Yellow patches and yellow pseudobulbs

Hi, I went into my shade house this morning and was alarmed at yellow patches and yellow pseudobulbs! Any ideas what this could be? We have had a bit of rain lately and I switched to a new fertiliser that I bought at an orchid show about a month ago that I mist all over the plant as opposed to the previous kind that I always applied with a watering can to the medium. The only other thing that I did was wipe some black off them with milk which was recommended to me as I get some black from trees that are nearby.
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The black that I mentioned is possibly residue or something similar from some very big gum trees that hang over a part of the shade house. They are far too big to cut down even if I wanted to and we also have a "preservation order" on our property which means we can not cut down anything (is fine by me but does make it hard to have flowers when you have very limited full sun positions).

I do think I have spider mites and have begun to attack them with White Oil and will do so weekly now. I have one other question (for now anyway) as suggested, I may have some fungus but Phisan is not available in Australis that I can see anyway, what else can I put through the potting medium to kill fungus? I am repotting a large number that are in big pots to try to ensure they get to dry out and also get enough air movement so that there is no root rot.

Sorry for so many questions but I seemed to encounter several issues all at once!

 

Ok thanks. One last question, after repotting and getting rid of any rotten roots, should I hold off on watering, fertilising and also when would it be safe to use a systemic fungicide?

 

Marni - I agree, I think Cattleya need more fertilising than a spray (ignore the sales pitch even though I bought it at an orchid show) back to the old ways for me.

KellyW -I definitely agree with the scale spreading quickly - I see it with my own eyes!

Lepetitmartien - With regard to caution on White Oil, I certainly will, I now have neem oil that I will mix with soap and I think I will alternate with Eco oil to hopefully stop them from becoming tolerant. I bought algaecide the other day as it was recommended in a locally produced orchid society book that I have now misplaced as well as by someone that let me get in their ear at a recent orchid show, but I need to find the dilution before I try it.

Are then any rules with fertilising and watering following repotting? It was not the perfect time to repot so I would like to minimise any added stress?

Thanks all.

 

I think I have success, I am certain I had spider mite and scale, not sure if I had mealy bug as well but I certainly had some root rot. I have repotted about 30 of my cattleya's and I have got rid of all signs of any pests which I will continue to monitor. I also will continue with my 3 in 1 spray.

Once I am confident I have everything under control, is it ok to put orchids on a lower shelf under all of my others in the shade house? I would love to start filling the lower shelf too but I have read that you shouldn't. As I have learned the hard way that a few things that I had thought were a bit pedantic actually have a lot of merit I wonder if this is another of those things!

Thanks again for your help!

 

Ok, I will do but if you have no pests or disease, does it really hurt if water drop below onto other orchids?

 

Thanks Marni

 

Ok, yes I hadn't thought about crown rot, will keep an eye on that. Thanks