Annual Bluegrass Weevil Weevil: a Metropolitan a Metropolitan Nightmare Nightmare 1 Life Cycle by Dr

A PRACTICAL RESEARCH DIGEST FOR TURF MANAGERS TURFGRMS Volume 8, Issue 5 • May 1999 TRENDS

ENTOMOLOGY IN THIS ISSUE

Annual Bluegrass Annual Bluegrass Weevil Weevil: A Metropolitan A Metropolitan Nightmare Nightmare 1 Life Cycle By Dr. Patricia J. Vittum, University of Massachusetts Look for Damage

he annual bluegrass weevil, Listronotus maculicollis, is also often called the Hyperodes Monitoring, weevil because it was formerly assigned to the genus Hyperodes. The insect is a major Setting Thresholds pest of golf courses in the northeastern United States, particularly in the metropoli- T Cultural, Biological and tan New York area, including Long Island; the counties just north of New York City; south- Chemical Control western Connecticut; and northern New Jersey. However, it has also been reported caus- ing damage on golf courses throughout New England, upstate New York, central and Back to Basics, How eastern Pennsylvania and around Toronto, Ontario, Canada. Tlirfgrasses Grow . .7 As its name suggests, the annual bluegrass weevil feeds primarily on annual bluegrass Leaf Initiation and Growth [Poa annua) and is particularly damaging on turf with low mowing heights. Damage is usually most severe on collars and approaches, tees, greens and fairways. The weevil can cause Flowers and Stems damage to fine turf wherever annual bluegrass grows in its perennial form. Since the mul- tiple generations overlap, damage can occur any time from late May through early Sep- Rhizomes and Stolons tember. In the metropolitan New York area, the damage is usually most noticeable in early Growth Responses June and again in late July and early August. To Adverse Climates

Refining Turf Where Weevils Exist Management Practices The annual bluegrass weevil has been reported in more than 30 states, but so far is only a problem on fine turfgrass in the Northeast and Middle Atlantic states. It was first report- Field Tips: Speeding Transition of Typical pattern of Overseeded Perennial annual bluegrass Ryegrass ...... 13 weevil damage along the edge of a collar.

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Executive Editor Sue Gibson 440-891-2729; 440-891-2675 (fax) ed as a turfgrass pest in Connecticut in 1931 becomes reddish brown, just before the sgibson@advanstar. com and on Long Island in the late 1950s. Ini- adult weevil emerges. Managing Editor Bruce E Shank, BioCOM tially, turf managers blamed "spring die out" 805-274-0321 of annual bluegrass on the agronomics of Technical Editor the plant, specifically its inherent intoler- Life Cycle Nancy Stairs ance of summer temperatures. However, in As with any insect, it is important to 440-891-2623 many cases the obvious and rapid decline of understand the life cycle and to know when Senior Science Editor the insect is vulnerable to control treat- Dr. Kari Danneberger annual bluegrass can be traced to weevil activity. ments. In the metropolitan New York area, Consulting Editor Chris Sann the annual bluegrass weevil normally com- pletes two or three generations per year. Croup Editor Vern Henry Weevil Description The insect overwinters in the adult stage,

Production Manager The annual bluegrass weevil, like most usually in nearby woods (especially in the Karen Lenzen weevils, is a beetle with a distinct snout litter underneath white pines) or in tufts of 218-723-9129; 218-723-9576 (fax) high grass between the rough and woods. As klenzen@advanstar. com (Figure l).The adult is about 1/8 inch long, slightly smaller than most turf billbugs, and temperatures warm, adults begin to migrate Circulation Manager Frank Christopherson the thorax only occupies about 25% of the toward the short cuts of annual bluegrass. 218-723-9271 total body length. The snout is shorter and The earliest movement typically begins in Group Publisher stouter than that of a billbug and the anten- late March, but many weevils do not begin John D. Payne nae are attached near the apex (far end) of migrating until early or mid-April. 440-891-2786; 440-891-2675 (fax) jpayne@advanstar, com the snout. Mature adults are dark brown or Once the females reach the low-mown black with gray or yellow-brown hairs and annual bluegrass (fairways or shorter), they Corporate & Editorial Office 7500 Old Oak Blvd. scales on much of the thorax and hind begin to lay eggs inside the leaf sheath. This Cleveland, OH 44130-3369 wings. Teneral adults (recently emerged usually occurs in late April or early May. Mew Subscriptions from pupae) are reddish brown. Eggs are reasonably well protected and take 1-888-527-7008 Females usually lay two or three eggs at about a week to hatch into tiny larvae. The Abstracts: 800-466-8443 a time, lined up end to end inside the leaf larvae are small enough that they can bur- Reprint: 440-891-2744 sheath. Each annual bluegrass weevil egg is row inside the grass stem and feed as borers Permission: 440-891-2742 Single copy or back issues: deposited between leaf sheaths. The egg is for about a week. Larvae molt once during Subscription/Customer Service pale yellow when laid, but turns smoky gray this stage. 1-888-527-7008; (fax) 218-723-9437 Website address: as it matures. It is elliptical, about three When the larvae grow large enough that www. landscapegroup. com times as long as it is wide. they must leave the stem, they move down The larva (Figure 2) is cream colored the outside of the stem to the crown of the with a brown head capsule, sometimes with plant and continue feeding. Larvae pass ADVANSTAR a slight gray coloration along the back. Lar- through a total of five larval instars (three or HOLD! N G S , I N C . vae are legless but have several distinct four of which are outside the stem), spend- Chairman and "ridges" along the body and can move quite ing about five to seven days in each stage. Chief Executive Officer Robert L. Krakoff well through the thatch and upper part of After the larvae have completed feed-

Vice Chairman the soil. They are somewhat elliptical, ing, they pass through a "prepupal" stage, James M. Alic although the midsection is often slightly which resembles the larvae but is slightly VP-Finance, CFO & Secretary wider than the fore or hind end. Larvae are longer. The prepupae carve out a little cell David J. Montgomery small (1/16-inch long when first emerging in the soil, just at the soil/thatch interface. Executive Vice President, to 1/5-inch long just before pupating) and (Often the tip of the larvae will "spin" in the Business Development spend most of their development inside Skip Färber soil when disturbed.) Each prepupa then grass stems in their earlier developmental transforms to a pupa, a quiescent stage dur- stages or near the crowns of plants as they ing where the insect does not move or feed. w mature. Many changes occur internally during this ADVANSTAC O M M UN |C A T 1R O N S The pupa has many adult characteris- stage, including the development of a repro- Executive Vice Presidents tics, including the developing eyes, man- ductive system and muscles to power the William J. Cooke dibles, antennae, legs and wings. Creamy wings and legs of the adult. The pupa stage Alexander S. DeBarr white when it first develops, it later lasts about five to seven days, after which Vice President & General Counsel Eric 1. Lisman

Treasurer and Controller Adele D. Hartwick Figure 1. The annual bluegrass weevil adult is a dark broum or black beetle about 1/8 inch long unth a short, distinct snout. Figure 2. Larva are cream colored, legless and small (1/16 to 1/5 inch long). They have a broum head capsule unth cheunng mouthparts. Adapted from Cameron and Johnson, 1971.

young ("callow") adults emerge. These September or early October, but we never adults are reddish brown for a few days and find these stages when we sample the same the exoskeleton is not as hard as it will be areas the following spring. once the insect matures fully. The callow adults tend to be more vulnerable to environmental extremes than the more mature Look for Damage "hardened" adults. Annual bluegrass weevil larvae, which The completion of the first generation is have chewing mouthparts, can cause severe marked by the emergence of adults the end damage to turf. Young larvae feed as borers of June or early in July. A second generation inside stems, sometimes depositing tan saw- then develops, with egg laying possible only dust-like material inside the stems. Howev- a week after the adults emerge. Each subse- er, the primary damage is caused by the quent developmental stage occurs more large larvae which feed at the crown of the quickly than in the spring generation plant. Studies conducted in the 1970s because summer temperatures are higher demonstrated that an individual larva can and physiological activity is accelerated. So sever 10 to 12 plants outright during its the large larvae of the second generation feeding (Cameron and Johnson 1971). often are active by the end of July or early Damaged areas first appear as small yel- August. They then pupate and 2nd genera- low-brown spots. Small spots eventually tion adults appear by mid August. coalesce into larger areas and take on a In unusually warm years, the develop- "water-soaked" appearance. Damage often ment of each generation can be accelerated coincides with, and can be confused with, enough that second generation adults anthracnose. appear in early August, which allows a third Damage from the larvae that are active generation to develop, resulting in larvae in the spring is usually concentrated along activity throughout August and into Sep- the edges of fairways or on edges of greens, tember. tees or collars. Damage later in the year can Regardless of the number of generations occur almost anywhere in the low-mown that occur during the summer, only adults areas. will survive the ensuing winter. We often Larvae feed primarily on annual blue- find large larvae or pupae in the soil in late grass, but we have been able to raise the larvae on perennial ryegrass in the laboratory. sampling the insect and determining the life In addition, several turf managers have cycle is confusing and challenging because reported damage to certain bentgrass of the generational overlap. stands. Although this activity remains rare, Some spring adults become active rela- it is possible that the weevil is expanding its tively early and might lay eggs in mid- to host range. late April. These eggs give rise to larvae that Adults also feed on annual bluegrass, but reach maturity by late May or early June their feeding is inconsequential. The wee- and young adults that may be active as soon vils chew tiny notches in the blades, well as late June. above the meristem, so the damage is These individuals begin to mate and mowed off regularly and appears to have no reproduce almost immediately. In the same detrimental effect on turf vigor. However, location, there may be spring adults that the characteristic notches can serve as a delay their movement so they do not reach diagnostic clue that larvae are likely to be short cuts of annual bluegrass until May and present. do not lay eggs until early to mid May. These give rise to larvae that mature in late June or even later. How to Monitor and The end result is that samples taken dur- Set Thresholds ing the summer often reveal small larvae, The easiest way to monitor for annual medium sized larvae, large larvae and bluegrass weevil larvae is to cut a wedge of pupae, all in the same area at the same time. turf with a large knife. Any medium or large However, if a turf manager takes samples larvae that might be present will be clearly regularly (ideally weekly) and notes what visible, with the cream color contrasting proportion of the population is in each against the dark soil or thatch. Another developmental stage on each date, the over- method is to remove a cup cutter plug of all pattern can be discerned. turf, bring the core to the maintenance area, pull the turf apart gently, and look for larvae. Put all the loose turf and soil in a buck- Cultural Control et or dish pan and fill the pan with luke Several aspects of the biology of the warm water. Any larvae that were not found annual bluegrass weevil can be incorporat- by visual inspection will float to the surface ed into turf management programs. First, of the water. the weevil overwinters in the adult stage, Adult weevils can be flushed to the sur- often in litter under white pine trees. face of the turf with a soapy flush — one or Anecdotal reports from turf managers in two tablespoons of lemon-scented dish the metropolitan area indicate that remov- detergent in one or two gallons of water ing pine needles in the autumn may remove poured over an area one or two feet on each some of the insulation the weevils need to side. The soapy solution irritates many survive the winter. While no scientific stud- insects and weevils will scramble to the sur- ies have been conducted, superintendents face within a couple minutes. who have removed pine litter for three or The tolerance level for annual bluegrass more years feel the overall weevil popula- weevil larvae appears to be between 30 and tion has declined in surrounding areas. 80 large larvae per square foot in the spring Adults lay most of their eggs in annual and around 20 to 40 larvae per square foot bluegrass and the larvae feed primarily on in the summer. The lower threshold is a annual bluegrass. Therefore, any program direct function of the additional stresses the that manages or reduces the amount of turf experiences during the summer annual bluegrass on greens, tees, collars or months. fairways will ultimately result in a reduc- Turf managers who have dealt with the tion in the weevil population. Alternative- annual bluegrass weevil understand that ly, any program that enhances the vigor of the annual bluegrass may enable it to out- than are currently included on the product grow damage or at least not be devastated label and the company has not included by larval feeding. annual bluegrass weevils on their label. So, Some superintendents let the annual at this point, further field work is necessary bluegrass weevil feed unimpeded as a form to determine whether Conserve will prove of biological control of the annual bluegrass. to be a viable option. But before you decide to take that route, be sure you know how much annual bluegrass you have! Even a relatively low population Chemical Control of annual bluegrass can become very The most reliable alternative for manag- unsightly if the weevil becomes established. ing annual bluegrass weevil populations involves application of traditional insecticides. The following discussion will concen- Biological Control trate on spring and summer There are a few biological control alter- applications directed toward natives that bear further investigation. weevils in areas where two Young larvae feed Steinernema carpocapsae, an entomopatho- generations occur per year. genic nematode, is effective against several Spring generation — The as borers inside stems. species of weevils. Laboratory studies have spring generation begins when The primary damage indicated that the nematode has the poten- adult females emerge from tial to kill annual bluegrass weevil adults as overwintering sites and begin is caused by large well. However, attempts to use the nema- to lay eggs along the edges of larvae, which feed at tode in field conditions have been disap- fairways and other short-cut pointing or inconclusive. grasses. Therefore, insecticide the crown of the plant, One possible explanation for the poor applications should be con- severing as many as performance may be the air and water tem- centrated along the edges. peratures at the time of application. Spring "Wall to wall" applications are 12 plants in a feeding applications are typically made during late not necessary. April, when water temperatures used to fill Spring applications are sprayers often are below 55°F. Such tem- most effective if they are directed toward peratures undoubtedly slow nematode adults just as they begin to arrive at the activity. Summer applications are typically oviposition sites. This typically occurs made in July, when air temperatures may between forsythia full bloom and dogwood exceed 80°F and nematodes are prone to (Cornus florida) full bloom (actually full desiccation. color of the bracts) —usually between mid- Microctonus hyperodae is a parasitic wasp April and early May in the metropolitan which is highly effective against the Argen- area. Applications should be watered in tine stem, a closely related weevil. Studies lightly (one or two passes of a sprinkler conducted in New Zealand in 1996 and head). 1997 indicate that the wasp is unlikely to be Until recently, chlorpyrifos (Dursban™) an effective parasitic agent against the annu- was the material of choice but, in areas al bluegrass weevil. However, a closely relat- where annual bluegrass weevils have been ed wasp (Microctonus aethiopoides) shows present in damaging numbers for several more promise and will be investigated in years, turf managers feel the material has the future. become less effective. In the last two years, Spinosad is a naturally derived product superintendents have begun to use synthet- from an actinomycete (a kind of bacteri- ic pyrethroids with generally good success. um), and is now available commercially as Our field trials have indicated there is little Conserve™. Studies with spinosad in 1996 difference in efficacy between the (conducted as a series of experimental for- pyrethroids, including bifenthrin (Tal- mulations), in the metropolitan New York star™), cyfluthrin (Tempo™), lambda- area, indicated that spinosad reduced larval cyhalothrin (Battle™, Scimitar™) and populations under field conditions. Howev- deltamethrin (Deltagard™), when used at er, the application rates were much higher their labelled rates. Note, however, that the labels vary — some include golf course turf made over a wider area. Insecticides should and some do not and annual bluegrass wee- be watered in lightly to move the material vil is not specifically mentioned on all the off the blades and into the thatch. products. Some formulations of pyrethroids are Some superintendents have used tank sensitive to high temperatures and Dursban mixes of a pyrethroid with imidacloprid can be sensitive to ultraviolet rays, so appli- (Merit™) or a pyre-throid with chlorpyri- cations should be made as late in the day as fos (Dursban). Again our field trials have possible — or, alternatively, as early in the found that tank mixes with morning as possible. The same materials Merit have been very effec- that are effective in the spring should sup- Concentrate on the tive, often providing more press populations in the summer as well. than 95% control. However, areas where the "risk the difference between the factors" are highest — tank mix and the pyrethroid Risk Factors alone is seldom statistically While some golf courses have had a his- for example, sites with significant, so the tank mix tory of annual bluegrass weevils and man- substantial amounts of might be providing an expen- age populations aggressively, many others sive form of "overkill." Merit only experience activity sporadically. Often annual bluegrass near alone is usually not particular- spot treatment can be very effective. Con- white pines. ly effective against annual centrate on the areas where the "risk fac- bluegrass weevils. Several tors" are highest — for example, white pines other insecticides are also nearby or substantial amounts of annual labelled for annual bluegrass weevils and bluegrass. can be effective. The keys to the spring generation are to concentrate on the perimeters, time the Dr. Patricia J. Vittum is associate professor in application to coincide with appropriate the Department of Entomology at the Uni- plant phenology and water in the material versity of Massachusetts, Amherst. She is a lightly. frequent contributor to TurfGrass Trends and Summer generation — The second can be reached at (413) 545-2283. generation of weevils is less predictable in some ways, because there is so much overlap in development. However, in the met- REFERENCES ropolitan area, adult activity often peaks Cameron, R. S. and N. E.Johnson. 1971. Biology of around July 4th. a species of Hyperodes (Coleoptera: Curculionidae), We are in the process of developing a a pest of turfgrass. SEARCH Agriculture Vol. 1 (7): degree day model to predict weevil activity 1-32. Cornell University, Ithaca, NY. and hope to validate that model this year. In the meantime, July 4th provides a good ini- Tashiro, H. 1987. Turfgrass Insects of the United tial target date. If larval damage was States and Canada. Cornell University Press, Ithaca, observed in early June, insecticide applica- NY. tions for the second generation probably Vittum, P. J. 1995. Annual bluegrass weevil, pp. 21- should be made close to July 4th. If larval 23 In R. L. Brandenburg and M. G. Villani, eds. damage occurred in mid- to late-June, sum- Handbook of Turfgrass Insect Pest. Entomological mer applications should be made about a Society of America, Lanham, MD. week after July 4th. Because adult activity will originate from where the larvae were present in the spring, the weevils may spread to virtually any part of the nearby fairways, tees or greens, so applications often should be Back to Basics How Turfgrasses Grow

By Dr. Richard J. Hull, University of Rhode Island Leaf initiation and Growth: As in most seed producing plants, all primary leaves urf managers see their grassed areas originate from a terminal meristem. When grow and respond by mowing. They a grass caryopsis (dry fruit enclosing a single Tobserve some grasses flower in the seed) germinates, the first organ to appear is spring. They note the recovery of divots and the primary root called a radicle that, fol- other mechanical injuries. lowing gravitational cues, grows downward While they would be concerned if these into the soil. manifestations of turfgrass growth failed to Shortly thereafter, the embryonic shoot occur (maybe not the flowering), most emerges and, true to its antigravitational managers give little thought as to exactly instructions, grows upward to where light what grass growth entails. This ambivalence should be found. The elongating shoot toward the growth process can be disastrous meristem and first leaf are protected as they because the developmental characteristics pass through the soil by a closed sheath of grasses place rather strict limitations on termed a coleoptile. how these plants can be manipulated. This When the coleoptile breaks the soil sur- short discussion will try to review the face and perceives light, it soon stops grow- process of turfgrass growth. ing and its tip is ruptured by the first leaf

COLLAR

TILLER

PRIMARY LEAVES

CROWN SOIL

COLEOPTILE

SEED ADVENTITIOUS ROOT

PRIMARY ROOTS

Growth structures of the turfgrass plant. which elongates and expands into the light. leaf sheath might continue elongating for a At the same time, the stem ceases elongat- while. ing and the shoot apical meri-stem is posi- Inner leaves will not form a collar and tioned at, just above or just below the soil their intercalary meristems continue pro- surface, depending on the grass species. At a ducing cells that elongate and allow these predetermined distance behind the shoot leaves to maintain their growth within the meristem, a node develops in the embryon- sheaths of older leaves. This constitutes the ic stem from which adventi- vegetative phase of shoot growth in grasses. tious roots emerge. These will It is the growth desired by a turf manager In a regularly develop into the permanent because it produces the most uniformly root system. textured turf. mowed turf, the flow- Once the first leaf has ering process is cut emerged into the light, the Flower induction and stem elongation: apical meristem continues to For many turfgrasses, a cold period or the short by mowing off differentiate nodes consisting seasonal changes in day length (photoperi- the stem apex above of a leaf primordium that ex- od) trigger the induction of reproductive pands laterally and develops growth: flowering. This initiates a profound the mower height, thus into a cowl-like, sheathing change in the growth of a grass plant. Stem preventing all further leaf. Just above the center of elongation, that had stopped when the this sheathing leaf a bud seedling coleoptile emerged into the light, growth of that stem. develops. The leaves elongate now resumes. Intercalary meristems at the as a roll enclosed within the base of each node produce cells that elon- first leaf sheath. gate and lift the apical meristem above the Leaf growth occurs from a basal inter- soil line eventually to assume a position at calary meristem that produces cells that dif- the apex of the plant. The leaves which had ferentiate and elongate into the rolled (or been telescoped within the sheaths of the folded) leaf sheath within the sheath of the oldest leaves now are fully displayed as their next older leaf. As this primordial leaf intervening internodes elongate and the grows, its intercalary meristem divides into true stem emerges. an upper and a lower intercalary meristem. At this time, the apical meristem ceases The lower meristem provides ^ells for the producing leaf primordia and begins to ini- leaf sheath while the upper meristem sup- tiate floral primordia. As the apex is elevat- plies cells for the leaf blade. The upper ed by elongating stem internodes, the apex intercalary meristem will eventually differ- differentiates into an inflorescence charac- entiate into the leaf collar (the junction teristic of the species. This can be seen as a between blade and sheath that is character- swelling within the sheath of the youngest istic of grasses and helpful in species identi- leaf as it matures into a terminal flag leaf. fication), although initially it is simply a sec- This is called the boot stage in grain and for- ond meristem contributing cells for leaf age grasses. elongation. When the sheath of the flag leaf has Because of the basal location of leaf elongated fully, the stem continues growth intercalary meristems, the tip is the oldest and pushes the inflorescence out of the part of a grass leaf and can be removed by sheath and into the atmosphere where it mowing without affecting the leafs contin- assumes its preordained position at the ued growth (elongation). Eventually the apex of the plant. There the florets mature, outer leaves will differentiate into the typi- anthers extend and shed their pollen, polli- cal sheath and blade characteristic of grass nation and fertilization occur and the fruit leaves and the upper intercalary meristem and seed develop. will form a collar and cease to exist as a In a regularly mowed turf, the flowering meristem. The lower intercalary meristem process is often literally cut short by mow- will continue to produce new cells and the ing off the stem apex as the elongating stem lifts it above the mower height. Removing and does not break free until its elongating the apical meristem, and the developing leaves rise above the level of the collar leaves enclosed within the sheaths of older (intravaginal tillering). Because each prima- leaves, prevents all further growth of that ry leaf contains an axillary bud at the base stem. of its sheath and these buds are all concen- Annual bluegrass, and some cultivars of trated at the base of the stem, several tillers Kentucky bluegrass, when maintained as a can emerge before the parent stem is mowed turf, do not experience much stem induced to flower. When flower induction internode elongation so the apical meristem does occur, the internodes between nodes, and developing inflorescence are not from which tillers have emerged, are not removed by mowing until the inflorescence stimulated to elongate so the tillers are not has fully emerged. This is why unsightly lifted from the soil during elongation of the inflorescences (erroneously called seed parent culm. In fact the tillers become pret- heads) are often observed in turf containing ty much autonomous of their parent culm these grasses during the flowering season. producing their own adventitious roots. Some weedy grasses, which assume a They fail to senesce when the parent culm prostrate growth habit in turf, are able to flowers and undergoes senescence. develop inflorescences and produce mature Tillers can remain vegetative and not seed because these organs remain below the flower until the following growing season. mowing height. Crabgrass and goosegrass As such, they serve as over- are notorious for this and are serious weeds, wintering portions of the grass in part, because they have an extended crown. In this way, an exten- flowering season which produces objec- sive crown re-gion composed Tillers can remain tionable inflorescences throughout much of of numerous tillers and culm vegetative and not the summer. bases constitutes the truly perennial portion of a turf- flower until the fol- Flowering triggers the death of a grass grass plant. lowing growing season. stem: A second undesirable feature of grass flowering is that it ends the life of a grass Rhizomes and stolons: As such, they serve as stem (culm). Because the apical vegetative Early in the life of some turf- overwintering portions meristem has become a reproductive inflo- grass plants, buds enclosed by of the grass crown. rescence meristem, further vegetative the sheaths of the oldest growth of the stem is impossible even if it leaves will resume growth. were not decapitated by mowing. This However, instead of growing means that the grass stem will produce no upright to form tillers, they assume a hori- new leaves and is destined to die. Such a zontal growth habit. In Kentucky bluegrass, developmental sequence would be disas- creeping red fescue and bahiagrass, these trous for turf maintenance were it not for horizontal shoots break through the sheath the plant's capacity to generate new stems of the subtending leaf (extravaginal growth) from buds present at the base of young and produce underground stems called rhi- shoots. This initiation of basal shoots is zomes. In creeping bentgrass, velvet bent- called tillering and is an indispensable fea- grass, rough bluegrass, buffalograss and St. ture of turfgrasses. Augustinegrass, horizontal extravaginal When a young grass plant (seedling) ini- stems grow along the soil surface and are tiates its fifth leaf, it has stored enough pho- called stolons. Some grasses, such as colonial tosynthetic energy (carbohydrates) to initi- bentgrass, bermudagrass, Japanese lawngrass ate growth of axillary buds. These buds are (zoysiagrass) and seashore paspalum, pro- located at the nodes inside the sheaths of duce both rhizomes and stolons. All of these basal leaves. Because the stem internodes turfgrasses form a dense sod and are have not elongated, these nodes are main- referred to as spreading or creeping. tained at or just slightly above the soil level, By comparison, perennial ryegrass, tall protected from mowing injury. fescue, chewings fescue and some colonial Basal bud growth initially occurs within bentgrass cultivars produce no horizontal the enclosing sheath of the subtending leaf basal shoots and are known as bunch-type grasses. These grasses depend on seeding injury. rate to produce a thick turf and do not I have not been able to determine exact- recover from mechanical injury as rapidly as ly what environmental or internal stimulus the rhizomatous or stoloniferous grasses. promotes horizontal stem initiation, but I Rhizomes and stolons differ from tillers, suspect it has something to do with the not only in their direction of growth, but in plant's energy status. In cool-season grasses, the fact that they grow entirely as a result rhizome and stolon growth occurs mostly of stem elongation. Their apical meristem is in the spring and fall. Those are the times covered by several layers of scale leaves and when such grasses experience their most is thereby protected as it favorable energy status. Even during the pushes through the soil or summer, grasses at the margins of turf areas Rhizomes and stolons along the soil surface. The will receive more solar radiation and are differ from tillers, not meristem produces nodes, more likely to produce rhizomes or stolons. each with a leaf primordium, Warm-season grasses experience their only in their direction bud and internodes, which most favorable energy status during the of growth, but in the elongate. summer. Their lack of photorespiration As a result, the horizontal makes these grasses more photosynthetical- fact that they grow stem differentiates into rea- ly efficient during the high light and elevat- entirely as a result sonably distinct nodes and ed temperatures of summer. It is then that internodes. At each node, the maximum rhizome or stolon growth of stem elongation. axillary bud is covered by a occurs. Photoperiod and day/night temper- scale leaf. Nodes also produce ature range might influence horizontal adventitious roots and these stem initiation, but I would bet on plant extend the plant's root system to encom- energy status being the primary trigger. pass a larger volume of soil. Rhizomes are normally shorter and their Depending on the grass species and on apical bud turns upward to produce a new environmental conditions, the tip of hori- shoot closer to the parent plant in the fall zontal stems will turn upward and produce than in the spring. This may be environ- a new terminal shoot at some distance from mentally controlled. the parent plant. When the tip turns upward, internodal elongation stops and Growth responses to adverse climates: the shoot that develops is like any other Cold, heat and drought are climatic vari- young grass plant; consisting mostly of tele- ables that will influence turfgrass growth. scoped leaf sheaths that overtop the shoot Cool-season grasses are generally stimulat- apex. The length of rhizomes and stolons ed to grow more vigorously when temper- varies with the species and environmental atures are cool and moisture is abundant. conditions. By contrast, warm-season grasses normally The intervening axillary buds will prob- grow best under hot temperatures and ade- ably not form shoots unless the apical quate but not excessive water supplies. meristem of the rhizome or stolon is As mentioned above, favorable growth injured, or the soil in which the horizontal conditions often stimulate tillering and hor- stem is growing is largely free of other izontal stem growth in species that have the plants. Under such conditions, several capacity for such growth. When the tem- shoots or branches can emerge from axillary perature drops to near freezing or below, buds along the horizontal stem. warm-season grasses cease shoot growth In a dense sod, rhizome and stolon and root growth is largely curtailed. These growth is limited. But, where bare soil is grasses essentially go dormant and will not available, the growth of these horizontal resume growth until an extended period of stems is stimulated. In this way, turfgrasses warm weather is encountered. that produce stolons or rhizomes can quick- Cool-season grasses do not go dormant ly invade disturbed sites and repair turf under cold temperatures. Photosynthetic activity continues and nutrient absorption tems, primary (seminal) roots that emerge by roots persists at respectable rates. Aerial from the seed (embryo) and adventitious shoot growth (leaf elongation) pretty much roots that emerge from the coleoptile node stops, but rhizomes might continue to grow, which develops when the coleoptile breaks if slowly. Root growth and cell divisions in through the soil and experiences light. root meristems have been observed in the The primary roots develop largely from heart of winter. In short, cool-season grasses seed reserves and also from current photo- continue growing under cold temperatures synthesis of the seedling. However, their at a reduced rate. They do not become dor- growth is limited and their function is pri- mant and will resume growth quickly when marily to establish water contact between temperatures warm. seedling and soil. Nutrient uptake will also Drought affects all turfgrasses in a simi- occur but this function is soon taken over by lar way. The first response is a slowing of the more rapidly developing adventitious growth, although shoots are more affected root system. The primary roots may survive than are roots. This reduces transpiration and make modest contribu- rates and helps conserve soil moisture. If dry tions to the plant during the conditions continue, growth stops altogeth- first year but not thereafter. In Cool-season grasses er. Under high-light conditions, most grass- some species, primary roots es will suffer leaf damage and turn yellow or disintegrate within a month or appear to be most brown. An induced growth cessation two. resilient to periods of occurs, which cannot be regarded as a true Adventitious roots emerge dormancy. When moisture is restored, most from the coleoptilar node and prolonged drought. turfgrasses quickly resume growth and establish the base of the Warm-season grasses recovery can be rapid and complete. crown. This is set at the same Because warm-season grasses are more depth within the soil regard- can sustain more efficient users of water, under drought con- less of how deeply the seed injury than cool-season ditions they are able to divert carbohydrates was planted. Because several to roots and stimulate deeper root penetra- adventitious roots normally but normally will also tion into the soil, thereby tapping a larger emerge from the coleoptile recover water supply. In this way, they can forestall node, and these branch freely, serious drought injury. However, once sub- the grass root system always jected to drought, warm-season grasses are has a fibrous structure. Tiller bases produce likely to sustain more injury than cool-sea- additional adventitious roots, as do the son grasses. nodes of horizontal stems, and these bene- Cool-season grasses have fewer energy fit the grass by extending its reach into reserves during periods of summer drought, unexplored soil. which limits their capacity to avoid mois- This capacity for rapid root generation ture stress through the stimulation of deep- also allows grasses to reestablish a root sys- er root growth.Consequently, they may tem following stress induced root death or exhibit drought stress more quickly than feeding by soil insects. Because such events warm-season grasses. However, cool-season are not uncommon during most growing grasses appear to be better able to recover seasons, cool-season turfgrasses often must from periods of prolonged drought than regrow much of their root system during warm-season grasses. Soil conditions late summer and early fall. Warm-season (depth, moisture holding capacity and aer- grasses are able to support more rapid root ation) will, of course, influence the timing growth during the summer and, therefore, and extent of grass responses to drought. enter the fall season with a more-or-less Root growth has been discussed above intact root system. in the context of development and environmental conditions. In an earlier Back-To- Basics article, I concentrated on seasonal Dr. Richard J. Hull is professor of Plant root growth as it influences nutrient absorp- Science and chairman of the Plant Sciences tion. It would be approriate to point out Department at the University of Rhode that seedling grasses develop two root sys- Island. His research is concentrated on nutrient use efficiency and photosynthate Ed, Chapter 2, Growth and Development. Prentice partitioning in turfgrasses and woody orna- Hall, Upper Saddle River, NJ. mentals. Youngner, V.B. 1969. Physiology of Growth and Development. Pages 187-216 In A.A. Hanson and REFERENCES F.V. Juska, Eds. Turfgrass Science, Agronomy Madison, J.H. 1971. Principles of Turfgrass Culture. Monograph No. 14, Amer. Soc. Agronomy, Chapter 1, Anatomy and Morphology of Turfgrass Madison, Wl. Plants. Van Nostrand Reinhold Co., New York.

Turgeon, A.J. 1999. Turfgrass Management, Fifth

Refining Turf Management Practices

Understanding the patterns and timing of turfgrass growth can help refine turf management practices. Some ideas that emerge from the above discussion are listed below. 1. Because of their capacity to expand by horizontal stem growth, rhizometous and stoloniferous grasses need not be seeded as heavily as bunch-type grasses. 2. The ability to repair mechanical damage to turf makes the inclusion of sod- forming grasses in any turf seed mix a sound practice. 3. Because flowering and inflorescence production detract from turf uniformi- ty and the flowering culms will die and introduce dead stems into the turf, select- ing cultivars that are less likely to flower under turf management conditions would be desirable. Careful use of plant growth regulators can minimize this problem. 4. Close mowing or drastic changes in mowing height should be avoided because the apical meristem of grass shoots is near the soil surface and will tend to be ele- vated and damaged by mowing when grasses are allowed to grow too much between mowings. 5. Tillering of turfgrasses contributes to stand density and is encouraged by mowing but not by removing so much leaf tissue that insufficient energy is available to support tiller initiation and development. 6. Because root loss during the summer is to be expected in cool-season grasses, it is wise to raise the mowing height during summer to provide the photosynthetic products needed for adventitious root regeneration. 7. Turfgrasses respond to drought conditions by allocating more energy for root system expansion. Therefore, it is best to reduce mowing frequency during mid- summer and allow more leaf surface to capture additional energy. 8. Because cool-season turfgrasses continue photosynthetic activity during the winter and root growth depends upon energy captured at that time, it is important to remove tree leaves promptly and avoid any unnecessary winter shading of the turf. 9. Turf growing in shaded locations will have less photosynthetic energy to support tillering and horizontal stem growth, so close mowing should be avoided. 10. Turf recovery from mechanical injury depends on tiller, rhizome and stolon growth which relies on photosynthetic energy. Such turf should be mowed as high as is compatible with its use and should be protected from shading even for short periods of time. Speeding Transition Of Overseeded Perennial Ryegrass

s the range of hybrid bermudagrasses Maintain irrigation — Do not let the expands and improved seeded rootzone dry out. Fall can be the driest sea- Abermudas gain acceptance, winter son of the year despite cooler temperatures. overseeding and spring transition are more Apply fungicides — Apply systemic important issues. During the winter, dor- fungicides to the bermudagrass in Septem- mant bermudagrass is camouflaged and ber to prevent spring dead spot. protected by overseeded ryegrass. But, when it's time for the bermuda to come back to life, lingering perennial ryegrass can Cultural Practices be a problem. For many years, turf managers and To find out the approved ways to dis- researchers have sought a foolproof scheme courage ryegrass and encourage bermuda in to insure a smooth spring transition. There the spring, TurfGrass Trends contacted two are several cultural practices recommended respected experts at Auburn University, to remove the overseeded turfgrass while Drs. Coleman Ward and Jeffrey Higgins. speeding recovery of the bermudagrass. Delay core aerification — This idea is opposite to popular thought. The theory Begin in the Fall behind early core aerification is to stimulate Successful spring transition starts with the bermudagrass with warm air entering good bermudagrass management in the fall. the soil through the aerification holes. In Make sure your bermuda goes into the win- fact, cold air, which is heavier that warm air, ter with healthy rhizomes and stolons. Sev- is more likely to settle in the core holes. It is eral practices will insure that this happens. best to delay aerification until bermuda- Potassium —Apply potassium liberally, grass is actively growing so closure of the especially during the fall. Apply a fertilizer, holes can occur as rapidly as possible. such as a 10-5-20,0-20-20, or 16-0-38, at a Closer mowing — Close mowing of the

rate to supply 0.75 to 1.00 lb. of KzO per perennial ryegrass should weaken the 1,000 sq. ft. monthly from September perennial ryegrass because it is a bunch through November. grass. Almost all of the ryegrass' stored car- Avoid scalping — Avoid scalping in the bohydrates are above ground and will be fall. When bermudagrass recovers from removed by close mowing. However, for scalping, it consumes stored carbohydrates this practice to be effective, it must begin which are needed for spring regrowth. Mow and end before the bermudagrass initiates low without scalping prior to overseeding. spring growth. Removing any new leaves Delay overseeding — Delay overseed- from the bermudagrass is extremely detri- ing until the bermudagrass becomes less mental to its recovery from dormancy. Car- competitive. Observe the amount of clip- bohydrate reserves in the bermudagrass' pings taken each mowing as fall progresses. rhizomes and stolons are drastically deplet- When it decreases, overseed. By delaying ed by the initiation of new growth. So, mow the date of overseeding, less vertical mow- the ryegrass lower early in the spring and ing and aggressive preparation (penalty raise the cutting height as soon as you notice mowing) of the bermudagrass will be new bermuda growth. required to reduce its competitiveness with Vertical mowing — Vertical mowing the germinating perennial ryegrass. Less thins out perennial ryegrass and permits scalping and vertical mowing means more light penetration to the bermudagrass. stronger bermudagrass. However, as described in relation to closer mowing, it is harmful to the bermudagrass tent spring transition. But before using a once it starts growing again. Vertical mow- herbicide to remove perennial ryegrass and ing is more likely to be beneficial where speed transition, turf managers should: perennial ryegrass was seeded at excessive- • Be sure base bermudagrass is alive. ly high rates (more than 400 lbs. per acre). • Check the activities calendar for events This practice could be more detrimental during the spring season. than beneficial when the bermudagrass has • Consult long-range weather forecasts. You begun to grow. might need to hold the perennial ryegrass if Withholding irrigation — Since peren- cool, wet weather is forecast. nial ryegrass requires more water than • Discuss spring transition options with bermudagrass, withholding irrigation users of the site to prevent surprises. should reduce its If an instant spring transition is desired The use of selective competitiveness and and acceptable, then metribuzin (Sencor postemergence herbicides enhance the transi- 75DF) can be applied in the spring at 0.67 t. r t tion to bermudagrass. lb. of product per acre. This will control the perennial ryegrass and allow the bermuda- can compliment cultural In practice this theo_ grass to grow. However, severe turf discol- has at east two practices to provide. . wflaws. First l, spring is oration will result for a couple of weeks due consistent spring transition. often the highest rain. to the removal of the ryegrass. fall period of the year. Napronamide (Kerb 50WP) can also be And second, the turf area may be in use and used to remove overseeded perennial rye- irrigation might be needed to keep it grass. Kerb should be applied at two pounds playable. of product per acre in the spring. This Increase nitrogen fertilization — treatment will not work as fast as Sencor. Applying high rates of nitrogen (more than The addition of a nonionic surfactant at 1.25 lbs. per 1,000 sq. ft. per month) caus- 0.25% volume to volume is recommended. es an increase in the top growth of both perennial ryegrass and bermudagrass. How- ever, increased nitrogen is more detrimen- Seed Selection tal to the root growth of perennial ryegrass Ward and Higgins believe that perenni- than bermudagrass. al ryegrass is the best choice for winter over- Furthermore, bermudagrass responds seeding high-use turf. While other cool-sea- favorably to much higher levels of nitrogen son turfgrasses can be used, they believe than does ryegrass. Increasing nitrogen is perennial ryegrass has superior wear toler- the one sure way, among the cultural prac- ance, establishes quickly, has excellent frost tices listed, to favor bermudagrass during tolerance, requires less mowing than some transition. This is especially true as night varieties and the advanced cultivars provide time temperatures exceed 62°F. The down- better disease resistance. They report that side to this approach is late season frosts can more than 50 blends and cultivars of peren- damage the bermudagrass after it has been nial ryegrass are currently available. fertilized. Some cultivars of perennial ryegrass, however, have demonstrated extraordinary heat and drought tolerance, which enables Making a Herbicide- them to tolerate many of the cultural prac- Assisted Transition tices described. Avoid these ryegrasses Cultural practices alone are often a very when purchasing seed in the fall. uncertain way to remove perennial ryegrass and reduce its competition with the base Coleman Y. Ward, Ph.D. is professor emer- bermudagrass. The use of selective poste- itus. Jeffrey M. Higgins, Ph.D. is extension mergence-applied herbicides can compli- turfgrass specialist at Auburn University. ment cultural practices to provide consis- He can be reached at (334) 844-3977. ¡FROM THE EDITOR

Editor's note: We must be doing something right! Our paid subscriptions are at an all-time high and the staff of TurfGrass Trends would like to thank you for subscribing. This brings me to my second point. The kind of material found in TurfGrass Trends is unique. There are probably many people in the industry — in academics as teachers or students and in the field who could benefit from each issue of TurfGrass Trends. If you know of other colleagues, students or researchers who would find TGT interesting, please let them know how they can subscribe. Here's a sample of the kind of material they'll find helpful. We're working on a number of key topics, including: gray leaf spot,humates, anthracnose, growth regulators, grubs, root growth, salinity and more. Again, thank you for supporting TurfGrass Trends! Sue Gibson

In Future Issues • Gray Leaf Spot • The Role of Humâtes • Grub Identification • Life Cycles of Nematodes • Managing Saline Irrigation • Soil Temperature's Impact

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