Sunflowers are one of the most important oilseed crops in Southern Africa, valued for their high oil content, which is used in cooking oil and margarine production. The by-product, sunflower cake, is also an excellent livestock feed. Sunflowers are a low-input crop, making them ideal for marginal areas and small-scale farmers. This guide will walk you through everything you need to know to successfully grow sunflowers, from soil preparation to harvesting.
Why Grow Sunflowers?
- High Oil Content: Modern hybrid varieties have up to 40% oil content.
- Versatility: Sunflowers can be grown in both rain-fed and irrigated conditions.
- Short Growing Period: Sunflowers mature in just 90 days, making them an excellent catch crop if your main crop fails.
- Drought Tolerance: Sunflowers are more drought-resistant than many other grain crops, making them suitable for marginal areas.
Climatic and Soil Requirements
Climate
- Sunflowers thrive in marginal areas with moderate rainfall.
- They are drought-tolerant but respond well to irrigation, especially during the pollination period.
- The crop can be grown as a winter irrigated crop in frost-free areas.
Soil
- Ideal Soil: Deep, well-drained loam soils with good physical conditions.
- Soil pH: Sunflowers are sensitive to acidic soils. The optimal pH is 5.3 (calcium chloride scale). If the pH is below 5.0, apply lime to correct it.
- Avoid Nematodes: Sunflowers are prone to root-knot nematodes, so avoid planting them in light-textured soils where nematodes are common. Heavier soils are preferred.
Crop Rotation
- Rotation Period: Do not plant sunflowers on the same land more than once every three years to prevent disease buildup.
- Avoid: Do not rotate sunflowers with other Sclerotinia-susceptible crops like potatoes, soybeans, groundnuts, or common beans.
- Good Rotation Crops: Maize and grain sorghum are excellent rotation crops for sunflowers.
Recommended Varieties
- Early Maturing Varieties: G.100, G.101, and SNK.37 (90–110 days).
- Mid-Season Varieties: Perodovik, Mopani, and Msasa (76–96 days).
- Long-Season Varieties: PNR.7371 and Pan 7351 (115–120 days).
Always consult your local seed merchant for the latest hybrid varieties with high oil content and disease resistance.
Planting Guidelines
Planting Date
- Rain-Fed Crops: Mid to late December is the optimal planting time.
- Irrigated Crops: In frost-free areas, planting can extend until February or March.
Seed Rate and Spacing
- Seed Rate: 4–6 kg of treated seed per hectare.
- Spacing:
- Irrigated Crops: 55,000 plants/ha (20–37 cm in-row spacing, 90 cm between rows).
- Rain-Fed Crops: 40,000–45,000 plants/ha in areas with reliable rainfall.
- Dry Areas: 30,000 plants/ha in areas with unreliable rains.
Planting Depth
- Plant seeds at a uniform depth of 5 cm, but no deeper than 7 cm or shallower than 3 cm.
Fertilization
- Boronated Fertilizer: Essential for sunflower growth. Apply a boronated compound fertilizer (e.g., Cottonfert 5:17:10 with 0.25% boron) at 250–300 kg/ha, banded at planting.
- Top-Dressing: Apply Ammonium Nitrate at 150–300 kg/ha six weeks after planting, depending on rainfall and irrigation.
- Micronutrients: If soil analysis shows low molybdenum levels, apply a foliar spray of Sodium Molybdate at 100 g/100 L water.
Weed Control
- Critical Period: Sunflowers are poor weed competitors, so keep the field weed-free for the first 6–8 weeks.
- Herbicides:
- Trifluralin: Pre-planting herbicide for annual grasses.
- Lasso®: Post-planting herbicide for grasses and some broadleaf weeds.
- Fusilade Super®: Controls emerged grasses.
- Gesagard®: Controls broadleaf weeds (use in combination with a grass killer).
- Avoid Atrazine: Sunflowers are highly sensitive to Atrazine residues, which can cause damage even two years after application.
Pest Management
Common Pests
- Root-Knot Nematodes: Avoid planting in light soils and practice long crop rotations.
- White Grubs/False Wireworms: Use Dursban® 4 E at 1.0 L/ha in the planting row.
- Cutworms: Keep the field weed-free and apply Karate® at 100 ml/ha.
- Bollworms: Use Thionex® 35 EC at 650 ml/200 L water/ha (not within 21 days of harvest).
- Aphids: Apply Rogor® 40 CE at 750 ml/ha or Metasystox® 25 EC at 500 ml/ha.
Disease Management
Common Diseases
- Septoria Leaf Spot: Caused by water splash. Manage by avoiding overhead irrigation.
- Rust: Common in hot, humid conditions but rarely serious.
- Sclerotinia Wilt and Head Rot: Potentially devastating. Practice long rotations and remove diseased plants.
- Bacterial Wilt: Severe but rare. Avoid planting in fields with a history of bacterial wilt in tomatoes or potatoes.
Irrigation
- Sunflowers are drought-tolerant but respond well to irrigation, especially during the 30-day pollination period.
- For winter crops, apply 80–85% of the water used for wheat.
Harvesting
- Combine Harvesting: Use a combine harvester with sunflower attachments when moisture content is around 20%.
- Hand Harvesting: Cut heads when the backs are yellow and dry them on the ground. Thresh using a maize sheller at half the drum speed used for maize.
Key Takeaways
- Sunflowers are a low-input, high-reward crop suitable for marginal areas.
- Proper weed control and soil preparation are critical in the early stages.
- Use boronated fertilizers and practice long crop rotations to avoid diseases and nematodes.
- Always read chemical labels before application and follow recommended guidelines.