use on leafminers. Insecticides containing acephate (Orthene) or imidacloprid can be effective if used before damage is severe. No systemics are currently available for non-commercial use on edible plants. Source: About
Citrus Leaf Miners - Fighting Back
This year the citrus leaf miners have gone from being a nuisance to all-out infestation. All summer I watched as each sprig of new growth was mercilessly attacked by the little jerks. They would attack every leaf, causing them to shrivel, curl, and eventually fall off, leaving barren green twigs that should have been covered in lush green foliage. Once the leaves were gone, they even began to attack green wood. I typically don't spray any of my trees at all, preferring to let the good bugs take care of the bad ones. Unfortunately the natural predator of the leaf miner (a parasitoid wasp) doesn't live in Texas, and until an effective predator is introduced their numbers continue to grow unchecked. After some of my very young seedlings were almost completely defoliated, I decided enough was enough. It was time to fight back.
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. source: Weebly.
Citrus Leaf Miners - Fighting Back