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Weed Management in Pecan1

Peter J. Dittmar and Jeffrey G. Williamson 2

Weeds compete with pecan trees for light, nutrients, and water. Weed interference can be minimized with proper cultural practices and use of herbicides. General maintenance such as controlling weeds in adjacent areas (i.e., nearby fields, ditches, and driving paths), preventing weeds from producing seeds, and cleaning mowing equipment of weed seed will prevent weeds from becoming a serious problem. Cultivation can be used but should be shallow to prevent root pruning and soil erosion.

Chemical Control

Herbicides available for weed control in pecan are included in Tables 1 and 2. Because soil types in Florida vary, consult the labels for application rate restrictions based on soil type. Bearing trees are fruit trees that are currently producing fruit. Nonbearing trees are trees that will not produce fruit for a year after application. The tables include preharvest intervals (PHI).

All herbicides should be directed to the base of the trees; this method provides coverage of the weeds while minimizing the contact to the trees. Young trees should be protected with nonporous wraps or growth tubes to minimize uptake of the herbicide. This is especially important for systemic postemergence herbicides (for example, glyphosate) and contact burndown herbicides (for example, paraquat, diquat, glufosinate).

Tank mixing can broaden the spectrum of weed control. A preemergence herbicide may only control the most problematic weed in the orchard and leave some weed species unaffected. A preemergence herbicide can be tank mixed with another preemergence herbicide that controls several weed species but not the most problematic weed in the orchard.

The most common method of tank mixing is a postemergence herbicide with a preemergence herbicide. This method provides control of the weeds that are above the soil surface and controls weeds for a longer period. Consult the label for compatible tank mixing partners. If concerned, use a jar filled with the herbicides and water then agitate the jar to see if the herbicides mix.

Practices for improving weed control with herbicides are as follows:

  1. Herbicide selection. Preemergence herbicides control the weeds before they emerge from the seed or break the soil surface. Postemergence herbicides control weeds that have emerged from the soil surface.

  2. Optimal timing. Preemergence herbicides should be applied in the early spring or fall before annual weeds emerge. Postemergence herbicide efficacy decreases as weeds grow. Consult the label for the correct size of weed to control.

  3. Sufficient coverage. Herbicide labels require certain nozzle types or applications of a certain number of gallons per acre (GPA) to ensure proper coverage. Before spraying, check that all nozzles have a correct spray pattern and correct output.

  4. Adequate activation. Preemergence herbicides require rainfall or irrigation to move the herbicide into the soil profile where the weed seeds are present. Postemergence herbicides require a nonionic surfactant, crop oil concentrate, or methylated seed oil for increased herbicide uptake.

Herbicide Resistance

Herbicide-resistant weeds are a continuous and growing concern for farmers. Methods for reducing the chances of herbicide resistance include the following:

  1. Rotate herbicides' mode of action. Each herbicide's mode of action (MOA) is assigned a numerical group. Tables 1 and 2 list the MOA for each herbicide. Rotate between modes of action/numerical groups.

  2. Include multiple MOA. Many herbicides allow for tank mixing. It is often suggested that preemergence herbicides be tank mixed with a postemergence herbicide. This method controls both weeds that have and have not yet emerged.

  3. Managing known resistance. If an area of the field is known to have a resistant weed species, use mechanical weed removal and prevent the weed from producing seeds or otherwise propagating itself. Please contact your county Extension agent to have the weed resistance confirmed and documented.


Table 1. 

Preemergence chemical weed control in pecan

Table 2. 

Postemergence chemical weed control in pecan


1. This document is HS95, one of a series of the Horticultural Sciences Department, UF/IFAS Extension. Original publication date October 1993. Revised June 2015. Reviewed January 2019. Visit the EDIS website at for the currently supported version of this publication.
2. Peter J. Dittmar, assistant professor; and Jeffrey G. Williamson, professor, Horticultural Sciences Department; UF/IFAS Extension, Gainesville, FL 32611.

The use of trade names in this publication is solely for the purpose of providing specific information. UF/IFAS does not guarantee or warranty the products named, and references to them in this publication do not signify our approval to the exclusion of other products of suitable composition. All chemicals should be used in accordance with directions on the manufacturer's label. Use pesticides safely. Read and follow directions on the manufacturer's label.

Publication #HS95

Date: 1/10/2019



    • Peter Dittmar