Hort Notes: Clippings from the Garden

A monthly e-newsletter from UMass Extension for landscapers, arborists, and other Green Industry professionals, including monthly tips for home gardeners.

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Announcements

Pollinator Steward Program Summer Cohort

Registration for UMass Extension's Pollinator Steward Program summer cohort is now open through May 31st or until full. This fully online, asynchronous, self-paced course provides essential foundations in pollinator ecology and habitat provisioning.

Learn more and register.

Landscape Pests and Problems Walkabout

Join us for UMass Extension's Landscape Pests and Problems Walkabout at Heritage Museum & Gardens in Sandwich, MA on June 24th.

Join Tawny Simisky, Extension Entomologist, and Russ Norton, Horticulture and Agriculture Extension Educator, for a walk through the landscape as they examine some of the most common insect and cultural problems of woody ornamentals, as well as discuss and demonstrate how to put IPM practices to work efficiently. We may even see a periodical cicada or two!

2 pesticide contact hours for category 36 and Applicators License available.
ISA, MCLP, MCA and MCH association credits are being requested. 

This in-person program will be held outdoors, rain or shine. 

Learn more and register.

Save the Dates

Turf Field Day: July 23rd

Invasive Insect Certification Program: September 

Hot Topic

Yellow Nutsedge Management in Turf and Landscape

Yellow nutsedge is commonly considered to be one of the most troublesome and “difficult-to-manage” weeds of turf and landscape. It is a member of the plant family Cyperaceae or sedge family and another common name is nutgrass or chufa. While this weed is a monocot, it is not a grass species. Despite it being tossed in the “difficult-to-manage” category, yellow nutsedge with proper product selection and application timing, can be managed successfully.

Life cycle and description: Yellow nutsedge is a perennial sedge reproducing by tubers (nutlets) at the end of short, scaly rhizomes and rarely from seed as population in turf are frequently mowed. While yellow nutsedge can occur in dry soils it is typically more aggressive in wet areas due to poor drainage and/or overwatering.

Upright, triangular stems arise from overwintering nutlets in very late spring and early summer. The triangular stems are the most useful characteristic for identification as you can feel the triangular shape by rolling the stem in your fingertips.

Yellow nutsedge leaves are light green, glossy, with a prominent midrib and taper to a sharp point at the leaf tip. Yellow nutsedge is most noticeable in summer because its leaves grow more rapidly than the cool-season turf during the hottest summer months. During spring and fall nutsedge growth is slower and not as easy to spot in turf. Yellow nutsedge produces a yellow to light brown seedhead, although they are seldom observed in frequently mown turf.

Cultural management strategies: The best method for controlling yellow nutsedge (and other weeds) is to encourage the growth of a healthy, dense, vigorous stand of turf that can compete with weeds. Encourage dense turf stands by following proper turf maintenance practices, including fertilization, appropriate irrigation, frequent mowing at the proper height of cut and over-seeding as needed. Yellow nutsedge is most problematic in turf that is mown too short and in areas where soils remain moist from poor drainage and/or overwatering. In the landscape setting, physical removal of newly introduced plants can be utilized before yellow nutsedge has a chance to take a foothold. Yellow nutsedge is commonly introduced into landscapes as a result of the weed being in the root ball in planted woody ornamentals.

Herbicide management strategies: Cultural management strategies will slow the spread of yellow nutsedge, however larger a established population will usually require the use of an herbicide program. Several herbicides are available for the control of yellow nutsedge. Regardless of the herbicide selected, yellow nutsedge is a “difficult-to-control” weed. Late spring to early summer is the best time to control it. During early spring emergence from the overwinter nutlet has not started producing tubers and it is easier to manage with herbicides. As the summer progresses, yellow nutsedge plants produce seedheads and nutlets. Since the nutlets are the plants’ primary survival structure, it is important to control yellow nutsedge early in the summer before it produces nutlets. Patience and diligence are required for successful management. Two to three years of control using herbicides is often required to reduce viable tubers in the soil. Herbicides often injure or only partially control growing yellow nutsedge plants and help prevent more nutlets from forming, but herbicide applications will not control nutlets that are viable in the soil but have not yet produced plants. Table 1. provides herbicides products available for yellow nutsedge management in turf and landscape and Table 2. provides information about formulation and application methods. Information in Tables 1 and 2 should not be used as a replacement for reading, understanding and following label directions for any product listed.

Table 1. Herbicides products are available for yellow nutsedge management in turf and landscape.

Table 2. Herbicides products are available for yellow nutsedge management in turf and landscape Herbicide: formulation and application methods.

Information should not be used as a replacement for reading, understanding and following label directions for any product listed.

Randall Prostak, UMass Extension Weed specialist

Trouble Maker of the Month

Tall Grass, Ticks, and No Mow May

No Mow May is a trend that originated in the United Kingdom. Despite differing ecologies, the trend has gained traction across the United States over the last several years.

For those who have never heard of Now Mow May, the general idea is simple: Don’t mow your lawn until the month of May is over. In doing so, you provide additional floral resources for pollinators, such as non-native dandelions.

While I am glad people are keeping an eye toward pollinators, I feel this trend has several shortcomings. Chiefly, native wildlife require floral resources and shrubby vegetation year-round – not just for the month of May. For instance, fireflies peak around the end of June and benefit from tall, shrubby vegetation, including grass. Many females perch in the dark on knee or waist-high vegetation, while their male counterparts flash from the skies.

Coincidentally, nymphal deer ticks (Ixodes scapularis) also peak in May.¹ Nymphs are about the size of a poppy seed. Due to their small size, they often go unnoticed during feeding. It is estimated that 80% of Lyme diseases cases are transmitted by nymphal deer ticks.²

Can you expect to see more nymphs if you engage in No Mow May?

Short answer: Not necessarily.

Contrary to the common myth, tall grass is not necessarily an indication of tick habitat. Nymphal deer ticks are highly sensitive to desiccation and struggle to survive at humidity levels under 82%.³ Locations conducive towards nymph survival include ecotonal habitats, shady edges along property lines, leaves, log piles, and rock walls.

The important part to note is that you can have tall grass without ticks. Likewise, you can have short grass with plenty of ticks. Lerman and D’Amico conducted tick drags on properties containing tall grass in Springfield, MA. Property owners had not mowed for up to 3 weeks, with maximum grass heights reaching over 10 inches. Following 144 tick drags over 2 years, the researchers did not find a single tick on any of the properties.⁴ In contrast, mowing in a forested hiking trail setting did not decrease the number of ticks found during tick drags.⁵

Given the above, I don’t expect participating in No Mow May to increase your likelihood of encountering ticks. If ticks were common before No Mow May, they will be common during and after.

Whether or not you participate, I recommend taking proper precautions against ticks. Wear EPA-registered repellents. Treat your clothing and shoes with permethrin. Conclude every day with a full body tick check.

If you want to continue supporting native wildlife, expand your goals beyond the month of May. Add plants that bloom all season long. Provide tall, shrubby vegetation patches throughout the summer. Allow leaves and stems to accumulate over years to create habitat for native plants and wildlife.

¹ Levi, Taal & Keesing, Felicia & Oggenfuss, Kelly & Ostfeld, Richard. (2015). Accelerated phenology of blacklegged ticks under climate warming. Philosophical transactions of the Royal Society of London. Series B, Biological sciences. 370. 10.1098/rstb.2013.0556.

² Mather, Thomas & Nicholson, Matthew & Donnelly, E.F. & Matyas, B.T.. (1997). Entomologic Index for Human Risk of Lyme Disease. American journal of epidemiology. 144. 1066-9.

³ Rodgers, S. E., Zolnik, C. P., & Mather, T. N. (2007). Duration of exposure to suboptimal atmospheric moisture affects nymphal blacklegged tick survival. Journal of medical entomology, 44(2), 372-375.

⁴ Lerman, S. B., & D’Amico, V. (2019). Lawn mowing frequency in suburban areas has no detectable effect on Borrelia spp. vector Ixodes scapularis (Acari: Ixodidae). PLoS One, 14(4), e0214615.

⁵ Lee, X., Maxson, G. A., & Paskewitz, S. (2023). Single mowing event does not reduce abundance of Ixodes scapularis (Acari: Ixodidae) and Dermacentor variabilis (Acari: Ixodidae) on recreational hiking trails. Journal of Medical Entomology, 60(1), 228-234.

Blake Dinius, Entomologist with Plymouth County Extension, reporting from the Plymouth area.

Q&A 

Q. Gardeners are encouraged to practice good sanitation to prevent plant diseases from recurring the following season, but I want to leave dead plant material in the garden because it provides an overwintering habitat for many pollinators. Is there any way to strike a happy medium?

A. We plant pathologists are always talking about garden sanitation as an important method of disease prevention. Many plant pathogenic fungi can overwinter in infected leaves and stems; at the same time, those leaves and stems can provide protection for overwintering pollinators and other beneficial organisms. There is no way to completely exclude the unwanted and welcome only the good, but there are a few things you can do to discourage diseases while protecting the beneficials.

• Selective clean-up. If there are plants in your garden that are known to have had an active foliar and/or stem disease in the previous season, clean up debris from those plants as thoroughly as you can before spring begins. If plants appeared to be healthy, you may consider leaving their debris in place until any beneficials have emerged. Some sources recommend waiting until apple trees are in bloom.
• Mulch the garden with leaf mold or good compost. A one-inch layer of mulch on top of plant debris can help prevent any fungal spores from being dispersed. While mulch can disrupt the nesting patterns of some beneficials, a conservative layer is often still navigable for these insects.
• Use drip irrigation instead of overhead. The spores of most fungi that attack leaves need them to be wet for a certain amount of time to germinate and cause infection, so do what you can to keep foliage dry. If you must use overhead irrigation, water before 10am on sunny days so the foliage will dry out as quickly as possible.
• Prevent gardens from becoming overgrown. Dense foliage raises the humidity within the plant canopy, which can also encourage disease-causing fungi. Prune and/or space plants to allow good air circulation.
• Manage weeds. Weeds can also contribute to the ambient humidity; in addition, they can negatively affect the health of garden plants by competing for nutrients, water, and sunlight. Some weeds may also harbor pathogens.
• If you have the time and space, consider starting a separate pollinator garden. Plant debris may be left in this area while vegetable gardens and landscaping are kept tidy. For more information about pollinators, see our educational briefs.

Dr. Angie Madeiras, UMass Extension Plant Diagnostic Lab with Nicole Bell, UMass Extension Pollinator Specialist

Garden Clippings: Tips of the Month

May is the month to . . . .

• Transplant tender flowers, vegetables, and melons. For plants that will not tolerate frost, towards the end of the month is the safest bet… Memorial Day weekend is the traditional time for this annual ritual. For the best possible start, acclimate transplants grown in warm environments by gradually increasing exposure to full sun and cool nights over a 7-10 day period before transplanting. Plant in the evening after the heat of the day has passed or on a cloudy day to further ease transplanting stress.
• Think about grub control. For lawn areas that have a history of grub problems, well-timed preventive applications are vastly preferable to curative options. The goal is to have the material in place when grub eggs hatch (typically mid-July through mid-August), thereby contacting the grubs when they are most vulnerable. Preventive products that contain chlorantraniliprole (Acelepryn^TM) as the active ingredient, however, take 60 to 90 days to fully activate in the soil, so are therefore best applied during the month of May. Later (or earlier) applications will be markedly less effective.
• LEAVE foliage of spring flowering bulbs… until withering occurs. To help ensure future success, it’s crucial to leave the foliage of spring flowering bulbs (daffodils, iris, hyacinths, etc.) intact after flowers fade. While it’s tempting to remove foliage to keep things tidy or make way for new plant material, foliage continues to photosynthesize. This activity produces the sugars that will be stored to enable emergence and flowering the following spring, so removing foliage prematurely could jeopardize the bulb. To further pamper bulbs, make a high phosphorus fertilizer application (bonemeal is a good source) when flowering ends.
• Take measures to support “floppy” perennials. Tall plants with delicate, vertical stems and large flowers such as delphinium, peony, gladiolus, hollyhocks, and dahlias commonly benefit from additional support. Taking appropriate steps for staking or caging now will provide these plants with a big assist in the way of staying upright and it is much easier early in the season before beds fill in and plants become large and unwieldy.
• Look beyond “No Mow May.” “No Mow May” is a widely publicized approach popularized by various pollinator advocacy groups and media, and the concept has accomplished a great deal in terms of drawing attention to the need for good pollinator stewardship. The actual practice, however, has limited benefit for pollinators and, depending on expectations, can be detrimental to lawn health and persistence over the longer term. In line with the “Trouble Maker” article above, for better pollinator support, consider dedicated pollinator spaces that can be planted and managed intentionally to provide robust pollinator resources throughout the year, along with collateral benefits like visual aesthetics and reduced maintenance.
• Monitor trees for spongy moth (Lymantria dispar) caterpillars. Eggs hatch at 80-100 GDD (base 50) which is around early May on average in MA. Oaks are preferred especially, but other potential hosts may include apple, poplar, willow, witch hazel, and several birch species. In many years a naturally occurring fungus called Entomophaga maimaiga is very effective at keeping spongy moth population densities below damaging levels, assuming adequate rainfall and soil moisture levels are present to sustain fungal levels and subsequent infection. For more info, see our Spongy Moth fact sheet.
• Mulch, mulch, mulch! Mulching of beds, gardens, and specimen plants offers tremendous upside, including the prevention of unwanted soil movement, suppression of weed germination and establishment, help in the retention of soil moisture, the creation of a buffer against extreme temperature fluctuations, and addition of organic material and beneficial nutrients to promote soil health. Mulching mistakes to avoid include applying mulch too thick or too often, mulching directly against the stems/trunks of plants, use of materials (like hay, for example) that may harbor weed seeds, and choosing materials that are mostly wood (like arborist chips or many “bargain” commercial mulch products) since they can skew soil carbon to nitrogen ratios and have a higher potential for harboring artillery fungus.
• Hang up those hummingbird feeders. Hummingbirds return to Massachusetts by late April/early May in most years, so strive to have feeders cleaned, in place, and filled by the first week of May. An ideal nectar solution is simple: 1 part cane sugar to 4 parts water, boil until sugar is completely dissolved (1-2 minutes), and cool completely before use. No other additives (especially food coloring, despite popular belief) are necessary. To create a more well-rounded “menu”, include hummingbird favorites like fuchsia, lantana, lobelia and petunia in plantings.
• Harvest asparagus. Spears should be cut when they reach 7”-10” in height and before the heads begin to open. Letting heads open too much will yield tough spears. Do not harvest or harvest very sparingly for the first two growing seasons that asparagus is in the ground. After, follow the ‘2-4-6 sequence’: harvest for two weeks the third year, four weeks the fourth year, and six weeks the fifth and following years. A well-tended asparagus bed can be productive for 25 years or longer.
• Install a rain barrel. If you’ve considered installing a rain barrel, May provides a nice opportunity, after the threat of freezing has passed and before summer watering needs ramp up. Rain barrels can be great tools for curbing the use of drinking water for outdoor irrigation and other chores and can help in stormwater management. Planning and setup is a little more involved than simply sliding an open vessel under the downspout, however, and should include considerations like barrel size, platform integrity, light transparency, mosquito and debris exclusion, and overflow management. Refer to the rain barrels fact sheet from the Massachusetts Department of Environmental Protection for more tips.
• Take a moment to appreciate spring’s majesty. The winter of ’24-’25 was an especially cold one here in New England, and May is the perennial reminder that we’ve made it to the other side. Warm, longer days finally arrive, and things really begin to happen in the landscape… flowers bloom, leaves and needles emerge new and fresh, gardens produce, and the grass grows. Try to linger a bit longer on a nice evening walk or pause with a cup of coffee on a mild morning to take in the welcome changes that surround us. It’s fleeting, and before we know it, this special time will be replaced by the dog days of summer!

Jason Lanier, UMass Extension Turf Specialist & Group Leader, Commercial Horticulture

Considerations in Biological Control: Choosing a Strategy for Your Needs

At its most basic level, biological control, or “biocontrol”, describes the use of living organisms to manage pests. In practice, this simple idea can be applied in many ways. A wide array of organisms may be employed for biocontrol, including bacteria, fungi, viruses, nematodes, mites, insects, and even vertebrates like birds. These organisms are natural enemies of pests and are referred to as biocontrol agents. Likewise, a wide variety of pests may be controlled through biocontrol, but in horticultural contexts, these are usually insects or mites.

There are several strategies through which biological control is carried out, with the two categories covered in this article being the most common and practical for growers. Each of these strategies has its own strengths and weaknesses, making them useful for different situations. All in all, these strategies share the goal of reducing the need for chemical pesticides which can be expensive, inconvenient, and harmful to human and environmental health. But biocontrol is not a perfect solution either – if used poorly, it can have just as many downsides as chemical management. Although it’s not a silver bullet, knowing which biocontrol strategies will be most effective for you can help you make the most of this tool for integrated pest management.

Conservation Biological Control

Conservation biological control aims to use natural enemies which are already present in an environment to control pests. This typically involves two types of actions: creating habitats to attract and support natural enemies and reducing harmful effects that may stifle their populations. Different habitat types can target different groups of natural enemies. For example, planting certain flowers can support many flying predators that rely on nectar and pollen as food sources (Fig. 1), including wasps, lady beetles, hover flies, and lacewings, while mulch, tall perennial grasses, and brush piles can support other predators such as spiders and ground beetles (Fig. 2). Reducing damage to natural enemies is often a matter of reducing unnecessary insecticide use and using less harmful chemistries. Broad-spectrum insecticides such as carbamates, pyrethroids, and neonicotinoids have harmful non-target effects on beneficial insects, but using targeted insecticides and those with lower residual activity can mitigate these effects.

This strategy is most effective in open, outdoor spaces with natural habitat nearby, meaning it won’t work in highly controlled environments like greenhouses where there are few natural enemies to attract. The unpredictable nature of relying on a constantly changing environment also means that complete pest control is unlikely and some pests must be tolerated, making this strategy unreliable for high value ornamental crops where even low levels of damage have a significant impact on aesthetic value. Gardens, orchards, and outdoor nurseries, however, can benefit greatly from conservation biological control as an alternative to expensive and harmful insecticides. This method can also be used in conjunction with chemical management to provide a greater level of control with fewer sprays, though care must be taken not to harm natural enemies. This form of management has other benefits as well. Native flower plantings can be an attractive addition to a landscape, and many of the same floral resources which support natural enemies for biocontrol also support pollinators.

Augmentative Biological Control

In situations where natural enemies are not already present in high numbers, biocontrol agents can be introduced to the environment. In this strategy, known as augmentative biological control, natural enemies are commercially reared in labs or collected from the wild and made available to order. These beneficials include predators which directly feed on pests or parasitoids which lay eggs and develop inside of a host, eventually killing it – these are usually tiny, stingless wasps (Fig. 2).

This strategy works best indoors in controlled environments that prevent biocontrol agents from escaping or being affected by rain and temperature fluctuations. However, beneficials that don’t readily fly away and are more tolerant of adverse environmental conditions, like some lacewing larvae and predaceous mites, can be effective even in more open systems like high tunnels or open fields. Augmentative biocontrols are available even in turfgrass, where parasitic nematodes can be sprayed to control soil-dwelling beetle grubs.

Because this strategy gives growers a greater degree of control, it can be highly reliable and maintain nearly complete control of pests, preventing outbreaks. Augmentative biocontrol is employed extensively in commercial greenhouses across the state, where many growers rely on sachets of predaceous mites and parasitoid wasp releases more than chemical insecticides. However, with this level of control come some notable complexities:

• Choosing the right biocontrol agent is important when dealing with augmentative biocontrol, particularly when it comes to beneficials with a narrow range of prey. For example, while lacewing larvae feed on many pest species, many parasitoid wasps are host-specific and will only attack one or a few species of aphids, making accurate pest identification important. Also consider other traits of various biocontrol agents, such as cost, mobility, compatibility with chemicals and other natural enemies, and how long they will be effective in your growing environment.
   
• Handling & storage of live organisms can be tricky. Biocontrol agents are not likely to be effective if they’ve been left in a hot truck bed for many hours while waiting to be unloaded. Even if kept in ideal conditions, they won’t live nearly as long as you can keep a bottle of insecticides in a cabinet, so planning is crucial. Fortunately, you can work with biocontrol suppliers to schedule shipments in a predictable and timely manner.
   
• Regular releases are usually necessary to maintain a population of beneficials in the growing space. Because pest populations can explode in a matter of days and shipments can be slow to arrive, biocontrol is generally ineffective at dealing with outbreaks after they have occurred, but an active population of biocontrol agents can prevent outbreaks before they occur. This requires regular purchases which can drive up costs, though this cost may be worth the savings from fewer insecticide sprays. This need can be mitigated for some biocontrol agents using banker plant systems (Fig. 2), small habitats introduced into controlled environments to provide an alternate food source for beneficials, allowing them to live longer and reproduce.

• Seasonal inoculative biological control (SIBC) is another form of augmentative control which involves introduction of a natural enemy to an outdoor environment where it can sustain its own population, but not indefinitely. An example is the mealybug destroyer, a lady beetle that can be released in the spring to control mealybugs on citrus, but that is unable to overwinter in cold climates and must be released each growing season.

Conclusion

A common misconception among growers and horticulturalists is that biocontrol is unreliable or not cost-effective. In reality, it can be highly reliable if done correctly and is often more cost-effective than relying entirely on chemical management. However, it is also complex and requires careful consideration of each situation. The relevant plants, pests, beneficials, suppliers, handling logistics, release rates and schedules, temperature, humidity, and more can impact the success of a biocontrol program, but the most impactful factors in many cases are knowledge, experience, and commitment.

Additional Resources

• Xerces Society – Conservation Biological Control Resources

Some prominent biocontrol suppliers:

• Arbico Organics
• Biobest
• IPM Labs
• Koppert
• NJ Dept. of Agriculture

Ali Shokoohi, UMass Extension IPM Specialist

Additional Resources

• For detailed reports on growing conditions and pest activity – Check out the Landscape Message
• For professional turf managers - Check out our Turf Management Updates
• For commercial growers of greenhouse crops and flowers - Check out the New England Greenhouse Update website
• For pollinator interests - Check out the Pollinator Buzz and on Instagram
• For home gardeners and garden retailers - Check out our home lawn and garden resources
• TickTalk webinars - To view recordings of past webinars in this series, go to: https://ag.umass.edu/landscape/education-events/ticktalk-with-tickreport-webinars

Diagnostic Services

• Landscape and Turf Problem Diagnostics - The UMass Plant Diagnostic Lab is accepting plant disease, insect pest and invasive plant/weed samples. By mail is preferred, but clients who would like to hand-deliver samples may do so by leaving them in the bin marked "Diagnostic Lab Samples" near the back door of French Hall. The lab serves commercial landscape contractors, turf managers, arborists, nurseries and other green industry professionals. It provides woody plant and turf disease analysis, woody plant and turf insect identification, turfgrass identification, weed identification, and offers a report of pest management strategies that are research based, economically sound and environmentally appropriate for the situation. Accurate diagnosis for a turf or landscape problem can often eliminate or reduce the need for pesticide use. See our website for instructions on sample submission and for a sample submission form at http://ag.umass.edu/diagnostics.
• Soil and Plant Nutrient Testing - The lab is accepting orders for Routine Soil Analysis (including optional Organic Matter, Soluble Salts, and Nitrate testing), Particle Size Analysis, Pre-Sidedress Nitrate (PSNT), Total Sorbed Metals, and Soilless Media (no other types of soil analyses available at this time). Testing services are available to all. The lab provides test results and recommendations that lead to the wise and economical use of soils and soil amendments. For updates and order forms, visit the UMass Soil and Plant Nutrient Testing Laboratory web site.
• Tick Testing - The UMass Center for Agriculture, Food, and the Environment provides a list of potential tick identification and testing options at: https://ag.umass.edu/resources/tick-testing-resources.