A cucurbit is any plant from the Cucurbitaceae family. These plants are climbing or trailing plants and include squash, pumpkin, gourd, watermelon, melon, cantaloupe, cucumbers, and marrows. They can be divided into the categories of pumpkins and squash (Cucurbita spp), melons (Cucumis melo), cucumbers (Cucumis sativus) and watermelons (Citrullus lanatus).
The popularity of these plants as a food source has lead to the crop being domesticated and cultivated to develop different varieties. Here are a few possible varieties you can consider planting:
- White Boer type/Light grey: Flat White Boer Ford, Star 7001, Star 7022 Queensland Blue, Crown Prince
- Hubbard: Green hubbard, Chicago worted
- Patty pans: Patty pan, Sunburst, Sunny Delight
- Ceylon: Rovaal
- Marrows: Caserta (home gardens), Salvador, Ambassador, Star 8022
- Table squash: Table king, Table queen
- Butternut squashes: Waltham, Atlas
- Baby gem squash: Star 8001, Rolet
Watermelons (disease tolerance)
- All Sweet (Fusarium and anthracnose)
- Charleston Grey (Fusarium and anthracnose)
- Congo (Anthracnose)
- Crimson Sweet (Fusarium and anthracnose)
- Empire (Powdery mildew, fusarium, and anthracnose)
- Jupiter (Powdery mildew)
- Odem (Powdery mildew, fusarium, and anthracnose)
- Sweet Baby (Fusarium)
- Sweet Princess (Fusarium and anthracnose)
- Hales Best,
- Honeydew Green Flesh,
- Imperial 45,
- Lyon Jumbo,
Climatic and soil requirements
Cucurbits need warm weather. Seeds do not germinate in the cold, nor do plants grow when the temperature falls below 10 ºC. Frost can also severely damage seedlings.
The best temperature is between 23 and 29 ºC during the day, and 15 to 21 ºC for the night. It’s advised to sow from September to November in moderate climates, but between August and October in warmer climates.
The ideal soils for cucurbits are loamy to sandy loam soils that drain well and prevent fruit rot. Soil should be slightly acidic, 6,0 to 7,5 pH. It is however possible to grow cucurbits in a wider pH range.
Pumpkins and squash are full of potassium and beta-carotene. They are used in soup, roast veggies, pies, or bread. It can be boiled, steamed, or consumed raw. The seeds are consumed as a garnish or snack and are rich in zinc. Pumpkins are also used as feed for livestock.
Cucumbers, watermelon, and melon are eaten raw as a snack or can be used in salads. Sometimes cucumbers are even boiled in certain dishes.
Start to prepare the soil by loosening it either with a plough or a hand tool such as a hoe, fork, or spade. Break up any clods. The soil bed should be fine and about 40 cm deep.
You can work some compost, fertiliser, or old manure into the soil. Cover crops can temporarily be planted. After about 5 weeks it can also be worked into the soil. Lime can be applied 4 weeks before planting to correct the pH of the soil.
Irrigate the field before planting.
Seeds can be planted 3 to 4 cm deep. Place 2 seeds per planting station, but slightly separate. Refer to table 1 for detail of planting for different types of cucurbits. Ensure that the seeds make good contact with the soil. Cover the seeds with moist to dry soil. Leave space between rows as well.
Protect the soil surface with a thin layer of mulch. Remove the mulch once plants have emerged to ensure they get enough sunlight to grow strong.
When plants are growing well after approximately 2 to 3 weeks, thin out the seedlings. Be careful not to harm other plants.
Remember to leave aisles between rows for spraying or harvesting.
Muskmelons and watermelons are normally planted in trays as cucurbits do not transplant well. With these two specific types, it helps with early marketing as well.
A soil analysis should firstly be conducted. Fertiliser should be added based on the results.
Roughly 1 000 kg/ha (100 g/m2) of a fertiliser can be worked into the soil before planting. The mixture can have the ratio of 2:3:4 (27). Manure or compost can supplement the chemical fertiliser.
A top dressing can be applied 3 weeks after seedlings have emerged. 120 to 150 kg/ha or 10 g KAN/LAN fertiliser per square meter. Take care to apply it 10 cm away from the stems. 5 weeks after this, another top dressing can be applied. Irrigate the field after applying fertiliser.
Do not irrigate the field heavily before seedlings emerge so that there is no crust for them to break through. Should it rain before then and a crust does form, make an effort to prevent the crust from forming through light irrigation.
The soil should be moist throughout the growing season. Irrigate the cucurbits regularly to prevent water stress. Ensure uniform irrigation.
Remember to reduce irrigation as the plants get closer to harvesting.
Fruits can be harvested carefully by picking them from the vines when mature. The harvesting calendar for different cucurbits are as follows:
- Squashes: 60 – 75 days
- Butternut squash: 90 – 100 days
- Muskmelons: 90 – 100 days
- Winter muskmelons: 105 – 125 days
- Watermelon: 95 – 120 days
- Pumpkin: 120 – 150 days
Yield estimate for pumpkins and melons: 30 kg/m2.
Yield estimate for squash: 20 kg/m2.
Pest and disease control
Good crop management such as weeding and practicing crop rotation prevents the spread of diseases and pests. Careful, shallow cultivation can destroy weeds, but be mindful of the shallow roots of cucurbits. Crop rotation can be practiced by planting a different crop type such as leafy vegetables the following season.
This disease is caused by Sphaerotheca fuliginea. It can escalate in severity when the weather is hot and dry. First signs of the disease is a powdery white growth on the leaves and stems. Leaves start to die off and the yield as well as the quality of the fruit is reduced.
The disease can be controlled with chemicals and planting disease tolerant cultivars. Practicing good weed control also helps.
Downy mildew is caused by Pseudoperonospora cubensis. It can be recognised by yellow or brown spots on the upper leaf surface, as well as grey/purple fungal growth on the lower side of the leaf. Wet, humid weather makes the plants more susceptible to this disease.
Control of the disease include chemicals and disease resistant cultivars. Over-irrigation should also be avoided. Ensure that plants are planted in well-drained soils.
This disease is caused by Fusarium oxysporum, and it leads to plants wilting and dying. It can be confirmed that the plant is suffering from this disease by cutting the stem. The tissue will have a brown discolouration. The disease is usually more prevalent in warmer soils and the pathogen can be seed-borne.
To attempt controlling the disease, first start by planting disease-free seed and tolerant varieties. Field sanitation can be done to control the nematodes. You can also look at the soil and adjust the pH to 6,5 with the use of nitrogen.
Gummy stem blight/black rot
Gummy stem blight, or black rot as it is also called, is caused by Phoma cucurbitacearum. The first signs of an infection are gummy stem lesions that eventually lead to the plant wilting and dying. On the lesions, small, black, pinpoint sized fruiting bodies can be seen — this is the pathogen.
With butternuts, large cream-coloured fruit rot can be seen.
In order to control the disease, chemical control and field sanitation can be practiced. Plant disease-free seed and make sure not to over-irrigate.
Phytophthora crown and root rot
The bottom half of the stems and roots show brown rot that leads to the plant wilting and dying. The fruits also eventually rot and show white growth on the outer surface. This is caused by Phytophthora capsica.
Steps to control the disease include chemical control and crop rotation. Avoid over-watering plants and make sure that the soil is able to drain well. Always use clean water.
Angular leaf spot
When cucurbits start to show brown spots bound by yellow veins on the leaves, it can be angular leaf spot. It is caused by Pseudomonas syringae pv. lachrymans. The way spots develop has an angular shape.
The disease can be controlled by planting disease-free seed or tolerant varieties. Crop rotation also assists in prevention. Use alternative irrigation methods that do not include overhead irrigation.
These small insects vary in colour, ranging from green and red to black or brown. They are soft-bodied insects that often appear in clusters.
Aphids feed on the plant juices and transmit viral diseases. Aphids can be controlled with registered chemicals. Alternatively, on smaller plots specifically, plants can be sprayed with a light liquid soap mixture or repellent. Ladybugs are their natural enemies.
These flies sting fruit smaller than 10 cm. They then proceed to lay eggs in clusters under the peel. This makes the fruits more susceptible to infection with pathogens and rot.
One way to control the flies is to put out bait when flowering starts. A mixture of Dipterex, sugar and water can be made. Change the mixture every 7 to 10 days.
Cucurbit leaf beetles
There are three common cucurbit leaf beetles known in Southern Africa that regularly attack pumpkins. The black and orange insects damage both the flowers and the leaves.
Take care to exercise control as soon as they are noticed in spring. They gradually migrate through cucurbit fields in a number of weeks. You will need to scout daily when the crop begins to emerge.
Field sanitation helps prevent an outbreak. This can be done by removing the debris of a harvested crop as soon as possible. Also store any implements or equipment properly and away from the field so that there isn’t any hiding place for beetles.
The information provided in this article is credited to the Agricultural Research Council Vegetable and Ornamental Plant Institute (ARC-VOPI). For more information, contact +27-(0)12-841-9611 or visit www.arc.agric.za.