Root-knot nematode

Root-knot nematodes are microscopic roundworms that feed inside grape roots, causing them to swell into small galls. Those galls disrupt the roots’ ability to take up water and nutrients, so infested vines behave like they’re under drought stress — stunted, yellow, and unproductive — even when they’re watered. Damage builds slowly over years and is usually patchy, hitting hardest on light sandy soils and on ground that has grown vines before.

It’s easy to confuse the root galls with phylloxera, but the two differ: phylloxera makes hooked galls on the fine root tips, while root-knot swellings sit along the roots themselves; crown gall, by contrast, makes one large tumour up at the crown or graft union. Because there’s no practical rescue treatment for a home grower, the whole strategy is preventive: plant on resistant rootstocks, don’t replant vines on tired vine ground without a break, and keep the soil biologically healthy.