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Tomato Root Growth and Care

Often the cause of poor looking plants is be due to bad root health. This article looks at different causes of poor root health by first describing the symptom, then the cause and where relevant solutions. It is the second in the series on tomatoes, the first looked at strategies for healthy tomato plant growth.

All the roots are dead. (brown-black etc.)

Poor sugar supply to the roots, from the plant, so the rate of root regrowth is less than the rate of root death leading to greater and greater stress on the plant. A bit of a vicious circle. Prevention is the best cure so ensure that the plant density (per m2) is correct for the seasonal light levels, that the truss pruning is correct and that the nutrition is suitable for the season.

Roots can be attacked by pathogens, usually fungal. This is typically connected to the first reason of plant stress as a healthy plant can usually resist fungal attack while a weak plant has reduced natural defenses resulting in a high-risk situation.

Possible root fungal pathogens are:

Pythium: A water mould which lives happily in the soil environment in water, with different pythium strains optimal at different temperature ranges. Attack the fine root hairs at first rather than the main primary root structure. So physical damage is not often visible to the naked eye but seen as wilting due to the reduced water uptake. Over time the infection can spread with the damage becoming visible with death (often complete) of the roots turning a brown-black colour.

Phytophthora: Similar behaviour to the pythium in that the roots turn a black-brown colour and will travel up the stem of the plant causing a black colour rot leading to wilting. The commonest Phytophthora species in New Zealand glasshouses is P.cryptogea.

Verticillium, and fusarium oxysporum (+ other less common fusarium species) both of which are usually seen as a collar rot. Collar rot can be seen as a general rotting and girdling of the tomato stem at the surface of the soil. These days this is not as severe as in previous years for soil growers. Modern varieties are resistant to some verticillium strains and the hygienic environment of greenhouse growing in media , rather than repeatedly using the same soil year after year, has reduced its occurrence.

Verticillium causes the plants to wilt from the base upward with the leaves turning yellow. Fusarium strains can be debilitating with f. oxysporum typically the most common. Other strains have do exist with Crown Root Rot a significant problem in Europe though some strains are resistant to this.

Colletotrichium coccoides: A fungal disease causing black dots to appear on the roots, this disease is seldom debilitating and is most likely just to cause a reduction in production.

Corky Root: Common in bags only and in soil in previous times. Causes hard nodules to develop on the roots.

Bacterial Diseases: The usual path of infection is through damage to the plant stem from during the seedling stage or from a leaf wound, root system infection is not so common.

Viral Diseases: Usually transmitted by insects such as thrips, aphids or whitefly rather than through the roots.

Brown root tips:

Often conencted to reasons related to sugar supply as described in the article describing tomato plant health. Look at ways to reduce the stress on the plant so more sugars are available for the plant.

Thick roots overflowing the hydroponic gully.

This is usually at towards the end of a crop or if the crop has been inter-planted. Most of the new root growth is at the base of the root mat or at the sides so if the roots get very thick then the depth of the water will increase with a cortresponding decrease in water flow rate and hence a drop in oxygen level. A sinple solution is to fold the roots underneath so reducing the width of the root mat by half with each outside 1.4 folded under. This is most successful on younger vigorous crops which are most able to grow new roots. Also only do this on a cooler cloudy day which will reduce the water stress on the plant providing time for root regrowth to establish.

Limited root growth:

Chances are if the tomato plants have limited roots then the tops also will be small and thin. Often root disease can be due to a high concentration of fungal spores in the hydrpooinc gully or pot which are killing any young roots as they grow out of the pot. The pots/system will need some form of treatment to reduce the fungal population to allow the roots to establish. In established plants, removing a truss will providea boost in the sugar supply allowing for more rapid root growth which can help. In severe situation it has been known for growers to top the young plants and then when the roots have established to grow on from a lateral. If this is a regular situation then check for possible sources of infection such as infected potting mix, poor quality water and a leak in the NFT system allowing soil water to enter the system. A shallow bore will also often result in infection by soil borne fungi especially after heavy rain when there is a markedly increased rate of runoff. Water from streams and rivers is often loaded with fungi and should ideally be treated before use.

Other possible reasons for limited root growth can be:

  • Poor nutrition (such as low nitrogen or phosphate) which will reduce the vegetative growth.
  • A low pH (acidic) less that 3.5 or a high pH of greater than 8 – 9 (alkaline) which at these level will burn the young growth. Check the pH with good quality pH slope and buffer.
  • A very high CF stunting new growth.
  • Poor intermittent water practice resulting in drying out of the young root mat so killing the young roots.

Young root nodules growing at base of stem.

A sign of root reduced uptake of water from the roots triggering the plants to try and grow new roots. Causes will be root disease or collar rot.

There are many different reasons for poor tomato root growth and this articles looks at some of the possible causes and care.

The article is intended only as a guide, as some growing conditions, such as high temperature levels, salt levels are very locality specific. Talk to your local garden center/ expert for information which is specific to your situation.

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