Tammy H. asks Annie:
Q What, other than mite infestation, would cause a stunted, tight center in av’s?
A Another great question, and one that I gave a short answer to on our Facebook page. I said, ” There could be other reasons, but, generally speaking, tight centers are often caused by too much fertilizer.” I knew there were other reasons, so I took this one to Joyce Stork.
Here is her excellent response:
Stunting is a symptom of a problem. It’s never a good sign.
I’ve heard people say that too much fertilizer causes tight centers, but the reason for it is more complicated. The excess salts of too much fertilizer (primarily the macro-nutrients of nitrogen, phosphorus, and potassium, cause burned edges along leaves. or the mottled yellow spots around the perimeter of outside leaves. When there is an excess of micro-nutrients in the plant and it reaches a toxic level, the center will stunt. The important thing here is that pH is often below 6 when this happens. When pH is in the 6-7 range, the plant is very unlikely to take on a toxic level of any micronutrient unless the grower is applying an exorbitant level (sometimes unintentionally because the tap water has too much of that element). This stunting looks as though the leaves have miniaturized or perhaps sported to a miniature size. At that stage it appears to be permanent and will not reverse even in leaf propagation.
Cyclamen mites are the most obvious cause of stunted centers and the symptoms of it may also include distortions on the leaves near the center, graying or failure of the leaves in the center of the crown, and /or twisting of flower stems with distorted flowers.
A fungus called botrytis blossom blight will also stunt center growth, but it is the final stage of a disease that first alters the color of the flower to be much duller than it ought to be. It is likely that other pathogens could also attack the center causing something much like stunt.
Pollution, such as a gas leak, will stunt centers also. If gas lines, or gas appliances (water heaters are the most overlooked) are anywhere near the growing area, the tiniest leak can cause problems. Typically it would be a small cluster of plants that is not growing well, and have stunted centers. Larger clusters could occur if the leak were larger. In my experience plants can grow out of this, once the leak is plugged.
INSV may also mimic stunt, depending on where the inoculation (usually feeding by thrips) occurs. INSV normally presents an odd combination of troubles which are unpredictable. If a grower had a number of plants growing with random distortions in different rows of leaves (not consistent from one plant to the next), with some having stunted centers, and/or spots on the leaf (especially circle-shaped marks), INSV should be considered, especially if that grower has also had an infestation of thrips. It is incurable.
Just a note, show plants, which have been disbudded and then are allowed to bloom, will often grow very compactly for a few weeks before loosening up again. This is a probably a response to ethylene gas and increased efficiency in growing. It is not stunt.
I hope this helps!
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