Major insect pests that attack sorghum

Major insect pests that attack sorghum

1. Stem/stalk borers

• Many types of stem borers affect sorghum in the field causing great yield loss.
• However, four types stem borers are common in Uganda in particular where their larvae are the destructive stage.
• These include the spotted stem borer, sugarcane borer, maize stalk borer and the pink borer.

Control

• Crop rotation
• Early planting on the onset of rains
• Planting Napier grass around the sorghum fields as a catch crop
• Intercropping sorghum with none host crops such as beans and cowpeas
• Spraying with an insecticide once every 2 weeks and integrated pest management is effective in reducing crop damage.

2. Sorghum shoot fly

• The shoot fly, Antherigona soccata, is a widely distributed pest in the sorghum growing semi-arid agro-ecological zones of Uganda except in the cold highlands above 1800masl.
• The female shoot flies lay cigar-shaped eggs singly on the lower surface of the leaves, at the 1-7 leaf stage from 5 to 25 days after seedling emergence.
• The eggs hatch within 1- 2 days and the larvae moves and bores into the base of the shoot, damaging it to cause wilting and subsequent dead heart symptom.
• The plant may produce tillers as a survival mechanism in response to damage.
• Shoot fly population is normally high if sorghum is planed late (usually a month after the onset of rains).
• During off season the shoot fly survives on alternative hosts such as finger millet and maize.

Control

• Use of shoot fly resistant varieties.
• Early planting at the onset.
• Use of systemic insecticides such as Carbofuran 5G granules applied at the root base of the plants.
• Alternatively, spraying the leaves and shoots of seedlings with imidacloprid 70 WS (2gms/ kg) or Endosulfan 35 EC.
• Use a botanical insecticide Neem oil 2%.
• A Combination of the above as integrated pest management is effective in reducing crop damage.

3. Sorghum midge

• Sorghum midge, Stenodiplosis sorghicola, is widely distributed in all sorghum growing areas of Uganda, except in the cold highlands above 1800masl.
• The female sorghum midge lays 30-120 eggs, which hatch within 2-3 days, in the flower spikelets.
• The larvae move and feed on developing ovary, preventing normal seed development. Larval period lasts 9-12 days and is the destructive stage of the pest that can cause up to 100% sorghum crop loss.
• Larvae pupate inside the spikelet and pupal period lasts 3-8 days.
• Before the adults emerge, the pupae move to the tip of the spikelet, and on emergence, the pupal case remains attached to the chaffy spikelet.

Control

• Early planting at the onset of rains to escape the sorghum midge population build up.
• Planting sorghum varieties with same maturity period at the same time within the communities.
• Sorghum that flowers later than the rest is exposed to higher populations of the sorghum midge for a longer period and suffers severe damage.
• Removing alternative hosts such as Johnson grass and Sudan grass to reduce on the initial early buildup of the pest.
• Field sanitation before the onset of the rains lowers the carry over effect of the diapausing larvae or pupae to subsequent seasons.
• Crop rotation with other none host crops.
• Land fallowing reduces the carry over and buildup of sorghum midge populations and use of resistant or tolerant sorghum varieties.
• Use of inorganic insecticides as the last resort to prevent severe damage can be done and a combination of the above sorghum midge control strategies as integrated pest management is effective in reducing crop damage.

4. Bird damage in sorghum
   

• Birds are very destructive pests affecting sorghum productivity in Uganda.
• Several bird species are destructive but the Quelea quelea and the weaver birds are the most important.
• The Quelea quelea affects mainly the soft dough stage of especially the white/cream seeded varieties while the weaver birds affect the hard dough stage.
• Depending on the season the red seeded varieties may be less affected.

Farmers allege sorghum planted in the second rains is less affected by birds; a reason why many farmers growing lowland sorghum plant in the second rains.