Aphids on wheat in South Africa

As with most crops in the agricultural industry, wheat production has many challenges which makes crop management critical. Wheat is host to various diseases and pests, but the problem most likely to give the farmer sleepless nights are viral diseases.

The biggest virus problem in recent years, on both dry land and irrigated wheat is Barley yellow dwarf virus or BYDV in short. BYDV is an internationally distributed problem that can infect various grass species, including wheat and barley. BYDV's symptoms can range from minimal signs up to a 30%- 40% crop loss in early season infections. The most common symptom of BYDV infection is stunting and leaf tip yellowing. On wheat, there is a yellowing to red change in coloring of older leaves. For barley, symptoms may appear bright yellow.

The only method of distribution of BYDV is by vector transfer via various aphid species. Aphids feed on infected plants by sucking out plant sap from the vascular bundles in their stilettos. The aphid, which is now a carrier of the "latent" virus, moves to another, healthy plant, places its stylet in the plant and then infects the next plant by means of saliva transfer into the phloem where it feeds. This method of feeding is the reason why viral damage frequently occurs in localized areas. Aphids can also turn into a winged form when conditions become unfavourable and they are forced to migrate. This allows them to travel very long distances in air currents. Through the migration patterns of aphids, BYDV can spread very far, which can make identification of the infection source very difficult.

How to get rid of aphids and the spread of viral diseases

The two most effective methods to combat BYDV are to plant resistant cultivars and to maintain a good aphid control (vector) program.

Aphid species on wheat in South Africa

The most common aphid species on wheat and barley in S.A. are the Oat aphid (Rhopalosiphum padi), Brown Ear Aphid (Sitobion avenae) and the Rose grain aphid (Metopolophium dirhodum). The most devastating species is the Russian wheat aphid (Diuraphis noxia), which usually occurs sporadically.

Oat aphid

The oat aphid is widespread in S.A. It is dark green in color with a reddish discoloration on the abdomen. The oat aphid usually occurs in the wheat at stooling stage and moves out of the wheat at the flowering stage. The Oat aphids feed on the stems where they can be found near the soil during early season infestations. During later infestation they can be found on the stem just below the ear. Oat aphids are known for their effective spreading of BYDV and the fact that they can infest wheat early in the growth cycle makes them potentially very dangerous.

Feeding damage has an effect on the crop, but the pest is a far greater risk when virus transmission is involved. It has a preference for moist Western Cape conditions and irrigation areas.

Brown ear aphid

The Brown ear aphid can occur in two colors, brown and green. The best-known feature of the Brown ear aphid is the long, pitch-black cornicles at the back of the abdomen. The brown ear aphid can occur from the flag leaf stage, but becomes a bigger problem after flowering as they move up in the ear, where they then feed and multiply. It has a preference for moist Western Cape conditions and irrigation areas.

Rose grain aphid

The Rose grain aphid is usually light green in color with a green stripe on its back. The cornicles of the Rose grain aphid are long and the same color as the body. Under favorable conditions this aphid appears at flag leaf stage and the numbers usually begin to decrease during grain filling. It has a preference for moist Western Cape conditions and irrigation areas.

Russian wheat aphid

Although the Russian aphid is very sporadic in its appearance, it is the most crop damaging aphid in S.A. The aphid can be identified by the two tails on the back of the abdomen and the absence of visible cornicles. The Russian wheat aphid has a preference for hot dry environmental conditions, as opposed to the other three aphid species which prefers the moist conditions. The main reason for the aphid's preference for warmer dry conditions is because it is highly susceptible to fungal diseases under moist, high humidity and dense plantings.

Aphids on wheat

BY HENDRI STRYDOM

INSECT ICIDE & FUNGICIDE PPC

* Talk to your Nulandis technical advisor for the best control option in your region. Efficacy and product preferences can vary from region to region.

References:

1. Prinsloo, G. 2017, June. Aphids and virus transmission on wheat:

What to look for. ARC-Small Grain, Bethlehem.

2. Figure 1 & 2: https://cropwatch.unl.edu/barley-yellow-dwarfvirus-

widespread-wheat

3. Prinsloo, G. Insect control on wheat in the Western Cape: Can I

plan for it beforehand? Agricultural Research Council Small Grain

Institute, a subdivision of the field crops Division, Bethlehem.

4. Prinsloo, G. 2016. Manual for the production of small grains in

the winter rainfall area 2016. ARC-Small Grain Institute.

Stellenbosch University.

5. Figure 3, 4 & 5 obtained from Dr. Goddie Prinsloo of the ARC

Small Grain Institute, Bethlehem.

6. 2017, January. Russian wheat aphid. Plant Health Australia.

7. Figure 6: http://www.agriculture.gov.au/pests-diseasesweeds/

plant/russian-wheat-apid

8. Bothes, A. 2018. The influence of different aphid species on

wheat,

9. Potgieter, F. 2019, Nulandis RSM Swartland. Personal

communication.

10. Van Zyl, K. 2019. A guide to crop management in South Africa.

A Croplife South Africa compendium

* Talk to your Nulandis technical advisor for the best

control option in your region. Efficacy and product

preferences can vary from region to region.