Carrot Sclerotinia Monitoring

This is the 9th report for carrot-sclerotinia risk monitoring in 2017. Overall, sclerotinia infection risk is high this week. New sclerotial germination has been seen at both sites, and therefore airborne spore inoculum will have been released. Crop canopies are generally vigorous and likely to have senescent or damaged leaves, which are susceptible to infection, particularly if they collapse onto the soil surface. At the the Suffolk site, germination activity this week produced a large flush of apothecia, 21% germination, up from 2% with no activity in the last three weeks (see chart below). The Nottinghamshire site also had new sclerotial germination (up 3% to reach 37%). Crops should be monitored for sclerotinia symptoms and other diseases. Clipping the foliage on the sides of beds when the foliage starts to fall over but before disease is seen, is a good strategy for reducing sclerotinia infection and one which is being increasingly used by growers to complement fungicide treatment. Fungicide treatments at 2-3 week intervals after the pre-canopy closure treatment should be continued. Carrot foliage will also be susceptible to other diseases such as alternaria but fungicides targeted at sclerotinia will help control these too.

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Suffolk

Crop canopy large with some senescent leaves. A sudden large flush of apothecia this week (now at 21% germination) with moist soil and mild temperatures. Weather has been damp and muggy with temperatures of 20^°C. Rain is likely to encourage further germination. No sclerotinia infection symptoms seen yet.

Sclerotial germination is now 37%, new activity again this week. There was significant rain fall (>25mm) and further canopy growth. Where possible the grower will make use of bed trimming to cut off the foliage falling into the wheelings between the beds, but the current soil conditions are a little too wet for this to work well.

Nottinghamshire and E. Midlands

31 July, Notts carrots, canopy closure

31 July, close-up of foliage; vigorous canopy

1st August, Suffolk carrots, canopy colsure.

1st August, close-up of new apothecia

Sclerotia Germination

Depots of carrot sclerotia are being monitored near Edwinstowe, Nottinghamshire (sclerotia buried 16 May in carrot crop) and Freckenham, Suffolk (sclerotia buried 8 May in carrot crop).

• New sclerotial germination activity this week at both the Suffolk and the Nottinghamshire site.
• Rain is likely to encourage further germination which is an indicator of recent spore release.
• Some crops have excessive foliage growth which is a risk factor for sclerotinia infection, especially if rainfall is high.

Key Points

• Many main crops have canopies which are now meeting across the rows. Where this is the case, and with the possibility of rain or irrigation, fungicide applications should be considered to protect the leaves and bases of plants. Sclerotial germination is likely to occur if soils are moist, and this may occur at nearby sites other than the carrot monitor fields.
• Sclerotina will infect dying or damaged leaves, so if the crop has senescent cotyledons or canopy damage, a protectant fungicide treatment should be planned.
• Additional fungicide applications should be made at 2-3 week intervals after the pre-canopy closure treatment, to continue protection of foliage. Ensure that products with different modes of action are used in keeping with anti-resistance management strategies.

Download all Carrot Sclerotinia Monitoring Bulletins

• 28th July 2016
• 15th July 2016
• 8th July 2016
• 29th June 2016
• 23rd June 2016
• 15th June 2016
• 5th June 2015
• 18th June 2015
• 23rd June 2015
• 9th July 2015
• 23rd July 2015
• 5th August 2015