Roses come in a variety of growth habitats from bushes to shrubs including the huge climbing roses. Roses need a lot of care to prevent the common pests and diseases. Dropped leaves can be a symptom of poor cultural practices, disease, pests or chemical contact.
Roses like dry feet, which refers to the moisture level around the roots. The roots should not sit in moisture. The peripheral feeder roots gather water as needed. Roses require a medium amount of water and it is easy with vague specifications to over or under water the plant. This stresses the plant and it drops leaves. Over fertilization, improper soil type and pH will also stress the plant. Plants respond to stress by shutting down some functions until the conditions improve.
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Roses are susceptible to outside influences. Over spray is a term used when herbicides or pesticides are sprayed in windy conditions and the mist drifts onto plants that were not targeted. In the case of herbicide, the unspecified plant succumbs to the chemicals. The effects can range from visual to systemic damage and may cause the leaves to fall off the plant. Toxic runoff from sewage, contaminated water and other environmental hazards can cause defoliation.
Seasonal Change and Temperature
Seasonal change is a huge reason for defoliation. Roses are deciduous and lose their leaves when temperatures drop in fall. This is usually around October to November, depending on location. Roses need three to four months of chilling to encourage the blooms and signal the time to releaf. This is a natural process and may occur early if there are sudden cool temperatures or a freeze. The foliage changes colors to golden yellow before they fall off the plant. Extreme temperatures will also cause the leaves to fall.
Pest and Disease
Rose diseases that cause leaves to fall off are often signaled by spotting, deformation or other changes in the leaves. Roses are susceptible to fungal diseases, which can cause defoliation. Pests are common causes of leaf drop. Some leaves show the signs of specific pests. Dropped leaves that have notches taken out are due to earwigs or cutworms. Prolonged feeding by mites and aphids will cause the foliage to starve and fall off the plant. Many diseases and pests could cause the defoliation of a rose plant.
- The Olympia Rose Society: Pests and Diseases; December 10, 2010
- Washington State University: Rose Problems; Milo Ball; January, 2005
- Gardening Know How: Reasons for Rose Leaves Turning Yellow; Stan Griep
- Gardeners Monthly and Horticulturist V26: Roses in Winter; Thomas Meehan
- Gardening Guru: Rose Problems and Prevention