Leaves with brown spot on cattleyas

[Merita]

In my cattleyas large brown spots are appearing. The night temperature is between 40 and 47 * F and during the day it rises to 70, the Sun stays strong and I have left the plants one or two hours in the morning without covering, I am seeing this in the new growths, What can I do or what should I apply?

[SouthPark]

Merita. It 'may' be sunburn/sunscorch. The leaves can be more prone to it if there has been any spray of plant treatments on leaves containing oily substances.

Also - the leaves appear to darkish green, as if the orchid hasn't yet been sun-hardened. If that's the case, then strong sunlight bombing the orchid leaves may well cause the dark patches. On the other hand, I can see at least two leaves (yellow-green) which do appear to be sun-hardened.

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Leaf burning can be expected sometimes for outdoor orchids, when light intensity from the sun at certain times of the year become a lot more than usual.

If this is/was happening, then shading is one way to prevent the scorching. If the leaves dry up and don't become mushy, and eventually changes from the black colour into a light brown or grey/tan colour (over a long time), then that will be good.

Has this orchid been on that tree for a relatively long time?

[Merita]

Originally Posted by SouthPark

Merita. It 'may' be sunburn/sunscorch. The leaves can be more prone to it if there has been any spray of plant treatments on leaves containing oily substances.

Also - the leaves appear to darkish green, as if the orchid hasn't yet been sun-hardened. If that's the case, then strong sunlight bombing the orchid leaves may well cause the dark patches. On the other hand, I can see at least two leaves (yellow-green) which do appear to be sun-hardened.

Click Here

Leaf burning can be expected sometimes for outdoor orchids, when light intensity from the sun at certain times of the year become a lot more than usual.

If this is/was happening, then shading is one way to prevent the scorching. If the leaves dry up and don't become mushy, and eventually changes from the black colour into a light brown or grey/tan colour (over a long time), then that will be good.

Has this orchid been on that tree for a relatively long time?

The brown spot appears in one day and is like sunburn, but can it burn so cold? This is happening in many plants and new shoots. Every day I am checking them and putting alcohol on the spots, some of these spots have turned light brown but are not removed. I have to transplant five plants and I dare not, the temperature is very unstable. These cattleyas receive a lot of light although they have that green color, their leaves are hardened and the anthocyanin has them purple. I wonder why this year is happening and not the past, will they lack calcium?

[SouthPark]

Originally Posted by Merita

The brown spot appears in one day and is like sunburn, but can it burn so cold?

I would expect that relatively low temperatures could help keep temperatures under control. But maybe if the energy is focused on the leaf for long enough, then that could take conditions into the damaging zone.

Appearing abruptly - out of the blue - could definitely be related to light levels getting toward the intense side.

A way to test is to take one of these plants and put it in the shade - and then watch all of the plants (every one of them) closely.

Some catts grown in high light can definitely exhibit interesting shades of red, or purple etc on leaves and bulbs. That's no problem.

If this is really a case of leaf-scorch, then it leads to questions of whether the orchid can get similar intensities from the sun during the hot times of the year.

Have these orchids been growing on that tree for several years? If so, then there's always the case of one-off intense days. And if the orchids shrugs off the damage endured, then maybe no problem - just as long any intense conditions doesn't cause damage to a major portion of the plant.

The generally nice looking leaves of your catts don't appear to be showing signs of nutrient or chemical deficiencies. The flowers look absolutely fantastic by the way.

[Merita]

Originally Posted by SouthPark

I would expect that relatively low temperatures could help keep temperatures under control. But maybe if the energy is focused on the leaf for long enough, then that could take conditions into the damaging zone.

Appearing abruptly - out of the blue - could definitely be related to light levels getting toward the intense side.

A way to test is to take one of these plants and put it in the shade - and then watch all of the plants (every one of them) closely.

Some catts grown in high light can definitely exhibit interesting shades of red, or purple etc on leaves and bulbs. That's no problem.

If this is really a case of leaf-scorch, then it leads to questions of whether the orchid can get similar intensities from the sun during the hot times of the year.

Have these orchids been growing on that tree for several years? If so, then there's always the case of one-off intense days. And if the orchids shrugs off the damage endured, then maybe no problem - just as long any intense conditions doesn't cause damage to a major portion of the plant.

The generally nice looking leaves of your catts don't appear to be showing signs of nutrient or chemical deficiencies. The flowers look absolutely fantastic by the way.

would expect that relatively low temperatures could help keep temperatures under control. But maybe if the energy is focused on the leaf for long enough, then that could take conditions into the damaging zone.

Appearing abruptly - out of the blue - could definitely be related to light levels getting toward the intense side.

A way to test is to take one of these plants and put it in the shade - and then watch all of the plants (every one of them) closely.

Some catts grown in high light can definitely exhibit interesting shades of red, or purple etc on leaves and bulbs. That's no problem.

If this is really a case of leaf-scorch, then it leads to questions of whether the orchid can get similar intensities from the sun during the hot times of the year.

Have these orchids been growing on that tree for several years? If so, then there's always the case of one-off intense days. And if the orchids shrugs off the damage endured, then maybe no problem - just as long any intense conditions doesn't cause damage to a major portion of the plant.

The generally nice looking leaves of your catts don't appear to be showing signs of nutrient or chemical deficiencies. The flowers look absolutely fantastic by the way.
If I only leave them in the sunlight for an hour or two and they are presenting this, I think I will not be able to give them an hour of sunshine like in the summer. The nights are cold and humid, the sun heats fast, I cover them when I feel that the leaves begin to warm, the intensity of the light is not the same in the garden, maybe these were more exposed because I am changing them and not I realized, I think it is best not to give them more sun.

[SouthPark]

Merita - I recall reading articles about temperature changes in orchid leaves. And it was something like issues observed when the temperature on the surface of the leaf dropped (relatively quickly) by maybe 4 degree celsius - relative to the temperature inside the leaf or the plant.

It's possible that rapid temperature change - regardless of a drop or a rise, could have some unwanted effects on an orchid.

It probably all boils down to how long these orchids were grown on the tree (eg. years?), and if they had been growing there for quite a long time, then it will be important to determine the mechanisms behind this recent situation.