There were a number of reports of excessive gold fleck (sometimes called gold speck) on tomatoes in Missouri this year. Gold fleck is characterized by the presence of a multitude of very tiny gold or yellow specks uniformly spread across the epidermis of the tomato fruit. When gold fleck is very heavy, the fruit takes on a yellowish-orange hue instead of being red.
It is easy to mistake gold fleck for feeding damage from insects such as thrips, spider mites or stink bugs. As a matter of fact, the cause of gold fleck originally was mistakenly identified as thrips feeding damage. However, insect damage produces larger yellow specks which usually are irregular in their distribution (often clumped in patches) on the surface of the tomato fruit whereas gold fleck is more uniform.
Gold fleck is a physiological disorder and not a disease. Disorders are not pathogenic in cause and cannot be spread from one plant to another, although a majority of plants in a planting might manifest the disorder. There are several theories relative to the cause of gold fleck; most involve the elements potassium and calcium making it a nutritional problem. It has been documented that calcium accumulation and calcium-oxalate crystallization in the fruit increases gold fleck severity. This helps to explain why those tomato varieties less susceptible to blossom-end rot (unfortunately) seem to be more susceptible to gold fleck. Most likely this is due to the tendency of BER-resistant varieties to accumulate calcium in their fruit.
Second, calcium frequently accumulates when potassium is not being properly supplied to tomato plants due to potassiumâ€™s tendency to antagonize calcium uptake. Therefore the potassium:calcium ratio of tomatoes is known to influence gold fleck severity. Growers who fertilize tomatoes calcium nitrate heavily without supplying additional potassium are more likely to experience gold fleck than those who rotate calcium nitrate with a fertilizer high in potassium such as 4-18-38.
Finally, gold fleck has been associated with humid conditions and high tunnels early in the harvest season certainly fit that description. There is some evidence that points to the fact that potassium uptake by the tomato is more rapid in low humidity and less so in high humidity. Slow potassium uptake would adversely affect the potassium to calcium ratio and gold fleck severity for the reason described above.
Just as beauty is only skin deep so is gold fleck. It does not affect the internal tissue of the tomato fruit nor alter its flavor. However, consumers associate appearance with quality and quality with price. Measures should be taken to control gold fleck whenever possible.
REVISED: December 1, 2015