Advice on managing diseases and pests in ‘variable’ beet crop

With the first cercospora spores caught in BBRO’s Spornado, experts advise growers to walk crops and keep their eyes peeled for disease in sugar beet.

Prime agronomist Philip Simons, who is based in Norfolk, alongside BBRO’s Head of Science Dr Mark Stevens and BASF Agronomy Specialist Hugo Pryce, stress that conditions are conducive to disease outbreaks, and growers need to be prepared for early onset.

Weather dictates growth stage and herbicide programmes

Philip Simons © BASF

“Norfolk’s beet crop has been very variable,” acknowledges Philip. 

“Early-sown beet benefited from available moisture, and the subsequent sunshine, which means they are now easily meeting across the rows. However, in mid-June we also have later sown fields with both 10-leaf beet and emerging beet.”

Weed control in those crops with growth stage variation has required careful management. Where fields contained small plants, Philip’s earlier herbicide applications were a ‘safe holding spray’ to try and keep on top of weeds while the crop got established.

“Later, we were able to go in with more robust mixes designed to control the larger weeds that we held with the first two sprays,” he says.

Hugo adds: “The challenge of controlling weeds in variable crops has been compounded by the variable size of the weeds and the recent hot, dry weather.

“The lack of rain and precious little soil moisture has hindered the germination of both the crop and the weeds. Dry soils will also have reduced the residual activity of herbicides especially where we’ve seen weed flushes coming a month after the crop was drilled. Emerging weeds will have developed waxier leaves in response to the weather, making it more difficult for the contact-acting herbicides.”

Aphid numbers on the rise

The weather and variable crop growth have affected aphid and virus management decision-making too.

“Initially the colder weather in January and February helped suppress aphid populations, but later, warmer conditions led to increases,” says Mark. 

BBRO first received reports of aphids in Yorkshire at the beginning of April. Since then, thresholds have been reached, especially on those small plants. The organisation is catching Myzus Persicae in traps, and Mark says numbers have increased throughout June.

“Be careful not to let virus in through the back door, especially in crops that are backwards and/or patchy,” he warns.

Philip agrees, and despite being on the east coast where prevailing winds tend to curtail aphid pressure, he isn’t dropping his guard.

“With the variation in crops and some still vulnerable to virus, we’re keeping a close eye. It is good to see that beneficial numbers are now on the rise though.”

Mark is also monitoring various moths, particularly the relatively new species, beet moth.

“In theory, there are two migrations of beet moth, but this year we’ve seen protracted activity.  Since the first notable reports in 2020, rain has disrupted their flight and we’ve not had a significant outbreak. However, we recently caught 133 moths at one site in Cambridgeshire.”

© BASF

Conditions conducive to high disease pressure

Many of the major diseases that affect sugar beet thrive in warm conditions. If the weather experienced so far this year continues, mildew and cercospora are likely to strike crops. 

“Growers will soon start thinking about fungicide applications,” says Hugo. “On the label, the first applications are at the onset of disease. Typically, that’s mid-July onwards but with the higher-than-average temperatures we’ve had in recent months, that may come forward.”

The first disease usually seen in beet is mildew. Dry weather, temperatures over 20 degrees Celsius and dew at night are the conditions conducive to its development.

“Mildew can reduce yields by 20% in sugar beet and is normally found first on individual plants. Though once it is in the crop, it can soon spread.”

“Powdery mildew has been a ‘non-event’ in recent years, but I’d never discount it,” adds Philip.

“Rust is a later-season disease and comes with the cooler conditions. Many of the varieties we grow are susceptible though, so that is one to watch from September onwards.”

For now, Philip’s attention is on keeping plants strong and healthy by ensuring that they have the nutrients they need.

“Although crops are looking green and deficiencies won’t show up until July time, we look at trace elements like magnesium, manganese and boron. BBRO’s work shows that beet crops are responsive to these nutrients and we don’t always get them applied early enough.”

© BASF

Cercospora spores caught in Spornado

Looking ahead, for both Philip and Hugo, cercospora is the key concern.

“Although it is usually powdery mildew that triggers the first treatments, I’ll be mindful of cercospora from the beginning. It is such a devastating disease. Probably the hardest hitting in terms of yield and one that you need to get on top of early,” explains Philip.

“I’ll be starting with Revystar. It’s my go-to for cercospora. The trials work has been impressive with the amount of green leaf retention. You could spot the Revystar-treated plots from the road at one site a few years ago.

“Over the last two years, growers I work with have used Revystar and got on well with it.”

It’s a sound strategy according to Hugo, who’s been heavily involved with BASF trials work.

“Extensive trials last year showed how important it was to start the programme with Revystar. Wherever we started with lesser chemistry and went back with Revystar, the programme didn’t perform as well overall, because there wasn’t the foundation.”

Hugo says that across all the programmes, for both margin over cost and adjusted yield, the best performing programme was two applications of Revystar.

“This programme delivered increased margin over fungicide cost by almost £500/ha and yield by 13t/ha.

“Current conditions, if they persist, are conducive to cercospora’s development,” adds Hugo.

Mark agrees, adding: “Cercospora likes warm, even hot, conditions. Free water is more important than relative humidity and with some thunderstorm activity in the forecast, the weather could start to favour the development of cercospora as we go through the next few weeks.”

BBRO has ‘Spornadoes’ installed at 20 monitoring sites across the country. The 3D printed vacuum systems hoover the air for small particles which are collected on a fine mesh and analysed.

“Spornado monitoring started in April this year and we have already seen rust and cercospora spores.  Although there haven’t been any reports of disease in our plant clinic, with some advanced canopies out there, I’m sure we will soon.”

Mark emphasises the need for a robust programme and sticking to best practice at application.

“Our trials have shown that there is a clear benefit to a one-spray programme for early-lifted beet and two or three sprays can ultimately give you up to 15 to 20 adjusted tonnes in crops lifted later. It is about appreciating when disease is coming in, being timely and looking after that canopy.

“If you’re leaving the beet in the ground until December up to 40% of yield develops after 1st September. Keeping diseases out, and the canopy healthy, is really important for maximising that yield return. Ultimately, that pays for the fungicide usage.”

Now that herbicide programmes are largely complete and attention is turning to disease control, Hugo encourages growers and agronomists to review the data behind Revystar.

“Revystar is broad spectrum and will protect crops from all the diseases we see in beet – rust, mildew, cercospora. It’s a complete package and the ultimate all-rounder. It doesn’t have a weakness when it comes to beet diseases.

“There are many crops with potential out there and, as Mark describes, it is well worth investing in two applications of Revystar to protect them.”