October 31, 2023

AGRONOMY NEWS

Maize Silage Makes The Difference!

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Maize silage is possibly the number one choice for high-yielding dairy cows, with high energy content and high intakes. But what makes a good forage maize variety? After six trials we have found large and consistent differences in yield and feed quality between various hybrids, which should help farmers choose more suitable varieties for high-performing livestock.

If we take fresh weight yield as a starting point, it is not surprising that the tallest and most leafy varieties like Pan 691, Seedco 73, and 30G19 produce the most biomass. Once this is adjusted for the actual Dry Matter, i.e. water removed, the true yields are a lot more similar.

Two very early maturity candidate varieties bred specifically for forage maize were included in the trial and were cut slightly later than ideal as their earliness surprised us, but the actual Dry Matter yield in tons per hectare was very high.

Fresh yield T/ha Dry Matter % Dry Matter yield T/ha DM Energy MjME/kgDM Energy/ha 000 MJ/ha NDF % NCGD %
DK777 67 28.6 19.2 9.99 191,428 61.6 56.2
Candidate A 65 39.1 25.4 10.3 261,775 41.9 68.6
30G19 77 28.4 21.9 10.3 225,240 65.7 56.8
SC73 81 30.2 24.5 10.2 249,512 63.6 55.7
PAN 691 70 23.0 16.1 10.1 162,610 60.1 57.8
PAN 15 41 29.4 12.1 10.2 122,951 58.0 60.1
PAN 14 64 30.2 19.3 10.1 195,213 57.9 61.0
H6506 86 32.9 28.3 9.9 280,111 57.7 59.5
Candidate B 57 42.6 24.3 10.1 245,208 45.2 66.4

Interestingly, these two candidates are the only varieties in which the metabolisable energy yield has been consistently above 10.5 ME; DK 777, for example, has averaged 9.5 ME over the six trials. The indigestible Neutral Detergent Fibre (NDF) is also very low.

The varieties which are often advised for Highland forage use in Kenya, H6506 and Pan 14, had significantly lower digestibility, and H6506 in particular has very low energy content averaging 9.5 ME.
The clear advice from this trial is that Pan 14 is the most suitable forage maize variety for highland areas, but above all, that Kenya would benefit from the introduction of proper forage maize hybrids developed specifically for the purpose.

Canola and Brassica Aphids – Know Your Control Options

Identifying the aphid species that you are dealing with is crucial to achieving good control in a safe manner, to do our bit balancing food production for the nation with protecting insects that are actually benefiting us as farmers.

Left: Green Peach Aphids under the leaves. Centre: Green peach beneath the pods. Right: Mealy Cabbage Aphids on the growing point.

Mealy Cabbage Aphid (Brevicoryne brassicae) – these dusty grey aphids build up during flowering at the top of the plant forming thick, dense colonies. They cause direct feeding damage and appear in distinct patches as they spread outwards from the initial infested plant. Where approved, Pirimicarb is the most effective way to deal with these and it is very safe to bees.

Pirimicarb needs warmth as it acts like a fumigant in the crop, so it must be applied above 16C, and with a fine spray quality to ensure good coverage of the tightly clustered aphids.

You often get some incidental control from pyrethroids such as lambda-cyhalothrin and cypermethrin, so in low infestations and in damp weather, these can sometimes be sufficient.

Pyrethroids however are very dangerous to Bees (quality lambda-cyhalothrin formulations have repellents in the formulation that greatly improve their safety by deterring bees, but they are still best avoided).

The second very common type of aphid is the Green Peach Aphid (Myzus persicae), or Peach-Potato Aphid. There is very widespread insecticide resistance in Green peach Aphid populations around the world, with various mechanisms that mean pirimicarb and pyrethroids are now largely ineffective.

If you identify these aphids building up before green bud stage, a neonicotinoid such as acetamiprid or thiamethoxam is very effective. Thiamethoxam tends to be more effective but is very persistent so increases the risk to bees later on. These products should never be applied in flowering canola, even if they are registered in your country or locality.

When you find Green Peach building up on the early pods and during flowering, be very aware of the risk to bees. Sulfloxaflor – once again where approved – is reasonably effective and is very safe to bees but often very expensive, and requires a fine spray quality to hit the aphids laying underneath the pods. Do not trust any claims of systemic activity in products at this stage; Green Peach hiding below canola pods require direct spray contact.

Flonicamid can be reasonably effective so is a good alternative where it is not very expensive; pymetrozine is a great option too and both are very bee safe, particularly if you can wait until after flowering when the bees are no longer foraging in the crop.

Active Ingredient Mealy Cabbage Control Green Peach Control Bee Safety
Pirimicarb Excellent No control Safe
Pymetrozine Ok Very good Relatively safe
Lambda Cyhalothrin Ok No control Dangerous depending on formulation
Alpha-cypermethrin Ok No control Dangerous but not very persistent
Flonicamid Ok Very good Safe
Acetamiprid Poor Good Dangerous, but not persistent
Thiamethoxam Ok Very good Dangerous and very persistent
Sulfoxaflor Poor Very good Safe

Maize Roots And Crop Rotation

I posted the picture below on Twitter last week suggesting that this is the “root” of the problem in Kenyan Agriculture and it garnered quite a response. The plant on the left is maize following maize. Prior to this, the field had a range of crops so this is the effect of just two years of maize. The plant on the right is after a break of sunflowers followed by peas.

The overall root mass on the left is small, the seminal roots are pruned with disease so there are very few small lateral roots (these finer roots make up the vast majority of the surface area of the roots in the soil to collect nutrients and water). The buttress roots are also poorly developed meaning that the crop has much less stability and is more prone to lodging.

We have always known that there are seven or eight species of Fusarium which build up in soils with maize and infect the roots, several species of Pythium and of Rhizoctonia, and various nematode species, all of which compromise the roots and the health of the plant.

What has surprised me is that even after just one year the effect is severe; imagine how the maize roots would look after 30 years of continuous maize. Then add in compacted soil from disc ploughing. How do we expect the crop to pick up nutrients and water?!

The answer lies in several simple steps. Firstly, crop rotation. It has be proven many years over, and in many cases will double the crop yields within two to three cycles. Secondly, get rid of the disc plough and use a chisel to loosen the soil and create a better structure. Ndume in Gilgil produce some excellent machines capable of being pulled by a 80hp tractor.

An in-line chisel plough designed for small 30-80hp tractors. An easy first step to improving soil structure. Photo: Ndume ltd, Gilgil.

Thirdly, think about the causes of compacted soil in your own shamba. Is it too many livestock? Driving the tractor on the fields when wet? Running incorrect tyre pressures on the tractor? Start to tackle these problems one by one and yields will improve without having to spend as much money on your crop.

Till next time,

David Jones,

Independent Agronomist

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