Codling Moth Damage on Egremont Russet Reduced with a Trappit Pheromone Trap

Egremont Russet flowers early, often in the third week of April in southern England, which puts its fruitlets ahead of many dessert varieties and squarely inside the first flight period of Cydia pomonella. The Trappit trap works on one narrow mechanism: a rubber septum loaded with codlemone, the synthetic form of the female moth’s sex pheromone (E,E)-8,10-dodecadien-1-ol, releases a plume that male moths track upwind into the sticky floor of a white delta housing. Females are never caught. The trap does not protect the fruit directly. It converts an invisible flight into a countable number, and that number drives every decision downstream.

Hang the trap at head height in the outer canopy, on the sheltered side away from prevailing wind, roughly two to four weeks before petal fall. One trap covers a single garden tree or a cluster of three or four; commercial monitoring uses one per five hectares, so a back garden is heavily over-covered by a single unit. Check the sticky base twice a week and record the count each time.

The biofix date is the number that matters

Counting moths is not the point of the trap. The point is fixing a date. Biofix is the first evening on which you catch moths and continue to catch them on subsequent checks, confirming that sustained flight has begun rather than a single stray male drifting in from a neighbour’s tree.

From biofix, egg-laying follows within a few days, and egg hatch, the moment the neonate larva bites into the skin of a fruitlet, is governed by accumulated warmth. Growers track this in degree-days above a lower threshold of 10 degrees Celsius. Roughly 250 degree-days after biofix, the first eggs hatch; a warm spell compresses that window, a cool wet fortnight stretches it. The Trappit count gives you the start of the clock, and a maximum-minimum thermometer in the canopy or a nearby weather station feeds the accumulation. This is why a trap hung too late is worse than useless: miss biofix and every subsequent calculation is anchored to a wrong day.

The larva spends only a short time exposed on the fruit surface before tunnelling toward the core. That surface window, a day or two, is the only period any surface treatment can reach it. After entry the larva is sealed inside, feeding on the seeds, and no spray, barrier, or predator reaches it until it exits weeks later to pupate.

When the count stays near zero

A trap that catches two or three moths across an entire first flight on a single Egremont Russet in a suburban garden signals a population too low to justify any intervention beyond the trap itself. Record the zeros. They are as informative as the peaks.

Reading a rising count against Egremont Russet’s habit

Egremont Russet sets fruit in tight clusters, and codling larvae exploit the contact point where two fruitlets touch, entering under cover of the join where the skin is thinnest and least exposed. This changes what a rising trap count means for this variety specifically. On a spaced dessert apple the larva must enter through open skin; on a clustered russet it slips into a protected seam, which means damage can appear even when catches are modest, because the entry sites are easier.

The russeted skin itself, the corky brown surface that defines the variety, offers no meaningful resistance to a neonate larva. Corking is a surface phenomenon a fraction of a millimetre deep; the larva chews through it in minutes. Growers sometimes assume the tough skin deters entry, and the assumption costs them fruit.

A count climbing past five or ten moths per week on a single tree, sustained across two checks, indicates a first generation large enough that the second flight in July and August will be substantial. Cydia pomonella runs two generations in most of England in a warm year, occasionally a partial third in the south. The second generation does the most harvest damage on a mid-season variety like Egremont Russet, because its larvae are entering fruit that is sizing up through August toward the late-September to early-October picking window.

The trap count from the first flight is your forecast for the second. A heavy first catch means the July trap needs watching closely; a near-empty first flight usually means the second is manageable. Reset the trap with a fresh sticky base between generations, because a floor crowded with dust, debris, and old moths loses its catch efficiency, and replace the codlemone septum according to its rated field life, typically four to six weeks, since the pheromone volatilises steadily and a spent lure reads as a false zero.

Mating disruption, the commercial alternative, floods an orchard with so much codlemone that males cannot locate females at all. It needs a minimum treated area of a hectare or more to work, because edge effects let mated females fly in from outside. On a single garden tree disruption fails for exactly this reason, which is why the monitoring trap, not a disruption dispenser, is the tool that fits a small planting.

Corrugated cardboard bands and the larvae leaving the fruit

Mature larvae exit infested apples in late summer and crawl down the trunk to find a sheltered crevice in which to spin a cocoon and overwinter. A band of corrugated cardboard, corrugations facing inward, wrapped around the trunk about a metre up and tied in place, intercepts them. The larvae settle into the flutes.

Remove and burn the bands in autumn once fruit is picked, and you have physically removed a portion of next year’s founding population before it can pupate. On a single tree this is a genuine reduction in overwintering numbers; the Trappit count the following spring will reflect it if the interception was thorough.

Where the trap stops being enough

At high sustained counts, the trap only tells you that intervention is needed and when. It does not deliver it. Codling moth granulosis virus (Cydia pomonella granulovirus, sold as products such as Madex) is the treatment that keys directly to the trap-derived timing, because it must be ingested by the neonate larva during that brief surface window before it tunnels in. Spray it at 250 degree-days after biofix, when hatch begins, not when you first see moths.

The virus is specific to codling moth larvae and breaks down under ultraviolet light within a few days, so timing against the hatch window is the entire game. Applied before hatch it degrades before the larvae emerge; applied after entry it never reaches them. The trap-derived biofix and the degree-day accumulation are what place the spray inside the only window where it functions.

Pheromone confusion, cardboard banding, granulosis virus, and simple removal of windfalls all lean on the same information the delta trap produces. Strip the trap out and each of them becomes guesswork against an insect that spends most of its life sealed inside the fruit where nothing can touch it.

What the trap cannot tell you

A pheromone count measures male flight. It does not measure how many of the females those males mated with actually laid viable eggs on your particular tree, nor how many of those eggs hatched onto fruit versus leaves. Two gardens with identical Trappit counts can end the season with very different proportions of tunnelled fruit, because egg-laying success depends on evening temperatures during flight, on humidity, and on how much fruit surface the females found. The trap forecasts pressure and fixes timing; it leaves the question of exactly how much of that pressure converted into damage on your Egremont Russet to be answered only by cutting open the apples at harvest and counting the tunnels.