The Pest You Can Barely See

And it’s true.  Thrips are tiny insects, barely visible to the naked eye, that feed on plants by sucking their juices.  There are many types of thrips, and each one prefers a certain type of plant, but they are not particularly picky eaters.  Flower thrips, for example, will feed on almost any plant that produces a flower.
Large infestations of thrips in a crop can kill it entirely, or reduce the yield dramatically.  And because of the way they feed, they transfer viruses from plant to plant, spreading them over large geographic areas.
Thrips thrive in hot and dry places, and rain or other atmospheric moisture is their enemy: a single drop of water can wash a hundred of them away with it.  As farmers world-wide have shifted to drip irrigation in order to conserve water, thrips have become a much larger problem for agriculture.  Climate change has also played a role in their success.
At Terra Firma, and in the Central Valley in general, thrips threaten two of our biggest crops: tomatoes and onions (including leeks).  In the tomatoes, they transmit several incurable and generally fatal viruses.  With onions, they simply suck the juices out of the succulent leaves until they die.
It’s not particularly hard to kill a thrip.  We spray plants with a mixture of water and plant oils (garlic, rosemary and clove).  The problem is that they keep coming back.  They breed in green grass and winter weeds, but when the rains stop and the foliage starts to die they flock to the lush green plants in our irrigated fields.  And as our crop plants get bigger, it gets harder to get the spray onto all the surfaces they are feeding on.  Our goal is keep the plants healthy until a month or so before harvest.
There is one crop we grow, however, that is unique impacted by thrips.  Nectarines are attacked by thrips in their first few weeks of life, while they are still fully enclosed in the flowers that give birth to them.  The tiny insects feed on the fruit while it is the size of a head of a pin. creating scars on the smooth skin that actually grow and expand as the fruit grows.  While they are closely related to nectarines, peaches are protected from thrip damage by their fuzzy skin.
Rain during nectarine bloom is a double whammy.  The wet weather drives the insects to seek out shelter inside the flowers, and it also keeps us from spraying to control them.  And the longer it continues, the more time the thrips have to damage the fruit.  This year’s late rains came just as our nectarines were setting fruit.  As a result the crop — which was already light — sustained heavy damage.
Just about every nectarine in our orchard has at least some scarring on it. Some thrip scars are purely cosmetic, making the fruit ugly but not affecting its edibility or flavor.   Others cause the fruit to crack as it grows, essentially ruining it.  We are sorting this year’s nectarines along these lines.  We appreciate you seeing beyond their physical appearance and focusing on their inner beauty.


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