Hort Notes 2023 Vol. 34:1

Join us for this virtual education program that will equip you with knowledge and skills you can implement in your management program for the upcoming season. Attendees can choose to attend either one day sessions, or the entire two-day program. Pesticide credits available for both days. 

LANDSCAPE TOPICS on DAY 1: Wednesday, MARCH 29, 2023 - 8:30 am to 12:00 pm

• 2022/2023 MA Update: Insect Pests of Trees & Shrubs
• If You Plant It, They Will Come: Troublesome Insect and Mite Pests of Annuals and Perennials in the Landscape. 
• Diseases of Trees and Shrubs: Predictions for the Upcoming Growing Season

TURF TOPICS on DAY 2: Thursday, MARCH 30, 2023 - 8:30 am to 12:00 pm

• Pre-Season Insect Pest Management Review: Old Foes, New Challenges
• Into the Weeds on the Group 4 Herbicides
• Below the Surface: Where Healthy Turf Meets Healthy Soil

For more details and to register, go to https://ag.umass.edu/landscape/events/spring-kickoff-for-landscapers-umass-extensions-landscape-education-days-0

Arbor Day (April 28) and Earth Day (April 22) are days to celebrate the importance of trees and to promote the benefits that trees provide for people and the environment. The MA Tree Wardens' and Foresters' Associaion Seedling Program celebrates Arbor Day / Earth Day by supplying bulk seedlings to promote the planting and caring for trees in Massachusetts.

Seedling purchasers include municipalities, garden clubs, private firms, arborists, and other interested individuals and organizations. Proceeds support annual scholarships for college arboriculture students. Seedlings offered for sale include both evergreen and deciduous trees and occasionally, large shrubs; species and prices vary from year to year based on nursery availability. Minimum order is 100 seedlings per species. Purchasers often distribute the seedlings in local schools, promoting Arbor Day or Earth Day, and tree planting in communities around the state.

The deadline to order is April 14, 2023, and seedlings must be delivered by May 6th in order to avoid damage from extreme temperatures during shipping.

For more details, including the seedling brochure and price list, go to https://masstreewardens.org/arbor-day-seedling-program

2023 will be the final year we offer this certificate program. Those who have taken some of the classes in this series in the past and still wish to earn the certificate of completion are advised to finish up any remaining classes in 2023.

While turf and landscape professionals might be very proficient in the development of a weed management program for turf and/or landscape, invasive plant management often reveals many new and unique challenges to these professionals. This 4-day program is intended to help participants meet these challenges when attempting to develop an invasive plant management program as part of their business. A certificate in Invasive Plant Management may be obtained by attending all four sessions and obtaining a passing grade on each. 

The four sessions are:

• Principles and Fundamentals of Weed Science (A1) - March 23, 2023
• State Regulations Pertaining to Invasive Plant Management (A2) - March 16, 2023
• The Invasive Plant Issue and Invasive Plant Identification (A3) - April 6, 2023
• Developing an Invasive Plant Management Program (B) - April 13, 2023

For more details, go to https://ag.umass.edu/landscape/education/invasive-plant-certification-program

To register, go to our Events calendar at https://ag.umass.edu/landscape/upcoming-events

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Septorioides Needle Blight

Septorioides needle blight has been an important disease of two-, three-, and five-needle pines in New England for over a decade. The disease is caused by the fungal pathogen Septorioides strobi, which was formally described only recently (Wyka and Broders 2016). Eastern white pine (Pinus strobus) is the primary host in southern New England. However, based on samples submitted to the UMass Plant Diagnostic Laboratory, additional hosts include Swiss stone pine (P. cembra), limber pine (P. flexilis), mugo pine (P. mugo), Austrian pine (P. nigra), ponderosa pine (P. ponderosa), red pine (P. resinosa), pitch pine (P. rigida), Scots pine (P. sylvestris), Japanese black pine (P. thunbergii), and red spruce (Picea rubens). Additional members of the Pinaceae may serve as hosts but infections are presumably uncommon. Symptoms and signs of the disease can be seen at https://ag.umass.edu/landscape/fact-sheets/septorioides-needle-blight

Septorioides is one of the primary pathogens responsible for white pine needle damage (WPND) in New England (Broders et al. 2015, Wyka et al. 2018). First documented in 2009, WPND is a chronic stress for eastern white pines throughout eastern North America. Symptoms of infection by Septorioides may first appear as a tip blight where the base of the needle remains green. Over time, entire needles become yellow-brown to brown and are prematurely shed from the canopy. Additionally, S. strobi is the most common needle blight pathogen found on P. strobus samples submitted to the UMass Plant Diagnostic Laboratory.

Many other soft (five-needle) and hard (two- and three-needle) pines frequently used as ornamentals can also serve as hosts (see host list above). In southern New England, infected trees appear scattered on the landscape and encompass all age classes. Like many needle blight fungi, S. strobi produces large volumes of spores that are blown and splashed to nearby branches and trees during wet weather. Climate studies have shown the northeastern U.S. is experiencing an increase in the frequency and amount of precipitation during the months of May, June and July, which is helping to fuel outbreaks of WPND (Wyka et al. 2017). The May–July period is when WPND pathogens, such as S. strobi, are most actively sporulating and older, diseased needles are shedding from the canopy. This coincides with the period of active needle and shoot development for many pines in the region. These immature needles are susceptible to infection during periods of wet weather or high humidity. Once infected, symptoms may take many months to develop and typically do not become conspicuous until the following spring, nearly one year after infection. 

Active management for any needle blight pathogen of conifers should focus on protecting the current year's foliage from becoming infected in the late spring and early summer. Pruning of heavily diseased branches, especially those in the lower canopy, and removal (or covering) of discarded needles can help to reduce disease pressure. Forest studies have shown a direct correlation between thinning density and needle blight severity. When diseased pines are provided more space, light and airflow, needle blight severity decreases.

Fungicides that should have some utility include azoxystrobin, benzovindiflupyr, copper hydroxide, mancozeb, metconazole, phosphites and thiophanate-methyl. Applications should be made on regular intervals from mid-May to early July as new needles are elongating. Even minor rain events may provide the necessary moisture for spore dispersal and germination. Needle blight fungi can have long latent periods before symptoms develop. Therefore, needles may be infected for many months before they become symptomatic. Symptoms from infection by Septorioides appear to develop more quickly, however, sometimes appearing during the summer and autumn after infection. Overall, much remains unknown about this pathogen and its association with eastern white pine. For more information on eastern white pine health, see https://ag.umass.edu/landscape/fact-sheets/dieback-of-eastern-white-pine

Citations:
Broders K., Munck I., Wyka S, Iriarte G., and Beaudoin E. 2015. Characterization of fungal pathogens associated with white pine needle damage (WPND) in Northeastern North America. Forests 6: 4088–4104.

Wyka S.A. and Broders K.D. 2016. The new family Septorioideaceae, within the Botryosphaeriales and Septorioides strobi as a new species associated with needle defoliation of Pinus strobus in the United States. Fungal Biology 120: 1030–1040.

Wyka S.A., Smith C., Munck I.A., Rock B.N., Ziniti B.L., and Broders K. 2017. Emergence of white pine needle damage in the northeastern United States is associated with changes in pathogen pressure in response to climate change. Global Change Biology 23: 394–405.

Wyka S.A. Munck I.A. Brazee N.J., and Broders K.D. 2018. Response of eastern white pine and associated foliar, canker and root rot pathogens to climate change. Forest Ecology and Management 423: 18–26.

Nicholas J. Brazee, UMass Extension Plant Pathologist

Q. This winter, my yard seems particularly hard hit by what I think are voles. A network of small paths has cropped up throughout the garden and I’ve spotted some small brown rodents with short tails scurrying around. A refresher on the critters and some management options would be helpful.

A. From your description, it certainly sounds as if you could have meadow voles (Microtus pennsylvanicus) inhabiting your yard. When observed, voles are sometimes mistaken for mice but are distinguished by their shortened tails and small ears. They can be anywhere from 5½ to 7½ inches long, with grey or brownish-yellow fur tipped with black, a greyish belly, and a bicolored tail.

While they can create underground nesting cavities, voles also find shelter in grassy or weedy areas, and mulch, leaf, or wood piles. Their telltale runways exist primarily at the soil surface under protective vegetative cover (or under snow, since they are active year-round). Voles are prolific reproducers: females typically have up to 5 litters a year, each litter generating an average of 3 to 6 young. Although the lifespan of voles is short (a maximum of 16 months is the norm), it’s not uncommon to see more voles periodically, as you’ve suggested, since they can cycle through population spikes every few years.

Voles have a wide-ranging herbivorous diet, including valuable lawn, ornamental, and edible plant material. Throughout the year (and especially in winter when food sources are less plentiful), they can damage garden shrubs and trees by gnawing bark at or just above ground level and causing girdling. With access, voles can attack crops growing under cover in greenhouses and cold frames and will chew seedlings and tender plants off at the base. In addition to above ground plant parts, bulbs, tubers, and roots are also susceptible to damage by voles, since they can tunnel underground and have been known to make use of existing tunnels made by moles (who do not preferentially eat plants). 

Gardeners are right to be wary of strategies purported to “control” voles, some of which have not been demonstrably effective, but can take steps to help manage populations and curb damage to landscape and garden plants:

• Remove potential habitat and cover for voles by mowing lawns regularly and keeping weedy, densely vegetated areas to a minimum, especially near gardens. Pull mulch away from the base of woody plants and frequently work over the mulch in landscape beds to keep voles from creating runways.
• Establish barriers around plants. Surround young trees and shrubs with hardware cloth cages loose enough to allow plant growth, tall enough (1½ to 2 feet) to work in snow cover, and set into the ground (to a depth of 6 inches if possible without damaging roots) to prevent voles from tunneling underneath. Fashion hardware cloth into barriers for the vegetable garden as well: staple it across the bottom when constructing new raised beds or retrofit older beds by wrapping it around the bed exterior to a depth of 6 inches or so (bend a few extra inches at the base of the cloth out at a 90 degree angle for additional protection). Use a similar wrapping treatment around the perimeter of greenhouses, hoop houses, and cold frames with vole intrusion issues. 
• Employ mouse snap traps in areas of high vole activity. Place traps in line with or at right angles to vole runways (with the snap end in the runway), baited with apple slices or peanut butter and oatmeal, or un-baited. Cover the trap to prevent children and pets from injury; cardboard boxes, small wooden clementine crates, and drainpipe sections make good covers.
• Only use commercially available rodenticides after becoming thoroughly familiar with product applications and evaluating the risks, e.g. the likelihood of pets and beneficial animals getting into the toxic bait or eating poisoned voles. Read and follow all label instructions.
• Consider using vole repellents, such as predator urine, capsaicin, and castor oil, as part of an integrated pest management plan — their effect tends to be short-lived. Various formulations are commercially available; follow label instructions, paying particular attention to whether or not products are approved for use around edible plants. 
• Welcome predators such as hawks and owls by providing perches and nest boxes. Regard predation not as a sole biocontrol — it’s had mixed results in research studies — but as one of many tools in a multi-pronged management approach.

For more information, visit:
Lanier, J. 2011. Vole damage to lawns, UMass Extension fact sheet

Njue, G. 2014. Preventing rodent damage in greenhouses, UMass Extension fact sheet

Highbush Blueberry Vertebrate Pests. NE Small Fruit Management Guide.

Preventing Rodent Damage to Overwintering Perennials, UMass Extension fact sheet

Jennifer Kujawski, Horticulturist

March is the month to . . . .

• March is a great time to prune. Prune young trees to develop good structure. For most trees, good structure includes a tree with a single central leader and a well defined system of scaffolds branches spaced evenly both horizontally and vertically on the trunk, with larger scaffolds at the base and gradually getting smaller toward the top. Remove or reduce branches greater than half the diameter of the trunk and remove or reduce branches creating competition with the leader. 
• Prune shrubs. Shrubs that produce new shoots at the base such as blueberry, elderberry, inkberry, spirea, viburnum and winterberry can be pruned annually to maintain vigor. Remove one or two of the oldest stems to promote sunlight into the base and promote new growth. 
• Force shoots of crabapple, flowering quince, forsythia, magnolia, peach, pussy willow and/or serviceberry. Place the cut shoots in a vase of water in a cool location; replace the water every couple of days. Shoots should flower in 1-3 weeks depending on the species. 
• The end of March is a good time to fix damaged turf before the grass resumes growth. Fix areas that were damaged by snow removal equipment. Use a landscape rake or leaf rake to fix areas damaged by voles and moles. A vigorous raking is helpful to remove turfgrass foliage that has become matted or damaged by snow molds.
• Beat the spring rush, do a soil test now to allow time for any needed amendments to take effect before the planting season begins. For info on how to take and submit a sample, see the UMass Soil and Plant Nutrient Testing Laboratory. The Routine Soil Analysis tests for pH, major and micro nutrients, and lead and provides recommendations based on what is being grown.
• Wet soils in late winter and early spring are particularly susceptible to being compacted. Compacted soils suffer poor drainage, poor water infiltration, impeded root growth and may become anaerobic, limiting plant growth. Prevent compaction by avoiding moving heavy equipment or materials over wet soils, or use sheets of plywood over wet soil to help distribute the weight. In areas with extended frequent travel or heavy equipment, use a 6-8” layer of arborist wood chips. 
• Don’t let winter annual weeds go to seed. Chickweed and bittercress can proliferate quickly if left uncontrolled.
• Start transplants indoors. March is a good time to start many annual vegetables and ornamentals inside. Use a sterilized seed starting mix to start seeds. Start seeds in small trays or pots and transplant into larger pots as they grow. When using supplemental light, set lights on a timer for 12-16 hours and keep the lights close to the foliage, about 6 inches above the tops of the plants. Vegetable transplants to start in March include spring brassicas (broccoli, cauliflower, cabbage, kale, etc), Swiss chard, lettuce, and other cool season crops. Ornamental annuals to start in March include ageratum, celosia, coleus, impatiens, and petunias. 
• Spring clean-up. Clean up perennial beds that may have been left to provide resources for wildlife, pollinators, and winter interest. Cut and remove old flowering stems and stalks. Ornamental grasses can be cut back as well. For sub shrubs like blue mist shrub, lavender, and Russian sage, wait until new growth is visible before pruning. 

Russell Norton, Horticulturist, Cape Cod Cooperative Extension

Being cool for millennia.

Deer ticks (Ixodes scapularis) have been surviving cold winters for thousands of years. One study estimates expansion into New Jersey around 50,000 years ago. With the northernmost population having survived the glacial maximum along the Mid-Atlantic region, they expanded outward into the Northeast. Winters up here are nothing new to them.

Winter: Just a part of life.

Deer ticks undergo a two-year life cycle from egg to adult. This means thriving in cold weather is just part of their natural development. Every spring, eggs are laid. These eggs hatch into larval ticks, which are active during the summer months. After feeding once on a small animal, these larvae molt into nymphs. These nymphal ticks will not feed for another 8 months or so. Instead, most will survive their first winter as unfed nymphs. Nymph emergence peaks around May and June. However, it’s not uncommon to find them much earlier. Significantly, nymphs pose the greatest risk to humans, being both small and capable of spreading many diseases. Like larvae, they will feed once before molting and will not feed again for several months.

The adult stage is the final stage. Adults become active in the fall of that year. They remain active into the following spring. This means this is the second time ticks will experience winter conditions. Unlike the nymphs, adults are active and searching for a large mammal. Generally, this means they are looking for deer, but a human, cat, or dog will suffice.

Any time temperatures are above 32°F, deer ticks can be active. However, they are a bit sluggish until you get around 40°F and up.

The cold never bothered them anyway.

Deer ticks have several adaptations and behaviors they use to tolerate cold temperatures. They synthesize an anti-freeze compound called glycerol. Glycerol lowers the temperature at which water inside the tick freezes. This mitigates lethal cold injury, even as ponds and lakes freeze over. Interestingly, Borrelia burgdoferi, the bacteria responsible for Lyme disease, is thought to use glycerol as a carbohydrate source for survival.

Deer ticks aren’t impervious to cold temperatures, though. If exposed to ~10-14°F or lower for a sustained period, they can die.

But, ticks have another trick up their sleeves. They will burrow under leaves and snow. Surprisingly, leaf and snow cover work very well as insulation. Don’t go by what the weather forecast says; you would need to know the local temperature underneath everything to see how ticks are impacted. Even if air temperatures drop to well below zero, temperatures could easily remain in the 20’s underneath leaves and snow. I would not expect that last cold spell to impact anything you do to prevent tick bites. Additionally, some data shared at the Annual meeting of the Society of Integrative and Comparative Biology suggests that deer ticks infected with Borrelia burgdoferi could be more resilient to winter temperatures.

Don’t adjust your thinking about ticks based on the weather!

Treat this time of year like any other time of year.

• Apply tick and flea prevention.
• Perform tick checks after going outside.
• Check your pets for ticks after they come indoors.
• Be cautious around piled leaves along yard edges and alongside trails.
• Clear away snow and leaves from your yard.
• Compromise: If looking to promote habitat by “leaving the leaves,” only clear leaves from the parts of your yard you expect to use often.

Blake Dinius, Plymouth County (MA) Entomologist

For details and registration options for these upcoming events, go to the UMass Extension Landscape, Nursery, and Urban Forestry Program Upcoming Events Page.

• 3/16/23 - State Regulations Pertaining to Invasive Plant Management (A2 of the Invasive Plant Certification Program)  
• 3/23/23 - Principles and Fundamentals of Weed Science (A1 of the Invasive Plant Certification Program)
• 3/29/23 - Spring Kick-off (virtual) - Landscape Topics
• 3/30/23 - Spring Kick-off (virtual) - TurfTopics
• 4/6/23 -   The Invasive Plant Issue and Invasive Plant Identification (A3 of the Invasive Plant Certification Program)
• 4/13/23 - Developing an Invasive Plant Management Program (B of the Invasive Plant Certification Program)

Pesticide Exam Preparation and Recertification Courses

These workshops are held virtually. Contact Natalia Clifton at nclifton@umass.edu or go to https://www.umass.edu/pested for more info.