Smallholder farmers in hill and mountain agro-ecosystems continue to rely on hand-operated knapsack sprayers that apply chemicals mainly to the top of the plant canopy, resulting in poor penetration, non-uniform pest control and high operator fatigue. This paper reports the design, fabrication and field evaluation of a compact, manually guided, engine-powered intra-canopy boom sprayer developed for row crops in hill farming conditions, using maize as the test crop. The sprayer combines a horizontal boom (two flat-fan nozzles) for top-of-canopy coverage with a vertical boom (four flat-fan nozzles, 40 cm spacing) for lateral, intra-canopy coverage, mounted on a mild-steel frame with pneumatic drive wheels and a rear caster wheel. A 20-litre plastic tank supplies a 10-12 LPM double-outlet reciprocating pump driven by a 1.13 hp two-stroke petrol engine, delivering 200-400 psi working pressure through adjustable sliding boom attachments. Nozzle type, operating pressure (1.5 kg cm⁻²) and forward speed (1.5 km h⁻¹) were selected from prior laboratory and soil-bin optimization. Field evaluation was carried out on Sikkim Sankul Makka-2 maize (row spacing 50 cm, plant height 450 mm, vegetative stage, 120-day duration) at a farmer's field in Samlik village, Sikkim. The developed sprayer achieved a theoretical field capacity of 0.15 ha h⁻¹, an actual field capacity of 0.11 ha h⁻¹ and a field efficiency of 73.33 %. Spray deposition, quantified with water-sensitive paper and DepositScan analysis, averaged 69.77 % coverage, 419.9 µm VMD, 70.81 deposits cm⁻² and 70.35 µL cm⁻² deposition on above-leaf surfaces, against 59.67 % coverage, 349.2 µm VMD, 58.66 deposits cm⁻² and 58.14 µL cm⁻² on under-leaf surfaces. At a fabrication cost of ₹22,600, the machine returned an operating cost of ₹78 h⁻¹, a benefit-cost ratio of 1.56 and a payback period of 1.7 years. These results demonstrate that a low-cost, single-operator intra-canopy boom sprayer can deliver satisfactory field capacity, uniform canopy penetration and favourable economics for row-crop plant protection in hilly terrain, offering smallholder farmers a mechanized, gender-neutral alternative to knapsack spraying.