Hello. I have four knocko... #200257 - Ask Extension


Hello. I have four knocko... #200257

Asked July 18, 2014, 8:10 AM EDT

Hello. I have four knockout rose bushes that are dying in the front of my house. (See pictures). I planted them during the fall of 2012. Last year during the spring some kind of bug ate the leaves (we saw little holes in the leaves), so we sprayed them with Sevin, and they seemed to do okay. This spring it looked like the same type of bug was eating the leaves again (similar holes in leaves), so we sprayed Sevin again. This seemed to fix the holes in the leaves problem, but later the leaves started turning yellow and have now fallen off (see picture). We have a soaker hose, so they do get watered regularly. The bushes are in a spot that gets sun late morning to late afternoon. Any idea what could be causing the leaves to fall off/how to remedy this? Should I just pull them out and plant something else there? Any recommendations for what else to plant?

St. Mary's County Maryland

Expert Response

We think that there is a combination of factors going on here.
First off, the area looks wet. How deep is your mulch? It should be no more than 2 inches or so, and definitely pulled back from the base of the plants. It should not touch the stems or crown. We would also recommend pulling it back from your home's foundation too. You do not want to hold water against your foundation or you encourage future pest problems. Additionally, consider putting on an addition to your downspout to move the water further into your yard to slowly soak in the ground there.
You should check the root areas around your roses. Use a screwdriver to see where water is going and how wet it is. The soil should feel damp and cool but not wet. Adjust your watering system.
How about soil? If you have never tested it, you probably should. Here are details to do that: https://extension.umd.edu/hgic/soils/soil-testing
When planted, was the garden new? How was the soil? Did you add any organic material like compost, aged manure or peat moss? If you have leaves in the fall, they make a great soil amendment- it helps to mow or crush them into smaller pieces first.
Finally, yes, the holes you saw were from a common pest here, the sawfly larvae, which look like tiny vibrant green caterpillars. The sevin would have worked on them.
 We can't tell, but it looks possible that they were planted too deeply or maybe just the mulch is too deep. You could try lifting them, improving the soil and replanting.

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