Landscape Alerts and Updates – MAY 2017

Slime Mold on Turfgrasses

Has your lawn been slimed?  Fear not, the grayish-black sooty substance on your turfgrass is a harmless soil protozoa that has temporarily migrated onto blades and stems to produce and disperse spores.  Diagnosis: Slime Mold,  Physarum and Fuligo sp./spp.  The occurrence is prompted by spells of humid, rainy weather during spring and early summer and is typically short-lived (1-2 weeks).  Aside from temporarily hindering photosynthesis, slime molds do not parasitize or damage the turfgrass.   Slime mold can be ignored, mowed, raked, or washed off with a pressurized stream of water.

Related Articles: what-is-this-unusual-growth-on-lawns


Lawn Burweed

If you missed the window of opportunity to manage burweed in your lawn in late winter/early spring, then you may be feeling it, literally!  The seed burs are now mature and a barefoot stroll across the lawn may inflict you with some painful hitchhikers.  At this point, applying a broadleaf herbicide product may kill the weed, but will not eliminate the existing burs that have formed, so mark your calendars for burweed scouting and control next February.  If an immediate solution is needed, locate individual plants and physically remove them.  Burweed tends to colonize compacted bare areas. For large areas of infestation it may be necessary to scalp and bag the clippings with a mower to remove the burs, followed by turfgrass renovation or establishment on those areas (assuming that you have a warm-season turfgrass species such as bermudagrass, it would not be advisable to scalp a Tall Fescue lawn in May).  For more information on scouting for lawn burweed, refer to the previous post “Winter Scouting for Lawn Burweed.”

Related articles: winter-scouting-for-burweed-soliva-pterosperma


Turf Aerification

Now is the time to aerify warm-season turfgrasses.  Last year, the dry conditions persisting from August through December depleted carbohydrate reserves in warm-season turfgrasses. A delay in turfgrass green-up was common this spring and warm-season turfgrasses are poised to replenish carbohydrate reserves and restore root systems.  “If there is a year to seriously consider core aerification, this is it,” says Dr. Clint Waltz, a Cooperative Extension turfgrass specialist with the University of Georgia College of Agricultural and Environmental Sciences.  Core aerification relieves compaction, improves air exchange and water infiltration, and stimulates deeper root growth.  Hollow-tine aerification is the preferred method, removing soil cores to a depth of 3-4 inches, and having longer-lasting benefits.  A light fertilizer application in concert with aerification can be beneficial, but heavy nitrogen applications should be avoided to allow for the replenishment of carbohydrate reserves (over-stimulating top growth depletes carbohydrates reserves).

To make sure soil pH, phosphorus and potassium levels are within recommended ranges for optimum growth, take a soil sample to your local University of Georgia Cooperative Extension office.

Read the full article on Core Aerification and find lawn care calendars for different turfgrass species at www.GeorgiaTurf.com .

Related Articles and Publications:

Turfgrass Fertility: Soil Texture, Organic Matter, Aeration, and pH (C 1058-1)


 

 

Weed Scouting in Mid-Winter

Weeds can be a major pest of lawns and recreation fields, competing for resources and sunlight while detracting from their natural beauty.

If your spring checklist includes lawn weed management, now is the time to take a closer look at the tiny mat of weed seedlings forming in mid-winter (Jan-Feb.), especially during spells of mild weather and precipitation. The winter-weed inventory is likely to include a mix of early-stage cool-season annual and perennial weeds such as chickweed, henbit, clover, annual bluegrass, burweed, and wild garlic. One advantage of mid-winter weed scouting and management is that many weeds are in the early growth stages and can be effectively controlled by herbicide treatments. In addition, warm-season turfgrasses such as bermudagrass and zoysiagrass are dormant and less susceptible to herbicide injury than during spring green up. Mid-winter is an excellent time to scout for cool-season weed species and get an early jump on management while conditions are favorable.

Below are examples of lawn weeds commonly observed in mid-winter:

Pictured above: Henbit (left), Plantain (center), Tall Fescue in bermuda (right).

POSTEMERGENCE WEED CONTROL

Selective control of broadleaf and grassy weeds in turfgrass can be an effective strategy in mid-winter using the appropriate postemergence herbicide product(s). It should be noted that during the winter months the visible effects of certain herbicides may be masked by cool weather (the weeds may be dead and not know it yet!) Mature perennial weeds such as dandelion, clover, and undesired patches of tall fescue can be effectively spot-treated during mid-winter using selective and non-selective herbicides. It is essential to select products appropriate for the particular species or turfgrass when selecting herbicides. St. Augustinegrass and Centipedegrass are particularly susceptible to certain herbicide injuries, even during the winter months. Combination products containing fertilizer and herbicides may be appropriate for weed control in cool-season turfgrass species such as Tall Fescue during the late winter. However, combination products containing nitrogen fertilizer are NOT recommended for warm-season grasses during the winter months. Applying nitrogen to dormant warm-season grasses in mid-winter does not provide benefits to the turfgrass and promotes the development of diseases such as large patch.

Remember, turfgrass and weed identification is essential to determining the appropriate herbicide product, timing, and application rate. There are no miracle products or “one size fits all” solutions to weed control. Herbicide recommendations are based on many factors including the turfgrass species, weed species, temperature range, and environmental factors. For assistance with turfgrass and weed identification, contact your local UGA Extension Agent at 1-800-ASK-UGA1.

Download the 2017 Turfgrass Pest Control Recommendations for Professionals at www.GeorgiaTurf.com for the latest information on weed management, scheduling, and pesticide information.

References:

McCullough, Patrick E. PhD, Waltz, Clint PhD, (2015). UGA Extension Bulletin (C 978). “Weed Control in Home Lawns.”

Winter Scouting for Burweed (Soliva pterosperma)

Burweed

Winter is the time to scout for lawn burweed (Soliva pterosperma), a broadleaf weed producing seed clusters in mid to late spring that delivers a rather irritating jab to bare feet.  The tiny spines on the seeds are actually quite fragile and tend to break off in your skin during the removal process, leaving an itchy reminder of their presence.  My children who love to run barefoot in the backyard can testify to the annual “de-spurring” event each spring.

December through February is the best time to manage this cool season annual because plants are juvenile and haven’t developed the seed burs. In addition, warm season turf species are dormant and have a better tolerance to certain herbicides. While control is possible in spring, spurs have already formed and will persist after treatment.  If the spurs are not a concern, the weeds will take care of themselves by May as the hot weather sets in and concludes the annual life cycle of this bandit.  A dense canopy of dormant or actively growing turf can deter weed establishment.

For broadleaf herbicide recommendations, reference the UGA Pest Management Handbook for your specific turf. Perform scouting several weeks after the application to determine if follow-up applications are necessary.

Other resources on this topic:

Willie Chance. (2015, May 5). Lawn burweed: What is this weed with sharp spurs in lawns? [Web log comment]. Retrieved from https://ugaurbanag.com/lawn-burweed-weed-with-sharp-spurs/

Are Temperatures Too High to Safely Apply Herbicides in Turf?

Are Temperatures Too High to Safely Apply Herbicides in Turf?
Are Temperatures Too High to Safely Apply Herbicides in Turf?
Herbicide injury to turf – Alfredo Martinez, UGA Plant Pathology

Patrick McCullough, Extension Turf Weed Scientist, University of Georgia

This is is a common question many turf managers will be asking before herbicide applications this summer.  Responsible pesticide applicators will always read and follow label directions before applying any product.  However, there is often confusion regarding the language on labels about this issue.  Many herbicide labels will contain a statement such as “Do not apply when temperatures are above 90° F”. These disclaimers are usually included on labels to limit the liability of chemical companies when turf managers apply their products during summer heat.  This disclaimer is often unaccompanied by anything else to explain or clarify the effects of temperature on potential herbicide injury on turfgrasses.

Turf managers who carefully follow label instructions will see these disclaimers and may hesitate before applying herbicides.  Others will question the exact interpretation of these warnings.  Examples of questions often asked include the following.

Is it safe to apply herbicides if:

  • temperatures are below 90° in the morning but above 90° in the afternoon?
  • temperatures are below 90° this week, but rise above 90° next week?
  • temperatures are above 90° now but are forecast to drop to the 80s?
  • the temperature is 89.9° and the label says do not apply at 90°or above?

Unfortunately, there are no correct (or incorrect) answers for these questions.  Herbicide applicators must evaluate their turf and factors that may increase turf injury.  Several factors turf managers should consider when applying herbicides in summer include:

  • Turfgrass species
  • Turfgrass stress
  • Herbicide chemistry
  • Weed species and population
  • Past performance of herbicides

Turfgrass species is a major factor in determining tolerance to herbicide applications.  The overall sensitivity level of a species should be evaluated before herbicide applications and closely monitored when temperatures are high. For example, bermudagrass and tall fescue are both labeled for treatments with sulfentrazone (Dismiss).  Tall fescue is naturally more sensitive than bermudagrass to sulfentrazone and rates must be reduced to account for lower tolerance levels.  Turfgrasses that are sensitive to herbicides under good growing conditions may be more susceptible to injury during periods of heat stress and other herbicide chemistries should be considered.

As temperatures exceed 90° F, cool-season grasses become stressed and consumption of carbohydrates exceeds production through photosynthesis.  Thus, grasses such as tall fescue with good tolerance to herbicides during active growth may be naturally more susceptible to herbicide injury during periods of physiological stress.  Warm-season grasses grow more efficiently than cool-season grasses under these temperatures and generally have minimal stress when water is not lacking.  Uninhibited growth of warm-season grasses at higher temperatures may be attributed to better tolerance to herbicide applications in summer relative to cool-season grasses.  However, herbicide tolerances for specific species are all dependent on the chemistry of the product applied.

Effects of temperature on herbicide activity

Turf managers must also understand potential effects of temperature on herbicide activity.  Many herbicide chemistries, such as synthetic auxins, have greater activity at warm temperatures compared to use during cooler weather.   For example, Trimec Classic (2,4-D + dicamba + MCPP) applications often have erratic activity in early spring but perform much more effectively in summer.  Sensitive species to these herbicides, such as St. Augustinegrass, have a higher risk of injury due to greater activity under excessive heat.  Switching to another chemistry, such as a sulfonylurea herbicide, may be a safer option especially at reduced label rates.  Enhanced activity of herbicides during these periods may also allow end-users to reduce rates and applications required to achieve desirable weed control.

Targeted weed species and the benefits of control should also be considered before risking turf injury from herbicide use in hot weather.  Warm-season weeds that spread laterally, such as spotted spurge or knotweed, will continue to grow during hot temperatures and out-compete turfgrasses for light, water, and nutrients.  If continued growth of weeds may result in loss of the overall turf stand, practitioners should consider applying herbicides.  Preventing annual weeds from taking over a turf area during summer may help reduce voids in early fall that may allow winter annual weeds to establish.  Thus, turf managers must evaluate the risk of turf injury at the expense of weed control and potential implications in long-term management.

Previous turf injury from herbicide applications during moderate temperatures may indicate risk of greater injury during excessive heat.  Similarly, past reports of turf safety under high temperatures may suggest a specific product has potential for use under local conditions.  It is recommended for turf managers to record air temperatures, soil temperatures, relative humidity, turf health, and other environmental factors that may influence turf tolerance to herbicides.  These records can be referenced to plan future spray programs for mid to late summer in subsequent years.

Other environmental factors influence turf injury from herbicides in summer.  While temperature is an important factor, high humidity increases absorption of many herbicides compared to low humidity levels. Herbicide applications in early evening when humidity and temperatures decline may help reduce injury potential compared to midday when these levels are higher.  However, subsequent heat and humidity may influence turfgrass translocation and metabolism of herbicides that could also limit tolerance levels after applications.

Unfortunately there are no perfect application programs or predictive models to determine safety of herbicides on labeled turfgrass species. It is recommended to spray a test area and evaluate turf injury before making broadcast treatments during periods of excessive heat.  Furthermore, if there is uncertainty over making herbicide applications turf managers should wait and assess the benefits of potential weed control. Applicators may wish to consult local extension agents for further information regarding herbicide applications during summer months.

Please share this information with others in the landscape & turf industry. For more information:

Call your local Extension Agent at (800) ASK-UGA1 or locate your local Extension Office

www.georgiaturf.com has a section on identifying weeds under Pest Management and weed control recommendations under the Turfgrass Pest Control Recommendations. (Follow all label recommendations when using any pesticide)

You can also find weed control recommendations in the Pest Management Handbook (Follow all label recommendations when using any pesticide)

UGA mobile app helps control roadside weeds

Patrick McCullough, a weed scientist with the UGA College of Agricultural and Environmental Sciences, decided to create the Georgia Roadside Management app after Georgia DOT officials approached him for help.

“The biggest problem they have is fighting invasive weed species, like broomsedge, vaseygrass and Johnsongrass. They are major species, and they are spreading, increasing maintenance costs and, more importantly, reducing safety for motorists,” said McCullough, a UGA researcher based on the campus in Griffin, Georgia.

Ray Dorsey, Georgia DOT agronomist manager, says tall weeds, like Johnsongrass, and invasive weeds, like kudzu, create “sight and distance problems,” especially at driveways and intersections.

“When we do road building, the contractors are required to replace the grass. Our permanent grasses of choice are bahiagrass and bermudagrass because they can help choke out weeds,” he said.

Using a partial research grant from Georgia DOT, McCullough designed the app using DOT terminology to make the tool user-friendly for workers. “All the information they need to make the best management decisions for controlling roadside weeds and vegetation is now literally at their fingertips,” he said.

The app debuted last fall, and Georgia DOT agronomists have now used it for six months.

“Everyone who’s downloaded it thinks it’s great,” Dorsey said. “We are one of the first DOTs to have an app for vegetative management,” he said.

Like all recommendations involving pesticides, the guidelines are frequently changed and updated. “Before, we had to make revisions, make paper copies and update all the training notebooks,” he said. “Now, we just ask Patrick to update the app.”

Unlike the paper notebooks, the app includes images of plant material. “It was too expensive to print color photos in the manual before. Now, we can look at a picture of the weeds and match them with what we see. (This app) is really a great tool,” he said.

The app covers much more than how to control vegetation. It also includes information on growth regulators, first aid, personal protection, equipment maintenance and mowing procedures.

Created for use on iPhones, the app can be downloaded for free on iTunes. “It’s specific to Georgia DOT and uses their codes, but DOTs in other states would benefit from it, too,” McCullough said.

Download the app for free on iTunes.

Lawn burweed: What is this weed with sharp spurs in lawns?

Lawn burweed: What is this weed with sharp spurs?
Lawn burweed plants can grow up to 6 inches wide and about 3 to 4 inches tall.

Lawn Burweed – It’s a Stick Problem

Tim R. Murphy – Retired Extension Weed Scientist, The University of Georgia
Edited from a longer article you can find here.


The weed in question is most commonly lawn burweed (Soliva pterosperma), a.k.a. spurweed, stickerweed, sandbur, sanbur and sandspur. Lawn burweed is a winter annual member of the Aster family. The weed germinates in the early fall months as temperatures cool and remains small or inconspicuous during the cold winter months. However, as temperatures warm in the early spring, or about the same time as spring sports activities, lawn burweed initiates a period of rapid growth and begins to form spine-tipped burs in the leaf axils. The sharp-tipped spiny burs of this weed can irritate the skin.

Key identification characteristics of lawn burweed are:

  • opposite, sparsely hairy leaves that are divided into numerous segments, or lobes
  • small, inconspicuous flowers, and c) spine tipped burs that are found in the leaf axils (junction of leaf and stem).
  • attains an overall diameter of up to 6 inches and a height of about 3 to 4 inches.
  • It is commonly found in the Coastal Plain and Piedmont regions of Georgia.
Lawn burweed: What is this weed with sharp spurs in lawns?
The seeds with their sharp spines grow in the leaf axils (where the leaf and stem come together)
Lawn burweed: What is this weed with sharp spurs in lawns?
The leaves are opposite, sparsely hairy and divided into numerous segments, or lobes

Lawn burweed is easily controlled during the winter months.

December, January and February are ideal months to apply herbicides to control this weed. Lawn burweed is small and easier to control at this time of the year than in April and May. Also, turfgrasses are not actively-growing during the winter months and have better tolerance to some herbicides.

See the UGA Pest Management Handbook for pesticide recommendations for your turf type. Two to three weeks after the initial application, lawn burweed control should be evaluated. If control is not acceptable, an additional application may be necessary.

Lawn burweed can be controlled in late-March, April and early May, however, two main facts should be considered.

  • Lawn burweed begins to die as late spring temperatures approach 90° F and the plant is harder to control once the spiny burs or stickers have formed. Multiple herbicide applications are usually necessary, which increases the risk of temporary injury to the turfgrass.
  • Additionally, it takes time for the herbicide to control lawn burweed, and after death, it takes time for the dead lawn burweed plants to decompose. Therein lies one of the main problems with late treatments. Dead lawn burweed plants contain dead, or brown spine-tipped burs. Dead or alive, the spiny burs still present a problem. The only recourse at this point is to allow time for the plant to naturally decompose.

For more information:

Find pesticide recommendations – UGA Pest Management Handbook

Identify lawn weeds

Find your local UGA Extension Office

Facelis or trampweed – Cottony weed invades lawns

“Cottony Weed” in Lawns

Tim R. Murphy, Retired Extension Weed ScientistFacelis
PDF Version of Cottony Weed article 

It seems that all of a sudden, numerous lawns in Georgia are turning white. Well it is not snow, nor is it left over cotton from last fall. The “cottony” appearance is due to the presence of a weed named facelis (Facelis retusa).

Facelis

Facelis, also called annual trampweed, is a winter annual member of the Aster family that reproduces by wind-blown seed. This weed reaches heights of 4 to 6 inches and has alternate wedge-shaped leaves with a small tooth at the tip. The upper leaf surface is green, while the lower leaf surface is densely gray due to the presence of leaf hairs. Flowers are very inconspicuous; however, seed have soft, white bristle-like hair. With severe infestations the lawn becomes white when seed are being released from the plant. Typically facelis is found in lawns with a low density of turfgrasses, as well as on open, droughty, low fertility sandy or clayey soils.

Facelis actually germinates in the fall and late winter months, produces seed in late April to June and then dies. May is not the preferred time to control facelis, as the weed is essentially in the process of dying.

There has been very little research done on controlling this weed in turfgrasses. Additionally, this weed does not appear on herbicide labels. However, herbicides that contain 2,4-D, MCPP, dicamba and triclopyr or atrazine applied during the mid-winter through early spring months should control facelis.

Since this weed is found on droughty, low-fertility sites, try to improve the turfgrass density through liming, fertilization and irrigation.

For pesticide recommendations see the UGA Pest Management Handbook.

Weed Control in Iris

Iris, Keith Weller, USDA Agricultural Research Service, Bugwood.org
Sweet Iris, Keith Weller, USDA Agricultural Research Service, Bugwood.org

Mark Czarnota, Ph.D., Ornamental Weed Control Specialist

This is an excerpt from a longer publication found here

Weed control in irises can be difficult. Fortunately, many annual broadleaf and grassy weeds can be easily controlled with mulches and the judicious use of herbicides.

Mulch is helpful in preventing weed growth, but it should be used sparingly (no greater than a 2-inch layer in irises) to avoid disease problems.

The preemergent herbicides in the following table are labeled to control a large spectrum of broadleaf and grass weeds in irises.

TRADE NAMESACTIVE INGREDIENT
Barricade and RegalKade (Granular)prodiamine
Dimensiondithiopyr
Galleryisoxaben
Freehanddimethenamid and pendimethalin
Pendulum, Corral (Granular)pendimethalin
Pennantmetolachlor
Snapshot (Granular)isoxaben and trifluralin
Surflanoryzalin
Treflan and Preentrifluralin
XL (Amaze)benefin and oryzalin
  • Most preemergence herbicides listed are available in both a granular and sprayable form. Granular herbicides are popular because they require no mixing and are more forgiving when an application error is made.
  • Most herbicides or herbicide combinations will control 80 to 95 percent of the annual weeds normally found in irises. Many weeds not controlled with preemergent herbicides can be removed by hand.
  • The herbicides listed are designed to control weeds germinating from seed not weeds coming from vegetative structures (tubers, rhizomes, etc.).
  • During iris establishment, and under heavy weed infestation, at least two herbicide applications should be made in most Southern states — usually in January / February and again in April /May — to control most spring and summer weeds.
  • Additional preemergence herbicide applications may be necessary to control annual winter weeds. Preemergence herbicides tend to be more useful on large acreages.

Several postemergence grass herbicides are labeled for use in irises.

TRADE NAMESACTIVE INGREDIENT
Acclaim Extrafenoxaprop
Envoy Plusclethodim
Fusilade II, Ornamec, and Grass-B-Gonfluazifop
Segmentsethoxydim
  • Postemergence grass herbicides are mixed with water and sprayed over the top of irises to control grasses that are actively growing.
  • These grass herbicides have no preemergent activity and will not prevent the germination of weed seeds.
  • Herbicide labeling can change, so always read and understand the label before using any pesticide.
  • As herbicides go off patent, some manufacturers market herbicides under different trade names, so the buyer must beware. For instance, glyphosate, the active ingredient in Roundup®, is now available from many suppliers under a wide range of trade names and formulations.

Herbicides containing the active ingredient glyphosate can be used to control problem perennial weeds that are unsuccessfully controlled by hand removal or mulches. Weeds growing among irises should first be carefully separated from iris leaves and then placed horizontally on bare ground or a piece of plastic for treatment. Next, paint or sponge a 5 percent solution of glyphosate (6 ounces of at least a 41 percent glyphosate concentrate per 128 ounces of water). A cover, such as a plastic bag, placed over the iris plant while treating the weeds will help shield the iris from the herbicide. Remove protective coverings once the herbicide has dried. The treated weeds will begin to die in 10 to 14 days. If weeds re-sprout, repeat the treatment procedure.

Broadleaf and other perennial weeds can be difficult to control in iris. Nutsedge (Cyperus spp.) and Florida betony (Stachys floridana), for instance, are two problem weeds with no labeled selective herbicides available to control them in iris.

The University of Georgia has conducted experiments with both 2,4-D (various trade names) for controlling select broadleaf weeds and halosulfuron (Sedgehammer® and Prosedge®) for controlling nutsedge. Neither product is labeled for weed control in Iris, but data has indicated labeled rates of these postemergence herbicides can be used on select Iris cultivars with little to no damage. It is suggested that users wishing to try this method test it on small areas of iris / weeds to be treated. Wait two weeks and then evaluate the iris plants for unacceptable damage before treating an entire area.

Always read the product label and contact your local County Extension office with any pesticide or plant culture questions.

For more information see Dr Czarnota’s entire publication found here

Follow herbicide label to avoid killing landscape plants and trees

phenoxy herbicide damage to willow oak trees2 Pugliese
Phenoxy herbicide damage to a willow oak tree. Image credit: Paul Pugliese.

Paul Pugliese is the agriculture & natural resources agent for the University of Georgia Extension office in Bartow County.

An herbicide designed to kill weeds in turfgrass can also kill neighboring trees and shrubs.

Herbicides in the phenoxy chemical class provide broadleaf weed control in lawns, pastures and hay forages. Some of the more common chemicals in this class include 2,4-D; MCPP; dicamba; clopyralid; and triclopyr.

Safe for animals but not always for trees and shrubs

These chemicals are considered very safe and leave very few toxicity concerns for animals. In fact, many of these herbicides are labeled for pasture use and allow for livestock to continue grazing without any restrictions.

Phenoxy herbicide damage to a willow oak tree. Image credit: Paul Pugliese.
Phenoxy herbicide damage to a willow oak tree. Image credit: Paul Pugliese.

However, pesticide labels should always be read and followed to determine if any special precautions should be taken for specific site uses.

Phenoxy herbicides provide selective weed control, which means they control many broadleaf weeds without causing damage to grass. Of course, each product is a little different and some are labeled for very specific turfgrass types, depending on their tolerance.

The label should be checked for application to a specific lawn type (tall fescue, bermudagrass, zoysiagrass, etc.). If the turfgrass isn’t on the label, don’t assume the herbicide can be applied to all lawns.

Unfortunately, phenoxy herbicides don’t discriminate between dandelion weeds or any other broadleaf plants, including many trees and shrubs. So, it’s very important to take extra precautions when applying these herbicides near landscaped areas with ornamental plants.

Wind and rain can spread herbicides

Consider the potential for drift damage to nearby plants and avoid spraying herbicides on a windy day. There is also the potential for movement of these herbicides through runoff and leaching in the soil. This is why the product label usually warns against spraying within the root zone of trees and shrubs and never exceeding the maximum application rates listed on the label.

Many homeowners and landscapers often overlook these label precautions. The information that is contained on the label can seem somewhat vague to inexperienced applicators.

The biggest misconception concerns where the root zone of a tree or shrub exists. The roots of mature trees and shrubs actually extend well beyond the drip line of the canopy. Research shows that absorption roots may extend as much as two to three times the canopy width.

Consider spot-spraying to target individual weeds rather than broadcasting applications across the entire lawn. And never exceed the labeled rate.

In landscapes that contain mature trees and shrubs, phenoxy herbicides may not be the best choice for weed control. These herbicides may be best reserved for wide-open spaces such as athletic fields, parks and pastures where tree roots are at a safe distance.

The high potential for herbicide damage to trees is another great reason to protect tree roots by providing a mulch zone that extends well beyond the drip line of the canopy. If you’re not trying to grow a manicured lawn underneath a tree, then there is no reason to apply phenoxy herbicides there for weed control.

Use the right herbicide for the job

Another way to avoid potential damage is to rely less on phenoxy herbicides. Other classes of herbicides have less potential to affect the roots of nearby trees and shrubs. Take the time to identify your weeds and choose a more selective herbicide rather than combination products that usually contain multiple chemicals in the phenoxy class.

Many pre-emergent herbicides can prevent weed problems in lawns. The key is to apply them at the correct time in spring and fall. Applying too early or too late often provides inadequate weed control and requires additional herbicide applications. Rotating pre-emergent herbicide classes will avoid the potential for resistant weeds. Also, be sure to apply water to the area according to the pre-emergent herbicide’s label to activate it in the soil.

For more information about the effects of phenoxy herbicides on landscape trees and shrubs, view the UGA Center for Urban Agriculture webinar at ugaurbanag.com/webinars. For assistance with weed identification and specific herbicide recommendations, contact your local UGA Extension office at 1-800-ASK-UGA1 or visit www.Georgiaturf.com.

You can also watch an online webinar on Effects of Phenoxy Herbicides on Landscape Trees and Shrubs by Paul Pugliese.

Is it okay to apply herbicides to lawns during green up?

Tim R. Murphy. Retired UGA Weed Scientist

Rank growth of winter annual weeds occurs at the same time that warm-season turfgrasses begin to green-up, or emerge from winter dormancy. These weeds compete with the turfgrass for soil moisture, nutrients, growing space, but most importantly for sunlight. Warm- season turfgrasses, with the exception of St. Augustinegrass, are not highly shade tolerant. Thick mats of winter weeds will shade the turfgrass at a time that root carbohydrates are being exhausted by the green-up process. Additionally, thick mats of winter weeds shade the turfgrass and decrease photosynthesis. The net result is a weakened, or less dense stand of turfgrass, that is readily infested by summer annuals such as crabgrass.

Purple Deadnettle, Robert Vidéki, Doronicum Kft. Bugwood.org
Purple Deadnettle, Robert Vidéki, Doronicum Kft. Bugwood.org

Preemergence herbicides

Research has shown that the preemergence herbicides, such as Balan, TeamPro, Surflan, XL, Ronstar and many others, that are used for summer annual grass control do not significantly affect the spring green-up of labeled warm-season turfgrasses. A possible exception is Pennant (metolachlor). There have been some significant delays in the green-up of hybrid bermudagrass with Pennant applications to dormant turf.

Postemergence herbicides

The situation with postemergence herbicides is dramatically different. Most postemergence herbicides will slightly delay the early spring growth of warm-season turfgrasses. These delays can range from a few days to a few weeks.

In the event of an overdose (an extremely high rate), delays in spring green-up can occur for a longer period of time. Usually, the turfgrass will completely recover within two to six weeks with proper cultural management.

With the exception of Image, most postemergence herbicides can safely be used during green-up. Some slight delay in green-up may be noted; however, this effect can be lessened by:

  1. Using the lowest recommended rate
  2. Insuring that the application equipment is properly calibrated
  3. Using spot treatments
  4. Following all recommended cultural practices, fertility, irrigation, etc. to promote rapid spring growth.

The use of postemergence herbicides should be avoided during the spring green-up of turfgrasses that have been poorly managed, or that are experiencing winter injury problems. Properly maintained, healthy, vigorous turfgrasses are more tolerant to postemergence herbicides than turfgrasses that have not been properly maintained or are suffering from winter injury.

Some postemergence herbicides state on the label “Do not apply during spring green-up.” Obviously, these products should not be used at this time of year. However, the use of other postemergence herbicides is warranted if there is a severe weed infestation on properly maintained turfgrasses. The slight delay in green-up from the use of these herbicides is more than compensated for by the removal of competition that dense mats of weeds exert on the turfgrass.

As always – read and follow all pesticide labeling directions!