The most easily overlooked part of harvest is the fruit that fell to the ground and the fruit left on the tree. It is tempting to think it need not be picked up, but it becomes the breeding ground of coffee's most troublesome pest. This is about the coffee berry borer.
The coffee berry borer causes over US$500 million of damage a year worldwide, and when damaged beans exceed 5% of the harvest, the grade drops. Because it eats the inside of the fruit, it cannot be seen until processing (Johnson et al., 2020).
What is truly frightening is that this insect becomes the door for mould. Through the holes it bores, rot-causing fungi (Colletotrichum and Fusarium) enter, bringing bitterness, astringency and loss of aroma (Bayman & Serrato-Diaz, 2025). Insect damage leads straight to taste defects.
One study reported that a single infested fruit left on the ground can infest about 959 fruits on the tree. Fallen fruit remains a nest for the insect for about 140 days (Constantino et al., 2021). One fruit turns into three figures.
So the first line of control is not chemicals but a harvest that leaves nothing at all. Integrated management guides also put field hygiene and harvesting fruit of every stage first, with post-flowering scouting and fungi the insect dislikes as supporting measures (University of Hawaiʻi CTAHR, IP-41). It has also been shown that infestation falls with altitude (Constantino et al., 2021). Cool highlands are an advantage for the insect problem as well as for taste.
The basis is, again, leaving nothing. On the tree and on the ground, ripe, unripe, over-ripe and even dried-out fruit, we take everything in that pass. Fallen fruit is picked up the same day. Fruit with bore holes is rejected by flotation. Before spraying anything, first deny the insect a nest.
How dangerous is this insect? It has the power to wipe out a whole village. Once it spreads, it can force farmers to cut down or burn their trees. Put the other way, diligent picking-up is enough to stop it getting that far. Modest work, but no control is more effective.
The completeness of harvest is not about this year's yield. It decides next season's insect density, reduces the door to mould, and in the end protects the cup. Pest management and quality management look like different jobs and are the same one. That is why we leave not a single fruit.
Because it eats the inside of the fruit and cannot be seen until processing, and the grade drops when damaged beans exceed 5%. Rot-causing fungi also enter through its holes, leading straight to taste defects.
Yes. A single infested fruit left on the ground can infest about 959 fruits on the tree, and fallen fruit stays a nest for about 140 days. The first line of control is not chemicals but clean harvest.
Infestation tends to fall with altitude, but it does not reach zero. Rejecting bored fruit by flotation is necessary at every altitude.
For leftover and over-ripe fruit see The upper deadline of ripeness; for handling after picking, Post-harvest holding; for altitude and quality, Does altitude decide quality; for the whole picture, Harvest and selective picking.
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