By David Jones, CropNuts Broad Acre Agronomist

Happy New Year! In this week’s THINK AGRONOMY we look at:

  • Which brands of tebuconazole you should use and which you should avoid

  • Why the yield of maize is determined NOW in the fallow period

  • And finally, is an inter row weeder a solution for TRUE no-till systems?!!!!

    Tebuconazole choices

    Once pesticides go ‘off-patent’ they are allowed to be copied and sold by other manufacturers. This competition in the market can be very good news for farmers, but it also bring with it risks.

    Although a formulation of a pesticide may contain equivalent amounts of active ingredient (which can be easily tested for in the laboratory), the other co-formulants such as surfactants, solvents, inert carriers and humectants can vary and do not have to be declared on the label.

    For this reason caution is needed when choosing products as the efficacy in the field can vary significantly. Cheapest does not always mean good value!Cheapest doesn't always mean good value!

    The Association of Independent Crop Consultants in the UK tested several formulations of chlorothalonil in the field against Septoria in wheat, and found that cheaper formulations were less persistent and resulted in a lower yield than branded product from the original manufacturer.

    What was particularly interesting in this scenario was that farmers and sprayer operators subsequently told us that the results correlated with what they saw in the field; cheaper formulations tend to flow out of the can better, and after several rain showers they appeared to wash off the leaf. Better formulations with better surfactants and stickers were retained on the leaf even after heavy rain.

    They also tested EC (emulsifiable concentrate) formulations of the herbicide Pendimethalin compared to the newer Capsule Suspension formulations which promised lower volatility, better weed control and easier spray tank cleaning.

    Remarkably the opposite effect was seen on both Ryegrass and Blackgrass; the older EC formulations actually gave better control by around 10% at 1,200grams of active ingredient per hectare.

    One of the most widely used fungicides

    Tebuconazole has been one of the most widely used fungicides since its introduction in the late 1980’s. Although field performance has dropped off against some diseases such as Septoria, it remains highly effective against many cereal Rusts such as Yellow Rust and Stem Rust, and for eradicating established Maize Rust.Wheat strip trials

    We designed a simple strip trial to compare several generic tebuconazole formulations against Stem Rust in wheat, applied to established disease at full ear emergence.

    All were 250g per litre formulations applied at 0.5 l/ha – the lower rate really tests the eradicant activity when the disease is already in the crop, and ensures that they should run out of persistence sooner, amplifying differences between the products.

    Spraying in the afternoon sun also brings out any products that are formulated with cheaper solvents and more prone to leaf scorch.

    In future years we will look to take these through to yield, but this is a rapid and effective way of identifying any particularly poor products to avoid.

    The trial is ongoing and the full results will be made available to Agronomy Clients through our network of agronomists, but at present the performance of Orius from Adama has provided the strongest reduction in disease, and interestingly the least expensive product which shall not be named, showed the lowest reduction in disease.


Pea Fungicides

Pea Plant

Last week I took the farm manager who is hosting our pea fungicide trial to look at treatments in a blind test. Despite the very low disease pressure this season he picked out the untreated plot immediately.

What was interesting however is that we could not pick out any differences between any of the fungicide treatments, which range from Ksh 6,200 to 16,500/ha ($62 to $165/ha)!!! We await the yield results…

Maize Fallow Period Management

Back in October I looked at the important of getting the fallow period right ahead of maize. Now that soils are dry, if deep structural repairs are needed, now is the time to do them.

I also pointed out that any patches of Cynodon or Couch needed to be cultivated back in October while there was moisture, so that they could be sprayed off while actively growing.

If this has not already been done or if the regrowth is very strong, I would strongly suggest leaving the very worst fields until the end of planting – this allows time for rain to arrive and regrowth to occur to allow successful glyphosate application.

For large areas, cultivate as a separate field with a false headland – this can be planted with separate planter depth settings so that it does not sink in to the soft ground.

Maize Seed Preparation Checklist

An inter row weeding solution for no-till farms?…

One of the big themes at the moment in world agriculture is glyphosate stewardship. How do we safeguard one of our most valuable tools against herbicide resistance developing?

A lot of data from recent conferences and studies that I have looked at sounds alarm bells about using glyphosate in crop as an inter row spray – or in crop as a total spray where GM Roundup Ready crops are approved.

Mechanically controlling weeds is very important but how can we do it without cultivating and disturbing the soil on farms that need to preserve residue cover?

I am massively excited about the recently released Chopstar Hybrid by Austrian firm Einbock:

The machine employs a vertical cutting disc followed by a horizontal disc which passes just below the surface, slicing the weed roots off without having to disturb the soil like a tine does and without disturbing the surface residue.

Fascinating concept and I look forward to seeing one working later this year hopefully.

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.