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Sunday 11 December 2016

Tough spraying season leaves crops at greater risk

Patrick Phelan

Published 24/05/2011 | 05:00

This is surely the most difficult spraying season in memory. Strong winds followed by brief spraying opportunities followed by heavy showers. It is doubtful that there was any chemical sprayed under ideal conditions over the past three weeks. Results will therefore be variable and it is critical that crops are inspected regularly to monitor efficacy.

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These inspections are very important on winter wheat after T2s. It is not safe to assume that crops are relatively safe for three weeks after spraying in a normal year and certainly not this year.

Winter crops look good, but there are some very poor spring crops following late sowing in loose, cloddy seedbeds. Manganese and magnesium deficiency symptoms are to be found on many spring crops.

The flag leaf is fully emerged on all apart from some very late sown winter wheat crops. Most crops have four to five leaves without disease symptoms but there are some crops with septoria evident on the third leaf.

Rust has been reported in crops in Louth and Meath. All crops should have their T2 applied by now, and if not, then at the next spraying opportunity. Fungicides cannot be expected to give any more than three weeks effective cover. Keep notes of all spray applications and the weather conditions under which they are applied.

These notes will be invaluable when deciding on the T3 spray which should be applied three weeks later. The T2 should consist of Chlorothalonil and a fungicide containing prothioconazole. Products containing epoxiconazole will be used on some crops. So far I have not seen mildew on any wheat crop but, if present, a morpholine should be added.

Most winter barley crops are flowering. Crops are generally disease free and appear to have good potential. Some thin crops have a lot of late tillers developing which may present a risk of late mildew.

Chlorothalonil should be included with all products. Bontima, Siltra, Cauldron and Venture Extra are combinations of triazole and SDHI chemistry. Fandango/Coyote, the barley packs or mixes of triazoles and strobilutrons provide very good options. Products such as Allegro Plus provide cheaper but effective alternatives. Amistar Opti with a triazole can also be very effective.

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Most spring barley crops have been sprayed for weeds and have got chlorothalonil and a half to full rate triazole. This should be adequate to hold crops until heading when a full rate triazole + strobiluron/SDHI should be applied. I saw one crop of Quench which has a considerable amount of Net Blotch. Control will be achieved with Proline/Stereo with a half rate strobiluron. Lumen would also be very effective.

Where manganese or magnesium deficiencies are still evident, apply a foliar application as soon as possible. Where there is a risk of crops lodging, Terpal or Cerone should be applied as early as possible after the second node is detectable. Wild oats may still be controlled with Axial or Avena but need a minimum rate of 0.25l/ha (0.3lha if mixed with a sulphonyl urea) once the wild oat goes beyond the first node.

Spring wheat has moved very rapidly through the growth stages with some crops now at flag leaf emerging. Crops are clean and most have received growth regulator. If farmers are still concerned about lodging Meteor can be used up to second node and both Terpal and Cerone up to "boots swollen".

Winter rape is, in general, looking very good. Early crops have finished flowering while some of the later-sown crops are in full flower. The latter should receive their final fungicide at the start of petal fall. Prosaro, Proline and Amistar or Caramba are all suitable.

Patrick J Phelan is a member of ITCA. Email: pj.phelan@itca.ie

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