Black spots on Catasinae

[Lars Kurth]

Hi,

in the last two weeks I had problems with the electricity in my greenhouse: I first thought one of the waterproof sockets tripped the RCD, but it turned out to be the fan. As a result the greenhouse was without heating and ventilation for a bit, during a few weeks of pretty bad weather.

On the weekend I discovered a few black spots (sunken in 5mm size on various Catasinae) on some leaves and bulbs. Anybody knows what it might be?

I treated with Previcur N and Dithane which should cure black leaf spot. Also installed the new fan such that there is air movement around the plants. Without knowing what it is, I wont be sure whether this will work though. Could not find anything on the web. Any experiences and advice?

Thanks
Lars
P.S.: On the upside most Cycnodes, Cycnoches are getting spikes. Some which have previously flowered this year are getting second spikes.

[isurus79]

Need pics. Are the black spots mushy or hard?

[Lars Kurth]

The spots are hard. Mainly on the leaves and leaf sheats. When removing an affected leaf, there is some slight colouration on the pseudobulb, but no sunken in burn as on the leaves.

[Anisa]

I wish I could help but... If it is not spreading I wouldn't worry too much, especially that catasetinae are deciduous and next year you will have brand new leaves.

[isurus79]

Looks like sunburn which is normally nothing to worry about. Keep an eye on the dark spots on the p-bulbs as they could easily get infected. That's how I lose most my Catasetinae, some small lesion or burn that gets infected. If they start to get even slightly soft or turn brown, cut them out and sprinkle the area with an antifungal powder or cinnamon. Healthy looking plant otherwise though!

[Lars Kurth]

Thanks Isurus: not quite sure how the sunburn could have happened as we did not have hot weather recently. But we had a lot of changeable weather: 4 seasons in 2 hours almost all of August. So it is quite possible that the sun came out after I watered ...

Healthy looking plant otherwise though!

Yes, I am quite pleased. Only really two months left to fatten them up Before the rest period starts to slowly kick in ... Some of the younger plants only have slightly bulbs than last years. Hopefully the extra two months will make a difference.

[Lars Kurth]

Unfortunately one of the plants seems to have developed a more severe issue despite the treatment with Previcur (propamocarb). Picture attached. I am not 100% certain this is the same issue, but possibly related. The earlier problem is restricted to leaves and sheats. When removing the leaves some dark colourisation remains, but only on the surface.

On the picture you can see a sunken in spot with concentric circles, that was soft and brown and went about 0.5cm into the tissue. I cut it out and treated with cinnamon and removed the plant from the collection.

Does anybody have an idea what this is? When I noticed the spots I have treated the greenhouse and all plants with Previcur N twice and added Physan 20 to my water butt (as suggested in this thread). However since then I lost a newly grown pseudobulb on 2 Paphinia's, 2 Gongora's and and one Cattleya (although that may have been something different: the sarong of that plant had an odd shape and collected water). It is some kind of soft rot: the attached picture shows how it looks like: on gongora and paphia it is harder to see (the new leaves go floppy first and then glassy from the base). What is odd is that infection is NOT clustered in one area of the greenhouse, but occurs spread across the greenhouse. Could be an indication for something bacterial that is spread through air movement rather than fungus.

Does anyone know what disease this may be? Without a correct identification, it will be hard to choose the correct remedy. It is obviously not something cured by Previcur, so I ordered some Thiomyl.

I am worried that I will loose some plants over the winter months. With the days getting darker, I will have a hard time keeping this under control if I do not manage to do this now.

Any help is appreciated!

Lars

[kavanaru]

it looks like have started as sunburns, as Steve already mentioned, but then being attacked by fungi... Sunburn is very easy to get here, actually.. you need only two hours of unexpected high sun intensity on plants not very used to it, and that's it.. I could show that right now in my greenhouse

I would treat all your plants with a systemic fungicide (I use systemic fungicide for roses, which you normally find in any garden shop, with great results!) and also give some treatment with a good bactericide (just in case!). Those plants with large deep parts affected, I would place them appart and cut off the infected section!

[Lars Kurth]

I would treat all your plants with a systemic fungicide (I use systemic fungicide for roses, which you normally find in any garden shop, with great results!) and also give some treatment with a good bactericide (just in case!).

Thanks for the confirmation.

Started doing both already: I am just going to have to rotate with different systemic fungicides and Physan, through the winter and keep the greenhouse drier than usual. Enough to stop all my Vandas from suffering )-:

But I have a bad feeling this is bacterial, but not 100% sure as I never had a bacterial infection before.All my plants are quite leggy this year. Aug and most of Sept were quite wet, but warm so my plants grew like mad, but did not harden well. As a result the greenhouse did not dry out as quickly as usual.

Just did a thorough search of the greenhouse and found an affected Bulbophyllum leaf (see picture). Just the leaf, the bulb is not affected. Does not really look like Erwinia. Could be Pseudomonas: the black entry point would indicate this.

Cheers
Lars

[stefpix]

Is it better a sulphur or copper based fungicide? in NYC I only seen these 2 by Bonide. Many products can not be legally be sold in NYC.