Seasonal Summer Insect Pests

At last, some warm weather of late, which is great for being in the garden and helping plants and crops grow. However it does also speed up the development of some seasonal insect pests. We look at how to control these pests naturally, including strategies to counter chafer grubs, thrips, box tree moths and wasps.

Chafer Grubs

From May onward Chafer beetles start emerging, this year some may have emerged a bit later due to a colder spring. Egg laying will have followed, and those eggs will now be developing into larvae/grubs. These white coloured grubs start feeding on grass roots in August. The first sign of this activity might be the appearance of birds pecking on the lawn to feed on the grubs. Badgers will also rip up turf looking for the grubs. Damage to lawns from birds or badgers feeding on them can be very severe. Other symptoms of chafer damage are yellowing lawns and grass with little or no root system. The natural solution for control of these grubs is the use of nematode applications against them. In hot dry summer months this can be more difficult, as nematodes need some moisture in the soil to be active and do not like bright conditions at the time of application. The key to successful nematode treatments in the summer is ;

  • Irrigate and water lawns before application
  • Apply nematodes with plenty of water
  • Avoid applying on bright, sunny days
  • Water lawns after application
  • Repeat nematode treatments with severe infestations
  • Try to apply when Chafer grubs are smaller i.e.in August/early September. Later applications are possible but tend to be less effective the larger the grub and the cooler the soil

For lawns that are damaged, it is possible to treat with some Bio stimulants such as the Lawn Grub Repair Boost product. This is specially formulated to stimulate new root growth and top growth of grass and turf, helping lawns recover from insect attack and make them more resilient.

Thrips

If you are growing indoors, in glasshouses and polythene tunnels, you may well attract tiny insect pests called thrips, which are the smallest winged insects. These minute insects can cause considerable damage for such small insects. The larvae and adult stages feed on plants piercing leaves and flowers. On leaves large silvery- grey areas can appear on leaves and grazing marks on flowers. Tiny black marks can sometimes be observed in the feeding areas. Leaves often turn brown and die and some fruit may develop twisted. Thrips can also spread harmful plant viruses that cause plants imperfections. The first step to monitor whether you have these pests is to hang up a few yellow or blue sticky traps to catch the flying adults. Also start examining flower heads and leaves for the tiny pencil shaped adults and orange-yellow larvae. There are now quite a few different predators and predatory bugs that can be applied to control thrips and knowing which to use can be a little confusing. Here is a very general guide for the summer months;

  • For young plants or for fast release of predators onto leaves, apply Amblyseius swirskii predatory mites directly from shaker bottles. These small predatory mites feed on thrip larvae but not the adults.
  • For preventative and longer term protection of plants from thrips, apply and hang on plants Amblyseius swirskii Ulti mite foil sachets. These sachets release the predators for 4-6 weeks and were developed for use in hot countries, so will last longer and produce more predatory mites than paper sachet alternative versions in the summer months.
  • For plants with high numbers of thrip adults, consider supplementing Amblyseius swirskii predators with Orius predatory bugs. These predators feed on thrip larvae and adults but can take time to establish and benefit from also feeding on pollen, so tend to establish better on flowering plants.

Box Tree Moths

Box Tree moths are now present in southern England and spreading northwards. Their caterpillars can devastate Box tree plants and hedges. In high numbers they can kill the entire plant and large areas of hedges. Their feeding leaves brown leaves and in high numbers webbing. The caterpillars are green and black and the moths white with a brown edge. The first step to help prevent an explosion in their numbers is with the use of Box Tree pheromone traps. These traps are supplied with a sex pheromone lure that attracts the male box tree moths. Once caught they are not able to mate with the females, which helps reduce egg laying. The traps provide an important early warning of impending caterpillar attack a few weeks later. Professional gardeners and growers have access to a natural bacteria product that kills the caterpillars but this is not licensed for use by hobby gardeners, despite being accessible on some internet platforms as a product called Xentari but this is not legal to use in the UK for gardeners. However there is a natural solution available in the form of nematodes. Box Tree Caterpillar Killer nematodes should be applied directly onto the Box Tree caterpillars. It is important to take time with your application, targeting the nematodes directly onto the caterpillars. It is easier to do this with a small sprayer or knapsack sprayer. Avoid applying in bright hot conditions. It is also good practice to repeat the treatment and Box Tree Caterpillar Killer is supplied with two packs, so that you can this. The un-opened pack can be stored in a fridge. Box Tree moths have several generations a season, so make sure your Box Tree Moth traps have active pheromone lures inside them and repeat nematode treatments each time you see a fresh outbreak of caterpillars.

Wasps

During the spring wasps have been busy building their nests and are quite useful as predators of caterpillars and aphids, as they collect them to feed their young. This changes as we reach mid to late summer. Their job building the wasp nest and feeding the young finishes. This triggers them to scavenge and often results in them targeting food and drink being consumed by humans outside, which results in conflict! To help reduce this problem, the Dragonfli wasp trap contains a natural attractant that only attracts wasps and flies. It is very efficient at catching large numbers of wasps. It should be placed a short distance away from drinking and feeding areas to draw the wasps away. The trap should be checked on a regular basis to ensure enough liquid attractant is in the trap. Each Wasp trap is supplied with attractant and refill attractant is also available to purchase.