Agronomy Update

Article taken from the Farmers Guide

Potato blight poses a significant risk to crops following the recent warm and humid weather so growers should waste no time in starting their fungicide programmes, warns Agrovista agronomist Craig Green.

“I’m advising growers to start spraying when rosettes reach tea-plate size and to stick rigidly to a seven-day programme as long as the risk remains high,” he says.

“For the first couple of sprays we’ll alternate fluazinam with cymoxanil/mancozeb.  This will provide good protection and some useful curative action from the mancozeb.”

After that it is important to alternate active ingredients to reduce the risk of resistance, says Craig.  “We want to avoid getting into a curative situation at all costs so keeping spray intervals tight and vigilance is key.

“There are plenty of volunteer potatoes in sugar beet and spring barley to harbour disease.  Combine that with the weather we’ve been having and blight is likely to remain a significant risk.”

Plantsystems’ Daily Forecast Extra is proving very useful in helping farmers to keep a close eye on the weather forecast, and in predicting disease risk and conditions where infection may occur, he adds.

Final herbicide sprays are now being applied to sugar beet as the crop meets in the row, to remove remaining thistles and volunteer potatoes.  Craig recommends Dow Shield 400 (clopyralid).

I’ll include Epso Top, which contains magnesium and sulphur, plus Beetrac which provides zinc, manganese, boron, copper and iron.  It’s a good general-purpose tonic to set the crop up for the rest of the season.  Boron is vital to prevent growing point death and hollow hearts, and magnesium boots green leaf area to absorb more sunlight.”

Disease pressure remains high in winter wheats, particularly septoria but also yellow and/or brown rust, says Craig.  “Sprayers should be back into wheats with a T3 application at early flowering – usually about two weeks after the flag leaf spray.  This will help protect against fusarium and also top up foliar disease control.”

Triazoles are effective, especially prothioconazole, says Craig.  “Growers will need to check what’s available with their distributor.”

Susceptible varieties should also be checked for wheat blossom midge.  Ears at mid-emergence are most at risk; once flowering starts the danger is past.  “If we have had a succession of BBQ evening s (i.e. little breeze and around 15°C or more) midges, if present, will be flying.

“If more than one midge is present on three ears in feed wheat, or one midge per six ears in milling wheat, then spray as soon as possible.”  A close watch should also be kept for aphids, he adds.

Maize crops will soon be ready for post-emergence herbicides, at 3-4 true leaves, says Craig.  Product choice depends on weed spectrum and whether sugar beet features in the rotation.

“Maize is very uncompetitive as a young plant, but its yield potential is determined between emergence and 6 true leaves.  It is vital to keep the crop clean at this early stage.”

Callisto (mesotrione) is favoured for its flexible timing and its good control of competitive weeds like fat hen, bindweed, charlock, poppy and mayweed.

If sugar beet is grown Templar (bromoxynil + terbuthylazine) should be used instead, either as a split dose at 1.0 then 1.5-litres/ha, or at 1.0-litre/ha with Gal-Gone (fluroxypyr) at 0.75-litres/ha at four true leaves depending on weed pressure.  Elumis (meotrione + nicosulfuron) at 1.5-litres/ha brings additional grassweed control but won’t control volunteer cereals.

Craig will try some MaisTer (foramsulfuron + iodosulfuron), new this season and said to be strong on grass weeds and cereals and with better following crop options.

Oilseed rape desiccation is only a few weeks away.  Given this season’s thick crops, high volume sprays will be needed to ensure adequate penetration, so lower leaves and stems are dried out effectively, Craig advises.

“Diquat at 3-litres/ha should be used on seed crops or where stems are kinked – this prevents glyphosate from being translocated.  As it only kills what it touches, we recommend applying it using 300-400-litres/ha of water.

“It’s not so critical with glyphosate, though it is translocated less effectively by plants that are shutting down.  I would still advise applying 3-litres/ha in 300 litres/ha of water to ensure effective desiccation of crops and any weedy growth.

“Whatever the product I’ll recommend Companion Gold on all my OSR desiccation sprays.  It is a true drift retardant and improves spray retention and rainfastness.  Used at 1-litre/ha, it also acts very like a pod sealant and aids the uptake of the desiccant, unlike some latex pod sealants.”

*Craig Green is an agronomist with Agrovista and is based at Great Ellingham, Norfolk (craig.green@agrovista.co.uk)