Weather During Flowering Created the Perfect Conditions for Botrytis and Sclerotinia – Arable Farming – Darryl Shailes

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Darryl ShailesWe have not got as many apples and plums as last year, but the pears are pretty good. The rain over summer has helped the wheat and barley harvests and also the fern growth on our asparagus which is much bigger than last season.

As we've only got a small area, we're able to practice good crop hygiene and remove all the old fern and reduce the amount of inoculum on the old stems so our stem-phylium levels are very low.

The hot, wet weather during June and July has had some interesting effects in potato crops, particularly in the East.

Botrytis and sclerotinia are evident in many fields and will now be having some effect on yield. Hot, wet weather during flowering (in the high 30°Cs) with heavy rain and thunderstorms were the perfect conditions for infection. Sclerotinia is particularly found in rotations with carrots, parsnips and brassica species and is pretty evident with the broken stems, large white lesions and the black sclerotia when stems are split open.

Botrytis is less distinctive and can be confused with blight, but has still caused early defoliation in some fields. Whether it is the season or the lack of fluazinam in the blight programme is not clear, as it has an effect on both diseases. So there may be justification for more fluazinam use in 2020 around flowering – even with the issue of Dark Green 37_A2 blight strain and its reduced sensitivity.


As we know, it is the last season for diquat use and it will be the first time many growers will be looking at flails in their management systems. Many crops are well advanced and their haulm is senescing much more than usual at this time of year. This means we should expect a bit easier time regarding haulm management than in a more normal season, but lessons will no doubt be learned.

We have our own demo of flailing and haulm management without diquat at our Fen demo and trial site at A.L. Lees later in September and it will be interesting to see what that shows.

Beet has also been affected by the hot weather and many crops on lighter soils have wilted and the outer leaves have scorched. This meant, when the thunderstorms arrived, the beet stood up again and now many crops are showing yellow symptoms, but not all caused by virus.

This wilting is not confined to very light soils and needs some further investigation to find out what is actually going on, as it may not be just drought.

Flagging beet crops can often be a sign of beet cyst nematode (BCN), where poor, stunted root systems cannot take up the water required for the crop and affected areas will wilt earlier and longer than in other parts of the field. A walk with a spade or a trowel can be a useful thing to do looking for the stunted and hairy root system with the white, lemon-shaped cysts attached.

There are several BCN tolerant varieties on the RL including Daphna, which is the top yielding variety, so identifying issues now influences how the crop can be managed more effectively in 2020. It wasn't that long ago that British Sugar advised against beet and oilseed rape in the same rotation due to BCN build up, as BCN affects both beet and oilseed rape.

Many poor areas of oilseed rape can be affected by BCN and looking at the roots can reveal those distinctive white cysts. So, it is important to identify any issues as it can affect more than one crop in the rotation.

Secondary infections of rust, mildew and cercospora are now being seen in beet crops so a second fungicide needs to be applied, especially for later lifted crops, and treatment should start as soon as the disease is seen on the plants.

Agronomist facts

Darryl Shailes is Root Crop Technical Manager for Hutchinsons, with a nationwide remit. He has been working in potato agronomy for more than 20 years.