Rosemary pests

Rosemary contains anti-bacterial and anti-fungal properties, which means that it is relatively trouble-free plant.

However, there are some pests that sometimes affect rosemary and we list the main ones below.

Just click on the pest to find out more about it and how to deal with it.

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Rosemary
Beetle

Pestbeetle

Froghopper
(Cuckoo spit)

Pestfroghopper

Tortrix
Moth

Pesttortrix

Leaf
Hopper

Pestleafhopper2

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Rosemary Beetles
Chrysolina americana

A native of southern Europe, this beetle was first discovered in the UK in 1994 at RHS Wisley. Since then, it has established in southern England and is reported from most English counties. Rosemary beetle is, at present, more or less absent from northern and southwest England, Scotland, Northern Ireland, Ireland and Wales. The adults are not very good fliers so the movement of infected plant material is the main way this pest spreads.

Identification of the adults is easy, the 6-8mm long beetles are unmistakable. The larvae are like small greyish-white slugs with darker stripes and when fully grown are 8mm long.

Both larvae and adults eat the leaves and flowers of rosemary, lavender, sage and thyme.

Pestbeetle1

Symptoms

Dieback of young shoots.

Leaf loss (this can be severe).

Death of plant.

First Aid

Give the plant a vigorous shake to dislodge the beetles into a suitable container (some recommend an upturned umbrella).

Squash the grubs. Prune out badly damaged areas of the rosemary and feed the plant to promote regrowth.

Biological Control

The only effective control is Homo hortus - the gardener!

Sprays

There are no totally effective (or safe) sprays in our opinion. Manual control is best.

If a plant is badly damaged the cost of a replacement plant may be less expensive than buying a chemical spray.

If you must spray, then do so only when there is no risk of the spray affecting beneficial or pollinating insects. For example, late evening or when the plant is not in flower (ideally both).
 

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Froghoppers (Cuckoo spit)
Philaenus spumarius

We only list this as a pest because people ask us how to deal with it. Froghoppers are only a "pest" in the larval stage. The larvae protect themselves by exuding a mass of sticky bubbles as they feed.

Pestfroghopper1

Symptoms

A frothy white mass around the stems, usually near the tips.

First Aid

Simply wash off with a strong jet of water

Controlling froghoppers

No biological or chemical control is needed.

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Carnation Tortrix Moths
Cacoecimorpha pronubana

In some years this can be quite a nuisance. The caterpillar of the moth uses silk to "stitch" leaves together to make a protective enclosure. The caterpillar then eats the leaves (and sometimes the stem), which leads to unsightly brown patches or even dead sections. The dead sections can look a little like rosemary beetle damage.

The moth usually has two generations each year in June/July and later in August/September. In a mild year overwintering eggs can produce an April/May flush of caterpillars too.

Although a plant can be made to look really tatty by this caterpillar it rarely kills the plant and the enforced pruning out of affected parts often results in a bushier plant.

Pesttortrix2

Symptoms

Leaves rolled or stitched together with silk.

Holes in leaves.

Sections of dead leaf or stem.

First Aid

Remove affected parts, squash grubs or leave them on the bird table!

If the infestation was severe feed the plant to help it recover.

Biological Control

No effective controls for the gardener to use. The best control is to keep an eye out for it and deal with it as soon as possible by physical removal.

Sprays

The caterpillar is protected by the leaves it has rolled together so sprays, even environmentally-friendly ones, will not work.

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Glasshouse and Sage Leafhoppers
Hauptidia moroccana and Eupteryx melissae

Leafhoppers are small (2-3mm long) torpedo-shaped, sap-sucking insects.

Both the adults and larvae feed on the underside of the leaves and cause small spots that go right through the leaf. They affect a large number of plants besides rosemary.

In protected environments it can be a serious pest. As well as disfiguring leaves, leafhoppers can transmit plant viruses.

This pest is rarely a serious problem with rosemaries grown outdoors.

Pestleafhopper1

Symptoms

Pale spots on the leaves.

Adults fly erratically when disturbed and can be mistaken for thrips or whitefly.

First Aid

Move the plant outdoors - this allows natural predators a chance to attack the leafhoppers.

Do not place the infected plant near any other members of the mint family (e.g., basil, lavender, mint and sage) to avoid cross-infection.

If you cannot move the plant then suspend a yellow sticky trap above the plant and brush the foliage with your hand. The disturbed leafhoppers should land on the traps.

Repeat regularly to trap subsequent generations.

Biological Control

There is no effective biological control for leafhopper in rosemary.

Sprays

As organic growers we never use, or recommend the use of, systemic insecticidal sprays - especially on a plant you might eat!

Sometimes it is necessary to resort to some form of spraying, in which case:

  • is it worth it? Sometimes a new plant can cost less than a spray!
     
  • use a pyrethrum-based spray. We find rosemary scorches when soft-soap (fatty-acid) sprays (for example, Savona, Bayer Organic Pest Control) are used. Also, the urea-based SB Plant Invigorator causes blackening of the growing tips. It is a common misconception that liquid detergents are effective against plant pests.
     
  • do not spray when bees, wasps or hoverflies could be affected. Spray in the late evening.

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Pestbeetle Pestfroghopper Pesttortrix Pestleafhopper2