Yard & Garden Line News Volume 8 Number 17                                                               November 1, 2006

Features this issue: Pigments of Fall Color Body Lice Settling In For Winter Without Plant Pathogens Garden Calendar Editorial Notes

Pigments of Fall Color
David C. Zlesak, Regional Extension Educator, Horticulture

Sugar maples produce golden-yellow fall color Carotenoid plus anthocyanin pigments together in one plant make an especially dramatic display on this sumac. Rose hips such as on this 'Angel Rose Mixed' polyantha rose seedling are rich in anthocyanin and persist on plants well into winter. Burning bush showing darkest red color on the upper right side, the side which gets the most sun.

American beauty berry (Callicarpa americana) produces dramatic purple fall fruit. 'Summer Wine' ninebark (Physocarpus opulifolius) has season long purple foliage. Sometimes the cause of variegated foliage  is a carotenoid mutation rather than the inability to synthesize chlorophyll.

All Photos: David Zlesak

Brilliantly colored leaves and fruit transform the fall landscape into enchanting scenes and is a hallmark of Minnesota and other Northern-tiered states. Heightened interest in plants and nature in the fall is evident as many take advantage of the opportunity to enjoy autumn camping, drives, and hikes and participate in seasonal artistic crafts and activities. As the window of peak fall color moves across the state, the details of when and for how long it will last each year is largely uncertain. Factors such as wind, temperature, and precipitation all influence how long we have to enjoy the fall display and motivates many of us to rearrange our schedules to make sure we do not miss the magnificent show. Changing colors signal timely biochemical responses as plants move their nutrient resources to prepare for the upcoming winter and make their fruit more appealing to hungry critters that will inadvertently transport seeds to other locations.

The colors we see in the foliage and fruit of plants are primarily influenced by three pigments- chlorophyll, carotenoids, and anthocyanins. Chlorophyll gives plants their green color and traps light energy so it can be stored in a chemical form through the process of photosynthesis. Chlorophyll is fat soluble and found within specialized lipid-containing structures called chloroplasts. Chlorophyll primarily absorbs blue and red light (grow lights help fuel photosynthesis and appear purple because they are rich in red and blue light). Carotenoids are accessory pigments to chlorophyll and help channel light energy to chlorophyll for photosynthesis and are typically yellow to orange in color. Carotenoids are found in chloroplasts with chlorophyll and in similar structures lacking chlorophyll called chromoplasts. Carotenoids help make more of the light spectrum (besides red and blue light) useful for photosynthesis and also help to protect chlorophyll molecules from being damaged by intense light. Chlorophyll is a relatively short-lived molecule, and throughout the growing season it continually degrades and new chlorophyll is synthesized to replace it. Carotenoids are critical to help extend the life of chlorophyll molecules.

Perennial plants adapted to our climate respond to primarily decreasing temperatures and shortening days (detected by plants as lengthening nights) to trigger the onset of dormancy. Nutrients within foliage of deciduous plants can be retained by the plant by reabsorbing and transporting it to overwintering structures (i.e. stems and roots). Synthesis of new chlorophyll to replace what has been degraded slows and less and less chlorophyll is found within the leaf. The colors of other pigments, once masked by the green color of chlorophyll, become evident. Carotenoid pigments provide the brilliant yellow and gold colors as typically found in foliage of aspen, ginko, and some maples.

Anthocyanins are another group of plant pigments and are made up of a molecule called anthocyanidin joined with one or more sugar molecules. Unlike chlorophyll and carotenoids, anthocyanins are water soluble and found within the water containing vacuole of plant cells. Anthocyanins typically appear as pink, red, scarlet, or purple. Anthocyanins share a common 15 carbon chemical structure. Many different anthocyanins with slightly different colors and other properties can be generated according to which carbon position sugars and hydroxyl groups are attached. Some anthocyanins such as delphinin typically produce colors more in shades of purple and blue, while other anthocyanins tend to be pink or red. In addition to sugar availability within the plant, other factors such as pH, metal ions, and temperature can influence how light interacts with anthocyanins and the final color we see. For instance, flower color of some plants like bigleaf hydgrangea can be manipulated by changing soil pH and manipulating metal ions such as aluminum.

Anthocyanins absorb strongly in the ultra violet (UV) spectrum and act as antioxidants protecting cells from direct UV damage and damage from free radicals. DNA, in particular, can be damaged by the high energy in UV light and anthocyanins help plants by serving as a natural sunscreen. Some plants have red-tinted young growth rich in anthocyanins to especially protect young, sensitive tissue. In addition, leaves growing under higher light levels often have more anthocyanin pigment than leaves in more shaded locations. This is commonly seen in fall where leaves deeper within the canopy appear lighter red than those at the top of the canopy. Another example is burning bush (Euonymus alata), a shrub well-known for its brilliant red fall color. Plants growing in more shaded locations tend to have less anthocyanin and appear florescent pink, while those in full sun have more and are burning red.

Some plant species naturally produce more anthocyanins than others and variants within some species have been selected which produce elevated levels of anthocyanin all season. Such plants typically appear deep purple during the growing season from a combination of anthocyanin and green chlorophyll. 'Purple Palace' coral bells, 'Chocolate' white snakeroot, 'Crimson Frost' birch, DiabloTM ninebark, and 'Crimson King' Norway maple are examples of plants with anthocyanin-rich, purple foliage throughout the growing season.

Anthocyanin production tends to increase in the fall to help protect leaves as degradation of cellular components and reabsorption of nutrients occurs. As cellular components are degraded, free radicals can be generated and anthocyanins help protect cells from damage. In addition, anthocyanins are beneficial to human health as an antioxidant protecting cells from free radicals as well and helping to prevent cancer. Many doctors advocate diets including antioxidant supplements and antioxidant-rich foods such as red cabbage and deeply pigmented fruits like cranberries, blueberries, and blackberries.

Fall anthocyanin accumulation can be unpredictable and varies from year to year. This is due to variation in such things as sugar levels in plants, amount of cloudy versus sunny weather, temperatures (cooler temps often favor anthocyanin production), and general plant health. Anthocyanin production can also be stimulated when plants are under stress. For instance in years where there has been drought going into fall, plants often color sooner and their color can be more intense. Carotenoid pigments on the other hand, are present at more consistent levels throughout the growing season and provide more consistency in fall color than anthocyanins.

Additional Notes: Many ornamental plant cultivars possess variegated foliage and origin of the variegation is frequently just a chance mutation within a particular cell layer of the growing point leading to reduced chlorophyll. With such cell layer mutations, at least one cell layer produces normal green leaf regions and at least one cell layer produces white regions in the leaf which is low in or lacking chlorophyll. Often the white region of the leaf is caused by cells not producing enough carotenoids rather than lacking the ability to synthesize chlorophyll. Without sufficient carotenoids to protect chlorophyll, chlorophyll is degraded quickly and such tissue can appear white or cream colored. In addition, plants which have uniformly colored, golden-green foliage may also be due to reduced carotenoid presence or function.

Hardening off tender plants grown under low light indoors before planting outside is important. By exposing plants gradually to increased light levels, wind, and temperature extremes, damage from sunscorch and dehydration can be minimized. During the hardening-off period carotenoid and anthocyanin pigments can be synthesized to help protect chlorophyll and other light sensitive components in plant cells.

Body Lice
Jeffrey Hahn, Assist. Extension Entomologist

Body louse. Photo: CDC

There have been some questions lately about body lice, Pediculus humanus humanus. This insect is considered a rare problem in the U.S., generally restricted in this country to homeless and transient people that are unable to shower or bath on a regular basis or have access to clean changes of clothes.

However, in less developed areas of the world, body lice can still be a problem. In one phone call received recently, body lice were associated with a visit to another country. Historically, body lice have been associated with overcrowding and unsanitary conditions, such as natural disasters and war.

A body louse measures about 1/12 - 1/6 inch long, about the size of a sesame seed. It has a flattened, light colored, bulb-like shaped body. The eggs are whitish or cream-colored and are very small, measuring about 1/16th inch long. Eggs are laid in folds and creases of clothing and bedding. It can take eggs up to 30 days to hatch.

Head lice, Pediculus humanus capitis, are very similar in appearance to body lice but are a little smaller. The best way to distinguish between these two lice species is where you find them. Head lice are found on heads, living and feeding on the scalp while body lice are typically found in creases and folds of clothes, moving to the bodies of humans just when they want to feed. Although they do not live on the human body all of the time, they do need to keep in close contact with their hosts and do not survive if they are off humans for longer than a week to 10 days.

The bites from body lice are usually very irritating causing people to itch a lot. They can occur anywhere on the body, although rarely on hair. The site of the bite is usually red and rash-like. If an individual is bitten repeatedly, they can become desensitized to the body lice and will not notice them much. Body lice are known to transmit diseases, like typhus, although the incidence of these problems have considerably decreased as body lice populations have gone down.

Unlike bed bugs, body lice are not a pest control issue but a medical problem, making it unnecessary to spray the premises with insecticides. If you need to eliminate body lice, it is a two pronged attack.

First, it is important to launder any clothes you have been wearing or any bedding you have been laying on in hot water and dried on a hot temperature (as hot as the fabric will allow). Cold temperatures will also kill body lice. The exact thresholds have not been researched, although temperatures in the 20ºF's and colder for a couple of days should be sufficient to kill them.

At the same time you are cleaning clothes and sheets, you need to eliminate the body lice from your body. The only necessary steps you need to take is a hot shower, using plenty of soap. If desired, you can also apply a shampoo or lotion labeled for lice (permethrin or pyrethrins) to your body to eliminate these insects. Follow all labels directions exactly.

As long as your remove the lice from your body and wear clean, uninfested clothes, you should be able to fairly easily eliminate a body louse infestation.

Get the low down on this month's insect pests at Insects
http://www.extension.umn.edu/yardandgarden/EntWeb/Ent.htm

Settling in for winter without plant pathogens
Michelle Grabowski, Regional Extension Educator, Horticulture

Black oblong structures inside this tomato stem are sclerotia from the white mold pathogen Sclerotinia sclerotiorum. They can survive years in soil and on plant debris. Small black spots on this powdery mildew infected leaf are cleistothecia, reproductive structures that survive the winter and release spores in spring.

As your garden plants are settling down and going dormant for the winter months so are many of the pathogens that cause plant disease in our gardens. Plant pathogens, which include fungi, bacteria, viruses, and nematodes, survive the winter in a variety of ways. Some pathogens, like bacteria, viruses and some fungi, survive in live tissue like perennial stems or inside dormant leaf buds. These pathogens can be very difficult to get rid of. Many fungi survive in a dormant state on plant debris or in garden soil as reproductive spores or dormant mycelium. These structures are capable of surviving cold temperatures and several months without a host plant. Some fungi form hard resting structures called sclertotia capable of surviving a wide range of temperatures and years without a host plant to infect!

Black spots on this tar spot infected maple leaf are fungal stromata, fruiting bodies, that will open and release spores in spring. Photos: Michelle Grablowski

Although it is impossible to completely free a garden of plant pathogens, some basic fall garden clean up can greatly reduce the number of pathogens surviving from one year to the next. Plant pathogens survive very well on plant tissue they have already infected. As infected leaves and green stems die back for the year, the fungi that caused leaf spots, rots and other problems either go dormant or remain active feeding on plant debris. When the weather becomes favorable the following spring, these fungi resume full activity and infect the next year's shoots and leaves. To break this cycle, cut back and remove the stems and leaves from any herbaceous perennial that suffered from disease problems this year. Annuals with disease problems can be completely removed from the garden. Leaves from trees suffering from leaf spot diseases can be raked up and collected.

Infected plant material can be composted in a backyard compost pile if the compost actually heats up to 160°F. Since this is difficult to achieve in a backyard compost pile, another option is to take the infected leaves and stems to a municipal compost or yard waste disposal site. Do not leave infected plant material near the garden, because pathogens can easily move back into the garden through wind, rain, or garden maintenance activities.

Many plant pathogens can survive on garden stakes and trellises. These can be cleaned with a 10% bleach solution as they are being put away for the winter or anytime before they are placed into the garden the following spring. Clean garden tools in the same way. Bleach can be very corrosive to metal, so a household disinfectant like Lysol can be used to clean metal tools.

Contributors: Nancy Rose Patrick Weicherding Bob Mugaas David Zlesak

Flowers, Fruit and Vegetables:

Calamagrostis xaucutiflora 'Karl Foerster'

Mulch flower beds as the ground freezes. Remember, you are mulching to keep the ground uniformly cool in spring. Soil heaving as the frost leaves the ground damages plant roots.

Mulch strawberry beds now, also.

Check house plants for signs of insects. Washing foliage will help dislodge them and remove any dust or soil. Don't wash fuzzy-leaved plants such as African violets. Do not use "leaf shine", buttermilk, mayonnaise on leaves. These substances clog the stomata (openings mostly on the undersides of the leaves) through which plants breathe. (Click on http://isotope.bti.cornell.edu/intro/story.html for a photo of tomato stomata and an interesting article on water movement in plants.) While many plants have stomata primarily on the undersides of the leaves, according to Botany For Gardeners, plants with upright leaves, like iris, have equal numbers of stomata on either side of the leaves. Aquatic plants, like water lilies, have stomata on the upper sides of the leaves.

Your bulbs should be planted. Tulips are the only bulbs you can still plant outside. Any other as yet unplanted bulbs should be potted and forced. See last month's garden journal for links.

Trees and Shrubs

Wrapped crabapple tree. Photos: Beth Jarvis

Continue watering all trees and shrubs until the ground freezes.

If you haven't provided winter protection for tender-barked trees, there's still time. Paper wrap is not very effective so use something that shades the south-southwest side of the tree. One possibility is to use flexible plastic tubing large enough to allow air circulation around the trunk.

Wrapping coniferous shrubs in burlap does help reduce desiccation that occurs when wind blows away the moisture layer surrounding the foliage. Conifers, AKA "evergreens" become everbrowns when the ground is frozen and their roots can no longer draw up the water to replace that lost to the winds. Screening coniferous trees and shrubs is also recommended to reduce moisture loss as well as winter burn. Winter burn occurs when sunlight reflects off the snow and injures the foliage. A V-shaped screen is can be put on the NW side to reduce desiccationtion or on the southwest side to reduce winter burn.

Lawns

There's probably still time for a late fall fertilization. You can apply fertilizer as late as the first week of November providing the ground is thaw and you can water the lawn after applying the fertilizer.

Dormant seeding can be done in early November before the ground freezes. To do this successfully, you need to be ablele to work up the soil surface to get seed into the soil. The idea is to plant it now so it will be ready to sprout in the spring. This is a gamble. If November turns wet and warm, the seed may sprout and die and you'll be replanting in the spring.

Editorial Notes

Tree lilac and spirea Photo: Beth Jarvis

The golden seed heads of the tree lilac pair nicely with the golden and russet of the spirea in this parking lot planting at the Arboretum.

Summer has gone much too quickly. The miserably hot days have been replaced with "November temperatures in October", per the TV weather people. I shudder to think which month's weather we'll get in November.

I'm completing an article on the hardy woody plants project. In an upcoming issue, we'll have an article by Nancy Rose on the trees of the family Fabaceae (bean trees). Bob Mugaas will be reviewing the latest on the corn gluten meal. I'm trying to find a Soils grad student to write about freezing and soil. It occurred to me that we make a lot of recommendations based on assumptions and what we were taught. Most horticulturists have had at best, two Soils classes and those dealt with soil fertility rather than thinking much about cold weather and soil.

Please feel free to cut and paste any of the articles for use in your own newsletters. All we ask is that you give our authors credit.

Back issues Yard & Garden Line News are on the Yard & Garden Line home page at www.extension.umn.edu/yardandgarden/.

Deb Brown will be answering a few gardening questions with Cathy Wurzer on MPR, the first Friday of the month during the fall and winter, between 8:30 and 9:00 a.m. Then in spring, she'll be back at her regular schedule, 10 a.m. the first Friday of each month. The program is broadcast on KNOW 91.1 FM, and available state-wide on the MPR news radio stations. (Scroll down for map.)

For plant and insect questions, visit http://www.extension.umn.edu/askmg. Thousands of questions have been answered, so try the search option in the black bar at the top left of the board for the fastest answer.

If you would like to receive an e-mail reminder when the next issue of the Yard & Garden Line News is posted to the web, just send an e-mail to: listserv@lists.umn.edu (note: the second E in listserve is omitted), leave the subject line blank, then in the body of the message, type: sub yglnewslist or to unsubscribe, enter: unsub yglnewslist

Happy gardening!

Beth Jarvis
Yard & Garden Line Project Coordinator


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