Question

Phlox   Hi, I'm located in upstate New York . My phlox are not looking good. The bottom leaves are withering and brown, the upper leaves are getting yellow areas. I had this last year .. After 15 years of trouble free and gorgeous phlox. I have a lot of phlox, they are the backbone of my garden. This spring I divided most  and cleared out almost 1/2 the plants hoping that would be the answer...but no.
What have I got going on here? Blight? mites? Blight and mites?
And most importantly, How do I stop it?

Answer
Hello Sue,

Withering and brown..hum. My candidates are aphids or spider mites. Both turn the leaves of phlox yellow and brown. Aphids multiply like crazy. They are basically able to reproduce without a mate, so you can go from having two to literally thousands. But, happily, they are easy to control.

If the leaves are also curling, you may have spider mites, which multiply in hot, dry weather.  Spider mites are more persistent, and you may have to treat your plants for a couple of weeks. You will know that you have them if you see tiny webs on your flowers.

Happily, both sets of creatures succumb to the same treatment- a sharp spray of water or insecticidal soap.There are two good ways to do it, and both are organic. The good thing about the aphids is that once knocked off plants they can't get up, and the birds come in and get them from the ground. If you have a garden hose with a spray arm, all you have to do is use the sharp spray setting, blast your plants, top and bottom (make sure that you get the underside of the leaves). Do this for several days in a row. Try not to skip a day, because if you do, like the Terminator - they'll be back!

The other alternative is to use insecticidal soap, which you can find in any garden center and many hardware stores. Buy the concentrate, dilute it in a spray bottle, and spray your plants, again, top and bottom, making sure to get the underside of the leaves, because they will hide there.

Lastly, if you are giving your plants a lot of fertilizer, hold back. Lush growth is a magnet for aphids. They love it. I used to overwinter a rose in my garage, so it was the first thing to break dormancy - long before outside plants. I would take it out of the garage to find it covered with hundreds of aphids, feeding away because nothing else was green. I would pull out my spray hose, give the plant a sharp spray for three days, and no more aphids.

Spider mites like heat and dryness.

Your act of clearing out about half your plants was an excellent strategy on your part, since crowded phlox tends to suffer from fungal diseases, and I believe you have prevented those.

Is this clear and helpful? If you have any other questions please do not hesitate to contact me.

Best wishes,

Donna