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Zimbabwe has a reputation of producing good quality tobacco, well sought after because of its unique flavour. For us to maintain this reputation of not only Zimbabwe’s most valuable crop but a top foreign currency earner, accounting for 10,7 percent of the country’s Gross Domestic Product (GDP), farmers ought to be wary of sap sucking aphids that destroy tobacco leaves since tobacco is priced by virtue of leaf quality.

Tobacco aphids have beak-like mouth parts through which they suck juice from the tobacco leaves.

Aphids build large colonies beneath the leaves, making them more difficult to see.

They transmit several viral diseases such as bushy-top virus, potato virus Y and alfalfa mosaic virus which reduce the weight and shrink the leaves, reduce growth of the plant and if nothing is done timely, ultimately the plant dies.

In addition, aphids produce a sticky waste product, honeydew, on which sooty mould easily develops, reducing leaf quality and weakening the plant.

Red and green aphid types are common on tobacco in Zimbabwe.

More often than not, four to six weeks after transplanting, tobacco aphid invasion generally begins with winged adults flying into fields and depositing young ones on plants.

When the colony starts to become crowded or nutritionally unsuitable, winged aphids are produced and these migrate sometimes over hundreds of kilometres carrying viruses to form new colonies.

There is need for proper management to prevent serious economic damage to the crop as aphids can lead to reduced yield.

One way is to adhere to legislative dates such as the earliest dates for sowing seedbeds and for planting as well as dates governing seedbed and stalk destruction.

Legislated latest plant destruction date of 15 May and earliest tobacco seedbed sowing date of 01 June, earliest planting date of 01 September help to minimise carry over of aphid-transmitted virus diseases such as bushy-top and potato virus Y.

Considering that the law gives the minimum standard for the dead period, heedful farmers could actually destroy stalk as soon as possible after reaping is completed instead of waiting for the legislated date.

Alas, some farmers wait for Plant Quarantine officers to fine them before they can comply with the Plant Pests and Diseases Act (Chapter 19:08) and destroy stalks and prevent re-growths, which not only serve as aphid hosts but are also virus reservoirs.

Tobacco Industry and Marketing Board encourages farmers to manage their costs if tobacco farming is going to be a lucrative business hence it urges tobacco growers to adhere to less expensive methods such as observing legislative dates.

Another way aimed at minimizing aphid-borne virus diseases involves farming practices that reduce aphid population through making the environment less favourable through farming practices such as crop rotation, sanitation, strip cropping, and in sectary planting.

Weeds also need to be removed from within tobacco fields and surrounding areas.

Isolated virus-infected plants and leaves should be removed early to prevent further re-infestations as they act as virus reservoirs for the further spread of viruses.

Use of chemical insecticides although more expensive than aforesaid methods, is yet another way to control tobacco aphids.

Though some chemicals are potent and can provide protection for up to three months, the downside to the aphicides is aphids can gain resistance to chemicals over time and plants can remain with pesticide residues, which when detected have a negative effect on the Zimbabwe tobacco industry.

Recommended chemicals for aphid control on conventional seedbeds include dimethoate, thiamethoxam and thiacloprid whilst imidacloprid, acetamiprid and thiamethoxam are registered for use on floatbeds.

Acephate for instance is banned and is no longer approved for use on tobacco.

Aphids also do have natural enemies like ladybirds which eat the aphids or aphid parasitoids like wasps, lacewings, syrphid flies, damsel bugs, parasitic fungi and entomopathogenic nematodes that parasitises the aphids thereby regulating aphid populations.

A tobacco farmer can use all the four aforementioned methods of controlling aphid population and this is known as the integrated pest management technique.

For any additional information please contact TIMB on telephone numbers 0772145166 /9 or 0279-22082 /21982 or 025-3439 or 067-24268 /29246 or 0277-2700 or 064-7280 or 0271-6772 or E-mail: [email protected] or visit our website on www.timb.co.zw