Last updated on February 18th, 2022
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Buddleias embody both beauty and strength, making them popular in gardens across the world and in some countries, there are even classed as invasive. These plants grow vigorously, and if left to their own devices, they can overtake the garden and be difficult to control.
However, no matter how strong these plants are, they are not immune to disease and pest attacks although most are not deadly, some will disfigure the foliage.
Below I cover several diseases and pests that can affect buddleia, some very common such as mildew and Aphids, some now so common but still worth watching out for.
Most of the diseases that affect buddleia are fungi related, therefore, moisture regulation is important to avoid issues such as root rot or downy mildew.
Downy mildew – grey mould on leaves and stems
Downy mildew is a common disease for buddleia but it’s common in a lot of other plants too, however it’s usually not fatal but can leave plants looking very unsightly. The fungal infection thrives in humid areas with cool temperatures. This infection manifests on the underside of leaves as a grey mould and eventually deforms the leaf. Ventilation is vital in keeping the plants from recurring infections.
Downy mildew is treatable using specialised copper fungicides or organic methods such as using neem oil sprays. I recommend removing badly affected leaves and treating at the first signs of mildew.
Root rot – Yellowing and drooping leaves
Root rot is a death sentence for most plants because it kills the roots. Root rot arises from Phytophthora and Rhizoctonia, which are both members of the water mould family and it invades the plant slowly. These microorganisms thrive in water-logged soils, and the disease has no chemical interventions that are proven to work as far as I am aware. Tell tail signs are yellowing and drooping leaves which eventually fall.
The best you can do to prevent root rot is to use well-drained soils which is the case with most plants and avoid overwatering. Infected plants should be removed and disposed of. With root rot prevention in the first place is key.
Verticillium wilt – Yellowing leaves and shrivelling of lower leaves, wilting and dieback
Verticillium wilt is another disease that may attack your buddleia as well as other plants. Although the occurrence is rare, it is good to know what to do just in case. This disease cannot be treated as a viable control method is yet to be found. It attacks the roots, causes the discolouration of the leaves, and eventual dieback of the stem. If you cut affected parts of the plant you will usually see black streaks down the inside of stems or in circular patterns in large branches.
If you have buddleia affected by this disease, you can try and encourage new growth and they sometimes recover in cool or wet conditions. Try feeding with an ammonium-based fertiliser (nitrogenous). Apply a nitrogenous fertiliser around the base of the plant. You can use sulphate of ammonia at 25g per sq m (1oz per sq yd), or urea at 50g per sq m (2oz per sq yd) one or two times during the growing season.
Ringspot virus affects the vigour of any plant it infects and is more common in the US but still rare. The virus will manifest spots on the leaves, causing mottling and discolouration of leaves. If left to spread to the rest of the plant, stunted growth is a possible outcome.
The disease is incurable; therefore, the best thing to do is to get rid of infected plants and leave the soil bare for a while for the nematodes to die.
Read next: How to kill invasive buddleias
Pests thats attack buddleia
Spider mites – Usually first indentified by the cobwebs
Buddleia shrubs are not the only plants that spider mites love to make their home. They invade hundreds of other plants found in the garden so there fairly common. These mites are not harmful to the plant in small populations, and you may not notice them because of their microscopic size. However, as the population increases, more leaves suffer as the insects continue to consume plant sap. Usually, the first sign of spider mites is the cobwebs they form on the plants.
Large populations cause wide scale discolouration of leaves, which affects the plant’s ability to make food. Control spider mite populations in your garden easily using insecticides or horticultural oil.
Aphids – caurse the leaves to curl and extrete honeydue that attracts ants
Aphids are probably the most common garden pests and they suck teh sap from plants and cause the foliage to curl but they also attract other unwanted pests too. As a by-product of feeding on plant sap, aphids produce honeydew on the leaves. The sticky and sweet substance attracts ants and other small insects further weakening the plant.
Aphids are also harmless in small populations but they can quickly infest plants. You can consider encouraging natural predators into your garden such as small birds which feed on aphids. You can also buy natural predators like parasitic wasps and ladybirds as a control measure and yes you can even buy these on Amazon.
Alturnentley, you can spray them with pretty much any pesticide you can get at your local garden centres and nurseries.
Read next: How to take buddleia cuttings
Nematodes such as those that cause the ringspot virus, require management before they invade the whole garden. Nematodes are not easy to control, but if you leave the soil bare for some time, the worm-like organisms will die off. Solarization has also proven to be effective in killing off nematodes from the soil.
Caterpillars – make holes in the leaves and can do significant damage
Since buddleia plants are butterfly magnets, you cannot miss a few caterpillars feasting on the leaves. Caterpillars eat the leaves, which affects the plant’s appearance, but they do not cause irreparable damage. Just remove them by hand or use a hose to force them off the plant. You can also consider spraying with a pesticide.
Japanese beetles – eat te leaves, leaving behind a skeletal appearance
Japanese beetles are voracious foliage eaters that affect the plant’s appearance. Unlike caterpillars, they consume the whole leaf, leaving behind a skeletal appearance. These insects, just like the others, are not dangerous in small populations, but if the population increases, the use of Pyrethrin insecticides will help control them.
Weevils – caurses patches on the leaves, which eventually discolour and die
Buddleia leaf weevils have a habit of laying their eggs on the foliage, which is harmless until the grubs emerge. These little grubs leave patches on the leaves, which eventually discolour and die. A plant with damaged leaves is unable to make food, which further weakens the plant.
Parasitic nematodes are a suitable method of control as they do a fantastic job of killing off these weevils or you can spray with pesticides.
It is difficult to protect your plants from all the pests and diseases, but you can try your best to prevent infections, especially with diseases. Remember to plant your buddleia in well-drained soil, space them for proper ventilation, and prune occasionally to remove diseased or dead sections.
With proper care and maintenance, buddleia will thrive and attract lots of butterflies into your garden.
Read next: Pruning buddleia, when and how