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Monday 20 February 2017

Complex mixes do more harm than good

Tillage

Gerry Bird

Published 07/06/2011 | 05:00

The recent good weather has helped to reduce the spraying backlog, which for a lot of growers was becoming critical. The problem with mixed weather is that when an opportunity to spray occurs, complex tank mixes are applied, which may not always be best practice.

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Multiple product mixes in a tank, with numerous different active ingredients applied in 150 litres of water per hectare, generally is not a great idea. Common combinations on spring barley are sulphonyl ureas and hormone herbicides, triazole, morpholine, chlorothanil fungicides, trace elements and growth regulators.

The composite effect of the various formulations, chemical interactions and general crop bombardment can result in very poor performance and crop damage. I can remember when there were lists of tank mixes available and when a three-way mix was considered adventurous.

Walking through winter wheat crops is particularly nice this year, with heads emerging on the early crops. Crops are well tillered with great canopy cover, have four clean leaves and are a good rich colour. The good crops never got a growth check and were well rooted, which minimised nutrient and moisture stress.

Sharp

Disease levels are generally at low to moderate levels concentrated on the lower leaves. I have noticed some sharp eyespot on wheat crops, with the eye-shaped lesions 15-20cm up the stem and the fungus evident under the stem sheath.

The comprehensive fungicide applications at T1 control common eyespot and, as a result, sharp eyespot can develop. The disease circles the stem and, depending on the severity, will restrict water and nutrient transport to the developing head.

The recent dry weather will have encouraged the disease, and the first time that growers may notice it is in the white heads dotted around the field.

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The tractor will also catch plants on the tramline on the T3 application, leaving white heads on the tramline after a few days.

Take-all is evident in some crops, a result of poor rotation, winter root lift, poor soil structure and nutrient deficiency. The weather sequence has facilitated the development of take-all, with the recent dry spell putting pressure on roots.

If you notice a weak patch in a crop of winter wheat or winter barley, dig a few plants and check out the roots. A few black root strands will help diagnosis, but the bulk of the damaged roots will have broken off and remain in the soil. Black roots could also be due to fusarium -- a rinse in a mild bleach solution will confirm take-all with roots remaining black.

Aphid numbers appear to be building up lower down the crop canopy. They were in exile during the recent stormy weather and will be on the move towards the head.

Aphids on the head cause direct damage by sucking on the developing grain and also provide a substrate for fungus development on the head. I noted creeping soft grass in a continuous winter wheat field, which has thankfully been a rare event in recent seasons.

The weed has the ability to completely outgrow the crop, first by starving it of nitrogen and subsequently smothering the canopy. It is very difficult to control, but moderate control in-crop can be achieved with Monitor, or possibly even more with high rates of glyphosate pre-harvest.

The very windy conditions did not appear to cause any serious lodging on cereal crops, due mainly to the early stages of grain fill. However, some forward crops of maincrop potatoes suffered stem breakage, unusual at this time of year.

I attended a meeting with Neil Fuller, a well-known soil specialist, and the role of soil biological additives and their future role in plant disease prevention was discussed. The concept that bacteria added to the soil provides a biological barrier around the root zone preventing soil-borne diseases attacking the root is fascinating. The current positive outlook for tillage encourages novel technical developments and this has to be good for the future.

Gerry Bird is a crop consultant and member of the ITCA. Email: gjbird@eircom.net

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