Box caterpillar and box blight
Box caterpillar and box blight can look the same from the point of view of the physical damage you see on the plants. With the damage caused by the caterpillars you will see cobwebs on the foliage
With Box caterpillar once treated the foliage will grow back with box blight the foliage will not grow back
With both problems feeding your box plants yearly with Growmore fertilizer and 4 feeds of liquid tomato feed through the spring and summer will keep them health and prevent diseases and pest attacks. Lots of gardeners and grows use high nitrate feeds to get the plants to grow to the required size but this can create soft growth prone to caterpillar and box attacks.
With the Box caterpillar attacks
- Where practical, caterpillars should be removed by hand
- Pheromone traps which can help monitor adult moth activity are available from several suppliers including Agralan, Dragonfli and Solabiol
- The mixed nematode biological control sold as Fruit and Vegetable Protection has some effect on the larvae
- Consider choosing alternatives to box plants (see below)
- There have been reports of birds such as blue tits feeding on the caterpillars in some locations. It is not yet clear if this predation will result in a reduction of box tree moth numbers
- Extensive infestations can be treated with an insecticide. Thorough spray coverage is required if control is to be achieved
- Forceful spraying is needed to penetrate into the interior of box plants through the webbed together leaves
- Organic contact insecticides containing natural pyrethrins (e.g. Bug Clear Gun for Fruit & Veg, Ecofective Bug Killer). Several applications of these short persistence products may be necessary to give good control
- More persistent contact insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Westland Resolva Pest Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer) and cypermethrin (e.g. Py Bug Killer)
- The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) is also available
With Box blight problems
Volutella blight is a disease of box caused by the fungus Pseudonectria buxi. Volutella blight has similar symptoms (twig and leaf death) to the more serious box blight, although the characteristic black streaks of box blight do not form and defoliation is not common. Spore masses, developing on undersides of leaves in wet conditions are pink for Volutella blight and white for box blight.
P. buxi requires wounds for infection and is associated with environmental stress or clipping in wet weather. It is not a serious disease and improving cultural conditions will usually lead to plant recovery. Diseased branches should be pruned out when the foliage is dry, and old fallen leaves removed from the interior of affected plants.
Box rust is caused by a fungus called Puccinia buxi. This is not particularly troublesome and seldom causes serious problems.
It can be seen as thickened rusty blister-like pustules on both sides of the leaves. The fungus forms only one type of spore which develops in autumn and winter and breaks through the epidermis of the leaves in spring. New leaves are infected in the spring and early summer. The fungus continues to grow during the summer and autumn and as a result the infected spots become thicker. Box rust does not have an alternate host.
To control it either clip off the affected shoots or spray with one of the fungicides labelled for rust diseases.The fungicides tebuconazole (Provanto Fungus Fighter Concentrate), tebuconazole with trifloxystrobin (Provanto Fungus Fighter Plus, Toprose Fungus Control & Protect), and triticonazole (Fungus Clear Ultra) are approved for the control of rust diseases on ornamental plants.
The following products contain a combination of both insecticide and fungicide, enabling the control of both insect pests and disease: myclobutanil containing cypermethrin (Resolva Rose 3 in 1, Rose Shield Bug & Fungus Killer, Roseclear Ultra Gun 2, Vitax Rosegarde) and triticonazole containing acetamiprid (Roseclear Ultra, Roseclear Ultra Gun).When a proprietary product contains an insecticide as well as a fungicide it would be preferable to use an alternative product if pests are not a problem on the plants treated.