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 usu- ally 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 envi- ronmental 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 lar- vae 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 lar- vae. 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 insecti- cides. 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 over- lap 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