Garden chrysanthemum

Rusts

What you will see

Pale spots on leaves that turn into spore pustules mainly on the underside of leaves (orange, yellow, brown, black or white); in severe attacks yellowing and early leaf drop.

The source says: chrysanthemums may be severely weakened by white rust.

How to protect

1. Prevention

   • Grow in warmth, sun and free-draining soil; tarragon dislikes damp, so do not overwater.
   • Clear fallen leaves, remove diseased parts quickly, clean tools and weed.
   • Do not over-feed with nitrogen — soft new growth is quickly attacked.
2. By handFor light attacks, strip off affected leaves early; remove large amounts carefully. Do not compost summer/autumn debris (spores overwinter).
3. Chemical — only when nothing else helpsFungicides are not recommended; for edible crops, gardeners have no fungicides available with good efficacy against rust.

Powdery mildews

What you will see

White powdery coating on leaves, stems and flowers; leaves may become distorted.

The source says: it is among the ornamental plants susceptible to powdery mildew.

How to protect

1. Prevention

   • Destroy fallen infected leaves in autumn; do not over-feed, and protect from drought (stress invites powdery mildew).
2. By hand autumnPrune out infected shoots early and destroy fallen leaves.

Grey mould

What you will see

Fuzzy grey-brown mould on dying buds, leaves, flowers and fruit.

The source says: it is among the perennials susceptible to grey mould.

How to protect

1. Prevention

   • Reduce humidity, improve airflow and do not plant too densely.
2. By handQuickly remove dead and affected parts (carefully, as spores spread easily), ideally into a bag.

Aphids

What you will see

Colonies of tiny insects on shoots and buds, sticky honeydew, curled leaves.

How to protect

1. Prevention

   • Check plants regularly from spring.
   • Encourage ladybirds, hoverflies, lacewings and parasitic wasps.
2. By hand as soon as it appearsRub off colonies by hand or wash them off with a jet of water.
3. Biological spring to summerRelease lacewing larvae, aphid midge larvae or ladybirds.
4. Gentle spray in a heavy infestation, repeatPotassium soap (fatty acids) or plant oil.
5. Chemical — only when nothing else helps only as a last resortA product authorised in your country against aphids.

Thrips

What you will see

Silvery speckling of leaves and flowers.

How to protect

1. Prevention

   • Outdoors, plants usually survive even with silvery speckling; encourage natural enemies.
2. BiologicalPredatory bug Orius laevigatus and mites (mainly in the greenhouse).

Spider mites

What you will see

Leaves are speckled and bronzing, with fine webbing on the underside.

How to protect

1. Prevention

   • Reduce dust and water stress; do not use broad-spectrum insecticides, which cause mite outbreaks.
2. By handA strong jet of water on the underside of leaves.
3. Gentle sprayInsecticidal soap or oil, thoroughly on the undersides; only after mites are confirmed.

Verticillium wilt

What you will see

Yellowing and wilting leaves, dieback of shoots.

How to protect

1. Prevention

   • Do not carry soil on tools and shoes; control weeds.
2. By handDig up a confirmed plant with its roots and destroy it; consider grassing over the area or a resistant replacement.

Leaf spots

What you will see

Brown to black spots on leaves; leaves turn yellow early.

How to protect

1. Prevention

   • Remove old leaves before they infect the new season.
   • Do not wet the leaves when watering; keep the plant unstressed.
2. By hand after the first spots; in autumnRemove affected leaves at once and destroy them; collect fallen leaves in autumn.

Root and crown rot

What you will see

Softening of the crown and roots; the plant wilts and browns despite watering.

How to protect

1. Prevention

   • Free-draining soil, no waterlogging (especially in winter).
   • Do not plant too deep.
2. By hand at the first symptomsDig up the affected plant; improve the soil with drainage; do not replant in the same place.

Lace bug

What you will see

Pale speckles on the leaves.

How to protect

1. Chemical — only when nothing else helps as per the labelOnly if the damage is severe: a product authorised in your country against: lace bug.

Chrysanthemum white rust

What you will see

Pale yellow spots on the upper leaf surface that later become sunken and brown; lumpy pale spore pustules on the underside that turn white in humid conditions.

How to protect

1. Prevention

   • Check plants regularly.
   • Keep newly bought plants or cuttings separate from your other plants for several weeks.
   • Do not take cuttings from affected plants.
2. By hand as soon as it is foundRemove and dispose of affected leaves; dispose of heavily infected plants completely.