INSECTS are having a boom time, so cast a net or two to keep them at bay

GARDENERS all over the UK have been enjoying a very productive - and at times, very challenging - year in the garden. I don’t think the watering cans have been busier since the drought of 1976. Water has been one of many issues facing us in the garden this year, along with much activity from garden insects, but on reflection, it has been a very good year for most of our plants.

The hot weather can provide ideal conditions for insects. Only a few months ago we were alerted by a local contractor to a damaged Euonymus shrub in the garden; upon further investigation, we found a very large shrub measuring 4m x 4m which was totally defoliated. The culprit was the caterpillar larvae from the Euonymus ermine moth. The caterpillars were accountable for the total defoliation of large sections of hedgerows. They are never a long-term issue and don’t develop into plague-like proportions year after year. In this case, the damage had already been done so the affected branches and leaves were removed and burnt and the rest of the plant has grown back from the base with the help of plenty of mulch and a good watering for encouragement. Spraying the caterpillars was an option but the density of the webbing would have prevented the chemical from reaching the pests and from an environmental point of view, the removal of the infected parts of the plant along with the caterpillars was a better and more proactive approach.

Due to the warm weather – and in some cases, milder winters – insects are having a boom time. The caterpillar larvae of the small and large white butterfly are enjoying a very good year. At Harlow Carr we are using fine mesh and netting to protect our crops of cabbages and broccoli. It has been highly effective, not just with the butterfly pests, but also many other pests that love to frequent the vegetable plot such as carrot fly, cabbage root fly, pea moth, cutworms, leaf miner and onion fly.

Careful consideration must be taken when selecting the size and type of mesh you use. Most insect pests can be prevented from entering and attacking crops with a mesh size of 0.8mm x 0.8mm. The type of netting is also an important factor: while we want to protect crops from pests, we don’t want to catch birds. To prevent this, avoid using a very fine mesh and stick to the type recommended for the particular job. This type of mesh has a light reduction of 20 per cent and so can help keep plants cool during very hot spells, thus preventing leaf scorch; this is especially important with young seedlings.

Larger netting can be used to protect fruit, especially soft fruit. A larger mesh size is most effective if stretched over or supported by a metal frame or cage. We have a cage-style construction in the Productive Garden at Harlow Carr which does a good job keeping birds and vermin away from the blueberries and strawberry plants. Squirrels can also be a very determined pest and at times have been known to be rather keen on these fruits and so a stronger and more durable form of protection might be required.

Working at the RHS flower shows and on the advisory desk at Harlow Carr, I have responded to a large number of enquires about Viburnum beetle. These beetles can be detected by looking for small holes and shredding in the leaves, but they can be hard to detect and the best form of control is the removal of leaf litter and mulch under the shrubs in the autumn and spring. This will disrupt the overwintering adults and larvae and will also remove vine weevil. Damaged stems should be cut out and back to younger more vigorous growth that naturally forms at the base of the plant. Apply plenty of feed and water to encourage new growth.

There has been another small beetle that has appeared this year: the flea beetle. It has caused damage to leafy vegetables including the leaves of rhubarb. The damage appears similar to that of the Viburnum beetle but can be more noticeable and intense. They can be removed by sweeping a yellow sticky fly trap by hand just above the tops of the infected plants; the beetles are caught as they jump up and onto the sticky trap. Soap-based sprays can also provide a good means of control.

Another beetle that can often be mistaken for a flea beetle is the pollen beetle which can be found inside the flowers of courgettes, collecting the pollen. They provide no real threat or concern to the plant but the sheer numbers located can be a little worrying.

Last week I was asked about some large black and orange bugs that had appeared on the underside of the leaves of salvia. In this case they were not pests but in fact young ladybird larvae that had been doing a sterling job of removing large quantities of aphids. Lacewing larvae and their adult forms can also be found at this time of the year; the adults look like a very large, slim version of the adult winged aphid with its large and very distinctive tear-shaped transparent wings and will account for many aphids in one sitting.

Remember, the next time you are investigating your plants for the culprits of damaged stems and leaves, make sure that you are not removing a good friend that you may have inadvertently mistaken for an adversary.