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Posted 02/01/2021 in Agricuture by Patience Chizema

Sugar beans pests - damage and management

Sugar beans pests - damage and management

Pests are always a problem whenever crop production is done. Zimbabwean sugar beans farmers are mostly affected by the following 4 pests.

1. Bean stem maggot

This is a very common problem pest experienced by most farmers so it is very important to take preventive control measures as it can cause yield losses as high as more than 50%.

Damage caused by this pest is more serious during the seedling phase.  The pest attacks the plant at the beginning of the unfolding of the first pair of leaves, and it continues to attack as other new leaves unfold.  The maggots feed onto the stem and disrupt water and nutrient transport, leading to leaves turning yellow, wilting and eventually the plant dies. 

How to manage the pest

Remove volunteer plants and weeds, especially those in the legume family.

Remove crop residues to prevent the pest from overwintering in the residues.

Crop rotation with non-host to break the pests life cycle by starvation.

Chemical use is also effective, Diazinon 30 EC is usually used as a preventative pesticide against bean stem maggot (repeat spray applications at 3, 6, 13, and 20 days after germination) and  Apron star is used as a seed dressing and the crop will be protected from the pest for about 60 days.

2. Cutworms


The pests damage stems on or beneath the soil surface and they can also cut young plants off at the base or near the ground level. Some of the cutworms may also climb up plants to feed on the foliage, leaving ragged holes in leaves.

The cutworm larvae which causes the damage is usually active at night and hide during the day in the soil at the base of the plants or in plant debris of toppled plant.

How to manage the pest

Farmers must remove all plant residue from the soil after harvest

They should also eliminate winter weeds within and adjacent to the field well before planting as they can act as alternative hosts for the cutworms.

Chemical application of Lambda, Carbaryl 85 WP is also effective.

3. Spider mites

Spider mites survive by sucking material from plant cells and large infestations cause visible damage. Leaves first show patterns of tiny spots, they may change colour, curl and fall off. The mites activity is visible in the tight webs that are formed under leaves and along stems.

How to manage the pest

Mite problems can be reduced by keeping fields and field margins clean of weed hosts.

Excessive nitrogen fertilization also may contribute to population buildup, so apply the recommended rates for nitrogen

Consider sprinkler irrigation; spider mites are usually less severe in sprinkler-irrigated fields than in furrow-irrigated fields. 

Use Diazinon 30 EC.

4. Aphids

These are small soft-bodied insects on the underside of leaves and stems of the plant. They are usually green or yellow in colour, but maybe pink, brown, red or black depending on species and host plant. If aphid infestation is heavy it may cause leaves to turn yellow and distorted, necrotic spots on leaves and stunted shoots. Aphids secrete a sticky, sugary substance called honeydew which encourages the growth of sooty mould on the plants. .Besides being sap-sucking pests, aphids are also vectors for sugar beans diseases like Bean common mosaic virus.

How to manage the pest

Always monitor your crop to keep in check of the pest infestation

Chemicals recommended include:




So generally pests have the following effect on sugar bean crops:

  1. Heavy pest attack may result in total crop failure.
  2. Pest infested crops have low value on the market.
  3. Pests eat up the leaves of the crops, thereby reducing the photosynthetic area of the crop.
  4. Pests cause crop injury, further proving pathogens entry into the crop.

By Patience Chizema

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Member since 11/04/2020

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