Pests & Diseases - National Dahlia Society (2024)

As shown in the photo, dahlias attract insects, some of which are harmful to the dahlia. Dahlias are also subject to several diseases which are described below.

1. Flowers & / or buds shrivelled and with fluffy white mould = Botrytis.
2. Flowers with mass of mites covering bloom (Generally seen when bloom brought into the house for decoration purposes) = Red Spider
3. Flowers with tattered petals = Earwigs
4. Flowers with light flecking on petals, many small long-bodied winged and wingless insects present = Thrips
5. Flowers with irregular holes and pieces eaten away and slime trail present = Slugs and Snails
6. Flowers with holes (centre of bloom) and petals with pieces eaten away; no slime trails present on or near flower = Caterpillars

1. Leaves with numerous pale spots = Smut
2. Leaves with white dust like covering = Powdery Mildew
3. Leaves variously crumpled with irregular, pale yellowish patterns with insects visible more so with a magnifying glass = Red Spider
4. Leaves variously crumpled with irregular, pale yellowish patterns with no insects visible with a magnifying glass = Virus
5. Leaves wilt; stem interior with brown or black streaks = Wilt
6. Leaves with irregular holes and pieces eaten away with slime trails present on or near plants = Slugs and Snails
7. Leaves with irregular holes and pieces eaten away; no slime trails present on or near plants = Caterpillars
8. Leaves with small tattered holes, especially at tips of shoots; buds sometimes killed = Capsid Bugs
9. Leaves, shoots and flowers infested by colonies of black, green or yellow wingless and winged insects; Foliage sticky and sometimes sooty = Aphids
10. Stem with soft, irregular swelling = Crown Gall
11. Stem base rotted, cottony white mould growth present = Sclerotinia Disease