Broomcorn Millet

May 2009

Identifying and preventing the spread of a plant pest

Broomcorn millet is a new and very fast-growing invasive weed causing major problems for sweetcorn and maize growers.

Mike Flynn is the field Manager for McCain Foods. He is also on Hort NZs process product group for research and development so can speak for the industry as well as McCains.

Andy Lysaght is a grower and contractor and also the process vegetable rep from Hawkes Bay for HortNZ.

Broomcorn millet is a very fast growing grass, which can grow as high as a sweetcorn or maize plant. Mike says it is progressing in the wrong direction. Every season it just seems to be worse and worse. But he says its difficult to define its economic impact on crops.

It is thought to have come in with imported birdseed, and it was first found at the back of a house in Marlborough. Now it has spread from there and been found in Waikato, Gisborne, Hawkes Bay, and recently Andrea found it in Wanganui.

It is moved around on machinery, especially harvesting gear. Even though contractors are now blowing down their machinery it still doesnt get all the seeds.

There are lots of things about the grass that make it a problem:

1. it germinates right through the season.

2. it has a very large and thick seeds with a shiny black coat. This gives it much more protection than a normal grass seed.

3. this also makes the seed persist longer in the soil, for five years or maybe longer. Normal grass seeds have a very short life, only surviving a couple of years at the most.

4. it grows about twice as fast as other grasses. This means a shorter time to control the weed with sprays (2-3 days max) before the sweetcorn or maize plant has emerged, compared with 7-10 days for normal grass weeds.

5. it also produces seed very quickly: after only a month in greenhouse conditions, and then only two weeks after that the seed is mature. This is much faster than other common grasses.

6. it makes harvesting very difficult contractor and grower Andy Lysaght says in one paddock a harvester lost four nose cones because of the weed. These cost $700 each to replace, and so instead of doing that they redesigned and rebuilt the head of the harvester using steel.

7. it is expensive to control and needs to be sprayed rather than mechanically weeded. Andy says it costs from $45-$76/ha just to spray the weed, not counting the cost of the chemical.

8. it is spread by harvesters from paddock to paddock.

9. it suppresses yield: maybe by up to 30% in the very worst cases. And it makes the most of the fertiliser and irrigation meant for the sweet corn crop.

The first thing is to correctly identify the plant: a new guide to grass weeds has been produced by FAR, and it was written by AgResearch senior scientist Trevor James from Ruakura.

Research is underway with FAR and HortNZ to find out how long the seeds persist in the soil.

HortNZ is applying to MAFs Sustainable Farming Fund for a project to look at emergent grates of broomcorn millet at different temperatures, and for two field experiments to look at how effective post-emergent herbicides are.