Dendrobium leaf issue?

[Sienna]

Hi,
I am new to the Orchid Board, and this is also the first time i have used a forum

I recently recieved a bulk lot of Australian Dendrobium orchids and i am a bit worried about some makrks on the leaves. They are all on different plants.

Does anyone know what causes them and what I can do to treat it?

I have some Previcure fungiside i can use, but I tend to avoid this where I can.

You can see in the photos that the tap water is causing a build up on the leaves, we are in the process of installing a rain water tank so i can give them fresh water. Any tips for dealing with this in the mean time would be great.

Thanks

[King_of_orchid_growing:)]

Welcome to the OB.

The first pic is either a minor bit of cold damage or a fungal infection.

The second pic is normal anthocyanin pigmentation from heavy sun exposure. It is acts as sunscreen in this case.

The third pic is a dead leaf. You can remove this easily.

The fourth and last pic is most likely from sunburn.

[King_of_orchid_growing:)]

I believe you own a Dendrobium kingianum which would be an Australian native orchid.

Or perhaps it's a hybrid of a few native Australian Dendrobiums.

Dendrobium kingianum is actually more of a lithophyte (grows on rocks, such as sandstone or granite), than it is an epiphyte (grows on trees).

Growing in sandstone or granite may save you time and money in the long run from having to constantly repot. It also puts less stress on the plant from repotting.

[Sienna]

Wow, thank you! thats great. and thank for the sp. tip, only some of them came with tags.

The leaf loss in the third image was a great concern to me as it seems to be dropping a lot of leaves. I inherited another 2 orchids the same and they are also rapidly loosing their leaves! Do you know what causes this or how I can fix it, I would hate to loose the plants. The person who gave them to me was a great gardener, but she said they had never been strong plants.

[King_of_orchid_growing:)]

I disagree with the lady who sent you these plants, they should be very sturdy.

I've had mine for about 2 or 3 years already. No problems here. I believe mine are about to bloom too. We'll see in a couple months or so.

Check the roots. There could be some root damage. If so, that's what could be contributing to the problems the woman who sent you the plants had.

During the warm spring and summer months, they should be watered anywhere around 3 to 4 times a week. Or an even better method of figuring out how often to water these would be to allow them to dry out slightly between waterings.

In the cool fall and winter months, watering can be reduced to once every 2 to 3 weeks!

They grow stronger and flower better under bright indirect light.

Den. kingianum goes by the common name of "Pink Rock Orchid".

There are two variants in plant size. There's a short caned Den. kingianum. And there's a tall caned variant of Den. kingianum.

Flowers are 1.25 cm (1/2" for those in the US). The colors range from pink to white. They're fragrant and smell like ambrosia (honey water).

If they're not Den. kingianum, but a hybrid involving it. The culture is similar.

[King_of_orchid_growing:)]

I forgot, sometimes old leaves from older canes will die. It can be natural too.

But it's all in context of what else is happening to the plant.

They shouldn't be rapidly dropping leaves.

Where are you growing them and how?

Please provide the following:

Temperature
Light
Potting media

Since it's a native Australian orchid and you're in Australia, I can skip humidity.

I also recommend a clear plastic pot in order for you to see what's going on with your plants' roots and in order for them to photosynthesize.

You read correctly, the roots on these plants can photosynthesize to some degree.

[Sienna]

Yeah good idea about the pot.

I recently re potted the 2 weak plants into a commercial orchid mix and the old mix was very old and soggy! All my orchids (I have quite a few Den. and Cym's) are all living under our pergola which is about 6m x 16m (not sure about US conversion) completly covered in some new fancy, light refracting poly-carb. very nice bright filtered light. They would recieve a small amount of morning direct sunlight. I usually water about 3-4 times a week and do a liquid fert evert 2 weeks. I have just found a new slow release fert. specifically for orchids that i'm trying, it is endorced by a few Aust. orchid groups. the temp. at the moment can go from prob 15C over night to 40C max during the day, but that is extreem, on average at this time of year 33C during the day (again, not sure of conversion). I live in south Aust. so it's not a tropical environment like north Aust. so I spray my plants a few times a week to create humidity.

I think I also have a large rock orchid that you were refering to (see pic) that was what I identifyed it as. Hopefully it will flower very soon (lots of spikes) and I can confirm.

[King_of_orchid_growing:)]

Pics of Den kingianum flowers (they're not mine, I couldn't take a very good photo of the ones I own, they're blurry because of how small the flowers are):

http://www.mobot.org/gardeninghelp/i.../Bloom1456.jpg

http://www.orchidphotos.org/images/o...mKingianum.jpg

Here's some info:

"This is a cool to warm growing lithophytic orchid from Queensland and New South Wales Australia at elevations of 50 to 1200 meters where it is found both on the coast and in the mountains growing lithophytically on rocks and cliff faces forming dense mats..." (Jay's Internet Orchid Encyclopedia, www.orchidspecies.com)

They bloom in spring.

A word of warning about the www.orchidspecies.com site. Always cross reference the info he has up on his site. It's not always 100% correct.

[Sienna]

Yeah that's the one I think, ill post some pics when it flowers.

So do you think I need to use the Previcure fungiside? If not do you know what I might use it for in the future?

[Andrew]

Hi Sienna,

The black spot in the 1st photo is a fungal infection. As you are growing the plant outdoors in South Australia the infection shouldn't spread and it is unlikely to need spraying. Ditto with the sunburn in the 4th photo.

Regarding the leaf drop, when did you pot these plants? Newly repot plants are susceptible to water stress which can cause premature leaf drop and if you are going to repot orchids as you're heading into summer you need to keep them protected from excessive light/heat/low humidity while they settle into the pot. South Australia has been hit with some hot, dry weather over the past couple of months. Even with the reduced heat/light transition-type polycarb (I'm assuming you're talking about something like Laserlite Apollo), the plants may be getting more light than they can handle in the heat and low humidity. Even established plants (especially seedlings) may need more shade during southern Australia's extreme summer weather than what polycarb will provide. As you enter into autumn, they should be fine to start taking more sunlight.

As for the suggestion of growing them in rocks. Stone or scoria does make a good addition to a bark or coir based mix. However, in my experience, Dendrobiums grown in 100% stone need a lot of water in southern Australia and, unless the plants are grown in a greenhouse or a moist area of a shadehouse, it's not practical and is unlikely to give you the results you'll get in bark or coir based mixes.

Andrew