Disease control in wheat and oilseed rape are occupying much of our agronomists’ thoughts this month
Disease control in wheat and oilseed rape are occupying much of our agronomists’ thoughts this month. Dominic Kilburn writes.
It’s a been a kind spring, said Nottinghamshire-based AICC and Arable Alliance agronomist Andrew Wells and, despite it being relatively dry, spring crops are away and looking good, he noted.
Sugar beet has generally emerged well, with only a small number of crops having suffered wind damage, and which will require re-drilling. The first post-emergence herbicides are getting underway now, commented Andrew, speaking in mid-April.
“There’s a lot of spring barley and spring wheat in the ground this season and, for those, it’s a case of maintaining effective disease control without spending too much money. We’ve had decent yields in the past couple of years with spring cereals but a dry year, for example, could result in lower yields.”
He said that there had been some weevil damage to spring beans, which should be addressed by the time this magazine has landed, while post-em herbicide applications of bentazone, for volunteer OSR and cleavers, will start at the end of April and early May.
T0 fungicide sprays on wheat were all but completed in mid-April and T1s set to begin on the most forward wheats during the last week in April following on into early May. Septoria is present as usual, said Andrew, but the cooler and drier weather had kept disease pressure to a minimum.
“I can find small amounts of yellow rust in later drilled crops which are a little stressed but the T0 sprays applied earlier have kept it under control.
“That said, there’s a bit more eyespot in crops than I expected and we will deal with it at T1 by including Tracker (boscalid + epoxiconazole) in the fungicide mix.
“Looking beyond T1 and further ahead to T2, it all depends on the rainfall and temperatures we get in May as these will determine how robust the T2 fungicide spray will be,” pointed out Andrew.
“The key thing is to do a good job at T1 to stay in control and not leave yourself exposed ahead of T2,” he added.
Autumn residual herbicides did well on grass and broad-leaved weeds and, looking around crops, there is less black-grass in wheat than at the same stage last year, he continued. More delayed drilling and better stacking of herbicides are two reasons for good control of black-grass – albeit at a greater cost – although one or two growers who drilled their wheat too early are still having problems with the weed.
According to Andrew, most oilseed rape had been treated with a light leaf spot fungicide in April – typically tebuconazole – the rate adjusted to give PGR activity where needed. “We’ve managed canopy size with nitrogen timings and rates and, looking forward to May, it’ll be all about sclerotinia and more light leaf spot control.”
Timings for sclerotinia sprays are based on a five-day rolling temperature average – when this exceeds 110C we need to ensure fungicide protection is in place, he explained. “Furthermore, when the rolling average temperature rises above 13-140C, and there is some moisture, then this creates the ideal scenario for sclerotinia development and crop infection.
“In recent years levels of sclerotinia have increased significantly when temperatures rose drastically,” he added.
Andrew said that prothioconazole plus either a strobilurin, or tebuconazole, will be applied to OSR crops throughout May for disease protection.
Other jobs for the early part of this month include T2 applications on winter barley based on products with broad-spectrum activity, he concluded.
AICC and Yorkshire Arable Advice agronomist, Andrew Fisher said that frequent night frosts, cool winds and dry conditions (especially in the east of the region) meant that crops were a little slow to get going this spring.
Also speaking in mid-April, he pointed out that a lot of second dose fertiliser applied to wheat is still sitting on top because of the dry conditions, which has also resulted in minimal amounts of disease entering the crops.
T0 fungicides were finished in the middle of April, 10 days later than usual, and decisions for T1 were being considered ready for applications beginning at the end of April/start of May.
“Septoria has been in crops all winter but a lot of the infected leaves are now dying off and with little rain the pressure has eased,” Andrew highlighted.
All his wheats had Cherokee (chlorothalonil + cyproconazole + propiconazole) at T0 -a cost-effective spray, he noted, with the important inclusion of chlorothalonil. “We will build on that at T1 with some growers wanting the inclusion of an SDHI at that stage, and others watching overall costs. If they opt for a SDHI at T1 then it’ll be one of the epoxiconazole + isopyrazam products such as Keystone, plus chlorothalonil, and using one of the other SDHIs for T2.”
Andrew said that oilseed rape was just starting to flower in mid-April with pollen beetle having appeared over the Easter weekend, although not in high numbers, before disappearing to the bottom of the crop because of cold, windy conditions, he reported.
“I’m not planning a spray for pollen beetle except for on a handful of backward crops if thresholds are met,” he added.
Light leaf spot appeared on crops in April that hadn’t had a fungicide top-up since November and this was addressed at stem extension or first bud.
“Hopefully the use of PGR Caryx (mepiquat chloride + metconazole) on forward crops will give them protection against sclerotinia through the early part of flowering. We are trying to keep a lid on input costs for oilseed rape at the moment with ex-farm prices so low, and so I’m only doing what’s absolutely necessary,” he explained.
Turning to spring crops; Andrew said that there was a small increase in the spring bean acreage to satisfy greening issues. The crop went in well and he is planning a bruchid beetle spray, tank mixed with fungicides, at early pod-set. “It’s crucial that quality is maintained if it’s to satisfy the export market,” he added.
Andrew Fisher can be contacted via email: [email protected] or tel: 07836 711918.