Passion fruit collar rot

a whole vine — or one big arm — suddenly wilts. The leaves droop, yellow and hang, and the vine looks thirsty even when the soil is wet. Over a few days to a couple of weeks the whole vine collapses and dies. On a vine you were already harvesting from, this sudden death for no clear reason is the classic warning.

you will find a dark brown to black, water-soaked, sunken rot ringing the stem at the ground. The bark is soft and cracked, may ooze or gum, and if you scrape it with a knife the wood underneath is brown, not green and living. Once this rot rings the stem all the way round (girdles it), everything above it is doomed — there is no cure.

scrape the soil back and the roots are brown, soft and rotten instead of white and firm. In wet weather, fruit hanging low and splashed with soil can show a firm grey-brown rot, and leaves near the ground can go dark and blighted.

with Fusarium wilt, the other vine-killer: split the stem lengthwise — Fusarium wilt shows brown streaks in the wood running up the stem, but the collar itself stays firm, not soft and wet. Collar rot is a soft, sunken, rotting wound at the very base (and Fusarium solani often joins in that same collar rot). Also tell it apart from woodiness virus (mottled leaves and hard, misshapen fruit, but no stem-base rot), and from plain waterlogging or drought (the vine wilts, but there is no browned, soft, cracked collar and no brown wood underneath).

through the wet season and every warm, rainy spell — from the young, just-planted vine settling in right through the vine growing its framework and carrying fruit (the establishment, development, flowering and fruit-filling stages). Warm (about 20–35 °C) wet soil is what the mould explodes in — step up your checks after heavy rain and wherever water pools.

every week, walk a big "W" shape so you cross all four corners and the middle — not just the row by the path. Make about 5 to 10 stops along the way, and always check the low, wet, poorly drained corners first, because that is where the rot starts.

pull back the mulch and soil and look closely at the collar (the stem-base at the soil line) for browning, softening, cracking or ooze; then look up for any vine wilting or yellowing for no clear reason. A wilting canopy above and a soft brown collar below together mean collar rot.

the threshold is the very first vine you find wilting with a soft, brown, rotting collar — 1 sick vine is enough to act, because it cannot be cured and it seeds the soil with the mould for years. And when warm, wet weather and standing water set in, act before any vine sickens — drain the water off, bare and dry the collars, and protect at-risk vines rather than waiting to find a dead one.

the moment a vine wilts with a rotted collar, dig it out with as much of its roots as you can and destroy it — burn it or bury it deep, well away from the plot. Do not compost it, and do not replant passion fruit in that exact spot. Disinfect your tools (wipe with bleach or pass through a flame) afterwards so you don't carry the rot to a healthy vine.

on high-value or at-risk vines you can use a phosphonate (phosphonic acid) as a trunk-paint or soil drench, or a metalaxyl-based soil drench, around the collar and root zone; a copper protectant on the lower stem and splashed fruit helps in wet weather. Understand what they do: they protect healthy vines and slow the spread — they cannot raise a vine whose collar is already girdled, so they must go on before or at the very first sign, never as a hoped-for cure.

cover your skin, eyes, nose and mouth; apply in the cool of the morning or evening with the wind at your back; keep the product off fruit you'll eat or sell soon, off drinking water and rivers, and away from children and bees. Respect the pre-harvest interval — the number of days the label says you must wait between the last treatment and picking or selling the fruit. Wash yourself and your clothes afterwards.

don't lean on one product forever — rotate to a different chemical group, and never rely on metalaxyl alone, because Phytophthora learns to shrug it off. Chemicals only ever buy time; pair them with the drainage, grafting and sanitation that actually keep the rot out.

if vines keep dying one after another down a row, the land is almost certainly too wet and now infested. Fix the drainage hard, stop replanting passion fruit there for several years, and rotate to a non-host crop on that ground. Start your next plot on fresh, well-drained land with grafted vines — that is the only way to truly get ahead of collar rot.