2012 Weed emergence in Wisconsin: uncharted territory

2012 Weed emergence in Wisconsin: uncharted territory

Mark Renz Extension Weed Scientist, Agronomy Department, University of Wisconsin-Madison

Time of first weed emergence is fairly consistent from year to year.  For example Jerry Doll monitored yellow foxtail emergence over a three year period in Arlington Wisconsin and found that on average it began to emerge on April 30th, differing by no more than seven days between years.  This reliability has been a huge benefit to growers as we can predict when these weeds will emerge and apply our PRE herbicides at the correct time.  A summary of these data along with the ability to create a graphic that estimates emergence and flowering time in your area can be found at this link (weedometer):

http://weedecology.wisc.edu/weedometer/

Realize that these average timings for emergence and potentially flowering presented on the weedometer will be several weeks late this year due to the warm weather this spring.  I visited the Arlington weed garden recently and documented emerged plants, and summarized what I saw compared to average first emergence for common weeds.

Refer to the table below for my observations of common weed species in Wisconsin.

Briefly, perennials are emerging and flowering three to four weeks ahead of typical timing. For example yellow rocket should be flowering at Arlington in 1-2 weeks this year which is 3 weeks ahead of the average timing. I expect the same thing to occur with biennials as there emergence was several weeks ahead of schedule.  Annual weeds’ response is much more variable, as species that had cotyledons present on April 4th on average emerged 19 days earlier, but the range was between 3 and 35 days depending on the species.

So you should plan on weed emergence to be several weeks earlier.  We can expect it to also speed up the development of these weeds and they will flower sooner, but other factors besides temperature can affect this change.  Also don’t forget we are one frost/freeze away from resetting the clock which is not uncommon in Wisconsin.  What will happen in this coming year is really not known as this is truly an atypical spring.

Weed species

Average date of first
emergence 1998-2000

(range observed in days)

Weed emergence as of 4/4/2012

Days earlier emergence than
average^

PERENNIAL WEEDS

Canada thistle

April 16th (15)

Y

Curly dock

April 10th
(24)

Y

Dandelion

March 29th (6)

Y

Field bindweed

April 26th
(4)

Y

Field horsetail

April 28th (7)

N

Hemp dogbane

April 28th
(1)

N

Common milkweed

May 6th (5)

N

Quackgrass

March 23rd
(24)

Y

White cockle

March 30th (12)

Y

Yellow nutsedge

May 12th
(3)

N

Yellow rocket

April 2nd (12)

Y

BIENNIAL WEEDS

Burdock

April 4th (24)

Y

Plumeless thistle

April 7th
(7)

Y

Wild carrot

April 7th (12)

Y

ANNUAL GRASS WEEDS

Barnyardgrass

May 3rd (8)

N

Fall panicum

May 5th (6)

N

Giant foxtail

April 27th (2)

Y*

23

Green foxtail

May 3rd (3)

N

Large crabgrass

May 14th (9)

N

Shattercane

May 13th
(10)

N

Wooly cupgrass

April 30th (6)

Y*

26

Yellow foxtail

April 30th
(7)

Y*

26

ANNUAL BROADLEAF WEEDS

Bur cucumber

April 29th
(5)

N

Common ragweed

April 7th (28)

Y*

3

E. black nightshade

April 30th
(16)

Y

Giant ragweed

April 8th (32)

Y

Common Lambsquarter

April 18th
(22)

Y*

14

Redroot pigweed

May 9th (2)

Y*

35

Waterhemp

May 5th (1)

Y*

31

Wild cucumber

April 16th (10)

Y*

12

Wild radish

April 12th
(18)

Y*

8

*If only cotyledons present on weeds

^ Only calculated if weed species appeared to have just emerged (only cotyledons present)

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