Amaranth is susceptible to damage by foliar insects such as leafminers, leafrollers, cutworms, aphids, flea beetles, and mites.
The most common is the pigweed weevil(Hypolixus haerens). Adult weevils feed on leaves, but the larval stage is more damaging because they bore into roots and stems.
- The adult weevil lays its eggs in branch crotches, and the larvae bore through stems to the root collar, causing hollowing of stems making them more susceptible to wind breakage.
- Plants wither and lodge.
- Rotting of bored stems and roots predisposing the plant to diseases.
- Extensive tissue discoloration, decay and cankers in branches, stems, and root collars
- Uproot and destroy attacked plants to reduce number of weevils
Bugs can cause severe damage to flowering head and seeds especial during the critical seed fill stage.
- Spray with permethrin, cypermethrin
The disease is favoured by high soil water content and low soil temperatures. Also dense planting without sufficient aeration enhances disease development.
Causal agent - Pythium aphanidermatum, Rhizoctonia solani and Aphanomyces sp.
- Seeds may rot in the soil before emergence (pre-emergence damping-off)
- Seedlings may exhibit stem canker above the soil line and/or root necrosis.
- Affected seedlings eventually wilt (post-emergence damping-off).
- Use disease-free seeds
- Avoid over watering
- Avoid dense planting
Infection is predisposed by injuries
The disease is spread by air currents and infected seeds. Warm, moist conditions favour disease development.
Causal agent - Choanephora cucurbitarium(a fungus).
- Wet rot of stems and leaves.
- Affected plant parts have hairy appearance (silk-like threads) consisting of fungal spores.
- Heavy defoliation during rainy season.
- Use resistant varieties where available
- Plant certified disease-free seeds
- Avoid dense planting to allow sufficient aeration
- Practice good field sanitation