The program for the control of annual weeds in the orchard should consider the weed free strip under the tree and the sod middles between the tree rows separately. The “Weed Control Season” in orchards starts in late fall, after harvest. The program implemented in the spring depends on what herbicides were applied the previous fall. If herbicides were applied in late fall, applications can be delayed until later in the spring. Residual herbicides should be applied in late winter or early spring after the soil is no longer frozen, if no late fall treatment was applied.
Annual weeds are weed species that live for less than one year. Winter annual germinate in the fall or late winter, flower in the spring or early summer, then die. Summer annuals germinate in the spring and early summer flower, and die in late summer or fall. Perennial weeds are weed species that live for more than two years. Control of these weeds must be considered separately.
Emerged annual weeds under the tree are controlled with a postemergence herbicide. Annual weeds that germinate throughout the remainder of the season are controlled with residual herbicides. Two applications of postemergence herbicide plus residual herbicides 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. In March, growers find themselves scrambling to apply insecticides and fungicides, and prune the orchards. Pruned branches must be removed or chopped before weed spraying can be accomplished after pruning.
The second application of residual herbicides should be applied in late spring, while the late fall application controls early season summer annual weeds. A postemergence herbicide may not be needed to control annual weeds in late spring if residual herbicides were applied in late fall, however, a postemergence herbicide may be included to control certain perennial weeds such as yellow nutsedge, Canada thistle, goldenrod species, or aster species.
Most residual herbicides primarily control annual grasses or annual broadleaf weeds (BLWs). A combination of an annual grass herbicide and an annual BLW herbicide is usually recommended. Rate ranges are recommended for most residual herbicides. Use the lower rates in orchards with coarse textured (sandy) soil low in organic matter, and the higher rate when soils are fine textured (silt and clay) and have higher organic matter.
Choose your residual annual grass herbicide for the coming season before the late fall/winter herbicide application. Options include Devrinol, Prowl H2O, Surflan, or Solicam. All four residual annual grass herbicides can be used at the rate of 4.0 lb active ingredient per acre per year. Apply half the yearly labeled rate, 2.0 lb active ingredient per acre, in the late fall/winter, and the second half, an additional 2.0 lb active ingredient per acre, in late spring.
Your residual BLW herbicides should be chosen considering crop safety, effectiveness, and price. For many years Princep (simazine) was recommended at 1.0 to 2.0 lb active ingredient per acre in the late fall/ winter, and Karmex (diuron) was recommended at 1.0 to 2.0 lb active ingredient per acre in the late spring. Both herbicides have been safe reliable, and cost effective choices for many years, and continue to good options in orchards where their use provides good weed control. Both Princep (simazine) and Karmex (diuron) share the same mode of action, inhibition of the light reaction of in photosynthesis. Unfortunately, triazine resistant weeds, with cross resistance to urea herbicides, including Karmex, are present at some sites.
Where a trizine resistant weed has become established, switch to a BLW herbicide(s) with a different mode of action. Use Chateau at 0.19 to 0.38 lb of active ingredient per acre or Goal (oxyfluorfen) at 1. to 2.0 lb of active ingredient per acre in late fall or late winter. Both products must be applied before bud break in early spring to avoid speckling and crinkling the crop’s foliage if spray drift occurs. The activity of both Chateau and Goal occurs at the soil surface as sensitive BLW seedlings emerge. Do not disk, till or otherwise mechanically mix Chateau or Goal into the soil after application, or the effectiveness of the herbicides will be reduced or eliminated.
Alion is a new residual orchard herbicide that controls annual grasses and annual BLWs, including triazine resistant species, when applied at 0.065 to 0.085 lb active ingredient per acre. Good crop safety has been observed in stone fruits and pome fruits. Alion does not leach readily, and therefore requires significant rainfall for “activation”. Summer annual broadleaf weed control “failures” have been observed when late spring applications are not followed by adequate rainfall or overhead irrigation for activation. Apply Alion in late fall or late winter when used in combination with Princep (simazine) or Karmex (diuron) for residual annual BLW control to ensure activation of the Alion during the winter months for the control of BLWs, including triazine resistant BLWs. Alion applications can be delayed until late spring when Chateau or Goal are applied in late fall/winter, or when no triazine resistant weeds are established. Then Princep (simazine) applied in late fall/winter can be relied on to control all winter annual BLWs and early season summer annual BLWs.
Matrix controls annual grasses and BLWs, and suppresses yellow nutsedge in stone fruits and pome fruits, and Sandea controls BLWs and yellow nutsedge in pome fruits. Both herbicides have postemergence and residual activity, and both are ALS inhibitors. Herbicides with this mode of action rely on a single site of action is susceptible weeds, putting herbicides with this mode of action at high risk for weed resistance development. Weed resistance to ALS inhibitor herbicides is already present in the New Jersey and the surrounding mid Atlantic region. Due to resistance management concerns, Matrix and Sandea are usually recommended for yellow nutsedge control, but not for annual weed control.
Stinger is a growth regulator herbicide with postemergence and residual activity labeled in New Jersey in stone fruits for the control of annual and perennial weeds in the legume and composite plant families. Legume weeds commonly found in orchards include vetch and clover species. Composite weeds targeted include horseweed (also called marestail or stickweed), dandelion, aster species, goldenrod species, Canada thistle, and mugwort (also called wild chrysanthemum). Stinger rates and application timing depends on the weed targeted.
When annual weeds have emerged before residual herbicides are applied, a postemergence herbicide should be included in the tank. In late fall, add 2,4-D amine at 1.0 lb of acid equivalent per acre to control BLWs. In late winter or spring, switch to Gramoxone or other labeled generic paraquat formulations at 0.6 to 1.0 lb active ingredient per acre plus nonionic surfactant at 0.25% of the spray solution if grapes, sensitive vegetables, greenhouses, or nursery stock are nearby (within a mile of the application site). 2,4-D should not be applied near sensitive crops. Spray or vapor drift from 2,4-D can cause serious damage to these crops. Roundup and other labeled generic glyphosate products can also be used to control emerged weeds in well established mature orchards without low hanging limbs, and can be especially useful where susceptible perennial weeds are a problem. The rate depends on the perennial weed targeted.
Consult the Commercial Production Recommendations for rates and additional information.