Here is a brief overview of the main diseases and pests that can threaten pumpkins, squash, calabash, marrow, watermelons and cucumbers and other cucurbits.
Caused by Sphaerotheca fuliginea. It starts as a white, powdery growth on the upper surface of leaves, and leads to reduced yield and poor fruit quality.
Control: Chemical control is essential; plant tolerant cultivars; control weeds.
Caused by Pseudoperonospora cubensis. The disease appears as yellow or brown spots on the upper leaf surface, with a grey/ purple fungal growth on the lower surface.
Control: Chemical control essential; plant tolerant cultivars; avoid over-irrigation; plant in well-drained soils.
Caused by Fusarium oxysporum. This disease favours warm soil temperatures. Plants wilt and die. When the lower stem is cut open, stem tissues are light brown in colour.
Control: Plant disease-free seed; plant tolerant varieties; adjust soil pH to 6,5 using nitrate nitrogen; control nematodes.
Phytophthora crown/root rot
Caused by Phytophthora capsici. The lower stem and roots become brown and rot, causing plants to wilt and die.
Control: Chemical control; avoid over-irrigating plants; use well-drained soil; use clean water (borehole or municipal water); crop rotation.
May be caused by cucumber mosaic virus (CMV), squash mosaic virus (SqMV), watermelon mosaic virus (WMV), and zucchini yellow mosaic virus (ZYMV). Symptoms include a mosaic pattern on leaves that, in severe cases, result in a shoestring effect. Fruits can be malformed and bumpy, and seeds can also be malformed.
The viruses are transported mainly by infected seed or insects such as aphids or cucumber beetles.
Control: Remove virus-infected plants from the land and destroy. Buy disease-free seeds from certified seed companies.
These soft-bodied insects often appear in clusters. They are very small and may be green, red, brown, or black. They suck plant juices and transmit viral diseases.
Control: Aphids can be controlled with registered chemicals. On smaller plots, spray with light liquid soap or repellent mixes, such as onion and garlic extracts.
This pest stings young fruit (usually smaller than 10cm) and lays eggs in a cluster under the peel. Infected fruit rots.
Control: Put out bait consisting of Dipterex, sugar and water when flowering starts. Control with pesticide every seven to 10 days.
Cucurbit leaf beetles
At least three common cucurbit leaf beetles attack pumpkins in South Africa. They are all black and orange and damage flowers and leaves.
Control: Cucurbit beetles must be controlled when they are first noticed in the spring. Daily scouting is essential during the emergence and early life of the crop while the plants are small and susceptible.
Source: Production Guideline for Summer Vegetables, ARC.