Recently, I came across a retail garden website saying grasshoppers could be considered as beneficial insects… just because birds love to eat them, Ion Staunton* writes.

As a Tree Crop reader, you may have a different opinion!

In early March, there were baby grasshoppers up on my roses eating the pink foliage, noticed only because I looked closely to see what was taking big arcs out of the leaves. I haven’t seen any wrens locally; the magpies and butcher birds aren’t interested, and the noisy miners are more interested in harassing the other birds than having a feed.

The difference between ‘grasshoppers’ and ‘locusts’ is no big deal. In general, we refer to them as ‘locusts’ when they are in swarming numbers and ‘grasshoppers’ when there is more space between them. There are long-horn and short-horn varieties which some long-gone entomologist based on under- or over-30 segments in the antennae.

Also, there are ‘wingless grasshoppers’ meaning the adults are without wings. Of course all grasshopper/locust nymphs are also wingless… except in the final couple of nymphal stages (instars) where a close look reveals wing-flaps going to almost halfway along their abdomen. Lastly on this pedantic naming topic, one thing is sure: the wingless grasshoppers will never be considered as locusts because they can’t form a flying swarm.

The life cycle length varies between species. Eggs (30 or so in a batch) are laid just below the soil by females pushing their ovipositor down through the grass thatch, and, when the eggs hatch, the first nymphs which seem to be mostly head and legs, can begin feeding on the grass or climb your trees (and my roses) to the foliage, especially the newest growth.

The Australian plague locust, Chortoicetes terminifera, gets its publicity because it builds its numbers in the grain-growing regions where there is either grass or grain crops to eat.

The build-up to plague proportions may take years until one fine day/week/month, there are hundreds of thousands (millions?) of 30-egg batches hatching over a couple of weeks. The nymphs hang out together as families, gangs, clans and then turn into a seething mass of earth-bound grass- or crop-eaters… until they all become adults with wings.

The swarming group mentality or instinct then really kicks in. After a few short flying-in-formation sorties have been accomplished, they set about doing what locust plagues have done since well before biblical times… fill the sky.

With a tailwind they can travel long distances to your tree-crop-growing district which, from their altitude looks pretty green and appetising. The swarm will settle for anything greenish, including your veggie patch, lawn and even green clothing on the line (cotton fabrics preferred to acrylics or polyesters).

If you scale the above description back a few notches to a swarm that has built up, usually in nearby pastures, grassland, or lightly treed areas, they are the local grasshopper/locusts which can severely damage your crop and pocket.

Sky-filling plagues haven’t happened much in recent years; state and federal governments can take much of the credit. There is a Biosecurity Act in some states and federally, the Minister for Agriculture and the Minister for Health have responsibilities and there’s even an Australian Plague Locust Commission.

But of course it’s the broadacre landholders who have to put in the effort to keep hopper populations low so they can’t get big enough to warrant TV news coverage. So, what do they do about control?

Controlling grasshoppers

The build-up of nymph numbers is easily noticed and, because it takes about a month for nymphs to become winged adults, they can be fairly easily killed off by boom spraying or aerial crop spraying techniques.

Yep, a tractor-drawn sprayer can out-run them and a droplet or three will cause the death of every individual nymph hit. This means that almost none of them get to become fornicating adults to lay more eggs and the re-population to swarming proportions is significantly reduced. As a Tree Crop magazine reader, it is probably appropriate for you to nod your head right now in a quiet ‘thank you’.

And yet, grasshoppers of many species, still threaten your business of harvesting saleable fruit in quantity. Here’s what you can do:

All through summer, keep your eye out for the wingless nymphs in nearby reserves, pasture or fallow land. Nymphs can readily hop to your orchard and climb trees but once they’ve become winged adults, they can more quickly fly to whatever catches their hunger-driven attention which is better than dry grass… and they have good eyesight.

Once groups of nymphs, having banded together are noticeable, you will make the mental jump to imagining them in your trees. Air-blasting orchard sprayers can become focused enough to do this job in a paddock. You only need to hit hoppers to kill them in minutes.

Spray drift from natural pyrethrum is degraded in a couple of hours of UV light so there are no residues. Fipronil, chlorpyrifos, bifenthrin and others with a residual life also do a good job but check the labels for withholding periods because of those residues if you have grazing stock.

The above suggestions should take care of the nymph-gangs approaching your tree crop, but grasshopper adult attack is different. They can fly in from anywhere and begin eating your trees, and simultaneously, the females may already have mated, and they decide to first lay their eggs under and around your crop ‘knowing’ their young will have good food choices on hatching. It only takes eggs a couple of days to hatch, and the nymphs have no fear of heights if there are green leaves above them.

Your spraying decision is then going to be based on: when is the leaf damage getting close to costing you more than it costs to get out the equipment and kill them all? Your decision becomes easier if jassids, caterpillars, bugs, thrips, etc., etc., numbers are building up too.

Ion Staunton of Pestech Australia is an entomologist and the manufacturer of PyBo pyrethrum insecticide. Questions? Email ion@pestech.com.au or phone him on 0407 308867.