Combating the Russian wheat aphid to safeguard SA’s crop

South Africa is the biggest wheat producer in Sub-Saharan Africa after Ethiopia. Resulting from a rise in wheat demand to feed the rising populace, manufacturing wants to accentuate.

Nevertheless, intensified agriculture by monoculture farming is the principle risk to various ecosystems, creating best habitats for economically necessary pests to ascertain, reproduce and trigger injury.

READ Administration of necessary grain illnesses

Roughly 75% of South Africa’s wheat is produced below dryland situations and the remaining 25% below irrigation. Winter wheat produced on dryland within the Western Cape accounts for about 50% of the nation’s whole manufacturing.

Within the winter rainfall space, wheat is planted between mid-April and mid-June and in the summertime rainfall space (japanese Free State) between mid-Could and the top of July.

Russian wheat aphid (Diuraphis noxia) is probably the most critical wheat pest in South Africa and most problematic in drier, low yield-potential situations.

Russian wheat aphid is indigenous to central Asia, southern Russia and nations bordering the Mediterranean Sea, Iran and Afghanistan. Nevertheless, this pest is now present in all wheat manufacturing areas of the world, except Australia.

In South Africa, it was first recorded within the Free State in 1978, however now happens all through the area. It solely reaches pest standing often within the central dryland areas of South Africa.

The Russian wheat aphid nymph resembles the wingless grownup feminine, however has a smaller physique.

The nymph develops quickly and moults 4 instances inside a time-frame of seven to twenty days earlier than reaching the grownup stage. The grownup is small, about 2mm in dimension, and has a yellow-green to grey-green and waxy look.

The grownup has an especially brief antennae, a few quarter of its physique size. Females can have wings or not. Each of those are related to one another, besides that the thorax and head of the winged kind is darker.

Females produce as much as 4 stay younger a day, totalling roughly 70 over their lifespan. There are quite a few generations yearly, with a build-up of huge numbers, particularly in cool to heat, dry situations.

Initially, all of the aphids within the colony are often wingless. Nevertheless, because the numbers improve, overcrowding outcomes and winged people are produced in order that the Russian wheat aphid might disperse to different beneficial habitats to begin new colonies.

The mix of their excessive dispersal price and excessive reproductive price implies that the pest can quickly attain damaging ranges over broad areas if not correctly managed.

Russian wheat aphid females are parthenogenetic, which means they don’t must mate to provide younger, and males are absent in Southern African populations. Males are solely identified to happen in chilly climates at excessive altitudes.

Host vary

This aphid feeds totally on the small-grain cereals, i.e. wheat (Triticum aestivum), barley (Hordeum vulgare), and, to a lesser extent, on rye (Secale cereale), oats (Avena sativa) and triticale (a man-made species developed by crossing wheat and rye).

Quite a lot of wild grasses can function host crops for the Russian wheat aphid and could also be necessary for aphid survival when cereal crops aren’t obtainable.

Cool-season grasses that host this insect embrace bromegrass (Bromus diandrus), wild ryes (Elymus sp.) and jointed goatgrass (Aegilops cylindrica).

Jointed goatgrass is exceptionally appropriate due to its shut relationship with wheat. Further hosts recorded in South Africa embrace rescue grass (Bromus catharticus), different Bromus spp. in addition to wild barleys (Hordeum murinam and Hordeum sp.).

Russian wheat aphid feeds on the upper-leaf floor of latest development, in axils of leaves, or inside rolled leaves utilizing their piercing-sucking mouthparts to suck sap from the vascular tissue.

Throughout this course of, saliva is secreted into the plant, inflicting injury to plant cells. Yield losses of 35% to 90% have been recorded on prone wheat crops, with the proportion infestation, development stage of the plant and the period of the infestation figuring out the severity of the injury.

Heavy infestations in younger crops trigger tillers to change into prostate and leaves to roll closed tightly.

In older crops, typical signs embrace white or pale-yellow stripes which might flip purple when chilly situations prevail, tightly rolled leaves and heads trapped within the rolled flag leaf.

Different management measures

Addressing the problem of Russian wheat aphid in South Africa requires a multifaceted method that mixes host plant resistance, and organic, cultural and chemical management methods.

Built-in pest administration practices may help cut back the reliance on chemical pesticides and mitigate the affect of this pest.

The mixing of a number of management measures is only when attempting to fight this pest.

A variety of pure enemies have been related to Russian wheat aphid. Parasitic wasps embrace indigenous species of the households Braconidae and Aphelinidae with two unique species, Aphidius matricariae and by chewing a gap by the host’s exoskeleton.

Parasitoid females feed on plant nectar and honeydew, a sugary liquid secreted by aphids and different sap-feeding bugs.

Additionally they feed on aphids to acquire vitamins for egg manufacturing by piercing or “stinging” the aphids with their ovipositor and consuming the insect’s blood from the wound, killing about two aphids per day by such feeding. Predators might embrace many species of ladybird beetles.

This contains the variegated ladybug, Hippodamia variegata, which was unintentionally launched into South Africa from the UK.

Different species embrace the alien invasive harlequin beetle, Harmonia axyridis, and different predaceous beetles. Floor beetle predators prey on aphids which have dropped from crops because of disturbance.

Woman beetle predators might trigger aphids on the crops to fall from the plant onto the bottom, the place they’re consumed by carabid predators. Each grownup and larvae of ladybirds are voracious predators of aphids.

This predation helps to scale back the variety of Russian wheat aphids in infested fields.
Hymenopterous parasitoids are extra generally discovered when aphid inhabitants densities are low, whereas beetles happen when larger inhabitants densities are current.

Conservation organic management is turning into more and more necessary for pest management to keep away from opposed results related to the usage of on-farm inputs. Farmers ought to purpose to implement practices to minimise the “inexperienced bridge” of volunteer and alternate grass-host species, on which aphids survive from one season to the subsequent.

The destruction or removing volunteer host crops may help cut back or delay the build-up of Russian wheat aphid populations. Typical methods which might be surrounded by, or in shut proximity to uncultivated land, which has totally different grass species, might improve aphid densities in these methods.

Decrease abundances of aphids have been discovered to seem in natural and diversified methods because of larger predator abundances in these methods.

Natural Techniques

Natural and diversified cropping methods resemble pure ecosystems in that there aren’t any chemical practices, whereas there’s a variety of various crops.

Growing agricultural habitats with excessive crop rotation, polyculture and canopy crops are advantageous to pure enemies and their efficacy of organic pest management of miscellaneous pests akin to Russian wheat aphid.

Abiotic elements akin to temperature, relative humidity and rainfall influences the density of pests and their pure enemies’ abundance, in addition to plant well being.

Due to this fact, the upkeep of enough soil moisture and fertilisation can cut back injury as a result of crops careworn for water or vitamins are extra prone to break from pests.

Out there resistant cultivars needs to be planted and fields inspected often as it could be needed to make use of chemical management towards the aphids ought to the populations improve.

When making use of chemical management, it have to be accomplished mindfully, as a result of spraying unnecessarily will intrude with the pure enemies of the aphid.

Conclusion

Wheat pests jeopardise each the amount and high quality of this crop. The implications lengthen past monetary losses for farmers, impacting meals safety and the nation’s capacity to satisfy its wheat wants independently.

A complete and sustainable method to pest administration is crucial.

E-mail Zunel van Heerden at [email protected].