Aphids on roses is more about a decrease in aesthetic value than actual rose disease, for although Aphids represent the major insect pest of many rose gardens they do not cause much damage or spread any major rose diseases.
The physical impact is minimal, although they can weaken new shoots, especially just below the new flower bud or on tender new leaves that are just beginning to unfurl.
The first warmth of spring will bring the first aphids and they will remain until fall, some even wintering over if winters are not severe.
Understanding the Aphid Biology and Life Cycle
The rose aphid (Macrosiphum rosea) is only one of 4000 or more species of aphid, all of which vary in color, size, mating habits etc etc.Rose aphids attack (for food) roses, pyracantha, photinia and many fruit trees. The rose aphid bears live youngsters, near host plants. These winter over and hatch in the spring and become mothers. They are all born female with their young within their bodies. They give birth to other females who are already pregnant with other females.
Thus, within days, thousands of aphids can be produced, and keep producing! Then, in fall, some males are born to mate with the females to produce eggs for over wintering for the next years crop.
These female aphids (called Nymphs) are wingless and termed ‘stem mothers’ as they congregate in groups on the new shoots to suck out the fluids. They also give off a sticky substance called ‘honeydew’ which attracts ants and causes a ‘sooty mold’ or fungus which grows in the honeydew.
This honeydew is a food for ants and amazing as it may seem, ants protect the honeydew sources and have been known to farm the sticky substance by moving aphids from one plant to another!
Knowing these life cycle facts help us in controlling aphids on roses.
We Can Do Five Things
1. The aphids love us to fertilize our roses with high nitrogen fertilizer because it quickly produces the new shoots they love so much. So step one is to greatly reduce the nitrogen we apply to our roses.
2. Next try removing them with a gloved hand. Just by gently squeezing and rubbing we can remove most of them and this stops the constant breeding process. Falling to the ground they will quickly be eaten by predators and they are not good climbers.
3. High pressure blasts of water will remove most of them as well, and ants don’t like to be around the water also. Just make sure it’s done in the morning so the leaves don’t stay wet to cause blackspot.
4. We could also rely on natural predators, of which aphids have many. So, if you are going to spray, use a spray that is for aphids, not a general pest spray, or you remove the aphids natural enemies. Read labels carefully!
5. Finally, spray a dormant season application of lime-sulfur to kill the over-wintering eggs. Make sure this spray covers the ground below the bush and gets into all the nooks and crevices.
Be careful because it can stain fencing. Again, read the dormant spray label!…….twice!!!(if it says wear a mask it means wear a mask!!!!)
Aphids on roses are more a nuisance than a major threat of disease and they are easily dealt with. If you follow a yearly plan they shouldn’t be much of a distraction.