Weed Seed Wizard case studies

Please note: This content may be out of date and is currently under review.

An early versus a late harvest

In 2007, Nigel Metz from the South East Premium Wheatgrowers Association (SEPWA) developed an online tool, the SEPWA Harvest Calculator. This economic model works on the theory that a crop can be harvested sooner by harvesting for longer periods each day under high-moisture conditions, limiting exposure to yield and quality loss. It is:

  • Pertinent to harvest programs that are delayed by high grain moisture levels
  • Yield decreases by approximately 0.5% per day after crop maturity for cereal crops along south coast of WA
  • Without weeds, the gross margins for both early and late harvests are usually the same; the cost of a reduced yield of a late harvest equals the cost of delivery penalties for high moisture levels at early harvest which equals the cost of blending or drying high moisture grain at an early harvest
  • But, the risk of weather damage increases the later the harvest.

Dumping the chaff at harvest

What about the extra yield loss in the following year due to dropped weed seed?

At grain maturity, a large percentage of annual ryegrass seeds can be captured by harvest weed seed management, either by a chaff cart, by burning narrow windrows or by using a Harrington Seed Destructor™. Delaying harvest, however, can allow weed seeds to drop on the ground prior to their capture. In weedy paddocks therefore, the risk of reduced yields the following year due to an increased seedbank also increases the later the season.

Using the Weed Seed Wizard, we examine a barley-lupin-wheat-wheat rotation on the south coast of WA with annual ryegrass (2009-12). There are two scenarios:

  1. Early harvest in 2011 (wheat year) using a chaff cart – 80% annual ryegrass collected (blue bars in Figure 2).
  2. Late harvest in 2011 (wet harvest) – 40% of annual ryegrass seeds collected (green bars in Figure 2).
Annual ryegrass dropped in two scenarios, an early and a late harvest
Figure 2 The annual ryegrass dropped at harvest in two Weed Seed Wizard Scenarios; an early and a late harvest

A late harvest in 2011 resulted in greater yield loss due to weeds in 2012 that the earlier harvest (Figure 2).

Figure 3 Harvest yields from two Weed Seed Wizard scenarios; Early Harvest at crop maturity where 80% annual ryegrass seeds caught in chaff cart and Late Harvest 1 month later where 40% annual ryegrass seeds caught in chaff cart
Figure 3 Harvest yields from two Weed Seed Wizard scenarios; early harvest at crop maturity where 80% annual ryegrass seeds caught in chaff cart and late harvest, one month later where 40% annual ryegrass seeds caught in chaff cart

What is the decision?

  • Harvest early although the grain moisture levels are higher and accept the increase in delivery costs.
  • Catch more annual ryegrass in the chaff cart and produce 0.3t/ha of wheat more in 2012.

Contact information

Page last updated: Thursday, 19 August 2021 - 11:07am