Weed competition is a leading cause for failure of young apple orchards.  Up to 90% of the trees roots are in the top 2 feet of soil and weeds growing in the root area of the trees are in direct competition with the tree for water and nutrients.  Apple trees are poor competitors.

 The good orchardist must remove weed competition, but at the same time must insure that valuable and irreplaceable topsoil is not lost.  The method of choice has become a weed free strip under the trees with a permanent sod strip between rows.  Mechanical tillage of the entire orchard floor was the standard of the past, but is rapidly losing favor, in most situations.  High density orchards with rows spaced less than 10 feet apart may need to have the entire orchard floor weed-free because of narrow row middles and heavy shade.

 Sod Middles -- Sod middles in properly contoured rows can stop or at least greatly reduce erosion and sod middles make the orchard accessible to harvest and maintenance equipment under most conditions.

 Many orchards use the natural stand of weeds and grasses as a sod middle; however, troublesome pests like sandbur, Johnsongrass, etc. can make this undesirable.  Bermudagrass can be maintained as a middle cover but its highly invasive growth requires regular herbicide application under the trees to minimize competition.  Never plant bermudagrass as a middle cover; use it only if it is already present.

 No sod grass that we can plant is ideal as a middle cover.  Buffalo grass is good in several respects and is less competitive than bermudagrass, but Buffalo is expensive to establish.  King Ranch (K.R.) Bluestem is a clump grass that is used some and appears to be one of the more practical options.  Kleingrass is another clump grass that will work well, but is more difficult to establish a good stand.  Fescue is another permanent cover that is used in northern orchards, but unirrigated row middles usually result in death of much of the fescue stand during typical Texas summers.

 Winter grasses like oats and rye are sometimes used, but these die in the spring and summer weeds usually invade the dead stubble.

 Tillage -- Mechanical tillage of the entire orchard floor should not be used on sloping sites because of soil erosion.   Tillage under the trees also cuts many shallow feeder roots.  Frequent tillage, as is commonly practiced in some unirrigated orchards, essentially turns the tilled 2 to 4 inches of topsoil into a mulch and forces the root system to develop below the tillage depth.  This soil mulch plus the complete removal of weed competition is the chief reason why regular tillage, barring negative aspects, is particularly effective in unirrigated orchards.

 Chemical weed control is very cost competitive with mechanical tillage because chemical control requires less costly equipment, less trips through the orchard, less horsepower and less fuel.  With chemical weed control, the only orchard floor equipment really needed is a herbicide sprayer and a mower.

 To use herbicides safely and effectively, the orchardist should have a basic understanding of the types of chemicals and application methods available.  A description of various options is presented here.
 
 

 Postemergence Herbicides

Contact Herbicides - These are simply postemergence chemicals that kill vegetative tissue on contact.  These types of materials provide quick kill of top growth on most weeds, but some well established annuals (grow from seed each year) and most perennials (lives for several years) will make new growth and require frequent application to keep weed growth under control.

 Gramoxone (Paraquat) is the most commonly used, labeled contact herbicide for apple orchards. Paraquat is very effective on weeds and is safe around apple trees as long as it does not directly contact green leaves or young tender bark.  Paraquat is highly toxic to humans and should be handled very carefully.

 Rely (glufosinate-ammonium), is a newly labeled herbicide with relatively low human toxicity.  Rely kills like a contact but is actually considered to be a transmodal (intermediate between contact and systemic) herbicide.  The chemical moves into the plant where it kills, by  ammonium buildup, without translocating further.

Systemic Herbicides - Systemic herbicides are postemergence chemicals that penetrate plant tissue and are moved throughout the plant and into the roots.  These chemicals usually kill slowly, but kill the entire plant, from the roots up.
 Non-Selective Systemic Herbicides containing glyphosate are widely used.  Roundup is a glyphosate labeled for use in apple orchards.  Roundup will kill a broad spectrum of weeds and grasses.  It is particularly valuable because of its effectiveness against highly competitive perennials such as Bermudagrass and Johnsongrass.  Roundup must be applied when weeds and grasses are in a succulent stage of growth for best kill.  Drought hardened plants are not as readily killed.

 Certain perennials such as perennial morning glory, nightshade and perennial ragweed are very tolerant of Roundup. The best result with glyphosate on difficult to kill weeds are obtained with fall applications in late September, October or early November at least several days before a killing frost. More food materials are being translocated to plant roots in the fall and more glyphosate will move to the roots as well and give a better kill.

 Glyphosate is toxic to apple trees and care must be taken to avoid direct contact or contact from spray drift on leaves or green bark.  Spray applications should be made when there is no wind.  Young trees should be shielded to prevent accidental contact.

 Selective Systemic Herbicides that will kill grasses, but not harm broad-leaf plants, including apples, are available. Fusilade (fluazifop-butyl) is labeled for use on non-bearing apples. The chief advantage of this type of material is around small apple trees where grasses may have gotten out of control and it is impossible to avoid contact of the spray material with trees.  In order for chemicals such as Fusilade to be effective, grasses must be in a succulent, young stage of growth. Two applications may be required for good kill.

 Fusilade is most effective against perennial grasses such as Bermudagrass while Poast (sethoxydim), another selective herbicide that also kills grasses only, is most effective against annual grasses such as crabgrass and sandbur.

 Preemergence Herbicides

 These chemicals generally do not harm existing weeds.  Their main effect is to kill germinating seedlings. They must be uniformly applied to the soil surface and then activated by shallow incorporation into the soil. Less stable materials such as Devrinol must be incorporated quickly by disking or by irrigation. More stable materials such as Solicam, Surflan, Karmex, Sinbar or Princep can be left on the soil surface for at least 3 weeks waiting for 1/2 inch or more of rain to move them into the soil. Organic debris should be either closely mowed or incorporated into the soil before applying a preemergence herbicide. A heavy cover of sod or plant reside may prevent much of the chemical from reaching the soil and thus reduce the effectiveness.

 The most effective times to apply preemergence herbicides are in January or February prior to germination of most spring weeds and grasses and in September before germination of most winter weeds and grasses.

 No single preemergence herbicide is effective against all weeds and grasses.  The choice of herbicide or herbicides should be based on the weeds and grasses present in the orchard. The table at the end of this section shows the relative effectiveness of most labeled preemergence herbicides against common weeds and grasses in Texas orchards.

 Total elimination of weeds is seldom achieved with preemergence herbicides.  Successive annual applications will gradually reduce problems of 'escape weeds' but periodic spot treatments with a postemergence chemical are usually necessary under most orchard conditions.

 Boom Sprayers

 Sprayers with a tractor or sprayer-attached boom are useful for application of all types of liquid applied herbicides. This is the only type of applicator suitable for preemergence herbicides. A typical boom is mounted about 18 inches above the ground and fitted with 80 degree flat fan spray tips spaced 20 inches apart. These sprayers do not require high pressure or  high volume spray delivery. A typical herbicide sprayer will not need to deliver more than 50 gallons of solution per acre and will need to generate not more than 30 psi pressure.

 Backpack (Knapsack) Sprayers

 These types of sprayers are ideal for spot treatments of weeds with postemergence herbicides.  A good operator can also accurately apply preemergence herbicides with them if he is able to maintain consistent pressure and steady walking speed.  These sprayers are better for applying liquid chemicals than wettable powders since they have no means of solution agitation other than shaking.

 Backpack sprayers offer tremendous advantage over hand-held pump-up sprayers. Hand-held sprayers can be used with a maximum of effort, to apply postemergence herbicides, but they should never be used for preemergence chemicals.

 Controlled Droplet Application

 Controlled droplet application (CDA) sprayers have spinning heads, which disperse the spray solution as fine, uniform droplets. They are available as hand-held units or with boom-mounted heads for tractor application. CDA is used primarily  with postemergence herbicides, especially glyphosate.  It offers advantages in chemical savings and in application with a minimum of water.  Hand-held CDA units can be used successfully to apply glyphosate on sizeable orchards.
 

 Wick Application

 Wick applicators or weed wipers are used primarily as a safe method of apply glyphosate close to small trees or under windy conditions where sprays can not be used safely. Wick application of glyphosate works best on tall, more easily controlled species such as Johnsongrass.  Lower growing and tougher to kill grasses such as Bermudagrass are controlled more effectively and efficiently by spray application of glyphosate, assuming it can be applied safely.

Calibrating a Herbicide Sprayer

 Accurate calibration of the spray rig is essential.  Application of too little chemical is ineffective and wasteful of the herbicide since an additional application will have to be made to get the desired results. Application of too much chemical can be both wasteful and dangerous to the trees.  Overdoses of certain preemergence herbicides can be especially hazardous.

 The operator must know how much spray solution is being applied to each treated acre in order to determine the amount of chemical to add to the tank. Numerous methods can be used to calibrate sprayers. One of the simplest is presented below. Calibration steps shown are for a tractor-mounted boom, but the same steps can be used to calibrate a backpack or a CDA sprayer.

 1.  Determine the calibration distance, based on your nozzle spacing from the table below.
    (Example: With a 20" nozzle spacing, measure a distance of 204 feet)

 2.  With all attachments in operation and the pressure set at 20 to 30 psi, set the tractor at a comfortable orchard speed  (usually 3 to 4 mph) and count the seconds that it takes to travel the calibration distance.

 3.  Collect all the spray from one nozzle for the number of seconds that it takes to travel the calibration distance. this should be repeated on other nozzles to check for uniform spray delivery.

(Example: continuing the above example and using an 8004 spray tip and 25 psi; in 35 seconds each nozzle should deliver 23 ounces of water.)

4.  The number of ounces of spray collected will equal the  gallons of solution that the rig will apply per acre.

(Example: If 23 ounces of water were collected, this means that the sprayer is calibrated to deliver 23 gallons of solution per acre.)

1.)  Select the appropriate herbicides(s) and rates for the expected weed spectrum and soil type present.

2.)  Thoroughly clean out spray tank, lines and spray boom.

3.) Partially fill spray tank with clean water, start pump and set to desired pressure.  Check spray nozzles for even pattern and uniform delivery.  Measure width of spray band.

4.)  Measure off a test area, for example, 100 linear feet.  With the tractor operating at desired ground speed and spray pump operating at desired pressure, time how long it takes equipment to travel over the test area.

5.)  With the equipment stationary, run pump at operating at the same rpm and pressure, measure the volume of water that is delivered in the same time it took to travel the test area from each of the nozzles.  Total the volume from all nozzles.  This will give you a water volume to area ratio that will allow you to calculate the amount of water volume being applied per treated acre.

Example:
Assume the boom covers a 5 foot swath and it takes you 20 seconds to travel the 100 foot test area.  If there are four nozzles and each puts out 15 ounces in 20 seconds, there are 60 ounces of water being applied over a 500 square foot area.  A simple ratio will allow you to calculate volume per treated acre.  There are 43,560 square feet in an acre.

   _60_   =  _X__
  500          43560

60 x 43560= 2613600  2613600/500=5227.2 ounces per acre

5227.2/128 (ounces per gallon)= 40.8 gallons per acre

If the amount of water is higher than desirable, a grower can gear up or decrease operating pressure.  If lower than desired, increase nozzle size, increase sprayer pressure or gear down.

With this knowledge, a grower will know how much material to put into the spray tank to correctly apply the right amount of material per acre.  Remember that while insecticides and fungicides are recommended at a given rate per acre of orchard or vineyard, herbicide recommendations are listed in amount of material per treated acre.
 
 

Postemergence

Contact

Gramoxone Extra (Paraquat)
Rate: 3 to 5 pints/acre in 50-200 gallons of water per acre. Add non-ionic spreader sticker at 8 oz/100 gallons
Time: Apply as a directed spray when weeds and grasses are succulent.
Weeds: Annual broadleaf weeds and grasses and top kill and suppression of perennials
Remarks: Do not allow spray contact with green stems, fruit or foliage.  Highly toxic to humans

Rely (Glufosinate-ammonium)
Rate: 3 to 5 qt/ac in minimum of 20 gals. water
Time:   When weeds are actively growing
Weeds: Most annual broadleaf weeds and grasses and top kill and suppression of perennials
Remarks: Not to be used within one years of transplanting.  Avoid direct spray or drift to green bark or desirable vegetation.  May be used to kill suckers on mature trees.

 Systemic

Roundup (Glyphosate)
Rate: Boom equipment: Annual weeds 10 to 48 oz/ac, perennial weeds 16-128 oz/ac in 10 to 15 gallons of water/acre.
Hand-held spot treatment equipment: 1-2% solution.
Wiper applicator: 33% solution
CDA: 4-16% solution
Time:  Apply as a directed spray when weeds and grasses are actively growing.  Hard to kill perennials are controlled best by application in the fall before frost.
Remarks: Do no allow spray or drift to contact green bark, foliage or suckers. Roundup does not provide residual weed control. Apply as a directed spray when weeds are actively growing.

Touchdown (Sulfosate)
Rate:  Boom and hand-held equipment (flat fan tips) - 0.25 percent to 3 percent solution in 10 to 20 gallons of water per acre, depending the size and toughness of target weeds; CDA - Use 1 1/3 to 5 1/3 pints per acre in 3 to 20 gallons of water per acre; Chemical mowing (grass suppression) - 4 to 10 ounces per acre in 20 to 30 gallons of water per acre.
Time:  Works best when applied to young, actively-growing weeds; works best on Johnsongrass and Bermudagrass after seedhead formation.
Weeds: Most annual weeds and grasses and many perennials
Remarks: Do not allow spray or drift to contact green bark, foliage and suckers; Touchdown does not provide residual weed control; a surfactant (2 qt. per acre) must be used with Touchdown; Control of tough weeds may be improved by adding ammonium sulfate (2 percent by weight or 17 pounds per 100 gallons of water) to the Touchdown solution; labeled for non-bearing apples only.

Fusilade 2000 or DX (fluazifop-P-butyl)
Rate: 24 to 32 oz of 2000 in 5 to 40 gallon/acre. DX is double strength.
Time: Annual grasses: when actively growing, 2"-8" high and before tillering or seed head formation.  Perennial grasses: similar to annual grasses dependent on species.
Weeds: All annual grasses, many perennial grasses, no broadleaf weeds.
Remarks: Non-bearing trees only. Add a crop oil concentrate (1%) or non-ionic surfactant at 0.25% of the spray solution. Better against perennial grasses than for certain annual grasses

Poast (sethoxydim)
Rate: 1.5 - 2.5 pt/acre
Time: When grasses are actively growing and before tillering or seed head formation.
Weeds: Most annual and perennial grasses, no broadleaf weeds
Remarks: Non-bearing trees only. Add a crop oil concentrate (1%) or non-ionic surfactant (0.25%) to the spray solution. Better against annual grasses than for certain perennial grasses.

Preemergence

Devrinol 50WP (Napropamide)
Rate: 8 lb of 50WP/acre in 15 to 50 gallons of water/acre
Time: Fall or spring before seedling emergence
Weeds: Annual grasses and various  broadleaf weeds
Remarks: Must be incorporated by shallow  cultivation, or 1/2" of irrigation or rainfall within one day of application

Karmex 80W (diuron)+ Sinbar 80W (terbacil)
Rate: Karmex 1-2 lb 80W/ac + Sinbar 1-2 lb 80W/ac in 15 to 50 gallons water/acre
Time: Before seedling germination in the spring (February)
Weeds: Broad spectrum of annual weeds and grasses
Remarks: Trees must be established for 2 years before use. Do not use on coarse sandy or gravely soils. Activated in soil by 1/2" plus of rainfall within 3 weeks of application or by shallow cultivation

Princep 80W or 4L (Simazine)
Rate: 2.5-5 lb 80W/ac or 2-4 qt 4L/acre
Tankmix rate: with Surflan, use listed rate; with Solicam, use 1.25-2.5 lb Princep 80W; with Devrinol, use 0.6 to 1.25 lb Princep 80W/acre
Time: One application per year spring or fall before seedling emergence.
Weeds: Broad spectrum of annual broadleaf weeds and annual grasses
Remarks: Trees must be established for one year before use. Tank mix suggestions are to combine superior annual grass control (Surflan, Solicam, Devrinol) with superior annual broadleaf weed control (Princep)

Solicam 80DF (Norflurazon)
Rate: 2.5-5 lb. 80DF/acre in 15 to 50 gallons of water/acre
Time: Before seedling germination in the spring or fall (February or September are ideal times in most areas of Texas)
Weeds: Broad spectrum of annual grasses and many annual weeds. Use tank mix with Princep where annual weeds are a serious problem
Remarks: May be used on newly planted trees. Good suppression of some perennial grasses including Bermudagrass or purple nutsedge. Incorporated by 1/2" or more rainfall within three weeks after application or by shallow cultivation

Surflan 75WP or 4AS (Oryzalin)
Rate: 2.7 - 8 lb 75WP or 2-6 qt. 4AS/acre in 15 to 50 gallons of water depending on length of control desired (2-12 months)
Time: Before seedling germination in the spring or fall (February or September are ideal times in most areas of Texas)
Weeds: Broad spectrum of annual grasses and various annual weeds. Use tankmix with Princep where annual broadleaf weeds are a serious problem
Remarks: May be used in newly planted orchards. Activated by 1/2" or more of rainfall within three weeks after application or by shallow cultivation.