By David Jones, Broad Acre Agronomist, Msc. Agriculture
Along with Brome Grass, disease – and specifically Net Blotch – is the main yield robber disease in barley here in Kenya. But with the range of fungicide products on the market, where do you start to ensure that you maximise the return on your fungicide spend and achieve top yields?
Firstly, let’s go back a step. Good disease control starts with:
- Clean seed – if you are farm saving try to do so from a crop with low Net Blotch infection.
- Get the soil structure and nutrition right to ensure a healthy plant.
- Set the plant population appropriately – get the seed rate right for your situation.
Assuming you have carried out the above, what is disease then costing you? Last September I set up the first barley fungicide trial at Timau. This was a fully replicated, 8 treatment trial which looked at a range of products and timings. Despite reasonable rainfall (the field averaged over 7 tons/ha), there was no visual difference in disease in the crop.
So much so that my test yields from small areas of the replicated plots actually showed no statistical difference in yield between the untreated control and a very robust four spray fungicide program, so the rest of the trial was not actually harvested.
Don’t skimp on fungicides
This is, one assumes a rare occurrence. But as an independent agronomist my job is to lay out ALL of the facts, not to present a particular picture, and this is indeed one outcome. In most severe Net Blotch scenarios a yield response to fungicides of 20-30% is more typical. For a 5 ton/ha crop this is around 37,000 Ksh (370 USD). In other words, it justifies the cost of a robust fungicide program.
Below is the result at the other end of the spectrum. Our barley variety trial in the same location this season has one whole replicate untreated, and the other three have received a full fungicide program:
The reason for this is partly to look at fungicide response, but mainly to examine individual candidate varieties’ disease resistance. The above picture shows what happens when the standard variety Cocktail is left untreated.
The candidate I001 is particularly impressive and the untreated still has some green leaf. Not perfect, but a lot cleaner than the Cocktail. The point of this exercise is to look at what happens if you get your spray timings wrong, or if disease pressure is extreme.
Which fungicide to use?
Now, let’s take a look at one of our fungicide trials. This one is in a crop of Cocktail north of Nakuru. Although the crop is only at the flag leaf fully emerged stage, the infection in the untreated is very visible on leaf 3 already.
The standard program of 1.0 l/ha Skyway followed by 0.75 l/ha Skyway has been extremely effective. In my opinion this is the only fungicide worth considering on barley at present. Prothioconazole is very strong on Net Blotch and the Bixafen SDHI is a step forward over Prosaro.
The real revelation is the addition of an inexpensive T0 spray at mid to late tillering. It is hard to capture in a photo but infection on leaves 4 and 5 is far lower than the two spray program.
I have also been looking at the addition of a strobilurin such as azoxystrobin, but have seen no yield response. This should not be a surprise as although it is a very useful product, it demonstrates very little activity on Net Blotch. The same is true for trifloxystrobin and picoxystrobin.
I always advocate keeping spray intervals to 3 weeks, or 4 at the absolute most. For this reason I am also looking at the addition of a final spray at early flowering. In order to use some different chemistry I am looking at Abacus to avoid over using Skyway in the program.
Pyraclostrobin is not the strongest on Net Blotch – like the rest of the strobilurins – but combined with epoxiconazole it is the next best option after Skyway in my opinion. My feeling at the moment is that this final spray is unlikely to be necessary.
On the link below is some Independent fungicide trials data is published by the AHDB in the UK. They are a levy funded research body paid for by farmers and have no commercial or sales interest. Some of the chemicals are not available here, but it gives you a good indication of what is effective.
Timing is everything
Unlike wheat, barley responds much more strongly to what we call the T1 timing spray at GS30. The number of spikelets (and hence grains) is determined at this timing. That is why I use a full rate Skyway at T1 then a slightly lower rate at T2 (flag leaf timing).
In many countries an SDHI seed dressing is proving to be highly effective against Net Blotch, reducing inoculum on the seed and protecting the young plant from day 1. Systiva in Australia and Raxil Star in Europe have performed very well.
Below is a trial that I set up with an SDHI seed dressing on the right and a standard fungicide program all the way through. If and when they do become available it will be a big step forward particularly as clean seed is virtually non-existent in Kenya.
However, overusing SDHI’s either as foliar sprays or seed treatments will shorten their life significantly. In Europe if you use Raxil Star you can only use an SDHI such as Skyway once on the crop.
Keep an eye out for a new disease…
One disease that I am looking at very closely is Ramularia. Seen here last week in an untreated plot, it is likely that it has been confused with Net Blotch in the past. The way to identify it is to look for rectangular lesions with yellow surrounding that penetrate right through the leaf. They are also constrained by the leaf veins which is why it sometimes appears to look like Net Blotch.
Coming up next week…
The BIG Fall Armyworm Experiment! Every product examined in controlled conditions and compared to our field results data.
Center for Excellence for Crop Rotation
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.