STRATEGIES FOR ORGANIC GRASSHOPPER CONTROL

© Frances Michaels 

Regardless of where you live in Australia the noise of crickets and grasshoppers is one of the background sounds of hot summer nights. The ‘song’ is produced by the male to attract a mate.

Crickets, grasshoppers and locusts as a group of insects are distinguished by strong chewing mouthparts and enlarged hind-legs designed for jumping.

• Crickets are usually nocturnal, some like the tree cricket are predatory, others like the mole cricket feed on roots and burrow in the soil.

• Grasshoppers are divided into short and long horned, with the ‘horns’ referring to the length of antennae, in long-horned grasshoppers the antennae are longer than the body. Long-horned grasshoppers are large, mainly plant eaters and often nocturnal.

• Short-horned grasshoppers, including the locusts, are active during the day. The name locust is given to species that can occur in swarms. This includes the Australian plague locust, which has a black patch at the tip of the hind-wing and some scarlet on the hind-legs.

Not all grasshoppers are plant-eaters; surprisingly some are predatory with front legs adapted for grasping prey. Check before you accidentally squash a ‘garden helper’ by looking for spiny front legs.

Grasshopper eggs are mainly laid in the soil, although some do lay eggs on leaves. The eggs lay dormant until it rains, sometimes for years. Once hatched, if conditions are right, the next generation can be produced within a month.

Crickets, grasshoppers and locusts attack a wide range of plants but it is in inland areas where the major impact is felt.

BIOLOGICAL CONTROLS:

• The most important natural enemies of grasshoppers are birds. In inland areas the swamp ibis is particularly important as a control for locusts and the draining of wetlands can increase locust plagues.

• Chickens not only like eating grasshoppers but seem to get a lot of entertainment catching them too! Keen gardeners in inland areas should consider designing a chicken run with a shared fence between the chook run and vegetable garden for as much of the garden perimeter as possible. This can reduce the fencing needed and create a ‘Fort Knox’ style vegetable or flower garden as far as grasshoppers are concerned.

• Guinea fowl are hardy birds, not suitable for urban areas as they are noisy but they could be a big help on larger properties, as they are famous for eating large numbers of grasshoppers and ticks.

• Other natural controls include sugar gliders, lizards, snakes, assassin bugs, frogs, ants, fungi and worms.

• Beneficial insects such as paper wasps, tachnid flies and parasitic wasps prey on grasshoppers. Robber flies are a major predator of grasshoppers, as they can make up to 1/3 of their diet. Habitat, such as a border of perennial plants, needs to be available all year round as a refuge for these predators. They can also be encouraged by planting suitable nectar-producing plants Good choices include sweet Alice, clover, coriander, dill, caraway and anise.

• No commercial biological controls are available in Australia; in the USA it is possible to buy a predatory protozoa Nosema locustae that controls grasshoppers.

PHYSICAL AND CULTURAL CONTROLS:

• As a variation on the old adage ‘the early bird gets the worm’ this is also a good strategy with grasshoppers. Catching them in the early morning is relatively easy, as they are less active in the mornings, especially after a cool night. Either catch them by hand or use a butterfly net.

• Digging or cultivating in spring, and leaving the soil exposed, can expose the eggs to predators.

• Physical barriers such as floating row covers or mosquito netting work very well for early-season protection. This will also protect your plants from other pests like fruit flies and caterpillars. Sometimes exclusion is a lot of work initially but saves heaps of effort over time.

• The colour yellow is meant to be attractive to grasshoppers, so there are various ways this can be used to trap grasshoppers. Long sticky tape traps are commercially available. Dams, ponds or children’s paddling pools, can be used to drown grasshoppers by floating pieces of yellow plastic in the water or suspending it from bamboo just above the water. Fish will happily eat the grasshoppers or they could be collected and fed to chooks.
• Small traps can be made out of jars or buckets filled with water and a 10% molasses solution, cover with a film of canola oil to deter bees and mosquitoes. Bury the containers up to their rim in the soil; clean and renew the bait as needed.

LEAST TOXIC CHEMICAL CONTROLS:

• Canola oil has been found to be a grasshopper attractant, it could be used to make baits more attractive to grasshoppers, combined with organic insecticides to make them more effective and floated as an oil on top of water traps.
• Insecticidal potassium soap sprays work best on small grasshoppers.
• Make up a garlic or chilli spray as a repellent.