MANAGING WEEDS IN WHITETAIL DEER FORAGE PLOTS

 

W. Carroll Johnson, III

Weed Scientist and Agronomist

Tifton, GA

 

A weed can be defined as a plant growing out of place that causes losses to man.  Any plant can be a weed, depending on the conditions.  Some weed species grow in the warm season, while some grow in the cool season.  Annual weeds are reestablished from seeds.  Perennials are reestablished from roots, tubers, or rhizomes.  Biennial weeds take two seasons to complete their growth; the first season is vegetative growth, and the second season is reproductive growth.  Weeds are adapters and survivors, which makes them the most expensive agricultural pests in the world to manage and control.

 

Weeds giveth, and weeds taketh away.  Some weed species naturally produce chemical compounds that inhibit growth of surrounding plants.  Weeds take away by competing with desirable plants for water, light, and nutrients.  Competition is usually the most significant way weeds cause losses.  The mere presence of a weed can be an aesthetic loss, as seen in ornamental landscaping or turf.  Some plants are weeds in one setting but are desirable in others. One example is a farm in northeastern North Carolina where I did research during graduate school.  That particular farm had an extraordinary population of johnsongrass, a tenacious perennial grass weed.  I was told that the farm had been owned by the same family since the early 1800’s.  For many years, much of the farm was planted in johnsongrass as a hay crop for mules and horses.  That same population of johnsongrass is costing the landowner thousands of dollars each year for herbicides to control it in soybeans, corn and peanuts.  Dr. Marshall McGlamery, a weed scientist at the University of Illinois, defines weed as "a plant whose virtues are unknown, but whose vices are."   That amusing anecdote is the best definition of weed that I have found.

 

Regardless of the type of loss, or the weeds and crops involved, there is a level of weed infestation where measurable losses begin.  Weed numbers less than this critical density are inconsequential.  In this case, control measures are not needed.  The insignificant loss is not worth the cost of control.  Conversely, numbers of weeds greater than the critical density cause significant losses, justifying control measures.  This critical density is specific -- to a specific weed, in a specific crop, under a specific set of growing conditions.  Weed scientists have determined through research the critical density for many weeds in major crops, but they have only scratched the surface.

Very little is known about the critical density of weeds in small acreage crops, such as forages planted for whitetail deer.  In these cases, one must use common sense to estimate the critical density of a weed.  In other words, use your general knowledge and intuition to guess if a weed or a mixture of weeds is present at a level sufficient to cause intolerable reduction in forage growth and yield.  The critical density of weeds will vary among people.  Some may demand no weeds in forage plots and will do whatever it takes to ‘eradicate’ weeds.  Others see a few weeds as an annoyance, but nothing to be overly concerned about.  This is where we are with forages planted for whitetail deer.

 

Integrated weed management is the use of a combination of cultural, mechanical and chemical weed control practices to prevent significant losses caused by weeds.  For years, weed management was equated with chemical weed control or using herbicides.  This is not the same as integrated weed management.  Judicious use of herbicides is an important component of an integrated weed management system.  However, herbicides are not the only means to control weeds.  Successful agricultural operations have found that depending exclusively on herbicides to control weeds is neither environmentally nor economically wise.

Commercial vegetable producers and homeowners use integrated weed management for different reasons.  There are very few herbicides registered for use in commercial vegetable production and for general homeowner use.  In these cases, there is more dependence on cultural and mechanical weed control practices, and less dependence on herbicides.  There are very few herbicides registered for use on forages planted for whitetail deer, and most are available only to commercial applicators.  Therefore, weed management in forages for whitetail deer needs to more heavily emphasize cultural and mechanical weed control.

Cultural weed control.  Cultural weed control is defined as the use of crop-production practices that give weed-control benefits.  Frequently, the strategy of a cultural weed-control practice is to maximize the competitive ability of the crop.  Any crop production practice that enhances a rapidly growing and uniform forage crop is a cultural weed-control practice.

 

Crucial first steps in establishing forages for whitetail deer is site selection and site preparation.  Obviously, factors other than suitability for forage production enter into choosing where to plant food plots for whitetail deer forage.  If you are going to the trouble and expense of establishing a food plot, choose a site where the forage will grow and thrive.  Consider terrain, soil type (avoid the extremes - deep sands or heavy clays), shadiness, and site condition (presence of stumps, rocks, tree tops, etc.).  Is the site readily accessible by tractors with implements?  A good site for a food plot (from an agronomic perspective) may hold moisture or be well drained, and be open to light for the majority of the day, free of large rocks and timber debris, and have a friable, tillable soil.  A site of this type will have the potential to grow healthy forage plants that will have a chance to compete with weeds.  If the site is of marginal quality, forage growth will be poor, and weeds will become an unending nightmare.

Site preparation involves thinking ahead and being pro-active.  Site preparation is not done a few days before planting a food plot.  Rather, site preparation begins several months before planting a food plot.  Site preparation involves removing debris, heavy tillage to define the limits of the food plot and loosen the soil, and shallow tillage to establish the final seedbed.  Beginning this process months in advance of seeding is essential for several reasons.  From a weed control perspective, the grower has the opportunity to control many troublesome perennial weeds such as briars, blackberry, privet, honeysuckle, broomsedge and tree saplings before planting.  Primary and secondary tillage will control these weeds, provided that tillage is thorough and repeated frequently enough to prevent regrowth.  Another tool for site preparation weed control is glyphosate (Roundup®).  Glyphosate is a nonselective systemic herbicide that can control a wide array of annual and perennial weeds, and is useful to control weeds before planting, during the site preparation phase of food plot establishment.  Refer to the glyphosate label and the local extension service for instructions and recommendations.  Regardless of the procedures used to prepare a planting site for whitetail deer forages, this will likely be the only opportunity to successfully control these species.  Failure to take advantage of this opportunity will greatly handicap efforts for good weed control in forages for whitetail deer.

 

Whitetail deer forages are often planted in areas that have not been recently tilled or planted to crops, areas in which nutrients essential for forage growth are often imbalanced or deficient.  Soil pH (acidity) is frequently outside the acceptable range for optimum plant growth.  Forage plant vigor and growth are directly affected by soil fertility.  When soil nutrients and pH are optimum, forages can grow rapidly, giving them the capability of successfully competing with weeds.  Soil fertility problems will result in poor forage growth, which exacerbate weed management problems.  Do not guess on soil fertility.  Use soil testing services to determine the soil fertility status of your food plot site.  Base fertilizer and lime use on results from the assay.  Land-grant universities in every state as well a numerous private laboratories provide this service.  A good time to sample soil and apply corrective fertilizer and lime is before tillage operations during site preparation.

 

Choosing the correct forage for your environment is a critical step in cultural weed control.  Not all forage species are adapted for plantings across all of the country. For example, some forage crops that grow well in Pennsylvania may not grow well in Georgia. The Whitetail Institute has done an excellent job of identifying forage climate tolerances for different parts of the U.S. and has different blends specially designed for different parts of the country. Also not all forage species are adapted for the wide array of soil conditions found in North America. For example, forage crops that grow well in heavy, moisture holding soils may not perform well in sandy well-drained soils. If the forage is not adapted to your region, it will not grow very well and weeds will be a problem due to a lack of competition from the forage crop.  Plant a forage that is adapted to your geographic region and environmental conditions.

 

Compared to non-improved selections of a crop, improved crop cultivars are excellent competitors with weeds.  Improved forage cultivars were selected for seedling vigor, rapid vegetative growth, and multiple pest resistance, in addition to the forage quality characteristics.  The attributes that enhance the vegetative growth of forages for whitetail deer enhance the competitive ability of the forage with weeds.  Each improved characteristic in forages helps in the competitive struggle with weeds.  While improved crop competition alone is not enough to suppress weeds, it is a critical component.

 

Quality of forage seeds is an often overlooked component of cultural weed control.  Poor quality seed may be old, improperly handled and stored, or harvested from stressed plants.  Regardless of the reason, poor quality seed will result in erratic forage stands.  Unevenly distributed or sparsely established forage seedlings provide opportunities for weed establishment.

Seeding rates are critical for correctly establishing forages.  It is tempting to reduce seeding rates to save on the cost of establishing forages for whitetail deer.  This will make weed management much more difficult.  Forage plants that are too widely spaced due to seeding at a lower than recommended rate are poor competitors with weeds.  Conversely, excessive seeding rates are cost prohibitive, with little measurable benefit.  Use the recommended seeding rates.

 

A stale seedbed is a seedbed prepared several weeks before seeding.  Between seedbed preparation and forage seeding are opportunities to till the soil, stimulate weed seed germination, and control the weeds with tillage before planting.  An excellent time for stale seedbed weed control is during site preparation.  This is a time proven practice used by practitioners of organic crop production.  It is also a proven practice in commercial vegetable production.  Weed seeds usually germinate and emerge from the top three inches of soil.  There is either insufficient light to stimulate germination of deep weed seeds or deep seeds are too small to emerge before carbohydrate reserves are depleted.  Shallow tillage will stimulate and control weed seedlings before planting the forage.  In theory, significant numbers of viable weed seeds are depleted by stale seedbed tillage before planting.  Once the forage is seeded, there are fewer weeds.  A good rule of thumb is to till the seedbed at least twice at two-week intervals before planting.  The most effective tillage implements are those that pulverize the soil, such as a power or rotary tiller.  A disk harrow and seedbed conditioner are nearly as effective.  Regardless of the implement used, the seedbed should be tilled no more that three inches deep.  A disadvantage of stale seedbed tillage is the depletion of soil moisture before planting.  If the seedbed is excessively dry after the last tillage, delay forage seeding until moisture conditions improve.

Mechanical weed control.  Tillage, mowing, and hand rouging are types of mechanical weed control that are viable and practical weed management techniques in forage plots for whitetail deer.  Shallow tillage cuts or uproots annual weeds, which should not re-grow if the weeds are small.  If forages such as millet, soybean, pea, or crucifers are planted in parallel rows, cultivation between rows can be effective.