By David Jones, Broad Acre Agronomist, Msc. Agriculture
Maximizing yield in commercial maize is tricky enough, but for seed maize there is the added complication of ensuring the female plants are adequately fertilised by the weak and variable male rows.
With the best intentions, inbreed male lines are fickle and without the heterosis effect of a hybrid, are often weaker than expected. But for me this is not the issue; the issue is the variability which means managing them contains a large element of guesswork, particularly to synchronise male tassling and female silking.
That said, there are some steps that can be taken to improve pollination. Most require planning and thought at planting, but now is the time to think ahead for next year.
Plan Planting Carefully
- Give the male plants the best start – it goes without saying that the inbreed plants will struggle in a poor seeded, with compaction or with inadequate nutrition. For me the Great Plains Accushot liquid fert system will be a must in future for placing ALL of the nutrients accurately, and next to the seed.
- Check the male seed; if it is inconsistent in shape or size or struggles to sit in the calibration discs in the planter, discuss it with the seed company. Playing with the vacuum pressure goes a long way with pneumatic planters, and in finger pickup or plate planters, planting speed makes a tremendous difference (more on this later).
- Get the seed rate right and minimise plant losses – seed should be uniformly treated, and only plant when conditions are right for the weaker male plants.
- I am a fan of planting the males at a higher seed rate than required (how often do you see gaps in the male rows of a metre or more?), then thinning out the rows at the 3 leaf stage if the crop is too thick.
- I know of some experienced growers who have gone through with labour and simultaneously thinned out stands AND planted seeds every half meter to provide a late flush of pollen just in case. In one major study, doubling male populations to 66,000 delayed tassling by 3 days but also increased seed yield by 0.4 t/ha.
- Don’t be afraid to plant males slightly earlier if you are particularly experienced with the variety and have suffered from poor pollination resulting from late, slow males. We have known for many years that pollen production is affected far less by high plant populations than seed production, yet I all too often see sub optimal male populations.
- Planting the males separately is time consuming, but it also allows you to plant them more slowly – remember how much more sensitive males are to even slight variations in depth and seed placement.
- Female populations. In some varieties, particularly flint types, female populations are planted high to minimise round seeds. But the thicker the crop, the less pollen is likely to move.
- Planting depth. CIMMYT work in 1999 looking at planting depth of male rows showed that increasing depth from 5 to 7cm delayed flowering by 2 days with no detriment to the females grain yield. CAUTION – do not plant too deep will affect the vigour of already weak males, and too shallow risks herbicide injury.
- Foliar applications of N and P in one study had NO effect on male maturity and overall grain yield.
- Work as far back as 1980 showed that cutting back male plants at the 4 leaf stage or even burning the leaves with gas flames had surprisingly no effect on yield and were very effective at delaying male flowering by up to a week.
Having said all of this, most crops are now tassling so what can be done at present?
Air circulation through the crop is an important way of maximising pollen transfer. Surprisingly, very little research has been carried out in this area, although it is acknowledged that using mechanical blowers or helicopters will help spread pollen to the centre rows.
Walking through the centre of the two male rows with a petrol powered blower is probably the most effective and most straight forward method of dispersing the pollen, and applying a fungicide at this time with a mist blower would make sense to carry out two jobs.
So how far does pollen move? Potentially very far is the answer as the graph below shows, but maize pollen is relatively dense, so unlike crops such as canola, unless there is sufficient wind and air movement in the crop, a helping hand can in theory, significantly improve pollination.
Manually spreading pollen is arguably an equally effective technique that could involve cutting off two handfuls of male tassles and walking them down the centre two rows of females, manually running of shaking them over the silks.
In the States, growers have found that cutting the end of the cob off to expose the tassles is surprisingly effective if the females are slow and behind the males, although it is very labour intensive.
Keep on top of fungal diseases, and above all keep out Fall Armyworm! Males are every bit as important as females and this year I have found up to 10 larvae feeding on emerging tassles in some seed crops.
In a South American study in 1986, growing six rows of females as opposed to five rows reduced seed yield by 9%. So why is this the standard set up in Kenya?
Most Hybrid Corn in the States is produced on a 4+1 or 5+1 ‘squeezed row’ system. For every 5 rows of female lines there is a single row of males, often planted between two female rows so that it is effectively a 37.5cm row (remember, pollen production does not suffer from high populations in the way that seed yield does).
This system is much more challenging in our Three-Way hybrids (female hybrid and an inbreed male) but it is possible. The greater challenge in Kenya arguably is that we tend to use taller varieties and hence taller (and thus more competitive) hybrid females, which would outcompete the male row.
That said, when you review the research there appears to be little evidence to support the need for male rows to be planted in pairs, provided that a single row is sufficiently well established.
My final thought? This probably tells us more about why Kenya needs to be growing shorter, compact varieties that are easier to manage, machine harvest, spray for Fall Armyworm and waste less energy producing tall stems.
Until next time,
David Jones is the Broad Acre Specialist at Crop Nutrition Laboratory Services Ltd. (CROPNUTS). David has a keen interest in soils and no till farming systems where he has undertaken work looking into weed levels and changes in soil structure, and has extensive experience in field trials and in the development of precision farming techniques. In his spare time he enjoys playing rugby.