I have in So. CA. All the leaves on my kumquat were like this last year and I end up pick all of them off. After being bare for several months, new leaves start growing but the tree is not the same anymore.

I just discover the same thing happen to my drawf meyer lemon tree. A lot of the leaves are yellow too. I already only water it once a week or once every 2 weeks.

What kind of disease is it? What can I do to save the tree.

Thanks!

That looks like Leaf miner damage. Look at the underside of the leaf.

It does look like miners. If you look at new leaves as they are developing, you can see the miners, they will be a small yellow worm about 1/8 inch long--once they finish the larval stage, they will fold a crease in the leaf or roll the edge to make a cocoon, if you open that before it has hatched you will see a small pupa.

They are difficult to eliminate, but you can keep the numbers down by spraying new flushes with 1% horticultural oil while it is cool in the mornings or evenings--never spray oil when it is above 85 F. The adult moth does not like to lay eggs on oily surfaces--they will usually lay eggs before the leaves are 1/2 inch, so you have to keep new growth sprayed pretty often.

There is also one pesticide that works pretty well--spinosad --sold under a variety of trade names.

After the leaf is damaged, should the leaf stay on the plant, or be removed? I have some damage on my Meyer lemon from the Leaf miner. I plan on leaving the leaves, figured a damaged leaf is better than no leaf.

Yes, leave the leaves attached to the tree. Citrus leaf miner (CLM) damaged leaves still produce much of the original amount of energy from photosynthesis as they did before being damaged. Although CLM does cause some harm to trees, the main "damage" is mainly ornamental. commercial growers normally do not even bother with any type of treatment. For home owners wishing to maintain a good appearence on their trees, there are sprays you can use. Put the words "Citrus Leaf Miners" in the search function of this forum and you will receive a lot of helpful information - Millet

I think Millet under estimates the damage that can be done by citrus leaf miners, especially to younger trees and where there is not a basic spray program like commercial growers use. As you can see in you pictures, at least a 1/3 of that leaf is gone, that is the trail of just one miner in the leaf. I have seen leaves that are even worse and uncontrolled miner infestation that get almost every leaf after the first flush of the year.

Millet has read articles that show no "significant" reduction in yield from mature trees in orchards that were sprayed to reduce miners vs orchards that were not sprayed. The term "significant" here has a statistical meaning-- depending on whether the researchers wanted to be 90, 95 or 99% sure their conclusion was correct. At the 95% confidence level, the difference would have had to be at least 3 time the standard deviation in production per tree--my guess is that could be over 50 pounds per tree.

In addition, commercial growers have to consider the cost/benefit ratio and since they have to pay for labor, equipment, fuel, and the cost of the pesticide or horticultural oil and the fact that they would have to spray the entire orchard several times a year more than they already do--it just is not worth it to them in return.

I have read studies that do show significant reduction in yield and decreases in photosynthesis proportional to the damage. In addition, there is an increase susceptibility to disease.

Like Millet said I would leave the leaf--as you said a part of a leaf is better than none at all. For me I spray oil often when there is new growth, I spray spinosad several times a year as well--my time is free, my equipment is a plastic spray bottle--hort oil is cheap. Cost/benefit for me is positive.

As Skeet states, mining can cause a retardation of plant growth of young trees and very young nursery stock. Studies in Florida have shown that significant stunting can occur if young trees are not protected from CLM with insecticides from the time of planting until the tree attains 4 years of age (Rogers and Stansley 2007). Therefore, for very young trees, a program to control CLM would be beneficial. However, the University of California, Division of Agriculture and Natural Resources states, CLM do not generally cause any crop yield losses in mature citrus trees. Because there is no crop reduction in mature citrus trees, growers do not bother to treat for CLM. Cost/benefit ratio, labor, equipment, fuel, and pesticide has nothing to do with it - Millet

http://www.lsuagcenter.com/en/crops_livestock/crops/citrus/Citrus+Leaf+Miner+Management.htm

www.cdfa.ca.gov/phpps/ipc/biocontrol/pdf/insects/cleafminer_citrus-may6-02.pdf -

from:http://www.fao.org/world/regional/rne/morelinks/PProt/CLMrpt.pdf
4. Economic importance
CLM causes severe damage to nurseries and young trees. Its effects on mature trees are not well understood. The economic losses caused by CLM still need to be assessed in monetary terms.

From Florida Pest Management Guide 2008:
Citrus growers must maximize profits via maximizing fruit production and optimizing expenditures to remain competitive during these challenging economic times. Basic horticultural inputs to maximizing production include the optimization of fertilization, irrigation, weed control and pest management of various foliar and soil pests. A fundamental working assumption to maximizing grower profits is that the cost of any input should be matched by an increased return of greater value.
Although close observations and pest monitoring, informed decision-making, and judicious pesticide application should reduce the level of input and associated costs in most seasons, psyllid and leafminer management remains a priority.


Crop loss is dependent on the severity of infestation:
Huang and Li (1989) reported that < 20% of the leaves are damaged and have no influence on growth and yield, and the economic threshold was estimated as 0.74 larva/leaf. The extent of damage depends upon the new vegetative growth and number of flushes in a year.

Skeet yes exactly, thanks, your post confirms what I was writing about, of why commercial growers don't ever bother to control leaf miners. As far as I know, no or almost no grower ever does. - Millet

I've had huge problems with leaf miners. They definitely set my young trees back. Now that they are larger, they don't seem to be as much of a problem, but then again, I'm spraying with Spinosad when I have new flushes of growth on my trees.

Actually, I think leaf miners may have been the reason I joined this forum in a pursuit to find a solution. Okay, okay I stepped into it . . . this is where you all say, "Leaf miners don't just cause problems in the orchard, but here on the Citrus Growers forum."

Phillip

Overtly this damage is exactly like the damge I am seeing in part to my "leaf curl" issues - but it is definitely not CLM. (That was confirmed by UC Davis). A little leaf damage; and evidence of odema but again nothing conclusive. Still the tree drops leaves and progressively degenerates.

It also tends to give the impression of under-nourishment as the vascular system of the leaf becomes somewhat washed out and the tips of the leaves become yellow. But according to UC Davis that is not the issue either.

Nobody knows.