Cucurbits (eg. melons, pumpkins, cucumbers) are a popular summer crop in many growing areas across Australia and are often seen as a low maintenance or ‘fill in’ crop. However to produce quality fruit an adequate nutrition program is essential.
ESTABLISHMENT – For early establishment & vine health, ensure your soil pH is not too acidic (ideally 6.0-7.0 water pH value). If your soil is too acidic it will lock out phosphorous which is required for root development and may have toxic levels of aluminium that kill root hairs & limit biological activity. Early LIG-POLYPHOS sprays are particularly effective for stimulating root growth & top development. Most low pH soils are also low in available calcium which is essential for general vine health and fruit quality. Lime or dolomite (if your soils are low in magnesium) applied at least 3 months prior to planting should correct any pH issues as long as you apply good quality lime with minimum ENV of 75%. However if you miss the boat you can go for a liquid lime option after planting which does work more quickly than bulk lime, though with less residual effects for following crops.
VINE DEVELOPMENT – The major challenge prior to fruit set is to establish an adequate vine or canopy area to support a crop while not promoting excessive vigour that will use up important nutrients needed for optimum reproduction. The key here as with all crops is a BALANCED nutrition program. Sure nitrogen will make things grow, however if it is not balanced with uptake of other essential nutrients (eg. P, K, Ca, Mg, Zn, B, Mo), plant health & fruit quality will be compromised at some point. The form of nitrogen is also a factor with nitrates and urea being immediately available and most likely to cause excessive growth compared to ammonium forms (eg. ammonium sulphate, MAP) that release soil nitrogen more slowly. Of course another option is to supplement conventional nitrogen fertilizers with SJB CR (control release) products such as CR NITROGEN, CR K-NIT & CR CAL-NIT + Boron. Trace elements such as zinc, iron, manganese and copper (see LIG-TRACE) are required for photosynthesis & vegetative growth and produce stronger plants with greater disease resistance characteristics. On sandy soils, magnesium is also likely to be an issue that can inhibit photosynthesis and vine development.
FLOWERING (REPRODUCTION) – Cucurbits are a bit different from most horticultural crops in that they have a high molybdenum (Mo) requirement for flowering. Molybdenum (see LIG-MOLY) is needed for pollen formation (boron plays a similar role in other crops) and a deficiency will result in low numbers of fruit set. Moly deficiency is most common in sandy acid soils and moly is the only essential trace element where availability increases as pH increases. This is another important reason why you need to correct low soil pH prior to planting. Thankfully molybdenum deficiency can be quickly corrected via foliar sprays and only requires a small amount of Mo/ha. Use of nitrate fertilizers will increase moly requirements and low moly in the vine can lead to high soluble nitrate levels that cause excessive vigour thus compromising flowering and fruit set. Other important nutrients for reproduction include phosphorous, calcium, zinc and boron.
FRUIT DEVELOPMENT – Critical nutrients for fruit sizing & filling include potassium, phosphorous & boron. Potassium literally fills up cells and also produces sugars while optimal boron allows more efficient movement of sugars to developing fruit. Both potassium and boron are anti-stress nutrients and help to maintain water uptake. Moisture stress is also the #1 cause of calcium deficiency in crops leading to fruit breakdown and shelf life issues. Phosphorous promotes sugar production and fruit ripening and can be used late in the season to enhance fruit colour where necessary. Nitrogen management is critical during this stage as you need to keep the vine healthy but not promote additional vegetative growth that diverts essential nutrients and sugars from fruit production. This is where foliar sprays such as VLP can be quite helpful for vine maintenance with less reliance on less predictable soil nitrogen.
Other products of interest for cucurbit production:
PHOSIC 600 (Systemic Phosphonate Fungicide)