New technique to tackle canopy collapse in carrot crops

Clipping foliage in carrot crops could help reduce the risk of Sclerotinia infection, trials have shown.

Carrot clipping can cut risk of Sclerotinia. Image: BASF
Carrot clipping can cut risk of Sclerotinia. Image: BASF

Consultant Howard Hinds has been working with BASF and irrigation firm Wroot Water on a technique that involves clipping foliage between plant rows to allow more air to circulate through the canopy.

Hinds, of Nottingham-based Howard Hinds Crop Consultancy, said: "The main UK carrot variety Nairobi is very prone to canopy collapse and lodged foliage will develop tissue rot when it contacts the ground. At this stage it becomes very susceptible to Sclerotinia.

"We have been looking at developing machinery that can clip off the canopy. Initially we used an adapted flail, but Wroot Water has now designed a single bed clipper that uses a round disc cutting into the soil at the edge of the bed."

Hinds said assessments in early September and October showed clipping can reduce infection by between 61 and 94 per cent.

"The disease is so destructive that we need to do everything we can to minimise disease pressure as well as optimising the effectiveness of the tools we have, throughout the crop's life."

Hinds stressed that this technique, although very promising, has to be part of an integrated approach. "As you can't clip early, you need to control Sclerotinia with an effective fungicide programme starting early in the season, before the canopy closes over."

Sclerotinia produces spores from soil-borne bodies underneath the crop canopy and these infect senescing plant tissue near or on the soil surface. "From here the disease infects stems and leaves and eventually the root crowns, resulting in core rots. So it is important that the first fungicide spray such as Signum is applied early on, well before the foliage has a chance to close over and starts to senesce. Once the disease is in the crop, it is impossible to get rid of it.

"Signum is one of the strongest materials we have on Sclerotinia and Alternaria and it needs to be used early in the programme. It needs to be integrated with other chemistry to comply with label recommendations and minimise risk of disease resistance. Many chemicals contain strobilurins, so special care is needed to make sure this chemistry is not overused across a programme that can be up to six sprays. The use of a fungicide such as Compass, which is non-strob, is a useful alternative to consider."

MONITORING

BASF sponsors a Sclerotinia monitoring system to help carrot growers assess disease risk.

Field vegetable product manager Robert Storer said: "It predicts when to apply the first fungicide treatment and helps in planning a control programme.

"Starting in June, weekly results are published on the Carrot Sclerotinia Monitoring link on www.agriCentre.basf.co.uk.

"The service is based on monitoring the germination pattern. Sclerotia germinate usually when soil is moist and temperatures are 5-25 degsC, with optimum temperatures being 15-25 degsC."


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