Pest on Rose Plants

(Question)

Every year my rose plants get a disease. After 1st blooming, the leaves are covered with beetles and small flies all over the leaves and leaves become brown and crinkle and holes. after that rose buds are eating by those insects. I can see some green color worms also here and there. All the other plants also get ruined by these pests. Please tell me what to do .
Thank you

 

(Answer)

Thank you for contacting Toronto Master Gardeners.

From your description, your rose bushes could be infected by aphids and/or sawflies.

Aphids are very common pests. Aphids are soft-bodied insects that can be red, green, yellow, or black. They feed primarily on newer leaves and on developing flower buds. Symptoms of aphid damage include malformed flowers and leaves which curl and pucker, turn yellow or brown and fall off. Aphids are often kept in check by natural predators such as lady bugs, lacewings, assassin bugs and pirate bugs. Alternative control measures include the use of strong streams of water to knock them off the plant, or insecticides as a last resort. (more information here)

The Sawfly (common rose slug) causes skeletonizing or window pane like damage to rose leaves in spring and early summer. The larvae look like caterpillars but are actually more closely related to bees and wasps. Common rose slugs are green with a light tan head and often have may hairlike bristles. Control can include hand picking and the use of horticultural oils or insecticidal soaps. (more information here)

Because pests frequently attack plants under stress, proper care and maintenance of all plant material will reduce the potential for problem development. The key to a healthy rose bush includes the following:

  • Pruning: Generally, the rose shrub should be pruned in early spring, at the end of its dormant season, which is April or May in Toronto, after the danger of a hard frost has passed. This is when the leaf buds are starting to swell and just prior to the start of new growth. As you pruned the shrub back in November, the rose may not bloom this year. Also, the type of annual pruning (hard, moderate, light) depends on the type of rose.  If you’re not sure of the type or rose, watch the shrub for a season. If it blooms on the new growth it sends out in the spring, prune it when it is just about to break dormancy (as above). If it blooms early (i.e., on last year’s canes), wait until after it flowers to prune it.
  • Removing dead-looking branches/weak stems: This should be done in early spring.
  • Ensuring good soil: Amend the soil with compost and well-rotted manure to provide a good growing environment. This provides nutrients for the rose plant, and also feeds the helpful organisms found in the soil.
  • Fertilizing: Use a fertilizer specially made for roses. In particular, phosphorus is needed for flowering (this is the centre number of the fertilizer) – e.g., A granular rose fertilizer ( 6-12-6) is an easy way to feed the rose bush. Follow package directions. It is recommended that the plant be fertilized in early spring, then just prior the blooming in June and a third time, in July. To ensure the plants can harden off before winter, fertilizing later than July is not recommended.
  • Watering: Water the plant deeply once weekly to ensure the entire root area is wet. If the top 5-10 cm (2 – 4 inches) of soil is dry, then water the plant.
  • Siting: Roses need full sun (at least 6 hours daily) in order to bloom. If, over the years, the area the rose bush is located has become shady (e.g., due to the growth of adjacent plants), see if you can alter the site (e.g., by cutting back other plants) to ensure full sun for the rose shrub.  If not, the shrub may need to be moved.
  • Good care throughout the blooming season: Deadhead faded blooms, get rid of suckers, and continue to remove canes/branches that grow towards the middle of the bush (the latter could compromise air circulation and access to light).

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