What Does it Indicate When You See Black Spots on Green Tomatoes on the Vine?

Bacterial Speck

• Bacterial speck, caused by the pathogen Pseudomonos syringae pv. tomato, appears on green fruit as small, slightly raised black spots about 1/16-inch in diameter. Leaves also develop black lesions with faint yellow halos up to about 1/4-inch across. Cool, moist weather encourages bacterial speck. The pathogen survives on weeds and in soil or on debris, so good sanitation practices will help to minimize bacterial speck problems. Bacterial speck is a very superficial problem, only affecting the tomato skin.

Blossom End Rot

• Blossom end rot appears as a brownish-black spot up to 1 inch in diameter on the blossom end of the tomato fruit. The sunken spot may gradually enlarge and develop a leathery look. Blossom end rot is a physiological disorder caused by a calcium deficiency frequently related to fluctuations in soil moisture levels. Cold soil, excessive nitrogen or a pH imbalance could also contribute to blossom end rot. Mulching around the tomato plant, watering the plant correctly and adjusting the soil pH, if needed, will prevent further problems with blossom end rot.

Stink Bug Feeding

• Various species of stink bug may feed on tomatoes. These insects are brown or green with varied markings and are shield shaped. Stink bug feeding appears on green fruit as dark specks surrounded by light discoloration that remains light colored as the fruit ripens. These pests can also introduce disease pathogens with their mouth parts. Stink bugs overwinter on weed hosts like legumes, blackberries, mustards and thistles, so keeping the area around the tomato planting free of weeds will help to minimize stink bug problems. These pests have several natural enemies, so preserving the populations of beneficial predators and parasites by avoiding the use of broad-spectrum, persistent pesticides is important.

Early Blight

• Early blight, caused by the fungus Alternaria solani, appears as black or brown spots about 4/10-inch in diameter on fruit, leaves and stems. On fruit, the spots are sunken and dry with a concentric pattern. Alternaria spores spread via wind and require moisture to infect the tomato; this disease can seriously affect the plants if weather is cool and humid for an extended period of time. Problems with early blight are minimized by avoiding overhead watering and using good crop-rotation practices.

Additional Possible Causes of Black Spots

• The fungal disease anthracnose causes water-soaked circular spots with a darkened center, but generally does not affect immature green fruits, as it tends to develop on ripe tomatoes. Lygus bug feeding first appears similar to stink bug activity, but the area below the feeding site draws out, causing slight cracking. Lygus bugs do not transmit yeast or fungal pathogens. Bacterial spot, caused by Xanthomonas campesiris pv. vesicatoria, also occasionally affects tomatoes. This disease first appears on green fruits as small, water-soaked spots that grow to 1/4-inch in diameter and become slightly raised with a brown, scabby center.