Sunday, June 1, 2014

Are your Weeds Trying to Tell you Something?

The distribution of weeds within your area can be influenced by biological factors such as habitat types and human activities.   Even factors such as incidence of insects or diseases on either weeds or associated crops as well as animal grazing and plant competition can impact the way weeds are distributed.  Weeds distribution is also dependent on environmental factors such as soil type, pH, soil moisture, light quality, precipitation pattern, and variation in air, soil, or water temperatures.  

Of course, there are weeds that will tolerate a wide range of soil and moisture conditions, but sometimes certain weeds can be indicators of soil conditions within the field.  This subject does not appear to be heavily researched, but based on observation.  Some examples given after scanning the web may be that thistles grow where there are low nutrients or heavy clay.  Prostrate knotweed or chickweed may be growing within compacted areas of the field.  The growth of purslane could indicate a poor drainage. 

Dr. Matt Montgomery, Burrus Sales Agronomist, visited a field in the river bottoms of Missouri.  There they struggle with horsetail or (Equisetum arvense), which is a perennial with a nasty, spreading rhizome root system.  In the spring, it sends out “fertile stems”, with a spore-bearing cone on top.  These stems lack chlorophyll, so they die shortly after releasing spores.  Later, “sterile stems”, with feathery leaves arise and reach around 2 feet in height (see picture below).  This is another weed that indicates wet or poorly drained field.  It is also TOXIC to livestock.



Grass control within a field can be challenging to say the least.  Some grass weeds such as giant foxtail, green foxtail, and yellow foxtail are indicators of nutrient rich soils; however, some grass weeds could be a “red flag” and indicate unsatisfactory soil conditions.  Recently, we visited a field in Southern Illinois with an uneven stand of corn.  Seeds that had not emerged were rotted with bacterial soft rot.  We often want to blame the seed, but perhaps a better drained seedbed was the way to go to achieve a better corn stand.  Since this particular grower had not applied his post weed control, we were also able to see that areas of his field were plagued with an unfamiliar, grass weed.  A little research let us know that this “unfamiliar weed” was Carolina foxtail (Alopecurus carolinianus). This foxtail only reaches a height of 4 to 6 inches and has compact little seed heads that can resemble timothy grass.  The other thing that I learned about Carolina foxtail was that it favors wet areas of no-till crops; therefore, this grass was yet another indication of the wet areas of this seedbed.  For additional information, refer to Dealing with Soil Moisture and Replant Decisions.

Carolina foxtail
As post herbicide applications are being applied, it may be helpful to view your weeds in a different way.  Weed identification may not only be helpful for control strategies, but also as an indication of soil conditions within a field, which could be further addressed, if possible.

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