The big question!

We had a question!

Every month we give you the opportunity to ask the terminator agro a question.

And finally, after a year of newsletters, we got one!

And it’s the big question. It’s as big as, “where did I come from?”, “what came first, the chicken or the egg?”, and “who was the better footballer, Polly Farmer or Buddy Franklin?”

The question, “how long does it take for the numbers to come down”?

And I don’t think they were asking their local policeman about their breathalyzer result. I’m pretty sure they were asking how long does it take to run down a ryegrass seedbank?

I have two ways of answering this question, one relies on science, and the other on personal experience.

The science answer is an epic piece of science. I dug out an AHRI newsletter from 2017 that reported on Michael Walsh’s research that may well be one of Australia’s most grueling pieces of Agricultural research.

He hit the road around the entire country with a team of helpers and a truck loaded with a harvester towing a Harrington Seed Destructor. They set up 24 trial sites across four states.

The team compared the destructor with narrow windrow burning and a chaff cart. The destructor was a tow behind machine fitted with a cage mill and it achieved about the same level of seed destruction as the modern-day Seed Terminator – around 99%.

Then, the following year, they went back to each site and counted the ryegrass to determine what level of seed removal had occurred.

The average number of ryegrass plants in crop at harvest at each site was 10 plants/m2

And each plant set, on average, 209 seeds per plant.

The result.

Harvest weed seed control reduced the ryegrass germination the following year by 60%, and all of the tools worked roughly equally.

But that doesn’t answer the question does it.

To answer the question, we need to consider what happens through time.

So I made a spreadsheet. It’s pretty simple, but you’ll get the idea.

Year zero is the year the research started. If we start with a seedbank of 1000 ryegrass seeds, and control 99% of them with herbicides and have 50% ant predation/decay etc., we are left with 10 plants/m2 in crop (i.e Mike Walsh’s starting point across his trials).

These 10 plants set 209 seeds per plant, and then harvest weed seed control (HWSC) removes 70% of them.

Why 70% I hear you ask, because the data above says the germination reduced by 60% the year after HWSC. This is because there is an old seedbank in the soil, so to get a 60% reduction in germination, we must achieve about 70% to 80% control with HWSC.

With HWSC – With 50% seed decay, 99% control with herbicides, and 70% removal of the weed seeds with harvest weed seed control (HWSC), the seedbank erodes to zero in year 8.

Without HWSC – With 50% decay of the ryegrass seed, and 99% control with herbicides, the seedbank slightly increases through time.

But…

A spreadsheet is easier than real life.

In real life things can go wrong. A hail storm that lodges the ryegrass, a late harvested crop that misses the opportunity to capture weed seeds at harvest, or a wet year when weeds get out of control and the seedbank blows out.

In real life, growers find that it takes about four years before they feel that they are having a win, and numbers are really coming down. But they rarely get to zero, especially in those high rainfall areas where ryegrass grows really well.

In summary, getting on top of ryegrass numbers, using HWSC in combination with herbicides, and anything else that we can throw at the weeds, is a long term project. It takes four years to feel like you’re having a win, and probably another four until the seedbank feels like it’s near zero.

It works, but it takes persistence.

The Terminator Agronomist
Proudly brought to you by Seed Terminator 

Please note this advice is general in nature and not based on your specific circumstances.