What's eating my chinese yam?

Chinese Yam is a vigorous climbing vine that is relatively pest-hardy. Aphids and scale insects attack the aerial stems; root-knot nematodes are the most serious threat to tuber yield. Mealybugs can colonise stems in warm conditions. Crop rotation and clean planting stock are the primary defences.

Microscopic worms invade the long tuberous roots, causing knotty galls and disfigured, stunted, and poorly-yielding tubers; symptoms often not visible until harvest. Rotate Chinese yam with non-host crops for at least 3 years; use certified clean planting stock; soil solarisation in hot climates; avoid transplanting soil from infested beds.

Colonies on the twining young stems and leaf undersides; honeydew and distorted leaf growth; vectors of viruses that can further reduce tuber quality. Water-jet knockdown; insecticidal soap or neem oil; encourage ladybirds, lacewings, and parasitic wasps.

White waxy patches on stems and leaf axils; sap feeding weakens vines; sticky honeydew encourages sooty mould on leaves and aerial tubers (bulbils). Wipe off with a damp cloth and 70% rubbing alcohol; neem oil spray; introduce or encourage parasitoid wasps; quarantine new planting material.