Wisteria pests and diseases to watch out for

Wisteria pests and diseases to watch out for

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Wisteria is generaly a problem free climbers with lack of flowers being the usually compliant or wilting and yellowing leaves, but like all plants, there are a few wisteria pests and diseases to watch out for. But as some of these cause the plant to not flower or to dieback they can’t be ignored.

Here’s how to identify what’s wrong with your wisteria and what to do about it.

Wisteria pests

Scale insects

Wisteria Scale Insect and How To Control Them

Scale insects were first found in Britain in a garden in London on 2001. These insects, with a soft-body beneath a hard shell, suck the sap of your wisteria leaves. They leave large, brown-black scales on the stems of the plant.

Wisteria scale insects are larger than other types of scale insects. You find the mature insects in the late spring on the stems of the wisteria. These insects often develop heavy infestations and thickly cover the stems. They deprive the wisteria of energy and the plant dies back.

What to do

If you have only a few scale insects on your wisteria, you can ignore them. Healthy plants can handle light infestations of these insects. The trouble arises when many insects move in.

Try an organic spray, such as natural pyrethrum, in May or June when the insects are newly hatched and vulnerable. You need to keep reapplying such types of pesticides as they have a short life.

For heavier use, use an insecticide that contains the organic compound acetamiprid, such as Bug Clear Ultra.

Always follow the instructions on the bottle of spray or insecticide.

Vine weevil grubs eat the roots

Vine weevil larvae eat the roots of wisteria which causes the wisterias to wilt and eventually die if not controlled

Vine weevil grubs are often found in the roots of wisteria grown in containers. These are insects of which the adults eat the plant leaves and cause notches around the edges; the grubs snack on the roots.  

The adults appear in the spring to late summer and the grubs in the summer through to the next spring. The adult vine weevils are about 9mm long and are dull black with yellow marks on the wing cases. The grubs are white and legless and grow up to 10mm long.

Plants can wilt and die in the autumn and winter as the grubs eat the roots.

What to do

Keep a look out for the notches leaves in the spring and summer so as to catch the adult weevils before they create the grubs. Pick off the adult weevils by shaking the shrubs over newspaper. Use sticky barriers around the plants to trap the adults. Encourage birds, frogs and hedgehogs into your garden as these are the vine weevils’ natural predators.

As for insecticides, use one such as Bug Clear Ultra Vine Weevil Killer as a liquid applied to the compost. This is an insecticide that contains acetimprid, an organic compound. This gives your plant four months protection form grubs. Treat the plant with this in mid- to late summer to cover the autumn to spring period.


Powdery mildew

Powdery mildew attacks the leaves and causes a white mould to spread to the leave and stems

Powdery mildew is a common fungal disease that’s difficult to spot on wisteria. It usually results in a white dust-like coating on the leaves, stems and flowers. Look closely to find this on your plant from spring onwards. You may also find irregular brown blotches ringed in yellow on the leaves as a symptom of this disease. And the leaves may wilt.

 Powdery mildews may not cause significant damage to the plant.

What to do

Remove any infected leaves from the plant. Destroy any fallen infected leaves in the autumn so that the spores won’t spread during the winter. Make sure that the plant is in its best environment so that it grows to be healthy and strong. Ensure good air circulation around the wisteria and that the soil is well-drained.

As for chemical solutions, you can use fungicides on the leaves to target the fungus. Consider a  combination insecticide and fungicide if you also have a pest problem.

Phytophthora root rot

Phytophthora root rot is a disease in the soil that attacks the roots causing them to rot

This is a common cause of root and stem decay in many plants, including wisteria. It’s caused by microscopic fungus-like organisms that create the root and stem bases of plants to decay. The organisms live in the soil where they may hang around for several years.

The roots of your wisteria are well decayed before you notice any symptoms above ground. The root problems are not exclusive to root rot and result in the plant not taking up enough water and nutrients. You may notice that the leaves are yellowing or wilting and the branches are dying back.

If you examine the roots below ground, you see that the root system has been disrupted. Many of the smaller roots rot away and all show evidence of decay.

What to do

Expose the roots and cut away all that are decayed or dead. If this leaves you with very few roots, then you have to pull up the plant and destroy it. If you can save enough of the wisteria, rework the soil so that it drains well and doesn’t become water-logged. Standing water is a prime environment for phytophthora root rot. There are no chemical treatments for this disease.

Honey fungus

Honey fungus is a collection of different species of a fungus that attacks a plant’s roots. It’s difficult to spot as its main symptom is a white fungal growth between the wood and the bark of the plant’s trunk mainly at ground level.

You may notice groups of honey coloured mushrooms on infected stumps in the autumn. This fungus can cause your wisteria to die in parts or totally. The leaves may be pale in colour and smaller than expected and the plant may not produce flowers. The ;eaves may also wilt. Below ground, the roots begin to decay and die.

What to do

Stopping the spread of this fungal virus between your plants is the main step in its control. Place a barrier of pond lining material between the plants below the soil so that it also sits 2cm to 3cm above the ground. That’s about it for what to do – there are no chemical controls available to help with this problem. You may need to remove and destroy the entire plant if it becomes heavily infected.

Coral spot

coral spot fungal disease
coral spot fungal disease

The coral spot fungal disease may show up when your wisteria is already weak and sickly. After a branch of the plant dies, small coral-pink spots form. This indicates that the plant has a lot of other problems.

What to do

When this happens, you probably know that your wisteria is in trouble. Treat as many of its problems as you can. Prune out any infections and dead material as soon as possible.

I have also covered some other wisteria problems in this guide.

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