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Spring and Summer Lawn Management Considerations for Cool-Season Turfgrasses

ID

430-532

Authors as Published

Michael Goatley, Turfgrass Specialist, Department of Crop and Soil Environmental Sciences, Virginia Tech; Shawn Askew, Turfgrass Weed Specialist, Department of Plant Pathology and Weed Science, Virginia Tech; David McCall, Turfgrass Research Specialist, Department of Plant Pathology and Weed Science, Virginia Tech; Peter Schultz, Extension Entomologist and Director, Hampton Roads Agricultural Research and Extension Center

There is no time of year that generates as much excitement in the management of lawns and landscapes as spring. Sales of all lawn and garden products soar as many homeowners strive for the best looking lawn possible. However, your enthusiasm for returning the lawn to tip-top shape should be tempered enough so that you make sound agronomic and environmental management decisions. Smart choices now will result in a healthy, dense turf canopy that will better withstand the environmental extremes of the summer months.

Soil testing. Sampling the soil to determine pH and nutrient levels is always a prudent choice in developing a management program for a lawn, especially if a soil test has not been done within the past three years (Figure 1). Any time of year is appropriate for sampling. The majority of Virginia's soils are acid and need to be supplemented with periodic applications of lime. For information on how to properly sample your soil, consult Soil Sampling for the Home Gardener, Virginia Cooperative Extension publication 452-129, at http://pubs.ext.vt.edu/452-129/.For additional soil testing information, see the presentation "Soil Testing for the Lawn and Landscape," at http://breeze.ag.vt.edu/p36588349/.

 

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Select the best turfgrass. The primary cool-season species (e.g. Kentucky bluegrass, tall fescue, fine-leaf fescues, and perennial ryegrass) are best adapted to the Northern Piedmont, the Ridge, and Mountain regions of Virginia. They also can be grown in the Southern Piedmont and Tidewater regions, but they will struggle during the heat and drought of the summer months. Use the "Lawns" link under "Home Gardening" in the Educational Programs and Resources section at the Virginia Cooperative Extension Web page at http://pubs.ext.vt.edu/ to find links to publications and articles on how to make the best selection of a grass to fit your needs. For a list of the best adapted cultivars for the state, review the current Virginia/Maryland Turfgrass Recommended Variety lists posted at http://www.vtturf.com/Publications%5CExtension%5C2005-06VarietyRecommendations.pdf. These select grasses are not likely to be available at the garden centers of large retailers, so you will need to approach stores that deal in specialty turf products, farmer's cooperatives, or specialty nurseries to obtain these varieties. And if you cannot locate a variety from the recommended list, all is not lost. Fortunately, most of the cultivars being sold at the garden centers of large retailers are still quality grasses that will likely perform satisfactorily in most parts of Virginia. If you are interested in starting with sod, you can obtain information on the locations of Virginia sod farms and the grasses they produce in the Virginia Sod Directory, Virginia Cooperative Extension publication 418-040, at http://pubs.ext.vt.edu/418-040/. Do some research, utilize the resources in the Web links from Virginia Cooperative Extension, and don't be afraid to ask the "tough" questions regarding the suitability and quality of grasses that are for sale. Always select certified ("blue-tag") seed and/or sod when choosing a grass. A lawn is something you expect to have indefinitely, so a commitment in choosing the best possible grass goes far towards long-term success.

The cool-season grasses will be the first turfgrasses to visibly resume active growth as soil temperatures consistently warm into the 50s (°F). Even early to mid-spring frost events will not significantly slow foliar growth. The renewed vigor in top growth is a result of the plant's effort to quickly maximize its ability to produce food (the biochemical process of photosynthesis). Much of the remaining food reserves that were stored for winter survival are now being used in the early-season production of new leaves. The root system also will eventually have a resurgence in growth and development, but it lags far behind shoot development. Left alone, the cool-season turfgrass does a pretty good job of balancing the distribution of food between new leaves and new roots. However, it is highly possible that you, the turf manager, in the quest to have that best looking lawn, will inadvertently alter the balance of growth between shoots and roots and cause more problems than you solve. The development and maintenance of a strong root system will be critical to turf success for the remainder of the season.

Spring establishments. Although the spring is not the ideal time to establish cool-season turfgrasses, the majority of cool-season turfgrass seed is sold and planted at this time. Spring is not the optimal time because cool-season grass planted in the spring has such a small window of opportunity to develop a mature plant with an extensive root system before the summer months approach. Cool-season turfgrasses are adapted to climates where daytime high temperatures are in the 60° to 75°F range. Much of Virginia will experience daily high temperatures exceeding this range by early June, and the temperatures will remain above optimal levels through at least August. If you can delay establishment until fall, your chances of success are far greater. However, there are many situations that require spring establishment (new construction sites, renovation projects following the loss of turf over the past fall/winter season, etc.), and your chances for success can be enhanced by considering the following strategies.

Cool-season turfgrass blends (combinations of two or more different cultivars) are recommended for most situations. Blends broaden genetic diversity (i.e. improve the chances of one grass better tolerating a pest or environmental extreme). There are other situations where certain mixtures (combinations of two or more species that have compatible appearance and growth characteristics) can be quite successful. For instance, for lawns with both sun and shade features, it is very common to select seed mixtures containing Kentucky bluegrass and/or perennial ryegrass (for the sunny locations) and fine-leaf fescues (for the shady spots). Note: not all mixtures are appropriate for the best quality lawn turf. For instance, mixtures of tall fescue and fine-leaf fescue, though these two grasses are closely related to each other, are not recommended because their leaf textures are so dissimilar. Uniformity in appearance is one of the first criteria that must be met in gaining an aesthetically pleasing lawn turf.

Timing in establishing cool season grasses. The timing of cool-season turfgrass plantings in the spring is absolutely critical for success. Research has shown that optimal seed germination and establishment occurs when soil temperatures at a four-inch depth reach the range of 55° to 65°F. Of course, this temperature range is also suitable for the germination and establishment of most of our biggest summer annual weeds such as crabgrasses (Digitaria spp.), goosegrass (Eleusine indica L.), and foxtails (Setaria spp.). Options in managing these and other weeds (many of which are warm-season weeds that will be extremely competitive with the cool-season turfgrass) during turf establishment are presented later in the Weeds section.

Soil preparation. For renovations that are needed due to an abundance of weeds, apply non-selective chemicals such as glyphosate or glufosinate in advance of planting to control existing vegetation. The temperature must be warm enough that the existing vegetation will absorb and translocate the chemical, so avoid making the application when temperatures are less than 50°F. When possible, completely till the soil to a four- to six-inch depth prior to seeding. If the soil test indicates lime or other nutrients are needed, apply them prior to tilling in order to incorporate the material into the profile. Apply a starter fertilizer emphasizing phosphorus (P) levels as compared to nitrogen (N). Typical nutrient ratios of N-P-K (potassium) will be 1:2:1 or 1:2:2. It is equally important to provide some degree of soil preparation even for interseeding situations into existing turf (Figure 2). A few passes with a coring machine (often called an aerifier), a power rake, or a vertical mower (often called a dethatcher) can be used to prep the soil prior to planting to encourage seed-to-soil contact. Simply applying seed over the top of an existing turf without any soil preparation usually does nothing more than feed birds and other wildlife. Be sure not to plant the seed too deep. A small-seeded grass like Kentucky bluegrass should remain very near the soil surface, while larger seeded grasses such as tall fescue and perennial ryegrass can be planted to depths up to one-half inch.

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You will need to do some tillage for the successful establishment of sod. Sod placed directly on top of an existing grass canopy without soil preparation most often will fail. More complete renovations likely will require more extensive tillage. Remember that suitable tillage does not mean destroying the existing soil structure by disking it into powder; ideally the soil will be tilled to a two- to four-inch depth, with a few clods present (Figure 3). For a complete discussion on seeding levels and methods in planting a lawn, consult Establishing Lawns, Virginia Cooperative Extension publication 426-718, at http://pubs.ext.vt.edu/426-718/.

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Initial irrigation and mowing strategies. After planting seed, irrigate lightly and frequently until seed germination is complete. Avoid excessive amounts of water because this could wash away or drown the seed. As establishment progresses, gradually cut back on the amount of water applied in order to start promoting a deep root system. The irrigation philosophy is similar for sod, but larger amounts of water can be applied to sod less frequently because the sod will have some amount of soil and root mass intact. Reduce watering requirements as establishment becomes complete. For further discussion on irrigation management during the summer consult Summer Lawn Management: Watering the Lawn, Virginia Cooperative Extension publication 430-010, at http://pubs.ext.vt.edu/430-010/.

Mow turf when it needs to be clipped according to its recommended cutting height and follow the one-third mowing rule that says you never remove more than one-third of the leaf blade at any mowing event. For example, given that the recommended lawn height for tall fescue is two to three inches, begin mowing as soon as your new lawn reaches a three-inch height and cut it no lower than two inches. Regular mowing at the low end of the recommended range for the respective grasses promotes tillering of new stems, increasing the grass density. Complete mowing height recommendations and guidelines for recycling clippings are presented in Mowing to Recycle Grass Clippings: Let the Clips Fall Where They May!, Virginia Cooperative Extension publication 430-402, at http://pubs.ext.vt.edu/430-402/. Be sure your mower blade is sharp, properly balanced, and that your soil surface is sufficiently firm so you do not cause ruts or footprints on the surface.

Fertility programs

Many of the fertilizer products available to homeowners to initiate spring fertility programs are "first step" components in a commercially available four- or five-step lawn-care programs designed for the entire growing season (spring through fall). The quality and handling characteristics of the products are usually exceptional. However, the levels of nitrogen contained in the mid-spring and summer steps in the program often exceed the recommended levels that cool-season turfgrasses can efficiently utilize in the spring and summer months. The application of one-half to one pound of water-soluble nitrogen per 1,000 square feet of lawn during the early to mid-spring is acceptable, but additional nitrogen can be detrimental to cool-season turf.

If a nutrient is not used by the plant, it is subject to loss, and this is both economically and environmentally irresponsible. While aggressive spring and summer nitrogen fertilization will likely lead to lush, dark green foliage, this growth is often at the expense of the root system and the process of food storage. An inadequate root system due to excessive spring nitrogen results in a turf that struggles to survive as the stresses of summer arrive. Consult Lawn Fertilization in Virginia, Virginia Cooperative Extension publication 430-011, at http://pubs.ext.vt.edu/430-011/ for more information on how to distinguish between nitrogen sources and their recommended seasonal application rates. Apply other supplemental nutrients (for instance, phosphorus or potassium) and lime according to soil-test results.

One alternative in selecting fertilizers for spring treatments on cool-season grasses is to choose products that contain 50 percent or more water-insoluble nitrogen (often called "slow-release" nitrogen) that is made available to the plant slowly either by way of controlled chemical or microbial decomposition. This provides a sustained growth response without a flush in shoot growth at the expense of the roots.

If you want an early-season color response, foliar applications of iron will provide a rapid greening response without a flush of shoot growth on actively growing turf. Since iron is a micronutrient, its application levels are very low. The color response is short-lived (typically two to three weeks) because the iron-induced color response in the leaves is removed by mowing. Other nutrients such as magnesium and sulfur can also provide a greening response, but applications of these elements should be based on need as indicated by soil tests.

Cultural management programs

Core cultivation. Core aeration (commonly called "aerifying" or "plugging") is the typical type of cultivation done on home lawns to relieve soil compaction (Figure 4). Aeration is possible as soon as the cool-season grass has resumed active growth in the early to mid-spring, but should not be done after temperatures warm to levels where the grass will likely be under stress. Extensive core cultivation done in the late summer to early fall gives the turf the optimum recuperative potential.

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Core aeration is very disruptive to surface smoothness, but it is the best way to relieve the physical effects of soil compaction and increase soil oxygen levels. Many commercial lawn-care services provide core cultivation or you can rent a machine.

Consider how spring cultivation might affect preemergent weed control if the herbicide is applied before aerating. If possible, aerate before the herbicide application in order to minimize the effects on the chemical barrier in the soil. If the spring cultivation is done after aeration, immediately return the cores to the turf canopy by breaking them up using a drag made from chain-link fence or a heavy piece of carpet. Spreading the soil over the turf surface will also help reduce thatch build-up.

Vertical mowing. Vertical mowing is not a means of relieving compaction and improving soil aeration. Instead, it is an excellent technique to prepare the soil as a seed bed for spring plantings. A primary reason for vertical mowing is thatch removal - vertical mowing is often referred to as dethatching. Thatch (Figure 5) is an organic layer predominantly comprised of living and decaying stems. It signals an imbalance between the growth rate of the turf and how fast the plant material is broken down by soil microbes. Thatch depths exceeding one-half inch require attention because turfgrass roots living in the thatch suffer from moisture stress during dry weather, and many problematic insects and fungi find thatch a favorable environment. However, surface disruption and damage to the existing turf will be extensive, and with the approaching summer months, vertical mowing is not recommended at this time.

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The only cool-season lawn grass that will likely have significant thatch accumulation over time is Kentucky bluegrass, a grass that has an aggressive rhizomatous growth habit. High-maintenance bluegrass lawns receiving three to four pounds of nitrogen per 1,000 square feet per year are likely to develop thatch over a two- to three-year period. Consider vertical mowing to remove thatch in late-summer to early fall, the time when the turf has optimal recovery potential.

Pest management

The best way to minimize pests is to maintain a healthy, dense turf. You can achieve this by following sound management programs based on the principles previously discussed and by buying the correct turfgrass for the situation. The seed of many cultivars of tall fescue and perennial ryegrass is marketed as "endophyte enhanced." This means that the seed you are purchasing contains a living fungus that is highly desirable! We most often think of disease and bad looking lawns when we think about fungi and turf, but in this case the fungus within the seed (and ultimately your turfgrass) helps reduce the likelihood of attack by insect and disease pests (reduce, not eliminate, pest attack). For situations where tall fescue or perennial ryegrass are used, it is well worth paying a few pennies more per pound to purchase "endophyte enhanced" seed.

Proper identification of the pest is obviously crucial in determining how (and even if) a treatment is made. Virginia Tech provides numerous resources for the identification of weeds, insects, and diseases. The general instructions on the proper way to collect and to submit a sample for identification are found at http://www.ppws.vt.edu/~clinic/instructions.html. For weed identification, there are two excellent resources available through Virginia Tech websites that serve as "do-it-yourself" programs. The Weed Identification Guide can be found at http://www.ppws.vt.edu/scott/weed_id/rightsid.htm. This website will lead you through each step in plant identification keys, as well as provide pictures of the plant. A website more specifically for turfgrass weeds is http://www.turfweeds.net/. This site is maintained by Virginia Cooperative Extension Turfgrass Weed Scientist Shawn Askew.

Pests will still invade turf periodically even with the best management programs in place. The occurrence of diseases and insects is usually sporadic, but it is highly likely that most lawns will have some level of weed pressure. The following sections detail only the primary pests likely to occur in Virginia's cool-season lawns and successful cultural and chemical strategies to deal with them. Complete details of pesticides, the pests controlled, and the application rates and timing are provided in the Pest Management Guide found at http://pubs.ext.vt.edu/456/456-018/456-018.html.

Weeds

Preemergent weed control in established turf. Summer annual grasses (crabgrass, goosegrass, foxtail, etc.) are the most common targets for preemergent herbicide treatment in the spring but many other grass and broadleaf weeds also germinate as soil temperatures warm and days grow longer. The rapid growth potential of these summer annual weeds warrants the use of preemergent herbicides to prevent weed germination and the subsequent reduction in turfgrass quality. The key to the effectiveness of preemergent herbicides is timing the applications to before the weeds emerge. Mother Nature provides reminders for proper preemergent herbicide treatment timing in the form of the following ornamental plants: daffodils, forsythia, and dogwoods (Figure 6). Apply preemergent herbicides for crabgrass and other summer annual weeds when these plants are blooming prolifically. Forsythia and daffodils bloom early in this window of application, and dogwoods bloom at the end of the recommended application period. Several preemergent herbicides are available for lawn applications and Table 1 lists some of the most common products.

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Table 1. Preemergent herbicide options available for home-lawn applications by the homeowner and/or professional applicators.
Common chemical nameSome popular trade names
BenefinStatesman, BalanTM
DithiopyrDimensionTM, Vigoro
PendimethalinScott's HaltzTM, PendulumTM
ProdiamineK-Gro, Sam's Choice, BarricadeTM
OxadiazonRonstar®

Corn gluten meal is an organic compound that is marketed for preemergent crabgrass control. Note that this material is also usually about 8 percent to 10 percent nitrogen by weight, and normal application rates to gain weed control will also typically supply approximately one pound of nitrogen per 1,000 square feet. This product's limitation is that it has rarely provided better than 60 percent weed control in research trials at Virginia Tech and exceeds recommendations for spring nitrogen fertility of cool-season grasses. Breakthroughs in crabgrass control are likely to occur.

In addition to applications of herbicides alone, many formulations of "weed-and-feed" materials (products with a preemergent herbicide impregnated on a fertilizer carrier) are popular in spring lawn applications. If you select weed-and-feed materials with high percentages of nitrogen, choose sources that are predominantly slow-release nitrogen (as indicated on the label). This reduces the chance of overstimulating the shoot growth of cool-season turfgrasses at the expense of the root system.

It is necessary for all preemergent herbicides to be watered in soon after application. Most products must receive at least one-quarter inch of water within 48 hours of application or the herbicide will begin to decompose due to the effects of the sun.

Crabgrass control at seeding. If you want to spring seed cool-season turfgrasses, you cannot apply any of the preemergent herbicides listed in Table 1. However, some of these herbicides can be safely applied when establishing warm-season grasses by sprigging or plugging (consult the label). Of the group of preemergent herbicides listed in Table 1, oxadiazon is the safest material to apply during sprig or plug establishment.

Two herbicides that have unique uses in spring and summer establishments are siduron and quinclorac. Siduron (TupersanTM) is a preemergent crabgrass herbicide that can be safely applied just prior to or at seeding of cool-season turfgrasses only. The other option is quinclorac (DriveTM), an herbicide that can be applied just before or at seeding of most cool-season and warm-season turfgrasses, or after emergence of both turf and weedy grasses. As a postemergent herbicide, quinclorac requires a proper adjuvant such as a crop-oil concentrate or methylated seed oil. Follow label directions very carefully with either of these chemicals in order to maximize crabgrass control without damaging or killing turf seedlings.

Postemergent crabgrass control in late spring and summer. The previously mentioned DriveTM is an excellent early postemergent crabgrass herbicide with safety for both cool- and warm-season grasses. There are also several arsonate products (for example, products containing MSMA) that can be used when temperatures are between 80° and 90°F. Additional products include fenoxaprop or fluazifop in the active ingredients list. These herbicides control only grass weeds and should not be applied in conjunction with any herbicide that controls broadleaf weeds or they will fail to control the target weedy grass. These four active ingredients; fenoxaprop, fluazifop, MSMA, and quinclorac are available in ready-to-use and concentrate formulations under such trade names as Greenlight, Scott's, Bayer Advanced, Ortho, and many others. For professionals, these products are available as Drive, MSMA Turf, Acclaim, Fusilade, Ornamec, and many others.

Spring and summer broadleaf weed control. In mature turf, you usually can make applications of broadleaf herbicides as soon as the weed is actively growing. Typically, this will be when air temperatures are higher than 70°F. Some of the most popular broadleaf herbicides and their combinations are listed in Table 2.

 

Table 2. Some popular broadleaf weed herbicides used in cool-season turfgrasses.
Common chemical name(s)Trade name
2,4 dichlorophenoxyacetic acid (2,4-D)yMany products available
DicambayBanvelTM and others
Mecoprop (MCPP)yMany products available
TriclopyrTurflon
CarfentrazoneQuicksilver
2,4-D + dicamba + MCPPTrimec, Three-Way, Weed-B-Gon
2,4-D + dicamba + MCPP + carfentrazoneSpeedzone
2,4-D + clopyralid + dicambaMillennium Ultra
2,4-D + Triclopyr + clopyralidMomentum
Carfentrazone + 2,4-DPowerzoneTM
2,4-D + TriclopyrChaser
Triclopyr + clopyralidConfrontTM
MetsulfuronManor, Blade (only in bluegrass)
y Two- and three-way combinations of these and other similar chemistries are readily available and their combinations are often desirable due to synergistic activity.

Controlling weeds before they flower is an excellent way to keep them from completing their life cycle and producing seed. This strategy applies to either perennial (e.g. dandelions, clover, plantains, etc.) or annual weeds. However, if the primary weed problem consists of winter annual plants (for instance weeds such as henbit, chickweed, or geranium) that have already flowered, then the herbicide will not reduce future populations since the weeds have completed their life cycle.

As temperatures warm, the use of many broadleaf herbicides require extra caution because of the potential for damage to the turf (particularly cool-season grasses) and desirable landscape and garden plants. Pay extra attention to environmental conditions such as wind and relative humidity in the summer because of the potential for off-site movement onto desirable plants. You should often delay broadleaf herbicide treatments until the early fall because of their potential to damage neighboring plants. In spring and early summer, ornamental plants are young and succulent or producing new buds and tissues that are highly susceptible to herbicide vapors. In fall, perennial plants consist mainly of old and tough tissues that are less susceptible to herbicide injury. In addition, susceptible tissues are just weeks away from a killing frost. Thus, herbicide drift is much less visible and problematic in the fall compared to early summer. Proper treatment timing will depend both on the need to control weeds and to prevent damage to desirable vegetation on the lawn border.

Control of sedges and "grass-like" plants. Sedges can be distinguished from grasses by their triangular stem. Sedges are highly competitive in poorly drained soils or over irrigated sites, but they can be a problem anywhere only in the landscape. Sedges often occur in home lawns equipped with automated irrigation. Make sure you water only when it is needed in order to conserve one of our most precious resources, save money, and promote a healthy lawn. Over watering is a major contributor to sedge problems. There are both annual and perennial sedges, but the primary sedge of importance in Virginia is the perennial yellow nutsedge. One of the most broad spectrum sedge-control products is halosulfuron (ManageTM), which controls most annual and perennial sedges. Other herbicides for sedge control include MSMA (many trade names) and bentazon (Basagran, Lescogran). Bentazon and MSMA control annual sedges and yellow nutsedge, but require timely application to young sedge shoots, and are only effective when applied at least two times. Treat sedges when they are actively growing in late spring through summer. In rainy years, sedge problems will increase and more herbicide treatments will be needed to achieve equivalent levels of sedge control when compared to dry years.

Wild garlic is another grass-like plant commonly found as a weed in home lawns. Wild garlic sprouts from bulbs in the fall and is most prevalent in winter and early spring. In warm-season turfgrass, glyphosate (Roundup, other names) is often applied to control winter weeds while turfgrass is dormant. However, glyphosate does not control wild garlic and this weedy plant is often the only green plant remaining on dormant turfgrass after glyphosate treatment. The best herbicide for wild garlic control is 2,4-D or products that contain high rates of 2,4-D. In cool-season turfgrass, wild garlic is often noticed by the "onion" smell that occurs during spring mowings. Wild garlic can be controlled in cool-season turfgrass with 2,4-D also.

Diseases

The first step in disease control is to properly identify the pest. Cultural management and chemical control options may vary from one disease to another. Pictures of the disease symptoms (leaf spots, patches, etc.) or signs (the fungus itself) of the predominant spring and summer diseases in Virginia lawns are provided here, but you might be facing another pest entirely. Utilize the disease diagnosis services mentioned under the Pest Management heading if you are unsure of the disease that might be attacking your turf. Be aware that a disease, such as the "dull mower disease" shown in Figure 7, might not be caused by a fungus. Providing as much information as possible will lead to a more rapid and accurate diagnosis. Information that is particularly useful includes patterns of the disease, symptoms or signs as seen in the lawn, chemical application history, and weather patterns when symptoms were first noticed. Providing digital images can also be very useful. A picture is worth a thousand words! The most important aspect of dealing with diseases is not knowing how to control them, but how to reduce the severity by sound preventive maintenance strategies. Healthy turfgrass will be better able to fight off disease when under stress than turf in poor condition. Cultural practices that can promote healthier plants and reduce disease severity generally include deep, infrequent irrigation in the early morning, avoiding heavy fertilization in the spring, and reducing compaction through core cultivation.

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Dollar spot appears in the spring during the first warm, moist periods of the season, and can continue to develop through the early fall. Dollar spot often indicates a deficiency in nitrogen fertility. Applications of nitrogen will not cure the disease, but allows the plant to "out grow" the disease. The cottony-like web of the fungus is clearly visible early in the morning when dew is present. Limited infections usually do not cause massive turf loss, but the plant can be weakened when it is subject to serious environmental stress later in the summer. The physical sign of dollar spot is a cottony-like fungal growth that can be confused with webs spun by spiders or insects (Figure 8). To confirm the damage is caused by the dollar spot fungus, inspect the leaves for the characteristic hour-glass lesions as shown in Figure 9. Dollar spot is often an indication of low nitrogen fertility, and increasing nitrogen levels is a good way to manage dollar spot in most warm-season turfgrasses, but is risky in cool-season turf because it can encourage other diseases (particularly Rhizoctonia blight, i.e. brown patch).

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Another common spring disease is leaf spot, caused by various fungi that can attack turf in similar environmental conditions as dollar spot. Disease is typically most severe in mid- to late spring. As its name implies, the initial symptoms are dark, water-soaked spots that appear on the leaves (Figure 10). If the fungus only attacks the leaves, it is more of a nuisance than a concern. However, if the disease is severe, it can move into the growing points of the stems and begin killing the plants (as is illustrated in Figure 10). Again, realize that dollar spot and most leaf spot diseases are typically considered "nuisance" diseases - something to notice and pay attention to, but rarely to treat. However, if their infections become severe, they can possibly lead to turf damage later in the summer when environmental conditions are more stressful.

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One of the most serious and noticeable diseases that routinely strikes Virginia's home lawns each year is Rhizoctonia blight, i.e. brown patch. Typical symptoms of brown patch are a circular area (often referred to as a "smoke ring" or "halo") as pictured in Figure 11. The blighted leaves have no characteristic banding or spotted lesions as previously described for dollar spot or leaf spot. This disease typically occurs in the summer during hot, wet weather. Cool-season turfgrasses that receive heavy spring nitrogen fertilization are particularly susceptible. This is another very important reason to avoid heavy spring nitrogen applications.

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Two summer diseases that can be serious on cool-season turfgrasses are summer patch and Fusarium blight (Figure 12). Both summer patch and Fusarium blight occur more frequently when soils are compacted such as turf in high traffic areas or near paved areas and buildings. A characteristic symptom often associated with Fusarium blight is a "frog-eye" patch containing a healthy ring of turf within a circular shaped area of blighted leaves. However, this symptom is not consistent for all outbreaks of summer patch and/or Fusarium blight. Carefully manage irrigation schedules in order to promote deep rooting in these hot, dry areas.

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Table 3 details the major home-lawn diseases in Virginia lawns and some of the most effective chemicals for their control. For a complete listing of all chemicals and diseases, consult the Pest Management Guide.

 

Table 3. Fungicides recommended for the control of the most problematic diseases on cool-season turfgrasses in Virginia lawns.
Common chemical nameyTrade nameDollar SpotLeaf spotRhizoctonia
Brown Patch
Summer Patch
TriadimefonBayletonTMX XX
MyclobutanilEagleTMX XX
AzoxystrobinHeritageTM XXX
MancozebFore RainshieldTMXXX 
PropiconazoleBannerTMXXXX
FlutolanilProstarTM  X 
y For a complete listing of diseases and control recommendations, consult the Pest Management Guide at http://pubs.ext.vt.edu/456/456-018/456-018.html.

Insects

On an annual basis, the most likely insect pests to cause appreciable damage to cool-season turfgrasses are grubworms, chinch bugs, and caterpillars such as armyworms, cutworms, and webworms. While all of these pests can cause damage, their occurrence in numbers significant enough to warrant chemical treatment is unusual. Again, proper identification of the pest and an understanding of where the pest is feeding (above ground or below ground) is necessary to maximize control. If you suspect an insect is feeding on your turf, a soap flush is an excellent way to sample above ground pests. Simply remove both ends of a large can of 6 or more inches in diameter, and drive the cylinder into the soil at least an inch deep (Figure 13). Fill the can half way with a soapy water solution (one-half ounce of liquid dish detergent per gallon of water works well) and watch for the pests to float to the surface. If you do not know what the pest is, the Virginia Tech Insect Identification Lab can help.

The most significant insect pest to attack Virginia turfgrasses is most often the grubworm or white grub. When disturbed in the soil the grub will curl into a "C" shape and lay motionless for a brief period as pictured in Figure 14. White grubs are the larval stages of several different scarab beetles, and they come in many different sizes ranging from less than one-quarter inch in length for grubs of the Black Turfgrass Ataenius to over one inch in length for the grubs of the Green June beetle.

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Most grubs have an annual life cycle similar to that pictured in Figure 15. Grubs feed on turfgrass roots with chewing mouthparts. Because of the damage to the roots, the most noticeable symptom is wilting during dry periods. Overwintering grubs burrow several inches into the soil to survive the cold and then begin to migrate to the surface as the soil temperatures warm in the spring, all the time feeding on plant roots.


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By late spring they will reach their maximum size as worms before they go through their final metamorphosis from grub to beetle. Due to their size, chemical control is very difficult at this time. The optimum time to treat for grubs is mid-July through mid-August after the next generation's eggs have hatched and the immature grubs are very small and near the soil surface. Insecticides must be watered into the soil according to label directions in order to be effective.

As winged, adult beetles emerge, most are only interested in mating in order to lay eggs for the next generation. However, the Japanese beetle (Figure 16) is a serious adult pest, feeding on many trees, shrubs, ornamentals, and vegetables around the landscape. The adults are often treated with insecticides for the damage they cause on these plants, but control of the adults is still fairly inconsequential as regards to controlling grubs that will attack turfgrass root systems.

    figure16.jpg

 

Spring is not the best time to treat grubs because their large size makes them difficult to control.

Any insecticide application should be carefully considered before treatment because of the potential for killing non-target, beneficial insects. In particular, it is not always necessary to treat for grubs because if only a few are present, their damage to turf is negligible. Scout the turf using a shovel to lift the sod in a one square foot area if you suspect grubs might be causing damage. Six to ten grubs per square foot justify treatment for most grubs. Don't be overly alarmed that you have a "grub problem" just because you see a few grubs when you are digging in your lawn and garden in the spring. This does not mean that you should apply chemicals for control! Grub damage will be associated with moisture stressed (i.e. wilted) turf that simply does not respond quickly to irrigation or rainfall events because its root system has been attacked. Another likely sign that you might have a grub problem is if you observe lawn damage by burrowing animals (especially skunks) that feed on grubs. As mentioned above, be sure to scout the soil to identify the problem before you make a broad-spectrum chemical application.

Chinch bugs (Figure 17) feed on turfgrasses above ground with their piercing, sucking mouthparts. They are gold and black in color and are typically one-quarter inch long. Both immature and adult chinch bugs feed on grasses, usually feeding on the stems under the protection of the leaf sheaths. This can make them difficult to see, so soap flushes as previously described can be beneficial. There can be multiple generations of chinch bugs over the summer and damage most likely will occur in full-sun areas. The turf will take on a mottled yellow cast that can be confused with a disease (the loss of color is due to the injection of a toxin by the insect into the stem). Since chinch bugs feed above-ground, foliar applications of insecticides are recommended and irrigation or rainfall after the application is typically not recommended.

    figure17-19.jpg

 

The most common caterpillars to attack turf are sod webworms, fall armyworms, and cutworms. These pests feed above ground on leaves and stems with their chewing mouthparts. Most appear in mid- to late summer and while their damage can be significant (particularly in dry periods), chemical treatment is often not necessary. The caterpillars will eventually pupate and transform into a moth as an adult. The fall armyworm can be identified by an inverted "Y" on its head and can be seen feeding on foliage at any time of day, typically notching the leaf as it feeds (Figure 18). The cutworm lives in a hole in the ground but emerges from the hole to clip the foliage off at the soil surface and returns to its hole. Similarly, the sod webworm resides in a hole in the ground and clips the turfgrass stem off at the soil surface. An important identification feature is the silken web that it spins to camouflage its hole (Figure 19). The web can be confused with the fungus that causes dollar spot or that of a spider, so check for leaf lesions or a hole in the ground to properly identify the pest before making any attempt at control. Since all of the caterpillars discussed here feed above ground, surface applications of insecticides are recommended.

The nontarget effects of any insecticide should be carefully considered before treatment because of the possibility that beneficial insects might also be controlled. Fortunately, many of the newest generation insecticides have greatly improved in their specific target pest and their safety in the environment. Apply insecticides only when damage (or potential damage) warrants treatment. If chemicals are necessary, Table 4 details some of the most popular chemicals recommended by Virginia Cooperative Extension entomologists for the major turf pests.

 

Table 4. Insecticides recommended for the control of the most problematic insect pests in Virginia lawns.z
Common chemical nameTrade nameGrubwormChinch bugCaterpillars
CarbarylSevinTM XX
ImidaclopridMeritTMXX 
HalofenozideMach 2TM, GrubexTMX X
z For a complete listing of insects and control recommendations, consult the Pest Management Guide at http://pubs.ext.vt.edu/456/456-018/456-018.html.

There are numerous biological control alternatives that have demonstrated significant activity on these pests also. The products that have shown the most activity are certain entomopathogenic nematodes, a bacterium called Baccillus thuriengensis, and a fungus called Beauvaria bassiana. These biological-control products require careful selection (particularly regarding shelf life and the target pest) and application in order to be effective. They typically do not provide pest control as complete as standard insecticides, but they are specific to target pests, do not harm beneficial insects, and are safe to handle and for the environment. Single applications of biologicals are rarely successful in significant control. You must make a commitment to make regular applications of these products in order to replenish their populations in the environment.

Summary

This publication should help you appreciate the limitations and possibilities in spring and summer management of cool-season turfgrasses. By following these recommendations on turf selection and establishment, fertility, maintenance, and pest management, you can achieve a healthy, visually appealing cool-season lawn that is up to the challenge of Virginia's ever changing weather extremes.

Disclaimer

Commercial products are named in this publication for informational purposes only. Virginia Cooperative Extension does not endorse these products and does not intend discrimination against other products which also may be suitable.

Rights


Virginia Cooperative Extension materials are available for public use, reprint, or citation without further permission, provided the use includes credit to the author and to Virginia Cooperative Extension, Virginia Tech, and Virginia State University.

Publisher

Issued in furtherance of Cooperative Extension work, Virginia Polytechnic Institute and State University, Virginia State University, and the U.S. Department of Agriculture cooperating. Edwin J. Jones, Director, Virginia Cooperative Extension, Virginia Tech, Blacksburg; M. Ray McKinnie, Interim Administrator, 1890 Extension Program, Virginia State University, Petersburg.

Date

May 1, 2009