Integrated Weed Management - the Only Way to Control Troublesome Weeds in Food Plots

W. Carroll Johnson, III
Agronomist and Weed Scientist

My career as an agronomist and weed scientist requires that I be knowledgeable of the research conducted by my predecessors.  This familiarity influences the direction of my research project.  In the context of weeds, the species that were common and troublesome to farmers a half-century ago are rarely a problem in the 21st century.  Conversely, our troublesome weeds in 2009 were rarely encountered decades ago.  Weed populations and species diversity are very dynamic and this is certainly the case in food plots.  We control one species and others quickly fill the vacant niche.  No rest for the weary.
It has been my personal experience that the successors to the easily-controlled weeds are usually a nightmare to control.  For five years, I had a series of food plots in a creek bottom in southern Georgia.  Early on, the weeds were mainly crabgrass and ragweed - both easily controlled with Arrest and Slay. By the time I had to find a different place to hunt, the food plot was infested with an array of weeds that I had never seen before - anywhere.  Furthermore, the herbicides at my disposal did not control any of the mystery weeds.  I am betting that many of you have similar stories, regardless of your location.

Under these circumstances, it is prudent to step back and re-evaluate the entire food plot system you use.  Avoid the temptation to focus solely on more or different herbicides.  Instead, develop a balanced, integrated weed management system of cultural, physical, and chemical controls to manage the troublesome weeds that challenge our intellect and bruise our pride.

A three-legged stool is balanced and stable. Remove one of the legs, the stool becomes unstable. A balanced weed management system relies equally on all three components.

Cultural weed control.  Any crop production practice that enhances crop growth and uniformity also improves the ability of the crop to compete with weeds.  This is true for any crop.  Another way of describing this relationship is equally relevant:  If a crop is not growing normally or uniformly, there is a parallel weed control problem.  Uniform crop growth is the single most powerful form of weed control in any cropping system, including food plots.  Forage selection, proper soil fertility (particularly pH), seedbed preparation, seeding rate, and overall growing conditions are cultural practices that provide weed control benefits of troublesome weeds.

Physical weed control.  I have always called this mechanical weed control.  I recently reviewed a manuscript in which the author used the phrase ’physical weed control’ and I liked that description.  This refers to physically removing or destroying a weed or its propagules (seed, rhizomes, roots, etc.).  Physical weed control includes tillage during site preparation or when conditioning seedbeds before planting.  Mowing tall weeds in Imperial Whitetail Clover is a form of physical weed control, along with hand weeding.  Earlier I mentioned the hornet’s nest of troublesome weeds in my own food plot.  One of the weeds that I did know the identity was dog fennel - a troublesome tall perennial weed.  I spent a long afternoon pulling large dog fennel out of Imperial Whitetail Clover.  That was my only control option.  Desperation led to extraordinary measures (and a sore back).

Chemical weed control.  Herbicides have certainly made our lives as food plot hobbyists easier.  However, there is a limited selection of herbicides available for use in food plots.  Furthermore, most forage plantings are multi-species blends which limit the use of selective herbicides.  Arrest can be used in many plantings for grass control.  This herbicide is a consistent and reliable means to control annual and perennial grasses, which are particularly troublesome.  Slay controls many broadleaf weeds in clover and alfalfa.  However, sometimes the troublesome weeds are also legumes (i.e. sicklepod or coffeeweed) and Slay will not control leguminous weeds.  Glyphosate (Roundup and generics) is a valuable tool, particularly for site preparation and control of perennial weeds during fallow periods.  For all the numerous benefits that herbicides provide, they are not a stand-alone for successful weed control in food plots.

Integrated weed management.  Recently, I have used the analogy of integrated weed management being a three-legged stool, each leg representing cultural, physical, and chemical weed control.  The stool with three functional legs is stable.  Remove any of the legs and the stool becomes unstable.  The same is true with weed management in food plots.  Balance is the key.  Consider the perennial grass common bermudagrass. Tillage alone will spread bermudagrass stolons and actually make the infestation worse.  Glyphosate and Arrest partially control bermudagrass, but re-infestations tend to occur.  An effective strategy is to weaken bermudagrass stands with tillage, followed by a properly timed application of glyphosate or Arrest.  This is an example of the synergy of an integrated approach to control a troublesome weed.  The integrated system is far more effective than the individual components used alone.

A real-world example of an out-of-balance weed management system is staring down on commercial agriculture in the U. S. There are numerous populations of pigweeds (Amaranthus spp.) in the coastal plain, mid-south, and mid-west that are resistant to several commonly used herbicides, including glyphosate.  Some pigweed populations are simultaneously resistant to three distinct families of herbicides.  Pigweeds have always been common, but now they are troublesome and changing the face of commercial agriculture.  In fact, this phenomenon is being compared to the boll weevil and how that pest forever changed agriculture in the south.  With herbicide resistant pigweeds, the effect could be nationwide.  And, I am not being melodramatic.

The factors that contributed to pigweed resistance to commonly used herbicides are conceptually simple.  One factor was the nature of the weed.  Pigweeds produce large amounts of seed (500,000 seed per plant), adapt to many environments, and cross pollinate which favors genetic mutation.  The other contributing factor has been the large scale change in how we manage weeds in the large acreage crops.  Most of the U. S. corn, soybean, and cotton plantings are transgenic varieties that have resistance to glyphosate.  Early-on, the overall effectiveness and simplicity of this technology led to widespread and extended use of glyphosate alone for weed control in these crops.  Together, these two factors created an acute selection pressure and the pigweed survivors proliferated.  Commercial agriculture has a mess on its hands and one could argue that it is due to over-reliance on a narrow-focused form of weed control; i.e. trying to sit on a one-legged stool.

Farmers are being advised to revert back to a more balanced form of weed management.  Cultivation is more common in row crops.  Deep tillage is being strategically reinstated in cropping systems to bury herbicide resistant weed seeds deep in the profile where they cannot germinate.  Wick-bar applicators are being pressed back into service.  Different herbicides are being used in all crops - not just sole dependence on one herbicide family.  I hope that this is not too little, too late.

Desperate times lead to extraordinary measures.  Last summer, I was visiting a peanut grower in southwestern Georgia.  We drove by one field where the farmer had a crew of workers pulling tall pigweeds that had escaped earlier control efforts.  The pigweeds were over 4 ft. tall.  It took two grown men to pull each weed.  They threw the weeds into the back of a flat-bed truck.  At the end of the rows, the truck dumped the pulled weeds into the woods.  I heard from others that this was repeated throughout the region.  

This is what happens when weed control is too narrowly focused and not balanced.  While this is an extreme case, it shows what can happen with troublesome weeds if we do not use integrated weed management.  Balance is the key.