Weeds Appearing in Unexpected Places

By W. Carroll Johnson, III, Ph.D., Agronomist and Weed Scientist

I am amazed by where weeds appear and conditions related to their sudden appearance. Our family has a small cabin on Lake Martin in the piedmont region of central Alabama. This reservoir was completed in 1926 to generate electricity and help control flooding downstream. As a result of the latter use, the lake elevation is intentionally lowered in the autumn by 10 to 12 feet to create storage capacity for winter rain.
In 1986, there was severe drought in the region and the lake never reached full pool during the summer. Near our cabin, a small stream flows into the lake, with a delta of sediment deposited in a broad plain—an artifact from when the surrounding landscape was in subsistence farming a century ago. That summer, the sediment dried for first time in recollection. The result was about five acres of cocklebur and small flower morning glory— common weeds of crop production. Presently, that small stream drains a watershed that is totally woodland, with no cultivated cropland. Seed deposited in the delta decades earlier remained dormant since the delta was normally underwater during the summer months. The dry summer of 1986 featured conditions that favored germination; in this case adequate oxygen and sunlight. Weeds appeared where they were not expected.

Weeds appearing in unexpected places is a perpetual headache for those who manage food plots, whether for hire or as a hobby. Understanding the phenomenon of the weed seed bank will help anticipate the problem and minimize losses. There are underlying factors to consider; previous land-use, seed production, and seed dormancy.


 There are few stands of true virgin timber in the eastern U. S. and much of our current timberland has either been previously harvested for timber or cultivated as farmland. These two disruptions will directly influence rapid changes in plant species diversity and many of these plants we categorize as ‘weeds’. If timberland becomes reforested, the ‘weeds’ become scarce and eventually disappear as the forest matures. Similar processes occur in cultivated sites after crop production ceases. Basically, these two examples are what plant ecologists call old field succession, but starting at different points in the process. In both examples, weeds produce large amounts of seed, tubers, and rhizomes that are stored in the seed bank.


Have you ever wondered how many seed a weed can produce? Weed seed production is influenced by species, weed density, and growing conditions. A large isolated weed will produce more seed per plant than a spindly plant growing in close proximity to others. Obviously, that effect can be offset by large number of spindly plants. Regardless of all the qualifiers, refer to Table 1 that lists seed production of several weed species. These numbers are the reason why preventing weed seed production is one of the overall goals of integrated weed management in any cropping system, including food plots. Consider an occasional escaped pigweed in a food plot; perhaps an eyesore but not necessarily enough to affect forage growth on a large scale. However, multiplying the number of escaped pigweeds by 200,000 seed per plant produces an enormous number. This does not take into account the unknown number of dormant pigweed seed already in the soil. Using this example, would it not be prudent to pull or chop the escaped pigweed before they produce seed and make a manageable problem much worse?


Dormancy is controlled by the genetic code unique to each plant species and environmental conditions. During dormancy, weed seed are in a protected state that may last for many years (Table 1). A useful strategy to reduce seed bank numbers in fallow sites is to stimulate large-scale weed seed germination with repeated tillage and control the emerged weeds, either with subsequent tillage, a non-selective herbicide like glyphosate, or both. This is termed stale seedbed weed control. The sequence of tillage to stimulate weed emergence followed by control will partially deplete numbers of viable weed seed in the soil. The longer this sequence is practiced, the better the results. Yes — it is costly and temporarily removes a potentially valuable food plot site from forage production. However, stale seedbed weed control can take a hopelessly weedy site and hammer the weed seed bank down to a manageable level.

Advocates of minimum-till production systems contend that this system brings weed seed from deep in the soil profile back to the soil surface where germination occurs. While minimum-till production systems offer many soil conservation and time-savings advantages, this is not the case with weed control. Research has shown that when fields are tilled, 80 percent of the weed seed near the soil surface are buried; with later tillage only bringing 38 percent of those seed back to the soil surface. In other words, tillage buries far more weed seed than it brings back to the soil surface — a significant net reduction. In contrast, sustained minimum till production systems cause an accumulation of weed seed near the soil surface where they can readily germinate when conditions are right. This phenomenon is presently occurring nationwide with widespread infestations of herbicide resistant pigweeds, frequently in minimum-till production systems. As a result, farmers are desperately reverting to conventional-tillage systems that bury accumulated pigweed seeds stratified near the soil surface and hopefully lessen incidence of a weed pest that has very limited control options. This is particularly unfortunate since many of these sites are highly erodible and need to be in a minimum-till production system.

Weeds often appear unexpectedly in food plots. This should be anticipated because of the large numbers of dormant seed in the seed bank. Aggressive measures are needed to reduce the weed seed bank and prevent weed seed production in food plots. These goals are critical for successful and sustainable weed management in food plots.

Table 1. Seed production and longevity of common weed.

Annual bluegrass
Common lambsquarters
Common purslane
Common chickweed
Common ragweed
Eastern black nightshade
Fall panicum
Large crabgrass
Pennsylvania smartweed
Field pennycress
Shepherd’s purse
Curly dock
Seed Production
Seed Longevity

Summarized data published in: Regnier, E. E. 1994. Teaching seed bank ecology in an undergraduate laboratory exercise. Weed Technol. 9:5-16. (Refer to that article for the original source of data for individual weeds.) Seed collected from soil beneath a meadow, pasture, or forest. Ages of weed seed were indirectly determined by the duration of the current land-use pattern. Seed recovered from archeological sites and longevity determined by carbon-dating.


The setting is World War I, the Somme Battlefield in northeastern France. Like many battles in World War I, combat was largely in a restricted area for an extended period. What had once been pastoral pastures and small woodlots was transformed into a wasteland of trenches and artillery impact craters. War had destroyed the topography of the countryside. The following summer after hostilities moved elsewhere, miles of the once barren battlefield were transformed into a sea of red poppies in full bloom. This was the inspiration of the present- day tradition of red poppies used to commemorate what we now call Veteran’s Day or Armistice Day. The Somme Battlefield was also the location of a detailed plant ecology study1 that catalogued the suddenly changed flora and factors that influenced plant diversity. Repeated artillery barrages pulverized the soil and when combined with the weathering effects of rain, snow, and freezing/thawing the net effect was akin to a gigantic plow that haphazardly tilled an entire region in France. Dormant weed seed (in this case red poppy seed) were exposed to oxygen, sunlight, and water. What was once pasture and woodland was destroyed by war, but later transformed to a sea of red poppies. Once again, weeds appeared in unexpected places.