Uncontrolled root proliferation and blocked drippers, tomato growers are increasingly familiar with the symptoms of crazy roots. Joris Mulders, a cultivation adviser at Delphy in the Netherlands, has been observing a rise in the bacterial disease among growers and is helping them manage the consequences of the excessive root growth.
Mulders sees a connection between the increase in crazy roots in the Netherlands and restrictions on the use of hydrogen peroxide. Until recently, continuous dosing of hydrogen peroxide was widely practiced by Dutch growers, but the Netherlands Food and Consumer Product Safety Authority (NVWA) has informed growers during inspections that this method of application is not permitted under current regulations.
At the same time, he notes that Germany has also seen a striking number of crazy roots problems this season. Mulders suspects that something went wrong at propagator level, allowing the harmful bacterium Agrobacterium rhizogenes to enter growers’ greenhouses despite the hygiene measures in place. “All the growers I visit received plants from the same propagator,” he says.
Light and air to the roots
The restrictions on hydrogen peroxide have increased the risk of crazy roots, according to Mulders. When problems do occur, there are some straightforward interventions available. One important measure is removing root wraps around the plant pot and cutting open the top of the substrate slab. This approach was already supported by scientific research years ago and has since been widely adopted. “By removing the root wraps and opening up the top of the slab, you ensure that sufficient oxygen and light reach the roots. Growers were already doing this alongside the use of hydrogen peroxide.”
A major risk with crazy roots is that the extreme root proliferation causes the plant to choke itself. Opening the top of the substrate slab helps in two ways: it increases oxygen availability in the slab and allows light to reach the roots, which has an inhibiting effect on root growth. “This intervention alone can already prevent part of the problem,” Mulders says.
Drippers
Root ingrowth into drippers, causing blockages, is another issue to monitor. Mulders advises growers dealing with excessive root growth to insert the dripper less deeply into the plant pot, or even to place it alongside the pot, to reduce the risk of blockage.
© Delphy
Balance between fruit and leaves
Both of these are labour-based interventions. Cultivation management also offers options. “Every plant that gets crazy roots becomes strongly vegetative. What you can do is maintain a healthy balance between fruit load and foliage.” Mulders advises growers with strongly vegetative crops to remove a significant number of leaves from the top of the canopy. This helps keep the plant productive and can prevent or reduce problems. Generative steering, for example through large day-night temperature differentials, is also beneficial.
Extra labor is sometimes a bottleneck
“Once you have crazy roots, you are mostly in damage-control mode,” Mulders observes among affected growers. Labour is frequently a bottleneck. “Growers sometimes find it difficult to take on the additional labour costs. Labour is expensive, and not every grower has enough staff to carry out the extra tasks. On top of that, not every grower has enough people who can recognise plants with problems.”
In the worst cases, plants affected by crazy roots can fail completely. The bacterial disease causing extreme root growth is not limited to tomatoes, it has also been observed in cucumber cultivation. Mulders notes that a post he shared on LinkedIn also drew attention from growers in that sector.
ToBRFV and Nesi
In addition to crazy roots, tomato growers are contending with a resurgence of ToBRFV and the rapid spread of Nesi this season. Resistant varieties and strict hygiene protocols are being used to manage ToBRFV, but concerns about the virus are growing again as it continues to mutate rapidly. Concerns about Nesi are also significant. Controlling the pest is the best growers can currently achieve, eradication is simply not possible with the strategies available.
For more information:
Joris Mulders
Delphy
[email protected]
www.delphy.nl