Hort Notes 2024 Vol. 35:4

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

Click on the headings below to jump to that section of the newsletter.

 

Seeing Insect Pests or Suspected Insect Damage on Your Trees and Shrubs?

Check out UMass Extension's Professional Insect & Mite Management Guide for Woody Plants!

This newly revised and updated online guide is a resource for professional land managers, including but not limited to: landscapers; arborists; urban and community foresters; tree wardens; local, state, and federal land managers; groundskeepers; and any landscape practitioner who is managing the health of trees and shrubs.

This searchable online guide includes over 200 potential insect or mite pests of ornamental trees and shrubs. New insects and insect relatives will be added as additional information becomes available. NOTE: While this guide may be useful to professionals in much of New England, the content is Massachusetts-focused.

Find information on each insect/mite such as:

• Growing degree day ranges for pest activity
• Host plants
• Descriptions of the insect/mite and damage caused
• Monitoring tips
• Management options

UMass Extension wants to hear from you! Please complete this brief survey as you use our Professional Insect & Mite Management Guide for Woody Plants to provide us with valuable feedback. Your feedback will be used to prioritize updates to this resource now and in the future. 

Need additional help identifying an insect pest of a tree or shrub? Submit a sample to UMass Extension's Plant Diagnostic Lab.
 

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Nitrogen Fertilizer and Soil Acidity

Many soils in Massachusetts are naturally acidic (pH below 6.5).  This is because we receive a lot of rain and over time alkaline minerals (like calcite) have been lost from the soil into groundwater. Since acidic soil can stunt growth, reduce nutrient availability, and can increase damage from soil-borne disease, landscapers and gardeners need to manage soil acidity when growing plants.

A large majority of plants prefer a neutral pH (6.5 – 7.5). Limestone, and similar rock powders, are used to raise soil pH and promote healthy plant growth. However, surface-applied limestone is slow to penetrate into the soil and lime is commonly underapplied. While lime is an important tool for managing or preventing soil acidity, it is not the only one. Choosing nitrogen fertilizers can also have a substantial effect on soil acidity.

Nitrogen fertilizer comes in a variety of forms and can raise or lower the soil pH. In Massachusetts, we are mainly concerned with the fertilizers which acidify since it is uncommon for regional soils to become alkaline (pH higher than 7.5). 

Nitrogen fertilizer is typically applied in one of four forms (or their combination):

Nitrate (NO₃^–): Because nitrate is negatively charged, plant roots release hydroxide (OH^–) into the soil when they absorb nitrate. The hydroxide actually neutralizes free hydrogen ions (H+) and reduces soil acidity. While this can lead to excess alkalinity in controlled environments, it is not a common problem outdoors in New England because our soil has a tendency to return to its natural, moderately acidic state. 

Ammonium (NH₄⁺): In contrast to nitrate, ammonium has a positive charge and, when directly taken up by plants, results in the release of free hydrogen by plant roots. This is how plants stay electrically balanced, but it can acidify the soil. In real world conditions, however, chemical processes in the soil reduce the acidifying effect of ammonium. When temperatures are warm, bacteria in the soil convert ammonium to nitrate. While this conversion does produce free hydrogen (H+), the absorption of nitrate by plants also produces a hydroxide molecule (OH^–) and these ions react to make pH neutral water (H₂O). Unfortunately, because nitrate commonly leaches into groundwater, the average effect of ammonium fertilizers is an acidifying effect.

Urea (CO(NH₂)₂): Urea is quickly transformed into ammonium in the soil and therefore has a similar effect on soil acidity.

Organic Nitrogen (compost, composted manure, animal and plant byproducts): Most organic nitrogen sources contain both ammonium and nitrate but also a wide range of buffering molecules. These amendments make the soil more neutral regardless of the original pH and can be used easily on plants which prefer a neutral soil pH.

When fertilizers contain multiple forms of nitrogen, their effect on soil acidity will be in between the effects of the components.

Side Notes: Some phosphorus fertilizers can also have acidifying effects on the soil. However, this is less worrisome because generally much less phosphorus is applied compared to nitrogen. Sulfur fertilizer can be highly acidifying if applied beyond plant needs but does not acidify the soil when applied according to fertility requirements. Remember that some plants (especially New England natives) can thrive in acidic soils. For these plants, sulfur is a good tool for lowering pH.

Take Home Messages:

• Nitrate or organic nitrogen fertilizers are preferable, especially in cold or wet conditions if keeping a neutral pH is important for plant health.
• When using ammonium or urea fertilizers, extra care should be taken to avoid over-fertilization. Make sure to regularly test the pH of the root zone soil.
• Make sure to consider the effect on soil acidity when choosing a nitrogen fertilizer along with other nutrient needs, price, and ease of use.

Arthur Siller, UMass Extension Soil Health Educator

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Trouble Maker of the Month

Wet, Warm Weather Means Mosquitoes

Mosquitoes require three ingredients: warm temperatures, food (e.g. organic detritus), and standing water. 

While I don’t have a crystal ball, I can pull up historical data. As of now, 2024 is looking like a very wet year. Mosquitoes require very little water to complete their life cycle – only about the size of a bottle cap. Cryptic locations often make the perfect little mosquito condos. For instance, each rung of a corrugated gutter extension can serve as mosquito breeding environment. Heavier than average rainfall could mean water is accumulating in new spots around your property, however this is less likely in areas tha drain quickly.

As we move into July, temperatures will continue to warm. Increased temperatures mean increased risk in several ways. Like many insects, mosquito activity increases with warming temperatures. The mosquito life cycle also accelerates. It takes the principal vector of West Nile virus, Culex pipiens, ~29 days to go from egg to adult at 61°F but it only takes ~9 days at 82°F. In addition, the capacity to transmit disease is enhanced.

In other words, there will be more mosquitoes that are biting more often. And each bite carries more risk.

All said, there are several easy ways you can reduce mosquito bites:

• Wear EPA-registered repellents with the active ingredients DEET, picaridin, or IR3535. These are the same repellents that will also protect against tick bites. Be sure to follow the label instructions.
• Limit the time you spend outside at dawn and at dusk. Many mosquitoe species prefer these times of day.
• Citronella candles are of dubious effect, but running a fan can help.
• Wearing specific types of clothing can help. Mosquitoes can bite through clothing, but loose-fitting clothing could potentially distance the mosquito enough from your skin to reduce bites. Like many biting flies, they are also more attracted to dark colors.
• Tip out standing water at least once a week. Plant saucers, clogged gutters, bird baths, upturned wheelbarrows, and so on also make great mosquito breeding habitats.

Blake Dinius, Plymouth County (MA) Entomologist

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Q&A

Q.  Gardening guides and gurus always say “practice good sanitation” to manage plant diseases. What does this really mean?

A.  Good sanitation is critical for disease management in the garden and landscape. There are several important elements of good sanitation:

1. Remove dead plant debris. Many gardeners will leave plant debris in the garden to provide shelter for overwintering insects, but if diseased plants are present, debris from those plants should be removed. Most plant diseases are caused by fungi. Many of them survive the winter in infected plant material and resume their life cycles in the spring, producing spores that are splashed by rain or blown by wind onto host plants. Removing the infected plant material before the spring warm-up removes this source of spores. Diseased plant material should not be composted but may be buried, burned, or disposed of in the trash.
2. Control weeds. Weeds compete with landscape and garden plants for nutrients, sunlight, and water. Common weeds are susceptible to some plant diseases and can act as reservoirs for the organisms that cause them. Abundant weeds can also increase humidity, creating favorable conditions for disease development. 
3. Control insect pests. Feeding by pests can stress plants and cause wounds that make them more susceptible to disease. Some insect pests can carry and spread diseases as well. 
4. Pruning and spacing. Proper pruning and spacing of plants increases air circulation, which decreases the humidity in the plant canopy and facilitates drying of foliage after irrigation or rain. Dead or diseased limbs should be removed from trees and shrubs. For more information on pruning, please see our UMass Extension fact sheets.
5. Disinfect tools, hands, and pots. Some disease-causing organisms can be spread mechanically. Disinfect pruners between cuts with 70% ethanol or isopropyl alcohol. Wash hands frequently with soap and warm water. If pots are to be re-used, wash them thoroughly to remove all potting media before soaking them for 30 minutes in 10% bleach. 

Angela Madeiras, UMass Extension Plant Pathologist

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Garden Clippings Tips of the Month

June is the month to . . . .

• Deadhead spring flowering bulbs and perennials as flowers fade. Deadheading is the removal of flowers from plants when they have faded or died. Most flowers lose their attraction as they fade. Removing faded or dead flowers from the plant can promote new growth and keep plants looking attractive and encourage more blooms. Flowers that go to seed consume large amounts of a plant’s energy, diverting it from vegetative growth. Regular deadheading directs energy into stronger growth and more flowers. Leave bulb foliage until it turns brown to maximize the amount of photosynthesis and therefore the amount of food stored in the bulb for next year's flowers. The more food is stored, the better the blooms will be.

• Direct seed summer vegetables. Seeds of summer vegetables such as beans, corn, squash, cucumber, okra, carrots and beets can be directly sown in the garden in early June after the danger of frost is past. Before planting, make sure you prepare the soil well and incorporate compost or manure by tilling it in 6 to 8 inches deep. Compost or manure improves the soil structure and adds some nutrients to the soil. However, they don’t supply sualy supply sufficient nutrients to support healthy vegetable crops or garden plants. Apply an additional organic or slow release fertilizer to ensure your vegetable crops have the nutrients they need for optimal growth.

• Plant annuals and perennials. Plant late summer or fall flowering perennials in the spring and spring-flowering perennials in late summer or early fall. Examine plants prior to purchasing for signs and symptoms of disease or insects. For perennials, check for roots that emerge from the bottom of the pot, which can indicate a root-bound plant. Before planting, amend sandy soils with well decomposed organic materials such as compost.  Incorporate this into the soil 10-12 inches deep. It is best to amend the entire planting area rather than just a single planting hole. Make sure root balls are well watered before planting. Never plant a dry root ball. 

• Thin seedlings as needed before plants start to crowd each other. Seeds of root crops such as beets, radish, and carrots are sown thickly in rows and thinned later to the desired stand to allow them to develop properly. Root crops such as carrots, beets, and radishes are thinned to a 2-inch spacing to allow the roots to develop properly. 

• Complete pruning of spring flowering shrubs. Shrubs such forsythia, viburnum, honeysuckle, lilac, azalea and rhododendrons are generally pruned soon after flowering. Spring flowering shrubs form their flower buds in mid- to late summer and flower the following spring on one-year old shoots. Pruning them after they have bloomed encourages formation of new flower buds for next season. 

• Be on the lookout for lacebugs on azaleas. Look for dark, black, tar-like spots of excrement deposited by immature and adult lacebugs on the underside of plant leaves. Lacebug damage on azaleas appears as white-yellow stippling on the upper surface of host plant leaves, with the insects being noticeable on the underside of the leaves. Use products labeled for control of lacebugs and be sure to read and follow the label directions.

• Mulch flower beds as needed. If the beds already have mulch from last year, a thin 1-inch top dressing with new mulch is adequate. For new beds, spread 2-3 inches of mulch and be careful not to spread mulch over crowns of perennial plants. Organic mulch such as ground bark, ground wood chips or shredded leaves can provide benefits such as weed suppression, conserve soil moisture, reduce soil temperature, add organic matter, and enhance the appearance of landscape beds.

• Water the lawn as needed. Avoid excessive watering of the lawn. Allow the soil to dry slightly before watering. This will enable the turf to develop a deeper root system which will make the turf more drought resistant in the summer. Deep watering less often is more effective than frequent shallow watering. Water approximately 1.0 to 1.5 inches per week as needed throughout the season.

• Mow lawns frequently but do not remove more than 1/3 of the total height when mowing. There is no need to remove clippings unless they become excessive.

• Thin excess fruits. Thin fruits from overloaded trees to leave fruits spaced at a hand’s width apart. After natural fruit drop of apples, pears and peaches occurs, thin excess fruits by hand. Thinning fruits helps the trees produce larger and healthier fruits at harvest time. Thinning also reduces total fruit load on the branches and prevents breakage. 

• Weed the garden. Weeds compete with plants for nutrients and moisture. Do not ignore weeds until they get out of control but control them early, which will be more effective and will take less time and effort. 

• Start regular scouting for insect pests and diseases. Starting to scout early for insect pests and diseases and taking appropriate control measures will help limit the damage to plants. Scouting involves observing plants regularly, looking at all parts of the plant including tops and undersides of leaves and at the soil line. You may need a hand lens to see some insects and signs of a disease. Before taking control measures, determine whether the damage is due to an insect pest, disease or cultural problem.

• Don't forget to get a soil test! Our Routine Soil Analysis tests for pH, major and micro nutrients, lead, and cation exchange capacity and provides crop-specific lime and nutrient recommendations. The UMass Soil and Plant Nutrient Testing Lab's website has order forms and info on how to take and send a sample.

Geoffrey Njue, UMass Extension Sustainable Landscapes Specialist

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Understanding Herbicide Modes of Action (MOA) for Better Weed Management

There are several important factors that play a role in the development and implementation of a successful weed management program. Landscape and turf professionals should have a strong understanding of weed identification, appropriate cultural practices, and herbicide selection, including rate and timing of applications. Additionally, an understanding of herbicide modes of action (MOA) can move weed management programs to the next level.

Plants are complex organisms with well-defined structures in which many vital processes take place in well-ordered and integrated sequences. Plants are made up of organs (root, stem, leaf, and flower); organs consist of tissues (meristems, conducting, photosynthetic, structural); and tissues are made up of cells. Plant cells contain subunits including walls, membrane systems (golgi, plasma membrane, nuclear membrane, endoplasmic reticulum) and organelles (mitochondria, nucleus, chloroplasts), as well as undifferentiated cytoplasm. Some vital metabolic plant processes include photosynthesis (capture of light energy and carbohydrate synthesis), amino acid and protein synthesis, fat (lipid) synthesis, pigment synthesis, nucleic acid synthesis (RNA - DNA essential to information storage and transfer), respiration (oxidation of carbohydrate to provide CO₂ and usable energy), energy transfer (nucleic acids) and maintenance of membrane integrity. Other vital processes include growth and differentiation, mitosis (cell division) in plant meristems, meiosis (division resulting in gamete and seed formation), uptake of ions and molecules, translocation of ions and molecules, and transpiration. One or more of thesrs vital processes must be disrupted for an herbicide to kill a weed.

What is “Mode of Action?” Mode of action (MOA) is the way in which the herbicide controls susceptible plants. It describes the biological process or enzyme in the plant that the herbicide interrupts which directly affects normal plant growth and development. Mode of action can also describe the injury symptoms seen on susceptible plants. Some modes of action are comprised of more than one chemical family, which vary slightly in their chemical composition but still control susceptible plants in the same way and cause similar injury symptoms. Herbicides can also be classified by their “site of action,” or the specific biochemical site that is affected by the herbicide. The site of action is a more precise description of the herbicide’s activity; however, the terms “site of action” and “mode of action” are often used interchangeably to describe different groups of herbicides.

The Weed Science Society of America (WSSA) groups herbicides by their mode of action with a number. This number can be seen on the first page of a product label. Examples are shown below of the labels of Sedgehammer^TM (Figure 1), Barricade 4FL^TM (Figure 2), and Lontrel Turf and Ornamental^TM (Figure 3), which belong to WSSA modes of action groups 2, 3 and 4, respectively.

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While herbicides labelled for weed management in landscape and turf settings fall into different mode of action groups, just a few groups contain most herbicides that a landscape and turf professional will utilize. The most common mode of action groups used is the green industry are Groups 1, 2, 3, 4, 9 and 14. Key characteristics of each group are shown in Table 1.

Table 1. Characteristics of some WSSA MOA groups used in landscape and turf.
WSSA GROUP	Mode of Action	Mode of Action Description	Landscape and Turf Herbicide Examples
1. ACCase inhibitors	acetyl CoA carboxylase (ACCase) inhibitor	Inhibition of the enzyme acetyl-CoA carboxylase (ACCase), the enzyme catalyzing the first committed step in de novo fatty acid synthesis, inhibition of fatty acid synthesis blocks the production of phospholipids used in building new membranes required for cell growth, broadleaf plants naturally tolerant because of an insensitive ACCase enzyme, natural tolerance of some grasses appears to be due to a less sensitive ACCase.	Acclaim Extra (fenoxaprop-p-ethyl) Envoy Plus (clethodim) Tapout (clethodim) Clethodim 2EC clethodim) Segment II (sethoxydim) Fusilade II T&O (fluazifop-P-butyl)
2. branched-chain amino acid inhibitors	acetolactate synthase (ALS) or acetohydroxy acid synthase (AHAS) inhibitor	Inhibit of acetolactate synthase (ALS), also called acetohydroxyacid synthase (AHAS), a key enzyme in the biosynthesis of the branched-chain amino acids isoleucine, leucine, and valine.	Sedgehammer (halosulfuron-methyl) ProSedge (halosulfuron-methyl) Vexis (pyrimisulfan) Arkon (pyrimisulfan) Celero (imazosulfuron) Velocity PM (bispyribac-sodium)
3. mitosis inhibitors	tubulin protein inhibitor	Binds to tubulin, the major microtubule protein. herbicide-tubulin complex inhibits polymerization of microtubules leading to a loss of microtubule structure and function, microtube spindle apparatus is absent preventing the alignment and separation of chromosomes during mitosis and the cell plate cannot form.	Dimension 2EW (dithiopyr) Dimension Ultra 40WP (dithiopyr) Dithiopyr 40 WSB (dithiopyr) Pendulum Aquacap (pendimethalin) LESCO PRE-M (pendimethalin) Barricade 4FL (prodiamine) LESCO Stonewall 4L (prodiamine) Primera One Prodiamine 4L (prodiamine)
4. synthetic auxins	endogenous auxin (IAA) mimic	Act similar to endogenous auxin (IAA), primary action cell wall plasticity and nucleic acid metabolism by acidifying the cell wall by stimulating the activity of a membrane-bound ATPase proton pump, reduction in apoplasmic pH induces cell elongation by increasing the activity of enzymes responsible for cell wall loosening, in low concentrations of auxin-mimicking herbicides also stimulate RNA polymerase, resulting in subsequent increases in RNA, DNA, and protein biosynthesis, abnormal increases in these processes lead to uncontrolled cell division and growth which results in vascular tissue destruction, in high concentrations inhibit cell division and growth in meristematic regions that accumulate photosynthate assimilates and herbicide from the phloem, auxin-mimicking herbicides stimulate ethylene evolution produce the characteristic epinastic symptoms (twisting, curling and cupping of leaves and stems).	Trimec Classic (2,4-D + MCPP + dicamba) Triplet SF (2,4-D + MCPP + dicamba) TZone SE (triclopyr + sulfentrazone + 2,4-D + dicamba) Lontrel (clopyralid) Turflon Ester Ultra (triclopyr) Vanquish (dicamba) On Deck (2,4-D +dicamba) Diablo (dicamba) Millennium Ultra 2 (2,4-D + clopyralid + dicamba) Q4 Plus (2,4-D + dicamba + quinclorac + sulfentrazone) Q-Ball (quinclorac) Quin-Way 1.5L (quinclorac) Mecomec 4 (MCPP) Garlon 3A (triclopyr) Garlon 4 (triclopyr)
9. amino acid synthesis inhibitors	enolpyruvyl shikimate-3-phosphate (EPSP) synthase inhibitor	Inhibition of 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase which produces EPSP from shikimate-3-phosphate and phosphoenolpyruvate in the shikimic acid pathway, EPSP inhibition leads to depletion of the aromatic amino acids (tryptophan, tyrosine, phenylalanine) that are required for protein synthesis or for biosynthetic pathways leading to growth.	glyphosate formulations (Roundup Pro, Roundup Custom for Aquatic & Terrestrial Use, Lesco Prosecutor Pro, Rodeo, Makaze, Ranger Pro, AquaNeat)
14. PPG oxidase or Protox inhibitors	protoporphyrinogen oxidase (PPG oxidase or Protox) inhibitor	Inhibition of protoporphyrinogen oxidase (PPG oxidase or Protox) an enzyme of chlorophyll and heme biosynthesis catalyzing the oxidation of protoporphyrinogen IX (PPGIX) to protoporphyrin IX (PPIX), Protox inhibition leads to accumulation of PPIX, the first light-absorbing chlorophyll precursor, PPGIX accumulation apparently is transitory as it overflows its normal environment in the thylakoid membrane and oxidizes to PPIX. PPIX formed outside its native environment is separated from Mg chelatase and other pathway enzymes that normally prevent accumulation of PPIX, light absorption by PPIX apparently produces triplet state PPIX which interacts with ground state oxygen to form singlet oxygen, triplet PPIX and singlet oxygen can abstract hydrogen from unsaturated lipids, producing a lipid radical and initiating a chain reaction of lipid peroxidation, lipids and proteins are attacked and oxidized resulting in loss of chlorophyll and carotenoids and leaky membranes which allows cells and cell organelles to dry and disintegrate rapidly.	Quicksilver T&O (carfentrazone) Powerzone (carfentrazone + dicamba + MCPA + MCPP) Speedzone (carfentrazone + 2,4-D + dicamba + MCPP) Dismiss (sulfentrazone) Dismiss NXT (carfentrazone + sulfentrazone) Momentum 4-Score (fluroxypyr + triclopyr + sulfentrazone + 2,4-D) TZone SE Broadleaf Herbicide for Tough Weeds (triclopyr + sulfentrazone + 2,4-D + dicamba)

 

In summary, an awareness of herbicide modes of action can improve your weed management programs. Additionally, knowledge of mode of actions plays an important role in preventing herbicide resistance. The rotation of herbicide modes of action is an important strategy for the prevention of herbicide resistance. Modes of action shown on the first page of a product label will assist those developing a weed management program with herbicide selection. For an overview of herbicide resistance, review “Herbicide Resistance: An Emerging Issue in Weed Science” in the May 2024 issue of Hort Notes.

Randy Prostak, University of Massachusetts Extension Weed Specialist

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Upcoming Events

For upcoming educational prgrams, go to the UMass Extension Landscape, Nursery, and Urban Forestry Program Upcoming Events Page.

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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 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

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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.