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Tomato Care: Stems and Fruit

There can be many reasons why the fruit of your tomato plants are in poor health or just look strange. This article looks at different causes of poor fruit health by first describing the symptom, then the cause and where relevant possible solutions.

This is the fourth in the series on tomatoes, the first looked at strategies for healthy tomato plant growth and the second on tomato root health and the third on leaf health.

Tomato Plant Stem Disorders

External symptoms

  • Brown spreading lesions on stem with brown or grey mould, sporulating freely… Botrytis
  • Brown lesions on site, not sporulating but fine black spots visible within lesion… didymella
  • Black spreading lesion encircling stem, white mould…late blight
  • Black spreading lesion encircling stem, possibly with small amber or honey coloured drops of exudate… stem bacteriosis
  • Black lesion with long fine black streaks up and down stem… double virus streak
  • Discrete black spots on stem, coalescing to form patches… bacterial spot.
  • White cottony mycelium covers stem, soft rot of stem under the mould, balck seed like bodies in the stem pith. Sclerotinina
  • Stems purple phosphorous deficiency cold.
  • Pale green or yellowish streak on stem silvering or chimera
  • Stem golden yellow around leaf base and down petiole tomato russet mite

Tomato Fruit Disorder Symptoms


  • Flat and dull. Beefsteaks are normally a bit flat in nature anyway, but if your have a normal high shouldered tomato which has developed flatter then first check that the seed have set sufficiently. The seed produce the hormones that make the fruit wall thicken and swell so if the seed are not set the complete cycle will be disrupted.
  • Flat sided. Due to seed in one of the internal fruit locules (divisions) not setting so that side of the fruit will develop abnormally. Also called Hollow fruit.
  • Tip on base. If the base of the fruit has an extended tip this is usually put down to being due to cool weather (possibly because the flowers do not fall off so easily). Raise the average temperature (if feasible) if it continues to be a problem.

Tomato Colour

Grey wall and green patches in the ripening fruit is usually put down to one of three causes.

  • Primarily a lack of phosphate disrupting the ripening process.
  • Low potassium will disrupt the ripening process.
  • Changeable weather, in a short time period, can cause this from very sunny through to very cloudy weather.

Some bigger fruited varieties are more susceptible to grey wall than the smaller types. This is a historic condition along with greenback (slow ripening of the shoulders) which has been mostly bred out of the modern varieties.


Some varieties have better taste than others. Some of the beef steak or long shelf life tomatoes generally have reduced taste that some of the smaller sized varieties, though this is a generality. Cherry tomatoes and plum tomatoes will often have more taste but this does vary with variety and the growing environment.

Factors that can affect taste are the nutrient balance in the hydroponic solution and the CF (conductivity factor measured in hydroponic crops) . Generally the higher the CF the better the taste due to a higher concentration of sugars and salts in the fruit. Though the higher the CF the slower the growth so balance is needed.

Other common tomato fruit disorders.

  • If the fruit is split down the side due exposing the inner seed cavity this is called cat face and the cause is unknown. Possibly the growing climate has been too cool.
  • Large, greenish black lesions enlargening rapidly… late blight copper spray required and damage should be evident on the stems and leaves also. Bacterial disease induced by cold wet conditions at any time of the year when conditions are right. Prevention is the best cure with correct greenhouse environmental conditions.
  • Brown to black lesions, may be scabby or water soaked. Bacterial spot.. due to wet conditions on the plant.
  • Small black pustules, which flake off when dry. Bacterial speck due to wetness again.
  • Irregular sunken, dark brown lesions cover most of the fruit surface. … double virus streak.
  • Rusty brown to black, roundish to horse show shaped. Lesions may be sunken or varnish like… spray injury.
  • Dark brown lesions at blossom end of fruit turn black. Blossom end rot due to insufficient calcium while the fruit is developing and growing. The calcium is transported within the plant with water so if water movement is restricted then this can happen
  • Greenish brown soft wet rot in nearly ripe or ripe fruit… botrytis funal mould.
  • Dense white mycelium on surface, soft wet rot beneath.. sclerotinia fungus most likely.
  • Grey brown lesions with concentric rings on the fruit… buck eye rot.
  • Black leathery lesions on top of ripening fruit … with minute black pustules..phoma rot or didymella
  • White raised blisters with fine central sting mark … green vegetable bug bite mark a possibility.
  • White birds eye spot with rough pustule at the centre – tomato canker a bacterial disease.
  • Small spots with white halo, often disappear in fully riped fruit… ghost spot…botrytis.
  • Fruit remains small, dull grey to greeny white…nutritional disorder or the fruit did not set.
  • Ripe fruit bleached white on top half, soft texture or watery beneath the lesion sunscald.
  • Fruit ripens with yellow or green shoulder, well defined division between affected and normal areas.. greenback a genetic disorder less common in modern varieties.
  • Fruit ripens with well defined yellow patches on sides, vascular strands beneath lesion necrotic.. blotchy ripening.
  • Fruit ripens with red and pale yellow marbled appearance… spotted wilt virus.
  • Fruit ripens with yellow or green stripe from calyx to blossom end… chimera or silvering, a genetic disorder.
  • Corky skin russet develops around calyx of green fruit commonly boron deficiency
  • Fruit remains small and russeted all over…. Tomato russet mite.
  • Fruit develops fine hair like cracking in patches or all over just prior to maturity… crazing often due to a high water content in the plant combined with high relative humidity. So the water in the fruit gets to high and the fruit splits.
  • Young fruit spilts open to expose seed cavity… catface
  • Fruit splits at maturity with cracks radiating from calyx… radial cracking
  • Fruit splits with concentric cracks around calyx – concentric splitting
  • Cracks and rot around calyx.. first part of fruit to appear over ripen… large calyx’s prevent drying of the fruit skin in this area…. Increase ventilation and possibly remove the leaf close to the truss to help this, especially with big fruited varieties if this becomes an ongoing problem.

The conditions described above are typical in New Zealand growing conditions. Some will only be seen in a greenhouse crop others are more likely in a home garden.