CSLB C-27 Landscaping ContractorPlanting and LandscapingHard
A client reports that newly planted roses are exhibiting distorted, crinkled leaves with a mosaic-like pattern, and some flowers are unusually small and malformed. The symptoms are spreading to nearby rose bushes despite insect control efforts. What is the most likely cause of these symptoms?
- ASpider mite infestation in hot, dry conditions.
- BSevere nitrogen deficiency due to inadequate fertilization.
- CRose Rosette Disease (RRD) caused by a virus.
- DBotrytis blight (gray mold) due to excessive moisture.
Show answer & explanationAnswer & explanation
Correct answer: C. Rose Rosette Disease (RRD) caused by a virus.
The described symptoms – distorted, crinkled leaves with a mosaic pattern, and malformed flowers – are classic indicators of Rose Rosette Disease (RRD). RRD is caused by a virus transmitted by the eriophyid mite (Phyllocoptes fructiphilus) and is highly destructive to roses, often leading to plant death. Its spread despite insect control for common pests suggests a mite-vectored disease.
Why the other options are wrong
- A. Spider mite infestations cause stippling (tiny dots) on leaves, fine webbing, and leaf discoloration (yellowing/bronzing), not crinkled, mosaic-patterned distortion.
- B. Nitrogen deficiency typically causes yellowing of older leaves and stunted growth, not distorted or mosaic patterns.
- D. Botrytis blight causes fuzzy gray mold on flowers and buds, and can lead to rot, but not leaf distortion or mosaic patterns.
Rose Rosette Disease (RRD)
A fatal viral disease of roses, transmitted by eriophyid mites, characterized by distorted, crinkled leaves, mosaic patterns, witches' brooms, excessive thorniness, and malformed flowers.
- Caused by a virus, spread by eriophyid mites.
- Symptoms include distorted, crinkled, mosaic-patterned leaves; redder than normal new growth; witches' brooms (abnormal clusters of shoots); excessive thorniness; and malformed flowers.
- No known cure; infected plants should be removed and destroyed immediately.
- Can affect all types of roses, especially multiflora rose.
Memory trick: Rose's RRD: Red, Ragged, Ruined - a mite's deadly gift!