Getting the seed treatment right is crucial with cereals to control seed borne diseases such as Fusarium Seedling Blight and Loose Smut, and to protect the young plant against aphid borne BYDV.
Recently I have heard many farmers tell me that they are planning to plant less – or no – maize this season and more wheat, or even barley and potatoes where contracts and machinery allow.
Cereal Seed Treatments
Firstly, it is important to realise that seed dressings are like vaccines in a way; they have led to massive declines in Bunt and Loose Smut for example to the point that when we do occasionally plant undressed seed, we may not even see these diseases. But if we all stopped using them to save 1,000 Ksh per hectare we would probably run into problems very quickly. So don’t take the risk – especially as BYDV and Russian Wheat Aphid still need to be accounted for and diseases can still be present on even certified seed.
All of the neonicotenoids including thiamethoxam, imidacloprid and clothianidin have good activity on insect pests and will typically give 6 weeks protection after emergence in our conditions. I remember looking at some work in the UK which showed that seed rate (and by virtue the amount of active ingredient put down per square meter) makes a big difference to the persistence of protection from aphids, so if you are planting as low as 45 kg/ha be mindful that the protection can run out early.
Also, my experience with cover cropping is that the green bridge does increase the transfer of aphids onto the following cereal crops particularly if you are terminating a cover crop with oats close to planting.
Apply the insecticide dressings at the full label rate and according to the manufacturer’s instructions, and you will find there is very little difference in activity or persistence between them.
When it comes to diseases, there are some subtle differences. Prothioconazole for example is weak on Septoria seedling blights in wheat, but good on Loose Smut which is prevalent in some barley varieties.
Conversely, fludioxonil + difenconazole mixtures are good on Septoria seedling blights but poor on Loose Smut (the same goes for Carboxin + Thiram which has some Net Blotch activity in barley but does nothing on Smut).
In some countries other actives are added to improve early Yellow Rust control which could be very useful here in areas such as Naivasha or Mau Narok, particularly with susceptible varieties like Kwale. As yet nothing is approved unfortunately.
If you are planting wheat after long term grass, a chlorpyrifos-based dressing can help on beetle larvae that may damage emerging seedlings, but rolling to create a firm seedbed is much kinder to beneficial insects.
TOP TIP – when treating the seeds for my trials, of which there are often a hundred or more varieties, I apply a one third dose before I put the seed into store, and a two thirds dose just before planting – this avoids the concerns over storage pests and overcomes the problem of chemical dust at planting. The extra time spent handling the seed is often time well spent, particularly if I keep the seed for longer than 6 months as I know the low rate of dressing will not affect germination.
What about Micronutrients on the seed?
One of the earliest published studies in the Rift Valley back in 1967 showed that seed dressing with Copper around Nakuru gave a small yield response, but far better results came from foliar copper applications. In practice, copper on the seed can delay germination and early vigour and does little to improve copper supply to the plant. Likewise copper coated fertilisers contain very low amounts that have minimal effect in my experience and in our trials.
Zinc can have a very vivid effect on greener plants at emergence, but unless soils are very deficient this is often very short-lived and almost an optical illusion that the greener plants are actually healthier. Most of the work I have encountered rarely shows zinc seed dressings following through to a yield increase at harvest, but farm for your own soils.
Stem Rust Update
Stem Rust is usually rare – or at least present at very low levels – in the Mount Kenya region. Yet this year has seen even new CIMMYT varieties showing far higher levels than is acceptable.
Varieties such as Robin will always have a notable amount of Stem Rust, but this year even Hawk, Korongo and Eagle 10 are almost as severely affected and it is easy to find symptoms on Kwale too.
Normally in Mt Kenya region Septoria dominates which is why the focus on Stem Rust can sometimes be lost, especially when it arrives when the crop is well on its way to harvest.
It is very unclear why the pressure is high this season but it reinforces the need to be mindful of Stem Rust when putting together fungicide programs for the year ahead; even in low risk areas, the addition of a half rate of strobilurin fungicide – with good Stem Rust activity – with the ear spray for Fusarium is a sensible step. Relying on triazoles alone in not sensible for high risk varieties.
Farming for the future requires a change of approach. Monoculture, soil degradation and climate change and soil degradation are threats to the future of how we feed the planet. Agventure Ltd set up the Center of Excellence for Crop Rotation to help farmers diversify cropping systems and introduce techniques which have a long-term outlook to improve soil health. The Center of Excellence for Crop Rotation works extensively with Crop Nutrition Laboratory Services Ltd (CropNuts).
Till 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.