Root rot of the processing tomatoes industry was associated with Phytophthora nicotianae var. nicotianae, which is a fungus-like water mould, technically called an ‘oomycete’. It has been a widespread issue, impacting direct-seeded, furrow-irrigated crops as well as crops susceptible to flooding following severe rains.
Yield losses due to root rot can account for 25% of the total annual production. Individual farmer losses might be substantially larger.
Symptoms of the disease
The above-ground symptoms of the disease include:
- a stunted appearance
- the die-back of tops
- buckeye rot of fruit.
Phytophthora commonly infects the tap roots, causing a brown discoloration in the vascular tissue around the crown (see photograph).
In extreme circumstances, the rot may totally cut off the tap root. Sometimes, a mass of fibrous roots will develop at the crown to compensate for the loss of the tap root.
When severely sick plants are stressed by water (for example, under hot, windy weather), the tops wilt and the plants may perish.
Buckeye rot of green and mature fruit looks as a brown, hard rot with water-soaked lighter-colored edges. That might happen when the fruit comes into touch with the ground or sits in water.
The disease may also harm young seedlings. Symptoms in seedlings include the collapse of the stem near the base of the plant.
Controlling root rot
In the past, many growers have managed to avoid severe disease outbreaks by long crop rotations or leasing new ground for tomatoes. Yet, when additional land becomes rare, producers are compelled to seek different management methods.
Some soil-applied systemic compounds have been found in studies to be effective as short-term therapies for root rot.
Since Phytophthora thrives in wet soil, you may limit the disease’s occurrence and severity by taking the following steps:
- enhance soil drainage – for example, by amending the soil with gypsum and raising the height of beds
- minimise the period required for each irrigation
- Overwatering should be avoided, particularly during the early phases of crop growth, since seedlings do not need as much water as mature plants and seem to be more vulnerable to severe illness.
Furrow irrigation times may be reduced by:
- increasing the slope or fall of the paddock
- reducing the length of the run.
Trickle irrigation and other alternative irrigation methods may also give more accurate water control.
Spread of disease
Phytophthora exists as resting spores in the soil.
When the soil is moist, these resting spores can develop sac-like structures known as sporangia. They contain a large number of swimming spores (zoospores).
As the soil becomes moist, zoospores are released and swim to surrounding tomato roots.
More sporangia form in infected root tissues as the illness progresses, and the cycle of zoospore release and root infection continues throughout the growth season.
Phytophthora nicotianae develops most quickly in temperatures ranging from 25°C to 28°C, which are common in the field throughout the tomato-growing season in Victoria.
Phytophthora thrives under moist soil conditions caused by irrigation or rainfall. This is because zoospores can swim in the water-filled pores between the soil particles.
Extended irrigation or waterlogging may lower soil oxygen levels, making root rot more severe. Soils that have slow water penetration or poor drainage will also provide ideal conditions for disease.
Survival of Phytophthora
Little is known about Phytophthora survivability in soil, however tomato crops have been found to be damaged by the illness even after a 6-year rotation.
Can tomatoes come back from root rot?
Tomato root rot is both lethal and spreadable. Remove the affected plant as soon as possible, taking care not to infect neighboring plants. Do not immediately plant a fresh plant in the same location; the soil is diseased as well. If it happens in a pot or greenhouse, remove the affected soil and make sure the illness is gone.
Can root rot be stopped?
The roots must be kept healthy in order to treat and prevent root rot in plants. One should avoid overwatering, allow good drainage, replace the soil if needed, and select healthy plants.
Does Epsom salt help tomato end rot?
One trick is to put a scoop of Epsom salt into each hole when planting tomatoes. Some gardeners swear it prevents blossom end rot. It’s past time to dispel that misconception. Epsom salt does not prevent blossom end rot; rather, it promotes it.
How do you fix root rot on a tomato plant?