The aim of any producer is a high yielding, high quality crop that satisfies the end user. There are a large number of agronomic factors which can influence this, many are within the control of the grower, under given growing systems, climatic and soil conditions.
The vast majority of melons – and virtually all watermelons - are produced in the field.
Some cooler climate crops are grown under tunnels to bring
forward harvest and catch early markets. Greenhouse or tunnel
cultivation of Cantaloupes is practiced in some countries. Is the
US, trellised or bush melons are commonly grown.
A wide variety of flowering types are used, varying from open
pollinated and F1 hybrids, to triploid or seedless watermelons
which need inter-planting with pollinator varieties.
Melons require long, warm, growing periods and plenty of sunshine. Most crops are grown in temperatures of between 77 - 95°F.
Plants are frost susceptible and low temperatures can cause growth abnormalities, poor flower and fruit set and, at later stages of growth, hollowing of the pulp.
Seed germination is inhibited at temperatures below 59°F. In watermelon, temperatures below 55.4°F will stunt growth; significant damage occurs below 45.5°F.
Most melons bear separate male and female flowers on the same plant. Female flowers, which are fewer in number, occur later that the male pollen-bearing flowers.
Insects, in particular, bees are important to aid pollination and fruit set.
Management practices that encourage bee activity – particularly during the morning - over the relatively short flowering period, need to be practiced e.g., reducing overhead irrigation or pesticide application.
In some parts of the world, e.g. USA, the introduction of bee colonies increases yields and brings forward harvest of more marketable crops.
Sunburn is a significant problem in melons, particularly if the area of the melon which is in contact with the soil is left exposed to sunlight. Darker green or striped watermelons are most at risk.
Long periods of high humidity and cloudy conditions result in crops of low °Brix and poor quality fruit.
Maturity occurs after about 1200 accumulated day degrees centigrade. For example, 48 days at 25°C (77°F).
Low temperatures cause growth Pollinating flowers Watermelon flowers, female
abnormalities (Photo courtesy: (left) male (right)
Melons can be grown across a wide range of soils. Best
high-yielding quality crops are grown on well-drained,
deep, highly fertile soils.
Melons have a shallow root system and are intolerant of
drought and waterlogging. Thus, sandier, lighter textured
soils are preferred. On heavier soils, watermelons are
more prone to cracking.
In poorly drained or low pH soils, Fusarium spp. and foot rot can be a problem.
The use of ridges or beds, that are faster to warm-up, will encourage quicker growth and earlier crop development. Beds will also provide better drainage.
A wide crop rotation is advisable, particularly where nematodes are a problem. In some areas, soil disinfection is carried out to minimize nematode damage and soil diseases. Where this is practiced, rotations can be shortened.
Optimum pH is between 6.0-6.6, but crops are grown in soils with a very wide range of pHs.
When pH drops below 5.5, magnesium and molybdenum availability drops and above 6.5, zinc, manganese and iron become deficient.
Seed should be planted at around 1 inch depth and needs warm temperatures of above 52 - 59°F to encourage germination.
The crop is best planted when temperatures will also encourage rapid emergence and early growth.
Increasingly, seed – particularly of more expensive hybrid varieties - is grown on and then planted in plugs prior to transplanting, especially when using plastic mulches.
Spacing is determined by local cultivation practice, the soil’s productive capacity, and factors such as equipment width, irrigation capability and whether mulch is being used.
Spacing will also influence the eventual size and sweetness of the fruit. Close planting will reduce the sugar content of the fruit.
Under trickle irrigation, efficiency of water use is increased, so planting density can also be increased.
Plastic mulch can bring forward harvest by around two weeks ensuring growers can catch any early, premium markets.
Black and wavelength-selective mulches warm the soil and prevent weed growth.
Melons require a constant supply of moisture during the growing season.
The most serious yield reductions result from lack of moisture during flowering and fruit-fill. This can result in misshapen fruit at harvest.
Furrow, sprinkler and drip irrigation is widely practiced in the
major melon producing countries.
Drip irrigation ensures better use of water and reduces disease
risks such as fruit rots as well as ensuring better management of
harvesting intervals. It also allows more precise application of
nutrients, reducing crop growth stresses and minimizing weeds.
Water quality is important. Water applied through overhead irrigation with an Electrical Conductivity (EC) reading of 1300-1400 u s/cm could cause leaf burn. This is less of a problem with trickle irrigation and water with an EC of up to 2000 u s/cm can be used.
As salinity increases, nutrient uptake efficiency declines – particularly of nitrogen and calcium.
In Cantaloupes, the amount of irrigation water needs to be reduced slightly at flowering. Then, during fruit fill, irrigation amounts are increased until the fruit starts to net.
Once the net has properly formed it is important to increase irrigation to levels that encourage fruit fill right through until just before maturity when irrigation again needs to be curtailed so as to ensure TSS
contents remain high. Blossom end rot (BER) becomes a problem if water supply during the rapid growing period is low or intermittent, resulting in low calcium uptake and poor distribution to the fruit.
Plant breeders are increasingly introducing varieties that are resistant to, or offer partial resistance to, a range of diseases, such as alternaria, stem blight, mildew and damping off as well as aphid-borne mosaic viruses.
Growers can minimize the impact of diseases by using appropriate fungicide programs. Integrated crop
management techniques that keep the soil and foliage dry will help minimize outbreaks of diseases such as dampingoff and blight.
Root-knot nematodes are a serious problem, impairing the root system and preventing effective nutrient and soil moisture uptake. Growers need to adopt a sensible rotation or use soil fumigation to reduce pest damage.
Insect pests that include white fly, thrips, cutworms, aphids, caterpillars and cucumber beetles all cause injury to melon plants. Soil or foliar insecticides should be used once local pest thresholds have been reached.
Weed control is essential to reduce competition for moisture and nutrients. This is particularly important at the establishment and early growth stage. Growers most commonly use stale-seedbed
techniques removing the weed burden prior to planting or drilling. Later on in the season, the creeping nature of the plant tends to smother and so reduce the weed burden.
Plastic mulches provide excellent weed control over the planted row – the interrow weeds can be sprayed using approved herbicides or pulled by hand.
Where no mulch is used, care needs to be taken when using appropriate post-emergence herbicides, as young plants are vulnerable to damage.
Plastic mulches also help protect the fruit from ground rot diseases.
Cultivation to remove weeds between rows should be shallow, so as not to disturb the delicate root system of the melon crop.
Gibberellic acid is sometimes used to stimulate fruit set - more commonly in Cantaloupes than watermelon – particularly during cool periods.