Orchid Culture Questions and Answers
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Orchid Culture - Questions & Answers from This Month
by Sue Bottom, from the St. Augustine Orchid Society Newsletter
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Spotting on Cattleya Leaf Tips
Spotting on Cattleya Leaf Tips
 

Spotting on Cattleya Leaf Tips

Q. My Epc. Plicaboa has an ongoing problem with spotting on the backside of each leaf tip. I have treated it with Dithane and Thiomyl regularly, but the problem persists. It usually stays on the backside, however some of it shows on the front side of the leaf. The plant is fine otherwise, and blooms regularly, but the leaves are rather unsightly. I was told this may occur as a result of heat stress?

A. If I had to guess, I'd say bacterial brown spot. Spray with one of the copper compounds, they are great bactericides. Dithane and thiomyl are good fungicides, but won't work on a bacterial infection. You may have to remove the severely damaged leaf tips, but it is usually a pretty slow moving disease in adult cattleyas.   (Jul-17)


Fuzzy Growth on Phals
 

Fuzzy Growth on Phals

Q. What should my neighbor do with this orchid?

A. That looks like a mealybug infestation. If there are that many on the flower stem, they are likely also hiding in leaf crevices and on the roots. Get a spray bottle of isopropyl alcohol and spray the flowers, flower stems, leaves, etc. all the aerial parts of the plant. Check the plant every day for mealybugs because they are very difficult to get rid of. You can drench the pot with one of the pesticides containing imidacloprid. If they are on the roots, you may have to bare root the plant to find all the mealybugs and then repot.   (Jul-17)


Angraecum Leaves Yellowing
Angraecum Leaves Yellowing
 

Angraecum Leaves Yellowing

Q. This is Angraecum Lemforde White Beauty (sesquipidale x magdalene). Iíve had this plant for about 2 years, it has grown and bloomed a couple of times. It is prone to some leaf spotting fungus at the tip of the leaves because they are like saucers holding water. This year whatever is happening begins at the edge of the leaf closer to the base, it looks like brown edging. The roots look fine except they have no growing tips and the other angrecoids I have are busy growing roots now. I sprayed my whole collection a week ago with Banrot. About 3 months ago when this first started, I cut off the the edge of 2 leaves, sprayed with peroxide and that seemed to stop the process but itís back. Could it be fusarium wilt?

A. Looking at the plant, two possibilities come to mind. The most troublesome would be one of the bulb, stem or root rots like Fusarium or Rhizoctonia. I don't see the wilt, or the graying tissue like you might expect with Fusarium, and if it were Rhizoctonia, you would expect it to be moving up the stem affecting the lower leaves first, not the fourth and the eighth leaf up. So I'm guessing that is not the problem.
  The other possibility is that water has been pooling in the leaf axils causing the problem. It looks like there is some rot around the leaf bases and of course the leaves are so close together it would be easy for water to collect, and then opportunistic bacteria or fungi could start growing. If that is what is happening, pour some peroxide into the leaf axils and figure out a way to reduce leaf wetness.
  Lucy wrote back "I think you are right on the tightness of the leaves possibly contributing to the fungus at the axils. I realized recently that the angraecums that get direct eastern wind off the pond that the house back up to are happier campers. Wind so strong sometimes it knocks them over but the leaves dry quickly. Iím going to move the Lemforde and a couple of other cranky ones to a very similar windy position and see how that goes."   (Jul-17)


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