By David Jones, Broad Acre Agronomist, Msc. Agriculture

15th August 2018

Current Fall Armyworm Update

  • Fall Armyworm pressure is manageable in most parts of the country at present, with the exception of hotter areas (>30C) where numbers are still very high in maize and sorghum.
  • Wheat harvest reports that I am getting are average in Narok, and early days in Mt Kenya and the North Rift.
  • Peas – early planted crops were most affected by Ascochyta and reports are not good universally. We are looking at newer varieties and fungicide programs, but this is a reminder that peas are a not a low risk crop.
  • My yield estimates in maize based on plant populations, average ear and grain numbers are average. Best crop I have seen so far is 8.4 tons (37 bags), but the later varieties like 691 and 8M series are still too early to assess.

Simple, On-Farm Trials Pay Dividends

A few weeks ago I looked specifically at Nitrogen topdressing and why it is so important to get it right. Here is an example of a strip on the left that has had 160 kg of N, and a trial strip on the right a few meters away that had an extra 50kg of N.

Nitrogen deficiency in maize

When you see the lower leaves yellowing to this extent, you know that you have left some yield out in the field.

I know that this is an exceptional year for Nitrogen leaching, but I am seeing a lot of this in many different crops around the country. On a very different soil type, the barley below on the left had 75kg of N, compared to 125kg on the right. When you have soil structure, disease control and weeds under control the grain N will still be well below 1.9%.

Nitrogen leaching

Barley on the left had 75kg of N, compared to 125kg on the right

This is of course just one season but it has been an object lesson in measuring leaf N levels and watching what the crop is tell you in the early stages.

Copper Deficiency

The prevalence of copper deficiency is well known across Kenya in cereal crops, particularly wheat and barley. As I have pointed out before with nutrient deficiencies, they are rarely as acute as you see in the textbooks.

Copper deficiency in wheat barley

Left; three foliar copper applications. Right, untreated – note the crinkled flag leaves and angular awns.

The above is a comparison from soil in Timau, showing a very subtle twisting of the awns at the top of the ear, and crinkling and wrapping of the flag leaf where no copper is applied. Easy to see when the ear has emerged, but more subtle at the crucial tillering stage:

wheat barley

Below is the soil report from this exact field pre planting (note the high Organic Matter which accentuates copper deficiency), and the leaf analysis taken at the time of the photo…

Soil Analysis Report

soil analysis report

Leaf Analysis

Leaf Analysis report

Whitening and limp, bleaching of the leaf tips can easily be confused with herbicide scorch, but if in doubt have a leaf test done to confirm the symptoms.

Tillering and early stem extension are the crucial timings to apply a foliar copper, typically with a fungicide, and usually 1 litres/ha of a 250g/l copper formulation is a sufficient dose. I am now advocating a 2nd spray at flag leaf emergence, but whatever you do it needs to be into the plant before flowering; any later is too late.

Does Copper in the seedbed really work?

I have been somewhat disappointed by copper placed in the seedbed in fertilisers. Often included at just 200-400 grams/ha, we can discuss the soil chemistry and reasons behind this at length, but the simple fact is that while they may make a small contribution early on, they do not eliminate the need for foliar copper to be applied later in the crops life.

Anything below 10-15ppm in the leaf analysis is too low in cereals, and of course the soil test result is a good guide to the likelihood of deficiency.

Work done in Canada on Copper deficiency suggests that foliar applications are the most effective and reliable. In fact, the flag leaf is the possibly the optimum time for applying foliar copper, however if you are delayed with the T2 fungicide this is a big risk. Crops grow faster here from GS 30 to 39 too, so better to get a dose on and into the crop as banker.

Interesting, even liquid copper in-furrow did not have a reliable effect at 1 kg of copper/ha, and Granular copper oxychloride (at 2,000g copper – 10x what most coated fert blends contain!!!) took 3-4 years to disperse and break down in the soil before it was fully effective.

soil Organic matter

Organic matter tends to lock up Copper. The barley above is in a 6% Organic Matter soil showing the effect of no copper on the left, and 5 kg/ha liquid copper mixed into the soil pre planting on the right. If only it was that easy in the field, but it demonstrates the challenge and importance of sorting copper nutrition!

Also remember that high rates of N have an antagonistic effect on copper, so when you are really pushing a crop on a high organic matter, fertile soil be sure to allow for extra foliar Cu to balance it.

Getting on top of Stem Rust

It is clear in our variety trials that popular varieties like Hawk and Korongo (both released in 2012) are breaking down to Stem Rust. Whilst this is an inevitability, it does put more importance on getting the fungicide program right to protect yield.

The trial below at Nakuru was based on four replicates and includes a range of commonly used fungicides. This was a visual assessment trial to look at what sort of differences to expect but it is clearly worth pursuing this further, so much so that I have set the trial up in Naivasha which will be taken to yield. Full results will be sent to Agronomy Service members in due course.

Stem Rust Fungicide Disease Assessment Trial

The incidence is the percentage of stems that have a lesion visible on them, while the severity is the area of the stems infected by visual assessment.

Certainly some big visual differences, and I cannot wait to follow this through to yield.

Stem rust in wheat and barley

Till next time,

Take care,

David

About David

 

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.