Last week’s seminars on maize production provided good maize husbandry advice. Start with your soil, then your variety, then control your weeds and keep an eye out for pests and diseases thereafter. A simple menu, but the intricacies can get a good deal more complex.

A few weeks ago, I covered the Department’s recommended list of maize varieties and emphasised the need for growers to choose well-proven varieties to help avoid unpleasant surprises in bad growing years. At the seminar, Cara Mac Aodháin from the Department explained what the recommended list does and its importance to farmers.

He also said that a large proportion of the maize area is currently sown to varieties that are not recommended. Some of these have been in trials but were either rejected because their performance over time was found to be inadequate or they were no better than proven existing recommended varieties.

“Over a quarter of the varieties sown in 2014 were not officially trialled, so there is no evaluation of their robustness and suitability to the Irish climate,” Mac Aodháin stated.

Given the significant variability of the maize crop due to seasonal influences, it is important that all commercial varieties have proven performance in poor weather years. If not, farmers are the ones who have to cope with the loss of production, the poor quality and the shortage of fodder that ensues.

The Irish climate is marginal for growing maize. This causes big annual yield variations and these drive subsequent area (see Table 1).

Since 1993, the production of maize was helped by the availability of area aid, but the benefits for the crop are now well recognised by livestock producers whose production systems can make good use of this feed.

Maize is an expensive crop to grow. Mac Aodháin mentioned a figure of €1,333/ha, plus an additional €300/ha if sowing under plastic. Plastic has been increasingly used to help ensure output quality, and is now likely to be over 80% of the crop.

However, plastic alone does not ensure performance and recommended varieties are also a very important factor, Mac Aodháin stated. Despite its production cost, Mac Aodháin indicated that maize silage can be a cheaper feed than first cut silage (€104/t of utilised DM versus €130/t utilised DM for grass).

Variety evaluation takes place over three years at multiple sites to help identify the varieties that perform well over several years. In the trials a number of varieties are chosen as controls, ie, ones that have proven performance to date and which are present in the trials for a number of consecutive years.

The performance of these control varieties in both sets of Department trials is sown in Table 2. The good crops in 2014 are evident in both planting systems, but so is the poor performance in 2012. While the performance under plastic was much better than in the open in 2012, it was still considerably lower than in the good years. Hence the need for evaluation over time. The average yield benefit from plastic was approximately 3.0 tDM/ha over time, combined with considerable starch yield benefits.

Variety choice must be based initially on your planting system, then site suitability and then planting date. Some varieties are always very early maturing and so very versatile. Other later maturing varieties risk grain quality when things do not go right for them in a less favourable season.

Mac Aodháin pointed out that the yield potential figure attributed to varieties on the recommended list is often misinterpreted. Varieties with a yield rating of 100, or below 100, are still very good, as this figure is evaluated against varieties proven to be most suitable over time. Where 100 relates to an average yield of 18 t/ha, a variety rated at 97 produced 17.46 t/ha on average – still a very credible performer.

June is a critical month

Eamonn Meehan presented some interesting findings from ongoing AFBI maize research in Northern Ireland. He stated that as little as a one degree centigrade increase in temperature makes a huge difference to a maize crop, and average temperature has increased by this amount in recent decades.

June is the most important month of the year for maize, Meehan stated. Based on the weather in June, scientists can now quite accurately predict the potential for the maize crop that year. This could be a very useful tool for growers because, depending on crop potential, the results enable growers to budget their forage or look for alternative forage sources.

Meehan also emphasised the need to have varieties independently tested before they are grown commercially. He produced a range of numbers to show significant year-to-year differences and to show significant season-to-season variability between varieties. Since 2001, the covered trials averaged from as low as 12 tDM/ha in 2002 to almost 19 tDM/ha in 2005. This variability was even greater in the open trials, where yields ranged from under 8 tDM/ha in 2002 and 2011 up to 19 tDM/ha in 2010.

Meehan stated that annual yield variability is greatly reduced by planting under plastic – 7.1 t/ha versus 11.3 t/ha when sown in the open. Starch yield is also always higher when sown under plastic and the year to year variability is much lower.

The variety evaluation system in the North is different to the Department’s recommended list system. It assembles all of the performance test data for individual varieties and a series of highly recommended and less recommended varieties are published based on their performance over time.

Varieties can go onto the list with provisional recommendation after two years, but they may or may not become highly recommended after three years. Growers then choose based on the characteristics they value most and the appropriateness of a variety for their specific situation.

The NI maize lists can be found at the following web address: http://eservices.afbini.gov.uk/recommendedvarieties/foragemaize/recommended-maize-2015.pdf

AFBI also produce two separate lists – one for sowing in the open and the other for sowing under plastic. But with virtually the entire crop now sown under plastic, evaluation for planting in the open is to be discontinued.

Husbandry pointers

Tim O’Donovan of Teagasc presented some very useful pointers for maize growers. He opened his presentation by acknowledging that, while a reliable variety is very important, other husbandry issues can be far more important and can have a big impact, even where the most proven variety is grown.

Start with your field. Site selection remains important regardless of the variety. The warm sheltered south-facing field remains a priority and such a favourable field gives you the option to plant a later maturing higher-yield-potential variety. But field alone will not be enough to counteract being further north, further from the coast or higher in altitude.

“Try to stay away from fields with a high risk or problems. For example, old, poorly managed grass leys can have a high risk of wireworm and there is now no effective control option,” O’Donovan said. Fields with perennial weed problems like scutch, docks or creeping thistles should be treated prior to planting. Indeed, where these problems are bad they should ideally be treated the previous autumn (if possible) to optimise the chance of reasonable control. Spring treatment may have limited results.

The big decision is plastic, or not. It adds cost but for most growers on less favourable sites or pushing yield to the maximum, plastic is a must. In general, plastic adds about 3 t/ha to DM yield while also increasing dry matter content, producing higher starch yields and higher dry matter digestibility. “Use of plastic decreases the weather risk when growing maize and this benefit will be greatest in a poor year,” O’Donovan stated.

Its high yield potential means maize has a big fertilizer requirement, bringing a big cost. Those with slurry can offset some of the cost. Teagasc put the cost of fertilizer for maize at €476/ha where no slurry is available.

Teagasc indicates that an application of 33 t/ha of cattle slurry will provide about 70% of the P and K needed in soil at Index 3 and above (ie, soil levels at or above 6 mg/l P and 100 mg/l K). Slurry should be applied in spring and ploughed in immediately to retain its N.

It is advised that approximately 24 kgN/ha and 20 kgP/ha be combined-drilled at sowing. This additional P will make up any shortfall from the slurry. In general, P can only be applied to soils with P Index of 3 or lower but up to 20 kgP/ha can now be applied to maize in the seedbed at planting on Index 4 P soils. The Teagasc N, P and K advice for maize is shown in Table 3. P in the seedbed may be less of an issue where plastic is used as availability is thought to be higher in warmer seedbeds.

Lime is also critical for maize production to help nutrient availability. O’Donovan indicated that pH 6.8 to 7.0 is ideal but you can get away with lower. He also highlighted the importance of trace elements by the 6-8-leaf stage of the crop.

Pests remain an issue for maize, as for any crop sown to a stand. Crows and slugs tend to be the main pests but leather-jackets, wireworms and cut-worms can also cause significant damage. There are now fewer options to control many of these pests so good farm husbandry and cultural control are increasingly important.

Weed control

Timely weed control remains important in maize. The use of pre-emergence residual herbicides help. Previous work at Teagasc showed the detrimental consequence of even low weed populations early in the life of a crop.

Rotation is an important aspect of successful weed control. Our narrow band of herbicides will succumb to resistance sooner or later, so we need to do all we can in other ways to help keep the pressure off them.

Successful control relies on early treatment and many use residuals because of this. But, to work well, residual herbicides need a fine, firm seedbed with plenty of moisture. In plastic-covered crops, the big challenge is the areas between the plastic rows, because the soil here can be cloddy and can dry out post-planting.

O’Donovan outlined a few options for both plastic and non-plastic situations.

Under plastic, if one was to try to do the whole job in one spray, then consider a combination of WingP/pendimethalin plus Cadou Star (1.5-0.75 kg/ha) or a Wing P/pendimethalin plus Calaris (1.0-1.5 l/ha) at sowing. If the ground is clean and fresh, then one might not need the second element of these mixtures. An alternative would be to use either WingP or PDM at sowing, followed by a top spray with Calaris (1.0-1.5 l/ha) after emergence.

In open crops, the main choice will be Calaris (1.0-1.5 l/ha at the 4-6 leaf stage. Pre-emerge options could still be used. Specialist products like Accent, Titus, clopyralid or fluroxypyr might still be needed for specific weeds.

Speaking specifically about disease control, Tim commented that foliar eyespot has been problematic in this country in some recent years. Control is awkward because if one waits until the disease warrants treatment, the crop can be up to two metres tall.

There is only one fungicide with overall clearance for use on maize and one other active with off-label approval. Growers must realise that all purchased products are recorded and that they are accountable, via their records, to show where such products were used.

There is no research to justify the use of fungicides on maize for eyespot control. The primary control should be rotation. O’Donovan outlined threshold procedures used in Britain and Denmark but neither might be applicable in Ireland.