Question
Hi Will,
I have a 36" (from soil to tip of top frond) Dracnea in a 12" pot.  It appears to be quite healthy but last week as I was watering, I noticed 2, 1" white grubs lying on top of the soil.  Their lower halves were a dark grey fading almost to black at their very bottom.  All of my plants spend their summers on my screened porch, but this is the first time this has ever happened.  What are they, where did they come from, would it be reasonable to assume there are more and how do I get rid of them and prevent further infestations?
Plant problem 2:  The lower fronds on my corn plant start turning yellow at the tips and in about 2 days, the whole frond is yellow and eventually turns brown.  I do not let the soil dry out because of its shallow root system, fertilize about every 12 weeks and try to keep the fronds dust free.  I have had this plant for 5 years and it has been doing this for the last 18 months and in the last 6 it seems to be happening faster.  I treated it for mites (I used a Spectricide pest controller) this summer.  It hasn't seemed to help.  The plant still looks showroom healthy but if something is wrong, I would like to nip it in the bud now.  Do you know what it is and how to treat it?  It is in a 15" pot and is about 46" from soil to tip of top frond.
Thanks for your time, Will.
KB

Answer
Hi Kate,

Thanks for the detailed information.

Grubs are not commonly found in indoor potting soil. I can only surmise that the grubs gained access somehow through the screened porch or they were in the potting soil that you or the grower used. For that reson, I recommend using only sterile, peat-based soilless potting mixes.

The grubs are unlikely to do any damage to your plant, but I am sure you don't want them inside the house. You may have found the only one in there, in which case you may not want to do anything until you see more of the critters. You could try plunging the pot up to its rim into a tub filled with clear water. Leave it for about an hour. The flooding should force the grubs up and out of the soil. Finally, a systemic pesticide applied to the soil as a drench would work if nothing else does.

I am not sure what to say about your corn plant. The yellow leaves could be caused by spider mites or by a root-related problem. Spider mites appear as tiny dust-like particles on the undersides of the leaves. If that is what you find, let me know and I will provide treatment instructions that are safe and effective.

I am concerned that you may be keeping the soil too moist. Corn plant roots are not shallow. Your plant should be watered thoroughly until some water runs through the drainage holes. Then you should wait until the top third of the soil feels dry before watering again. In addition, a 15" pot is quite large for a 4-foot corn plant and overpotted plants are subject to root rot.

In this contaxt, if your corn plant is the cane-type, then squeeze the lower portion of the bark-covered cane. If the bark is loosed and papery, then the roots have rotted and the cane is on its way out.

If you e-mail a photo of your corn plant to me I may be able to detect something else that would help you.

Please let me know if any of this is unclear or if you have any additional questions.

Regards,
Will Creed, Interior Landscaper
Horticultural Help, NYC

You can E-mail me directly at: [email protected]

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