Weed Science Webinar Series

Two applications of residual herbicides plus postemergence (if needed) herbicide are recommended annually in the weed free strip under the trees. The first application should be applied in late fall, after the trees are dormant, but before the soil freezes, or in late winter before the trees’ buds break in the spring.  This application targets the control of winter annuals and provides early season control of summer annual weeds.  Most growers are more easily able to apply herbicides to the orchard in late fall, usually after Thanksgiving in New Jersey. Consider a labeled glyphosate product if perennial weeds are present and spot-treatment is recommended in the fall.

Most residual herbicides primarily control annual grasses or broadleaf weeds.  A combination of an annual grass herbicide and an annual BLW herbicide is usually recommended.  Rate ranges are recommended for most residual herbicides depending on the soil texture. Refer to the herbicide label to determine the appropriate rate for your soil texture.  Consult the 2021/2022 New Jersey Commercial Tree Fruit Production Guide for rates and additional information. https://njaes.rutgers.edu/pubs/publication.php?pid=e002

Residual herbicides applied in fall are the most effective at preventing weed emergence when:

• Applied on unfrozen bare ground so that herbicide spray is not intercepted by weed residues at the surface of the soil.
• Applied before targeted weed germinate. If weeds have already emerged, use a residual herbicide with postemergence activity or tank-mix a postemergence herbicide.
• Applied at the appropriate rate for your soil texture.
• Receiving enough water within (at least 0.5”) 7 to 10 days after application so that herbicide can be “activated” (penetrate into the ground) and protected from photo-degradation or volatilization.

Herbicide application should be accomplished with a “conventional” fixed-boom sprayer calibrated to accurately deliver 40 to 60 gals. of water/A using flat fan nozzles and 30 to 40 psi, unless otherwise stated.

Weed-free strip for newly planted trees should only be sprayed with herbicides labeled for use on newly planted trees. Additionally, newly planted trees should systematically be protected from potential injury by a tree guard, a waxed container, or another non-porous wrap or guard.

Broadleaf Weeds and Grasses Residual Herbicides for Fall Application

• Alion 1.67SC (indaziflam). Use 5 to 6.5 fl. oz./A Alion 1.67F. Apply in late-fall to weed free soil, or add an appropriate postemergence herbicide to kill existing vegetation. Primarily for the control of annual broadleaf weeds and annual grasses. Tank-mix with Prowl H2O or Solicam DF to improve annual grass control. Tank-mix with Chateau 51SW, Karmex or Princep 4L to improve annual broadleaf weed control. Alion does not leach readily, and therefore requires significant rainfall for “activation”; therefore, Alion should be preferentially be applied in fall. Apply to stone fruits and pome fruits established a minimum of 3 years.
• Casoron (dichlobenil). Use 100 to 150 lbs./A Casoron 4G or 1.4 to 2.8 gals/A Casoron CS (Casoron CS is currently unavailable) Apply between 11/15 and 02/15 (before weed growth begins and daily high temperatures exceed 50°F) to control labeled annual and perennial/biennial weeds. Casoron is volatile in warm temperatures and must be irrigated or incorporated immediately after application if applied in warm weather. For apples, pears, and cherries established a minimum of 1 year.
• Chateau 51SW (flumioxazin). Use 6 to 12 oz./A of Chateau 51SW. Chateau controls many annual broadleaf weeds, and controls or suppresses annual grasses. Tank-mix with Prowl H2O, Surflan 4AS, or Solicam 80DF to improve control of annual grasses. Do not apply to trees in the field less than one year old unless trees are protected by a tree guard, a waxed container, or another non-porous wrap or guard. Do not use more than 6 /A in orchards where the soil contains more than 80% sand (sands and loamy sands) until the trees have been in the field for three years. For newly planted AND established apples, peaches, pears, plums, and cherries.
• Zeus Prime XC (sulfentrazone + carfentrazone). Use 7.7 to 15.1 fl oz./A Zeus Prime XC. Zeus Prime XC primarily controls annual broadleaf weeds. It also suppresses yellow nutsedge at the highest labeled rate. Thus, Zeus Prime XC is a better fit for early spring residual herbicide treatments in orchards infested with yellow nutsedge. Tank-mix with Prowl H2O, Surflan 4AS, or Solicam 80DF to improve control annual grasses. Sequential applications of Zeus Prime XC can be applied when directed as a banded application (50% band or less of orchard floor) so long as total use rate does not exceed 15.1 fl. oz/A on a broadcast basis within a year and the second application is not applied within 60 days of the initial application. For apples established a minimum of 3 years.

 Broadleaf Weeds Residual Herbicides for Fall Application

• Karmex (diuron). Use 1.25 to 3.75 lbs./A Karmex 80DF or 1 .0 to 3.0 qt./A of Direx 4L. Primarily for annual broadleaf weed control. Tank-mix with Prowl H2O or Solicam DF to improve annual grass control. Use one-half the labeled Karmex rate when used alone for the soil type, to improve crop safety, and the range of weeds controlled when tank-mixing with an annual grass herbicide. Apply to apples and pears established a minimum of 1 year, and to peaches established a minimum of 3 years.
• Princep (simazine). Use 2.2 to 4.4 lbs./A Princep 90DF or 2.0 to 4.0 qt/A Princep 4L. Primarily for annual broadleaf weed control. Prowl H2O or Solicam DF to improve annual grass control. Use one-half the labeled Princep rate when used alone for the soil type, to improve crop safety and the range of weeds controlled, when tank-mixing with an annual grass herbicide. Apply to apples, cherries, peaches, and pears established a minimum of 1 year.
• Motif 4L (mesotrione). Use 6 fl. oz./A Motif 4L. Provides both residual and post-emergence control of susceptible broadleaf weeds, and is especially effective for the control of horseweed and common lambsquarters. Tank-mix with an annual grass herbicide to provide control of annual grass. Do not apply more than 12.0 fl. oz./A in one year. Do not use on soils containing greater than 20 percent gravel. Apply to apples, pears, peaches, and plums established a minimum of 1 year.
• Trellis 4.16 SC (isoxaben). Use 16 to 31 fl oz./A Trellis SC. Apply in late-fall to control many small-seeded broadleaf weeds. In newly planted trees, allow the soil to settle and fill any depressions around the tree before application. ank-mix with an annual grass herbicide to provide control of annual grass. For newly planted apples, peaches, pears, plums, and cherries, AND For established apples.

Grasses Residual Herbicides for Fall Application

• Surflan 4AS (oryzalin) Use 2 to 6 qts./A Surflan 4AS. Use the high rate for long-term control (4 to 8 months) and the low rate for short-term control (2 to 4 months). Surflan primarily controls annual grasses. Tank-mix with Princep or Karmex to control annual broadleaf weeds. Apply half the yearly labeled rate in the late fall/winter, and the second half in late spring. For newly planted AND established apples, peaches, pears, plums, and cherries.
• Prowl H2O 8SC (pendimethalin). Use 2 to 4 qts./A Prowl H2O. Use the high rate for long-term control (4 to 8 months) and the low rate for short-term control (2 to 4 months). Prowl primarily controls annual grasses. Tank-mix with Princep or Karmex to control annual broadleaf weeds. Apply half the yearly labeled rate in the late fall/winter, and the second half in late spring. For newly planted apples, peaches, plums, and cherries AND for established apples and peaches.
• Solicam 80DF (norflurazon). Use 2.5 to 5 lbs./A Solicam 80DF. Primarily for annual grass control, Solicam may provide partial control of many broadleaf weeds. Tank-mix with simazine plus Princep or Karmex to improve the control of broadleaf weeds. For newly planted apples and peaches AND established apples, cherries, peaches, plums, and pears.
• Kerb 50WP (pronamide) – Restricted use pesticide. Use 4 to 8 lbs./A Kerb 50WP. Apply in November when soil temperatures are between 35° and 55°F. Primarily controls perennial grasses, including quackgrass, bluegrass, ryegrass sp., fescue sp., and provides early control of annual grasses the following spring. Tank-mix with Princep for postemergence and residual broadleaf weed control. For established apples, peaches, pears, plums, and cherries.

Postemergence Herbicides for Tank-Mixing with Residual Fall Herbicides

• Embed 3.8SL (2,4-D choline). Use 1 to 4 pts./A Embed to control a wide variety of broadleaf weeds. Effectiveness depends on herbicide rate, weed species, and growth stage. Apply to weed foliage in the fall after harvest. Fall applications are more effective and reduce the risk of herbicide drift injury to adjacent crops. Weeds are most susceptible to 2,4-D when they are growing vigorously, not under stress, and before flower buds appear. Apply before the leaves of perennial weeds lose normal, summer green color. DO NOT apply on loamy sand or coarser soils. For established (bearing) apples, peaches, pears, plums, and cherries.
• Gramoxone 2SL (paraquat) Restricted use pesticide. Use 2.5 to 4 pts./A Gramoxone SL2.0. Contact killer only; no translocation or residual activity. Best results occur when weeds are 6 inches tall or less. Regrowth may occur from the root systems of established weeds. Use a surfactant to be 0.25% of the spray solution (1.0 qt./100 gals. of spray solution). DANGER: Do not breathe spray mist. Read safety precautions on the label. For newly planted AND established apples, peaches, pears, plums, and cherries.
• Rely 280 2.34SL (glufosinate). Use 48 to 82 fl oz/A of Rely 280 to control most annual broadleaf and grass weeds plus some perennials. Apply as a directed spray at a minimum of 20 GPA. The addition of ammonium sulfate will enhance glufosinate activity on difficult to control species; however, the addition of surfactants and crop oil will increase risk of crop injury. For optimal performance, spray under cloudless conditions and when sun is high in the sky. Do NOT allow Rely to contact ANY GREEN, IMMATURE PART or SUCKERS of the tree. For newly planted and established apples, peaches, pears, plums, and cherries.

Work conducted by Dr. Brad Majek a few years ago indicated that direct application of glufosinate to the mature brown bark of the lower trunk may cause severe injury by killing the cambium layer at the point of contact. However, this type of injury is not systematically associated with glufosinate application as we observed it in a trial conducted in 2017 at the Snyder Research Farm on mature “Pink Lady” apple trees which were not damaged following glufosinate application  (Rely 280 at 64 fl oz/A). Additionally, injury in the form of vertical cracks in the of trunk bark have also be observed on apple trees exposed to glyphosate (https://nyshs.org/wp-content/uploads/2016/10/Pages-23-28-from-NYFQ-Winter-12-12-2013.cmc_.pdf), not only to glufosinate.

As highlighted by Dr. Dave Rosenberger (retired Plant Pathologist at Cornell’s Hudson Valley Lab) on his blog (https://blogs.cornell.edu/plantpathhvl/2014/06/30/apple-summer-diseases-herbicide-problems-and-irrigation/), “NEITHER glyphosate nor glufosinate cause trunk injury to apple trees EVERY time that they are used or in every orchard in which they are applied”. Field reports suggest that injury is detected when trees are exposed to specific conditions that still need to be precisely defined. Dr. Rosenberg’s opinion is that “the potential for damage is significantly higher if tree trunks are hit with either of these herbicides during or just prior to periods of drought stress”. Under these drought conditions, “the additional desiccation from herbicide exposure may predispose the trunks to invasion by Botryosphaeria dothidea, a canker pathogen that is incapable of killing the cambium in healthy functioning trees, but which becomes very pathogenic in drought-stressed trees”. Dr. Rosenberg also suspects that similar injury can be observed on young trees following application of paraquat. Other stress factors, such as cold injury or previous bark damages, may also increase the risk of herbicide injury.

So, to safely apply glyphosate or glufosinate in peaches or apples, it is important following some guidelines that will help minimizing glufosinate damages to the bark. As specified by the label for glufosinate products and the Rutgers 2021-22 E002 Rutgers Tree Fruit guide, contact by the herbicide of parts of trees other than mature brown bark (including suckers) can result in serious damage. It is therefore especially important to protect young trees from potential glufosinate injury by wrapping them with grow tubes or waxed containers. For mature trees, the use of a shield boom is required for minimizing as much as possible contact between the herbicide spray and the tree bark. Shields will also minimize the bounce-back from bare soil that sometimes allows a haze of small droplets to drift upward into the trees. Avoid applications of herbicides during periods when trees are already experiencing water stress or where water-stress can be expected in the near future. Additionally, weed control efficacy of glufosinate can severely decrease when weeds are under heat stress. Keep the pressure as low as possible (no more than 30 psi) to minimize generation of small droplets. If not feasible, use air-induction nozzles to reduce the production of small droplets.