Two spots, one problem
Early leaf spot — roughly circular brown lesions with a yellow halo, mostly on the upper leaf surface, appearing from about a month after sowing.
Late leaf spot — darker, nearly black lesions with little or no halo, sporulating on the underside, appearing later and generally more damaging.
Both defoliate from the bottom up. Severe infection strips the plant, and a plant without leaves does not fill pods.
Why preventive works here
The lesions you can see represent infection that happened one to three weeks earlier, and the disease accelerates steeply once established. Waiting for a visible threshold means treating a curve that is already climbing.
In high-pressure areas a scheduled protectant programme from about 30 days, at intervals through the season, is standard practice and it pays. Rotate the FRAC group between applications.
The rest of the programme
- Resistant or tolerant varieties, where they suit your duration and market.
- Rotation. Groundnut after groundnut builds leaf spot, stem rot and nematodes together. A cereal between crops is worth more than an extra spray.
- Destroy the crop residue; both fungi carry over on it.
- Adequate spacing so the canopy dries.
- Potassium and calcium sufficiency, which measurably improve tolerance.
Rust, where it occurs
Reddish-brown pustules on the underside, and unlike leaf spot the affected leaves tend to stay attached. Frequently present together with late leaf spot, and managed by the same programme.
Stem rot and collar rot
Different problem, soil-borne, and no foliar spray reaches it. White fungal growth at the base with small mustard-seed-like structures. Managed with Trichoderma enriched into farmyard manure at sowing, seed treatment, rotation, and avoiding heavy residue near the collar.
The end of the season
Defoliation at pod filling costs directly. If a crop is going to be protected at all, the protection matters most in the four to six weeks before harvest — which is exactly when farmers stop spending on a crop they think is nearly finished.
Read the label and the leaflet on the pack before use. The approved crops, dose and waiting period printed there are what count.
