Limes turning black

[dingdongrb]

Sorry I don't have any pictures but I am wondering if anyone can tell me why the limes on my small tree are turning black and what I can do to stop it.

 

The tree is only a meter or so tall and young.

 

I'm thinking maybe too much water but since I've never tried growing limes before I have no idea.

 

FYI, the location of the tree is in Surin area.

[drtreelove]

Possible "sooty mold" that grows on the surface where "honeydew" excretions from aphid or scale insects has dropped and formed a sugary coating that the sooty mold thrives on. The sooty mold is not harmful by itself, except where it gets real heavy on the leaves and blocks sunlight for photosynthesis. And of course would affect maket value of a commercial crop.

 

If that's what it is, there will be sooty mold on foliage and stems too,, not just the fruit. If  the blackening is only on the fruit, then it is something else. Does the skin of the fruit appear hardened? Is the blackening on the upper side of the fruit as it hangs on the tree, or does in encompass the entire sphere?

 

Normally, if you control the aphids or scale pests, you will control the sooty mold, but with some lag time after the honeydew source dries up.

Aphids (small crawlies, flying, sucking insects, often on the underside of the leaves) on citrus are usually pretty easy to control with water jet wash, or a low toxicity (for mammals) contact insecticide like a pyrethroid (permethrin or cypermethrin).

Scale insects on citrus are usually soft-scale, that appear as bunches of small turtle shells implanted on small twigs in the foliar canopy. These are the adults that fix and suck sugary sap from the phloem. They are protected by the shell from contact sprays, so you have to go after the "crawler" stage, immature scale that are moving around before they implant, and are not protected with a shell. Crawler stage is usually in the early spring in temperate climates, not sure when that happens in Surin.

But with a small tree like that you can use "manual" control and wipe the little buggers off with your hand. You will want to use a rag or cotton glove.

If you don't see the scale at first, you may notice an ant trail going up the stem into the canopy. Ants farm the aphids and scale for the sweet honeydew,  and protect the pest from natural enemies.  Control the ants and you bring about some level of control for the sucking insect pests.

 

Too much water can cause root and crown rot, but not blackening of fruit. Although heavy watering and fertilization can cause excessive vegetative growth which is attractive to the insect pests. Slow release natural fertility, soil building with compost and mulch will help optimize plant resistance to pests and diseases.

 

Hope that helps. Don

 

Edited January 25, 2017 by drtreelove

[dingdongrb]

On 1/26/2017 at 2:05 AM, drtreelove said:

If that's what it is, there will be sooty mold on foliage and stems too,, not just the fruit. If  the blackening is only on the fruit, then it is something else. Does the skin of the fruit appear hardened? Is the blackening on the upper side of the fruit as it hangs on the tree, or does in encompass the entire sphere?

 

Hope that helps. Don

 

Thanks for the reply Don.....  I'm currently in Chiang Mai and the tree is at my place in Surin so sorry I cannot provide any pictures or even take a closer look at some of the suggestions you have provided.

 

I don't believe it is any insects causing this as that's the first thing I looked for and saw no signs.

 

The blackening is on the fruit only. That is, I didn't notice any on the leaves or stems. The blackening seemed to only be occurring at the very bottom areas of the fruit.

 

The fruit was still small and young so I really didn't cut any open to see what possibly was going on in the inside. Maybe I'll do that the next time I am there.

 

Again, thanks for the time you took with replying.

 

 

[drtreelove]

If not sooty mold from aphids or scale, consider 'citrus rust mite' (Phyllocoptruta oleivora),  You will not be able to see the mites without magnifying lens. But compare signs with Google images like the attached.

A regular (every two weeks) spray program with a neem product (Azadiractin) would be my first choice, maybe add a horticultural oil for one or two applications until mite infestation is suppressed, then the neem as ongoing preventive for other pests too.. If not an organic program, then there are strong synthetic miticides available like abamectin. But this chemical is "translaminar" (partially systemic) and can penetrate/contaminate the fruit.

IPM considerations include optimizing good growing conditions, soil and water management, and pruning to thin the foliar canopy for air and light circulation.