plant injury due to turfgrass broadleaf weed herbicides ... · tively kill many broadleafed plants...

PThe herbicides 2,4-D, MCPP, and

dicamba are used to selectively killbroadleaf or dicot weeds in thelawn—such as dandelion, plantain,chickweed, and ground ivy. Theseherbicides are available as individualherbicides or mixtures. They are soldas liquids, in granular form, andcombined with fertilizers.

Because these herbicides selec-tively kill many broadleafed plantsbut do not kill turfgrass whenapplied at label rates, they arepopular products for people whowish to rid their lawns of susceptibledicot weeds. However, careless herbi-cide application, wind drift,volatilization (evaporation), andother mistakes can cause herbicideinjury to desirable broadleaf plants—including trees, shrubs, flowers, andvegetables. Grapes and box elder areespecially susceptible. Tomatoes,beans, melons, roses, maple trees,and many other species are also sen-sitive to these herbicides.

Herbicide drift occurs whenspraying takes place on windy days.Spray droplets are blown downwind,sometimes for great distances, andcontact any plants in their path.

Some herbicides such as 2,4-Dare available in ester formulations.Esters are volatile, so if the herbicideis applied in hot weather it mayevaporate (volatilize) and movedownwind as a vapor. The vaporenters plant stomates or leaf open-ings and injures sensitive plants.

Besides drift and volatilization,desirable plants can be injured if youuse grass clippings as mulch from a

lawn recently treated with herbicide.Damage can occur if you fertilizeflowers, vegetables, trees, or shrubswith fertilizers containing herbicides.Herbicide damage can also resultfrom herbicide-contaminated clothes,gloves, pots and flats; applying insec-ticides or fungicides with a sprayerthat is contaminated with a herbicide;or spilling herbicides on seeds andmulches.

SymptomsBroadleaf weed herbicides such

as 2,4-D, MCPP, and dicamba usuallydo not kill plants at extremely lowapplication rates. Instead, these her-bicides act as growth-regulating sub-stances. They disturb growth byaffecting cell shape, cell size, and celldivision. Some tissue ceases to growwhile other tissue grows andexpands—this results in a distortedplant.

The herbicide 2,4-D is the mostcommonly used broadleaf weed her-bicide and its symptoms of injury aretypical of these types of herbicides.These include: n stem twists outward and down-

ward (epinasty);n stem thickens and flattens

(fasciation);n narrowing of leaves with elon-

gated veins abnormally closetogether (strapulation)

n curling of the leavesn excessive callus formation on

roots and stems along with sec-ondary root growth.

In some cases of plant damagedue to broadleaf weed herbicides,elongating cells stop growing length-wise but continue to expand. In otherinstances, young leaves no longerexpand but the vascular tissue con-tinues to grow—forming rough,leathery leaves.

These symptoms vary dependingon how long plants are exposed tothe herbicide and the amount towhich they are exposed. Nontargetplants rarely die, since they do notget the lethal dose of herbicidedirected at the weeds. Instead, theplant usually continues to grow nor-mally above or beyond the distortedparts, unless tissue was damagedwhile it was still immature.

In addition to distorting plantstructure, broadleaf weed herbicidesaffect photosynthesis and rootabsorption. The effect of these herbi-cides on such processes can kill aplant or weaken it so that competingplants, such as turf, kill it.

Although evidence of long-terminjury due to herbicides such as 2,4-Dand MCPP is not conclusive, damagefrom the herbicide dicamba may showup a year or so after application.

ControlAlthough broadleaf weed herbi-

cides usually do not kill nontargetplants, herbicide damage is not desir-able when trying to get rid of weedsin the lawn. Thus, extreme care isneeded when using this type of her-bicide—either by itself or incorpo-rated in a fertilizer.

lant injury due to turfgrass broadleaf weed herbicides

A3286

M . F . H E I M A N N a n d R . C . N E W M A N

Effects of 2,4-Don geranium.These symptomsdid not occuruntil a fewweeks followingexposure.

Cupping ofmaple leavesexposed to2,4-D.

This rose wasexposed to2,4-D. Note thestem twistingout and down.

Cupping ofmaple leavesexposed to2,4-D.

2,4-D injured thistomato plant,causing leavesto twist and curl.

Curling of yewneedles causedby 2,4-D.

Grapes are espe-cially sensitiveto 2,4-D. Thenarrow leaveshave veins thatare abnormallyclose together.

2,4-D causednarrowing(strapulation) ofthese petunialeaves.

Zucchini leavesshowing damagecaused by aphenoxy-typeherbicide.

Spruce damaged by2,4-D. Althoughneedles are notdistorted, abnormalterminal growthoccurred.

Phenoxy-typeherbicidestypically causethickening andflattening ofstems (fasciation).

Exposure to2,4-D resulted inepinasty on thisfloweringcrabapple.

Another exampleof fasciationcaused by aphenoxy-typeherbicide.

Leaf distortionon Euonymusresulting from2,4-D.

Slight twisting ofstrawberry leafdue to 2,4-D.

Symptoms ofphenoxy-type her-bicide damage onalfalfa, dandelion,and burdock.

The first step toward avoidingherbicide drift is to apply the chem-ical on a day that is not windy.Frequently it is calmer early in themorning or in the evening. If you useherbicide sprays, keep the spraynozzle head or boom close to theground and aim it directly at thetarget weed. Spray under low pres-sure to minimize the amount of finespray droplets. Also, use the amineform of the compound rather than theester (check the label) to avoidvolatilization. Do not spray in hotweather to avoid additional evapora-tion.

Follow these three basic ruleswhen using herbicides to get bestresults and avoid damage to non-target plants:1. Apply herbicides in May before

you set bedding plants in thegarden, or in September aroundthe time of killing frosts.

2. Apply dry formulations of a her-bicide with a drop spreaderinstead of a spinner or rotaryspreader so the herbicide hitsonly target weeds.

3. Apply herbicides according tolabel directions and observe pre-cautions regarding wind and tem-perature.

You can help control weeds in thelawn without depending solely onherbicides by integrating good man-agement practices with herbicideapplications. Successful lawn man-agement results from controllingweeds by preventing them fromgetting a start.n The best defense against invading

weeds is a dense stand of peren-nial turfgrasses. Vigorous turf-grasses successfully compete withweeds for light, moisture, and soilnutrients. Use improved turfgrasscultivars that are disease resistantwhen planting or renovating.

n Mow tall—about 2 to 3 inchesand don’t remove any more than30 to 40 percent of the grass plantat one time.

n Water correctly—grasses requireabout 1 inch of water per week.Water only once each week, andavoid frequent light wateringbecause it encourages shallowrooting.

n Control insect pests and diseasesbefore serious damage occurs.

n Establish red fescue in shadyareas or use a ground coverwhere shade is too dense forgrasses.

n Fertilize correctly—too much ortoo little fertilizer leads to weedproblems.

Copyright © 1997 University of Wisconsin-System Board of Regents and University of Wisconsin-Extension, Cooperative ExtensionAuthors: M.F. Heimann, O.S.F., is distinguished outreach specialist and R.C. Newman is professor emeritus of horticulture, Collegeof Agricultural and Life Sciences, University of Wisconsin-Madison and University of Wisconsin-Extension, Cooperative Extension.Produced by Cooperative Extension Publications, University of Wisconsin-Extension.University of Wisconsin-Extension, Cooperative Extension, in cooperation with the U.S. Department of Agriculture andWisconsin counties, publishes this information to further the purpose of the May 8 and June 30, 1914 Acts of Congress; and providesequal opportunities and affirmative action in employment and programming. If you need this material in an alternative format,contact the Office of Equal Opportunity and Diversity Programs or call Cooperative Extension Publications at 608-262-8076.This publication is available from your Wisconsin county Extension office or from Cooperative Extension Publications. To order,call toll-free 877-947-7827 (WIS-PUBS) or visit cecommerce.uwex.edu. A3286 Plant Injury Due to Turfgrass Broadleaf Weed Herbicides SR-05-97

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