Crop & Pest Report


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Waterhemp is Beginning to Flower (07/13/17)

I was collecting notes in one of my waterhemp control experiments last week and observed evidence of flowering.

Waterhemp is Beginning to Flower

I was collecting notes in one ozollingerf my waterhemp control experiments last week and observed evidence of flowering (see attached image). Why is flowering important? Because female waterhemp plants produce a tremendous amount of seed and seed remains viable for 4 to 6 years. Waterhemp plants growing in noncompetitive environments can produce greater than 500,000 seeds per plant (fewer under competitive environments).

A few scattered waterhemp plants in a sugarbeet or soybean field do not rob yield. However, they make seed and great seed production facilitates the rapid spread of waterhemp, especially when the seeds are scattered by harvesting and tillage equipment. Applying herbicide to waterhemp approaching the flowering stage is not recommended because this practice does not significantly reduce the amount of seed waterhemp plants produce.

Researchers at Iowa State University and the University of Illinois examined how long it takes female waterhemp plants to produce viable seed after the flowers were pollinated. Female waterhemp plants were pollinated for 24 hours and then separated from the male plants In the Illinois study. Branches from female plants were harvested at various intervals after pollination and placed under either warm (86 degrees Fahrenheit) or cold (-4 degrees Fahrenheit) conditions for 48 hours, then stored at room temperature. Researchers then measured germination to determine how soon after pollination seeds were viable. They found seeds stored for 48 hours under warm conditions were viable 7 to 9 days after pollination; seeds stored under cold conditions were viable 11 days after pollination.

Hand-weeding is recommended for removing scattered, flowering waterhemp plants from a field, especially near the borders of field. Take a plastic garbage bag to carry out any female plants since seed might already be viable.

Rich Zollinger

Extension Weed Specialist

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