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How to control yellow aphids in sugarcane crop

By George Mbakanya

Traders hawk sugarcane cutting to commuters in a vehicle at Keumbu Market along Kisii Nairobi Highway. Keumbu Market is one famous market stocked with farm produce from local farmers to passengers en-route to Nairobi and other towns. A small stack of sugarcane retails here at Sh20. [Photos Sammy Omingo/standard]

Yellow aphids —a ferocious pest — are giving farmers in sugarcane growing areas sleepless nights. The sugarcane aphid which also attacks sorghum, is capable of causing substantial damage to the crop if left unmanaged.

However, with timely management, its effects can be minimised. Once sugarcane has emerged, it is recommended to scout the fields at least once a week for signs of the aphid.

Once aphids are found, fields should be scouted 2-3 times a week. Sugarcane aphids excrete honeydew, a sticky, shiny substance on the lower leaves, which is often the first sign of a sugarcane aphid infestation.

Damage

Feeding initially results in yellowing and reddening of leaves, depending on host plant and temperature. Prolonged feeding can lead to premature senescence of leaves and plant or stalk (sugarcane) death.

Yield reductions usually occur due to feeding damage to early plant growth stages, including reduced tillering. Cultivated crops known to host include maize, rice, sorghum and sugarcane.

Yellow sugarcane also reproduces on lawn and pasture grasses. Loss of plant sap, caused by the sugarcane aphids feeding on the leaves, takes away nutrients from the plant that would otherwise be utilised for plant health.

Sugarcane aphid feeding, along with black sooty mold and other secondary diseases, eventually cause the leaves to turn yellow and die. The result is often stunted growth. Depending on the growing region and growth stage, growers are encouraged to treat for aphids as soon as the action threshold is reached.

Management

A general guideline is to apply an insecticide when 25 per cent of the plants have been infested with 50 aphids per leaf, but there are specific threshold levels suggested for different growing stages and geographical regions. Local experts should be consulted. Regardless of the threshold level used, it is critical that insecticide application occurs as soon as possible to avoid severe loss.

Insecticide use

Applications targeting lower infestation levels are likely to be more effective and prevent an escalating population of aphids that will be much more difficult to control. Try spraying cold water on the leaves. Sometimes all aphids need is a cool blast to dislodge them. Typically, they are unable to find their way back to the same plant. 

Studies suggest that aphids are relatively difficult to control with standard aphid insecticides. Use of pyrethroid is not recommended because they are not effective. This is because, they may lead to aphid resurgence due to their negative effect on aphid natural enemies (lady beetles, minute pirate bugs, wasp parasitoids). Controlling sugarcane aphids should include a management system that facilitates beneficial insects, including pollinators, as well as appropriate timing of insecticides. Two effective products in controlling the aphids are Sivanto Prime by Bayer Crop Science and Transform WG by Dow Agro Sciences.

One of the benefits of both is they are not harmful to beneficial insects, which is important for the control of sugarcane aphids.

Care should be taken in adding other insecticides to the mix that could be harmful to beneficial insects.

Additionally, movement of Sivanto prime and Transform in the plant is minimal, making coverage essential for adequate control. Regardless of the product used, good spray coverage is important. Control may be improved by ensuring that the undersides of the leaves are well covered.

[The writer is an expert in sustainable agriculture]

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