The problem is not humidity -- in that case, the higher the better. It is because of our high humidity that we can use much lower-grade oils than can be safely used in California or Arizona. On the other hand, yes, heat is a problem. Commercial growers often spray early morning or evening, or even at night, to try to apply when the air temperature is below 80 F. Most commercial Florida citrus is sprayed once in the summer with oil, and the most common grade used is FC-435-66. Unfortunatly, it can be a challenge to determine how oils available to homeowners compare to the commercial stuff. If you use "ultrafine" oil, it should be safe, if not applied in the heat of the day. Don't use any oil more than twice a year, and once is best, in this climate.

Thank you for the information, Dr. Manners. I did not know that I'm supposed to spray so seldomly. It creates a problem. The main pest hurting my citrus right now is leafminers. I'd say over 90% of the leaves are "mined." The trees look really terrible. I've been reading, and some things I've read suggest oil sprays are a way of controling them--so long as I spray often, every few weeks, to protect new growth.

Would it be damaging to the trees to apply an oil spray more often? Some of these oil sprays I'm reading about contain fish oil or neem oil or other botanicals.

Bill

Bill, in Central Florida, having too many leafminers (or scales, or aphids, or whiteflies) usually means you are spraying too often, or with the wrong material. The best advice in this climate is not to spray for bugs at all. Ever. By spraying too often, you keep killing off all the beneficials which would normally eat the bad guys.

We had less leafminer this year than any time since it arrived in Florida, in Lakeland. We have not sprayed our trees in the last 3 years, and when we last sprayed, it was with oil only.

Spraying multiple times with oil weakens a tree, in that oil sprays are stressful. Trees won't become as cold-hardy, fruit won't be as sweet, Fruit won't color up, and the tree won't grow as much. These are symptoms of too-frequent petroleum oil sprays. I'm not sure how the plant-based-oil sprays compare. But in any case, there is no reason to use them.

Malcolm

I have never sprayed them with anything, but they have really taken a beating from pests, especially the leafminers. Like I say, neary ever leaf on the trees have been "mined." I have a no-spray, mostly organic garden, with lots of natives, wildflowers, and I see many types of lady bugs, wasps, etc.--but so far the leafminers and aphids are winning out.

They are young trees. I planted them two years ago. And because they're on flying dragon rootstocks they're small trees. So maybe they are more vulnerable? Or maybe the beneficials that kill leaf miners haven't arrived to my garden yet?

Certainly young trees are more affected by clm than older trees, since they have fewer total leaves, and since they make growth flushes more often. If you are seeing lots of leaves with mines, that's not necessarily a bad thing, so long as the leaves remain on the tree, green, and photosynthesizing. If the tree is sparsely foliated, that would be a different matter. As far as I know, the parasites and predators of clm are pretty well distributed in central and southern Florida.

The upcoming spring flush should have far less problem, in that the clm has a population crash in the winter (nothing to eat), and doesn't build back up until after the spring flush. So that should give your trees a crop of relatively clean leaves. The same is true of brown citrus aphid. (I'm presuming that's the only aphid of significance on your citrus?)

The aphids on my citrus are dark brown/black and large, for aphids. Should I use an insecticidal soap on them--or would the soap also reduce beneficials?

What's happening is just what you describe. The leaves are "mined," but they stay on the tree (most of them are badly curled though). The few leaves that are not mined are from last year's spring flush.

I'm not going to spray anything and see how they do this year.

I'm wondering if the feeding schedule I'm following is making the leafminer/aphid problem worse. The nursery I bought these trees from suggested giving the trees a small monthly feedings rather than a big feedings further apart (twice a year, I think). Would this be creating more growth in summer rather than in spring? I'm wondering if I gave them the big spring feeding, the way some of my garden books sugggest, if they wouldn't have a bigger spring growth--and less growth in the summer, when the leafminers do the most damage.

Thank you again for all of your help.

Bill

Your aphids are likely brown citrus aphid, which ranges from brown to black. The easy way to identify it is to wipe a hand or white cloth over them. The stains from those which burst look very much like drying blood. All other aphids on citrus make clear "juice" when they burst. The other thing which identifies BCA from all other aphids on citrus is that they make big colonies on the stems as well as leaves. Other aphids tend to go for leaves only.

Yes, you could use an insecticidal soap on them, and that should not much disrupt your beneficials. I'd make it pretty dilute, and if it doesn't do the job, try again later with a more concentrated solution. I'd look carefully, first, to see if there are any ladybugs present, or ladybug larvae (do you recognize them? Like little orange-and-black dragons) present. If so, I'd not use even the soap. The LBs will clean up an aphid infestation very quickly. LB eggs are bright yellow, maybe 1/4 the size of an aphid. If you do use soap, you can further reduce the chance of burning your leaves by rinsing it off thoroughly with plain water, half an hour or so after spraying. The aphids will be dead by then, if it's going to work at all.