Orchid Culture Questions and Answers
image

 
Orchid Culture - Questions & Answers from This Month
by Sue Bottom, from the St. Augustine Orchid Society Newsletter
Email us with any orchid question, if we can't answer it we'll find someone who can! Send photographs too!
Click image for close up view

Vanda Roots Dried and Cracked
Vanda Roots Dried and Cracked
 

Vanda Roots Cracked

Q. I have a few vandas that have cracked roots and some that are very plump but yellowing. I am concerned this may be fusarium. I have treated with Switch already. I am hesitant to cut the stalk to check for the ring because I did that once and found no ring but ended up killing the vanda. Can you take a look at these roots and tell me it is a disease or just normal root death?

A. I think your vandas look totally happy and fusarium is probably not an issue. If it were fusarium, it would be travelling up the stem and lower leaves would be infected and dropping, and that doesn't seem to be what's happening. More likely it is just the natural aging process. It is a sympodial orchid that is growing upward and adding several leaves each year, so the bottom stem slowly gets woody and the roots attached to the woody dying stem likewise perish, but their function is replaced by the roots that emerge higher up. I'm starting to see new rootlets on my vandas, it's that time of year. I cut away the nonviable roots as they are brought out in the spring, just to get the pleasure of seeing all the roots green up when watering and fertilizing.   (May-17)


Cattleya Sheath Doesn't Develop
 

Cattleya Sheath Doesn't Develop

Q. This cattleya has just finished blooming two beautiful fragrant blossoms. I just noted a dark discoloration at the base of one of the leaves. The rest of the leaves appear to be fine. It had a small amount of scale at the base which I treated and otherwise has been healthy.

A. That scale infestation might have been a little worse than you suspected, it looks like it destroyed the tissue at the base of the pseudobulb. Scale will move from plant to plant, it also comes into your growing area from your outdoor plants. You should probably consider the possibility that you have scale somewhere on your plants, most likely in the papery sheaths at the base of the plant or in leaf axils. Put on your bathing suit, get a spray nozzle set on flat, and go through your cattleyas. Blast away all the papery sheaths on older growths, if they don't want to come off the younger growths, don't force them, but blast the plants and see what you find. When you're done, if you found scale, you can spray them all with a suitable insecticide.   (May-17)


Fusarium in Phalaenopsis
Fusarium in Phalaenopsis
Fusarium in Phalaenopsis
 

Fusarium in Phalaenopsis

Q. I have had my own catastrophic event with my phalaenopsis this winter. I have hundreds of phals and thousands of phal seedlings growing in my basement that represent more than 20 years of hybridizing. During one cold night I left the window open and the plants directly in front of the window got chilled. About a one month latter the plants started getting yellow spots that progressed to sunken areas followed by leaf death.
  The small necrotic spot at the center line of the leaf is frequently the first symptom usually at the base of the leaf. Sometimes I detect a very pale purple discoloration in the leaf that turns into a sunken spot on the underside of the leaf.
  Thanks for your article on cold stress and secondary fusarium invaders. I clicked on the link you provided and looked at the control page for fungicides. The fungicide “Switch” you recommended did not get a positive rating in the chart. I am confused as to why you chose this. I have been trying Daconil and Physan 20 but I don’t think they are preventing the spread. Can you suggest a drench for the whole pot?

A. The Switch recommendation came from Hark Orchideen, a most excellent site to assist in the diagnosis and response to disease organisms. It was this site that led me to the fusarium diagnosis after my heater failure. Their website says "In the case of Fusarium infestation at the base of the leaves, spraying with Cyprodinil + Fludioxonil (Switch) can be useful to stop it spreading in the stand and get the infestation under control." Their recommendation for the use of Switch is basically to stop the spread of fusarium on the aerial parts of the plants, not to treat the basal or rooted portion. For drenches, Daconil, Heritage and Empress are highly rated.
  I have about a dozen plants that looked like they survived the infection and the next winter began displaying the symptoms again, from which I can only conclude that fusarium is incredibly difficult to eradicate. You may also have to get out the razor blades and cut away the severely infected tissue and then keep spraying and drenching.   (May-17)




 
image