Fall herbicide application improves weed control in fruit orchards

Fruit growers have the opportunity to experiment with fall herbicide application.

With little or no fruit to harvest this fall (2012), Michigan fruit growers have the opportunity to experiment with fall herbicide application. Growers often comment that they don’t have time to apply herbicides in fall because they are too busy with harvest and shipping. This year with the frost-reduced or eliminated crop, they may consider trying new and different herbicides and methods of weed control.

Fall is a good time to apply herbicides for control of many weeds, but especially persistent weeds and late-germinating weeds that usually escape or tolerate preemergence herbicides, as well as perennial, biennial and winter annual weeds. Weeds such as horseweed,yellow rocket,mallow,wild carrot,dandelion,white campion (cockle) and quackgrass are more susceptible to herbicides in fall than in spring. Most of the residual preemergence herbicides registered for tree fruit, bush berries and grapes are labeled for fall or spring application.

Fall herbicides should be applied after frost has killed most annual weeds and new growth has ended for the year and before soil freezes. November is normally a good time to apply. Fall rains help to move the herbicides into the soil and "activate" them. Cool soil temperatures reduce herbicide dissipation and degradation of the active ingredients.

Kerb (pronamide) is very effective against quackgrass when applied in fall. Kerb may be used on pome, stone fruit and blueberries. Apply up to 4 lbs. product/acre in a band on both sides of the row. Kerb suppresses quackgrass up to about July 1. Kerb should be applied with another herbicide such as Chateau or Alion to expand the weed control spectrum. Inclusion of glyphosate (Roundup or generic) in the tank-mix will kill emerged weeds.

Chateau (flumioxazin) is very effective against most annual weeds when applied in the fall. It does not control horseweed (marestail) adequately when applied in the spring, but fall Chateau application plus glyphosate provides good, overall weed control until mid-July. Chateau may be used on pome, stone, blueberries and grapes. An early spring application of a photosystem II (PS II) inhibitor, such as Karmex (diuron) or Princep (simazine), will broaden the weed control spectrum. Another application of glyphosate in late May or June will kill most emerged weeds and provide bare ground into August.

Sinbar (terbacil) is labeled for both fall and spring application in apples, peaches and blueberries. (Sinbar should only be used on trees that are 3 years or older. It is moderately soluble and should not be used on sand with less than 1 percent organic matter.) Sinbar suppresses many annual grass and broadleaf weeds, and if applied with glyphosate in the fall, it will control most weeds for two to three months in the spring. Sinbar does not control common groundsel and loses control of pigweeds by mid-season. Sinbar is a PS II inhibitor and should be used in alternate years to avoid weed resistance.

Sandea (halosulfuron) may be applied in the spring in apples and blueberries at 1 oz per acre. It will suppress most broadleaves and also improve yellow nutsedge control. Sandea may be applied again later in the season at 1 oz per acre for post-control of broadleaves and yellow nutsedge. Sandea in the spring after Sinbar in the fall controls most annual broadleaves and grasses.

Solicam (norflurazon) is effective when applied in the fall. It provides good suppression of most annual grasses and yellow nutsedge. It should be combined with or followed the next spring by Karmex or Princep for broader and longer weed control.

September is a good time to apply Stinger (clopyralid). Weeds in the Asteraceae (composite) family, such as dandelion, Canada thistle, common groundsel, horseweed, fleabane, goldenrod and white heath aster are susceptible to clopyralid (Stinger, Spur, other generics). Legumes (alfalfa, clover, trefoil) and nightshades (eastern black nightshade, hairy nightshade, ground cherry, horsenettle) also are susceptible to clopyralid. Fall is a good time to kill these very tough weeds with clopyralid. The weeds should be sprayed while they are actively growing so that they absorb and translocate more of the herbicide. Wait at least two to three weeks after Stinger application before applying residual herbicides and glyphosate. Stinger currently is labeled on stone fruits and blueberry.

Some herbicides are more effective when used in the spring. The mitosis inhibitors Prowl (pendimethalin), Surflan (oryzalin) and Devrinol (napropamide) are effective preemergence annual grass herbicides. They are good tank-mix partners with PS II inhibitors in the spring. They are non-phytotoxic to young and recently-transplanted trees and bushes, and can be applied soon after planting trees.

As a general practice for fruit weed control, use at least two residual herbicides with different modes of action each year (fall or spring) plus a post-emergence herbicide at least twice (fall and spring). Change the herbicides each year so that tolerant weeds do not build up.

There are several other herbicides labeled for some or all the fruit crops, which can also be included in the rotation. Check MSU Extension bulletin E-154, 2012 Michigan Fruit Management Guide, for all fruit crop herbicide recommendations.

Dr. Zandstra’s work is funded in part by MSU‘s AgBioResearch.

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