When rose shoots wilt or die for no apparent reason, the shoot borer may be at work. The larvae feed inside the stalks, often only a small borehole is visible. How to recognize and fight the rose pest.
In a nutshell
- Rose shoot borers belong to the sawflies
- two different types in which the damage is slightly different
- Rose shoots can wilt or break off
- Cut out infested areas to combat
- other control measures show moderate success
Recognize rosette borers
Two different shoot borers feed on roses:
- Cladardis elongatula
- Roseate Borer (Ardis brunniventris)
Both insects are difficult to distinguish from their external characteristics because they are very small. They are only a few millimeters long when fully grown, are dark in color and have yellowish legs.
The larvae almost double in size and are brightly colored. Because of their way of life, they are also called tube worms.
life cycle
Feeding passage of the descending roseshoot borer (left) and that of the ascending one (right)
The females lay their eggs on the rose shoots in spring. The larvae eat their way inside and, depending on the species, form very specific feeding passages:
- Upward-climbing borer: Beginning at a branch, larvae eat upwards, length of the feeding tunnel up to 10 cm
- Descending shoot borer: Eggs at shoot tip, larvae eat downwards, feeding passage about 4 cm long
After they are fully grown, they leave the rose in early summer and overwinter in the soil around the plant. They pupate there the following spring. The finished insect hatches, multiplies and can immediately lay new eggs on the rose.
damage picture
Whatever the species, since they eat the inside of the shoots, they cause them to wilt over time and eventually die. In the early stages, hardly anything can be seen from the outside, only tiny holes can be seen on the roses, sometimes there are also small crumbs of larvae droppings at this point.
Ardis brunniventris
The adult insects do not harm the roses. Only the respective larvae eat the marrow of the shoots. Suddenly breaking off branches can be an indication of the descending borer. These are then eaten hollow inside.
Notice: Roses do not always respond to the shoot borer. Sometimes you don't notice them and the only damage is the small holes in the shoot.
Fight rosette borers
1. Cut back roses
This is the most important and most promising measure of all. As soon as the infestation is recognizable, the affected shoots should be cut generously from the plant. Cut down to healthy wood. So that the animals cannot complete their development cycle, do not wait until after flowering, but act immediately.
A generous pruning has proven its worth when infested by rose bush borers.
2. Dispose of infested plant parts
Any parts of the plant where the larvae might be should not be discarded on the compost. They belong in the household waste or are incinerated.
3. Fight larvae in the shoot
Depending on the size of the hole in the shoot, the larvae sitting inside can be expelled with the help of a thin wire. However, this requires not only a lot of patience but also a sure instinct.
4. Control of adult insects
To prevent an infestation with the larvae of the shoot borers in the first place, the adult insects can be treated with the appropriate pesticides in the spring.
5. Disturb larvae
Since the larvae overwinter in the ground, it makes sense to regularly hoe and loosen up the area around the rose plants. This not only disturbs the larvae, but also the pupae come to the surface and may be found and eaten there by beneficial insects.
Notice: There is hardly any pesticide that reaches the pests in the rose. Therefore, it does not make sense to use chemical pesticides.
Prevent
It is not easy to prevent the rose shoot borer. The most important thing is to only choose young plants that are strong and healthy. These are naturally more resistant to pests. More options:
- Plant-based tonics, for example nettle manure or horsetail broth
- regular pruning that is not too tight keeps the roses young and vital
- frequent pest control
Freshly prepared nettle manure
frequently asked Questions
Does the rose shoot borer have natural enemies?It is difficult for most beneficial insects to get to the borer once it has started feeding. Nevertheless, it makes sense to encourage beneficial insects in the garden, as they can protect the roses from other pests.
Can the rose shoot borer kill the roses?Since the insect prefers young, soft shoots, it normally cannot kill the rose. Unless they are very young specimens or plants that are additionally weakened for other reasons.
How do you keep roses healthy?In addition to choosing robust varieties and the right location, proper care plays a major role. Roses need to be pruned regularly. They need fertilizer, water during dry periods and, if necessary, winter protection. With all these measures you can prevent both pests and diseases.