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How to manage disease in late drilled wheat crops this spring

With some winter crops only just getting in the ground, and margins particularly tight, fungicide programmes will need careful consideration this season.

 

Late drilled cereal crops will require particularly close monitoring because although pressure for some diseases should be lower, the phyllochron, or number of day degrees required from one leaf emerging to another, may be shorter.

 

Discussing fungicide strategies for the season ahead at the AHDB Basingstoke Monitor Farm meeting this week (February 6), Steve Cook, agronomist at Niab Tag said: “Late drilled crops will produce smaller leaves a bit more quickly when they start moving through stem extension. In May they could be throwing a leaf out every seven days if it’s very warm.”


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Programme

 

Urging growers to keep a close eye on crops, Mr Cook recommended a three-spray programme for late drilled crop, but said timings will need some care.

 

“T1 is more likely to be at GS31 and GS32 on late sown crops, and the T1-T2 gap could be shorter than normal. It is normally three-four weeks, around April 20-25, but it could be as short as three weeks and we might be looking at the first week of May in some situations.”

 

Crops will also be shorter at this stage, with less leaf biomass, but they will still require the same level of protection, because although leaves may be small, lesions will potentially take up a bigger proportion, he said.

 

What might normally appear as GS32 could this year be the stage that late sown crops are at flag leaf emerging, because they have less nodes and therefore less leaves.

 

Mr Cook said: “In later sowing, flag leaf could be just a little later than normal, but they do tend to catch up and it is normally day length dependent by that stage. The key will be working out which leaf is emerging at the time.

 

“It may be easier to work back from where we think that flag leaf timing will be, three weeks prior to this, about the first week of May.”

Pressure

 

Cereals drilled later in the season should, in theory be under less pressure from septoria because there will be less inoculum in the crop, Mr Cook advised.

 

“However, there will still be windblown spores, so it is weather dependent. Yellow rust pressure will be higher, while brown rust should be lower depending on the weather at the end of the season. T0 probably won’t be needed unless yellow rust or brown rust is active.”

 

A T0 could also be required to protect against mildew in susceptible varieties, which later drilled crops will be more prone to, Mr Cook added.

 

“Overall, for later sown wheat, disease risk is lower, but there isn’t a good correlation between yield potential, which could be lower, and response to disease. So, whether it’s 7 tonne/hectare or a 10t/ha crop, the marginal response to disease control could still be the same, even though yield potential is lower. Fungicide spend is actually based on disease and not potential yield.”

Dressings

 

There are also potential savings to be made this spring by dropping seed dressings that protect against bunt, smut and fusarium, Mr Cook said.

 

“We know fusarium is around. In wheat I haven’t seen smut or bunt yet, but we know it can happen. The need [for seed dressing] should be determined by testing.

 

“If someone is homesaving [seed], I will advise them to get it tested. The risk of these diseases is quite low if you’re saving from treated, certified seed. Untreated seed will not deteriorate as much as treated seed, and undressed seed can be returned to the barn as long as it’s not been contaminated.

 

“When we had Redigo Deter, it was easy to treat, because we were treating other things and we had to buy the fungicide with it. It has become a bit of a prophylactic treatment and it should be avoided if it can be.”

Use CTL while you can

With the cut-off date for applying chlorothalonil (CTL) looming (May 20), Mr Cook advised growers to consider an earlier application at T1.5 if the flag leaf has not emerged by T2.

 

He said: “CTL is still the most cost effective fungicide we’ve had for a long time and it should still be in those programmes. Next year we may have to adjust rates to counteract the fact we haven’t got that CTL in there.”

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