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Pests and Diseases


Slugs and Snails

These can be a real threat to newly planted Dahlias, both to seedlings
or green plants, and the new growth on tubers.

Apply slug and snail bait at planting time, and if not using one
of the moisture proof ones, reapply at regular intervals.
If your Dahlias are planted as part of the general garden, scatter the bait
amongst old established plants such as lilies, red hot

Thrips and Mites

These occur all through the season, and by using a insecticide
at regular intervals they can be kept under control.

Red Spider

These minute spiders attack during dry weather, and feed off the foliage
and will eventually destroy the whole plant if not treated.
Normal insecticides aren't usually very effective, so use a mitecide
for these pests.
Yellowing and browning of the foliage are the visual symptons.


These can cause a lot of damage to buds, foliage and blooms.
Some growers screw up newspaper into a loose ball and place it
in amongst the foliage. The earwigs crawl into the paper to hide, and they can then
be disposed of quite simply, either by squashing them, burning the paper in the incinerator
or dropping it into a bucket of hot water. Alternatively, you can spray at regular
intervals with a systemic spray to keep them under control.
Hollow canes can be a good hiding place for earwigs, so a small amount of insecticide
or spray mix can be poured into the canes to kill off these pests.
There are several herb type plants which can be grown in amongst or along the front border
of your Dahlias, which will act as deterrents. The common Marigold is very good for this.
There are also herbal sprays on the market which work well, and these don't kill the predatory insects such as Praying Mantis
or Ladybird, which should be encouraged.


There are two main categories of diseases when dealing with Dahlias.These are viral and fungal.

Powdery Mildew

Planting too close can cause a lack of air circulation around the plants.
This in turn can lead to the formation of Powdery Mildew, which forms a white
coating on the leaf surface. Remove the bottom three or four leaves on each stem,
and thin your bushes out a bit and this will improve the air circulation.
Using a systemic spray at regular intervals will also prevent this problem from occuring.

There are many kinds of viral diseases, and many of them have no cure.
The best thing to do if you suspect a virus is present in certain plants,
is to pull the affected plants up immediately and dispose of them
by burning or dumping. Don't put them into your compost bin!

Some of the signs of virus are lack of vigor, wrinkled contorted leaves,
unusual light green or yellow spots along veins, drooping florets,
clusters of multiple shoots instead of the normal one or two.

Take some of the affected leaves into your local garden shop,
or if you belong to a Dahlia Club seek help and advice from the experienced growers there.