Northeast - Winter 2021

Marcia Mathews, Singh, Raghuwinder, Strahan, Ronald E., Fontenot, Kathryn, Kirk-Ballard, Heather

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Fall Is the Time to Plant Trees


Here in the ArkLaMiss, winter months are the perfect time to install trees and shrubs into your landscape so they will be less susceptible to transplant shock. Plus, the soil is still warm enough to allow the root system to expand and become well-enough established for spring bud break.

A black and white diagram showing the root ball of a tree being placed in a hole. The diagram shows the proper planting depth of the root ball. Mulch should only cover the edge of the root ball. Top 10% of root ball should be left above ground.
Diagram shows the correct planting depth and mulch placement for trees and shrubs.

As with any horticultural endeavor, careful planning before planting will ensure a healthy tree or shrub for years to come. First, have the soil tested to ensure pH and nutrient levels are where they need to be for the species to be planted. Azaleas, blueberries, camellias and gardenias, for example, will need a more acidic soil (a lower pH) than most other species. Soil test results from the LSU AgCenter should include instructions on what to amend your soil with.

Taking time to prepare a good planting hole will pay dividends in years to come. Underground roots are positively geotropic. That is, they will automatically grow downward, toward Earth’s center. Focus on the width of the planting hole instead of depth. Make the hole two to three times wider than the root ball or, if a potted tree or shrub, the pot. This will give roots plenty of room for growth and expansion. Some sources say to build a mound of soil in the center of the planting hole to set the tree or shrub on. If your soil has good drainage, this isn’t necessary. If you’re planting bare-root trees or shrubs, building a mound of soil in the hole is a good idea as it will encourage roots to start growing outward. If you’re planting grafted trees, make sure the graft union is above soil level.

Marcie Mathews
Research Associate
LSU AgCenter Northeast Research Station

Cool-Season Heirlooms for Northeast Louisiana Cottage Gardens


What are heirlooms? These are our old-time favorite flowers that are passed down from generation to generation by seed, division or simply by existing undisturbed in a landscape over the years. Perhaps you remember the hollyhocks growing along the wall of your grandmother’s house or the Johnny-jump-ups bordering the flowerbed of your childhood home. These plants embody the nostalgia of days gone by but not forgotten. You can keep these plants going along by reintroducing them to your landscape. Not only do they perform well in our area, having survived years or even centuries of cultivation, but they also add great beauty to our outdoor spaces. Here are some cool-season heirlooms to plant this winter in your cottage gardens and mixed borders for a uniquely Southern appeal.

Bachelor’s buttons, also known as cornflower, are native to Europe and have been around for centuries. They have since become naturalized, growing wild in some north Louisiana parishes. Pick up just about any wildflower seed packet and cornflower is usually in the mix. They come in an array of blue, white, and pink blooms atop swaying pale green foliage. They grow to about 2 to 3 feet tall and look great in mixed borders and make excellent cut flowers. Seed packets of various colors, mixes and sizes are available in garden centers and can be sown in a full sun location in late fall to early winter. Bachelor’s buttons will bloom heavily through spring into early summer. Plants are very cold tolerant, surviving most frosts and freezes.

A plant that has rounded leaves speckled green and white. The flowers are taller than the plant and are a bright orange color. The plant is on the edge of a flower bed and is spilling over the side.
Nasturtiums are annuals that can easily brighten your winter landscape.

Nasturtiums are an old-time garden favorite. Introduced to the U.S. in the early 1800s, they are originally native to South America, where they grew as perennials. Now, they are grown as self-seeding annuals and are widely available in many growth habits and bloom colors to suit your gardening needs. The foliage and flowers make a spicy addition to salads, and the seeds can also be pickled and used much like capers. Plant nasturtiums in full sun to light shade. They perform quite well in poor soils, so little if any fertilizer is necessary. Nasturtiums look great as low borders or in mixed containers. Seeds germinate quickly usually within a week. Sow seeds in late winter to early spring. Plants will tolerate light frosts, but zone 8 can be susceptible to hard freezes.

Calendula, or pot marigold, is one of the oldest cultivated garden plants, dating back to the third century. It was brought to the New World with the first European settlers for its edible and medicinal uses. The flower petals were eaten or used to color cheeses. The leaves were added to soups and salads but could also be used in poultices to stop bleeding. Today, calendula is grown for its cheery daisylike blooms in an array of orange, yellow, cream and pink hues. Seed packets for the many varieties available can be purchased through garden centers or online retailers. Sow seed directly in the garden in a sunny spot in late fall or early winter. Due to their compact, upright growth habit, these plants make great fillers in mixed borders and flowerbeds. Calendula is very cold hardy, blooming faithfully until daily temperatures exceed 80 degrees Fahrenheit.

Snapdragons have a long history in the garden and for good reason. Brought to America by early settlers, snapdragons quickly became a widely popular garden plant for their colorful and unusual flowers. Children throughout the centuries have enjoyed pinching the flowers to make the petals snap open and shut like a dragon’s mouth, hence the common name. Available in many colors and growth and flowering habits that range from tall to dwarf and mounding to spiking, there is a snapdragon out there to meet your needs. Shop your local nursery or garden center in the fall for the best selection. Plant in full sun in the fall, placing tall and spiking varieties to the backs of beds, or dwarf and mounding types to the front as a border. Snapdragons are exceptionally cold tolerant, surviving the winter with ease into the spring, when it puts on show. Plants usually die back with the summer heat but can be grown as a perennial if planted in the right microclimate.

A collection of different flowers with different flower sizes and colors. The focus is on a grouping a small blue flowers on the left side of the picture.
Chinese forget-me-not are a good choice to bring bright blue flowers to your garden.

Chinese forget-me-not was introduced to the United States specifically for ornamental horticulture purposes in the 1920s. The dainty true-blue flowers of Chinese forget-me-not made it a favorite among early American gardeners. Its charming name, derived from various legends of love and devotion, added to its appeal. This species offers more ornamental value than its native relative, the woodland forget-me-not. Firmament is the most common and widely used variety and is usually included in wildflower mixes. Use fresh seed and sow twice as much to achieve the desired germination rates. Sow in full sun to part shade in the fall. Chinese forget-me-not is grown as a cold hardy annual that will reseed.

The Louisiana Super Plants collection offers several alternatives to these traditional heirlooms for your cool-season cottage garden. Camelot foxglove, Diamonds Blue delphinium, Sorbet violas, Jolt dianthus, Homestead Purple verbena, Supertunia Vista Bubblegum and Swan Columbine are all cultivars of tried-and-true heirloom plants that make perfect additions to any home landscape, cottage garden or flowerbed. These plants have been put to the test and are more widely available as transplants in most nurseries. Whether you use Louisiana Super Plants or go old-school with plants from seed, you are sure to have a show-stopping landscape with these cool season beauties of times gone by.

Marcie Mathews
Research Associate
LSU AgCenter Northeast Research Station

Plant Trees and Shrubs During Cold Months


A tree with low hanging branches with plenty of small red berries of the holly tree. Several birds are perched on the branches eating the berries.
American robin on a native holly. Photo by Norman Winter

Winter is a great time to get outside and get things done in the garden. We are very fortunate here in the South to have good weather during the winter months for gardening, and it is an excellent time to plant trees and shrubs in the landscape.

Although deciduous trees and shrubs are in their dormancy, roots are still actively growing. Planting during December, January and February provides plants with several months to develop a strong root system before they put out a new flush of leaves and flowers in spring.

The structure of trees and shrubs in our lawns and gardens is very apparent this time of year. Dead branches, low-hanging branches and branches that cross one another are visible now and should be removed. Take this opportunity to trim your trees and shrubs. Removal will be much easier without the additional weight of leaves.

As retail nurseries begin clearing out Christmas trees and merchandise, they will be bringing in a new stock of woody trees and shrubs. Tropical plants will be available later in the warmer season when they are less likely to be damage by colder temperatures.

The National Arbor Day Foundation has started the Time for Trees initiative to highlight how “trees clean our air, protect our drinking water, create healthy communities and feed the human soul.” Founded by J. Sterling Morton in 1872 in Nebraska City, Nebraska, where an estimated 1 million trees were planted, Arbor Day is celebrated every year. In 2021 it will be celebrated in most of the country on April 30. On this day, individuals are encouraged to plant trees.

Louisiana celebrates Arbor Day on the third Friday of January. The LSU AgCenter Botanic Gardens at Burden will hold its annual Arbor Day event on Jan. 23 from 9 a.m. to 1 p.m. Free and open to the public, this event will feature educational talks on native trees given by experts from the LSU AgCenter. You and your family can plant a tree while there and get GPS coordinates so you can come back and visit “your” tree and watch it grow for generations to come.

When deciding what trees and shrubs to purchase and plant, it is best to sit down and consider the year-round interest of those plants. A great design will have beauty and interest in each season. That can include evergreen plants, flowering plants and deciduous plants that have excellent fall foliage change.

Evergreen trees and shrubs provide year-round greenery and are popular in almost every landscape design. Some good, large evergreen trees include live oaks (Quercus virginiana), Southern magnolias (Magnolia grandiflora), Leyland cypress trees (Cupressus × leylandii) and American holly trees (Ilex opaca).

The Southern magnolia has fragrant white flowers in late spring to midsummer, and in winter the female American holly trees sport gorgeous red berries that attract birds and other wildlife.

Some medium-sized evergreen trees are the Southern wax myrtle (Morella cerifera), camphor tree (Cinnamomum camphora) and red bay (Persea borbonia).

You can choose from several small evergreen trees with many different functions. Some have flowers and put on a display in the late fall into early spring. These include the camellia (Camellia japonica) and camellia sasanqua (Camellia sasanqua).

A close up of a cluster of white flowers. There are several unopened buds with a light brown fuzzy covering over the buds. A bee is in the lower right hand corner of the picture nectaring the flower.
Loquats are great evergreen trees with sweetly scented flowers in late autumn.

Other fragrant flowering trees include loquat (Eriobotyra japonica), banana shrub (Michelia figo) and sweet olive (Osmanthus fragrans). Other trees — including the Burford Chinese holly (Ilex cornuta ‘Burfordii’), yaupon holly (Ilex vomitoria) and eastern red cedar (Juniperus virginiana) — provide ecosystem services such as wildlife food.

Compared to evergreen trees, deciduous tree have a much larger selection for use in Louisiana. Some large deciduous trees with good fall foliage change that are also great as shade trees for the landscape are American beech (Fagus gramdifolia), bald cypress (Taxodium distichum), basswood (Tilia americana), pecan (Carya illionensis), tulip tree (Liriodendron tulipifera), sycamore (Platanus occidentalis) and cucumber magnolia (Magnolia acuminate).

Some outstanding small, spring-flowering deciduous trees are the fringe tree (Chionanthus virginicus), flowering dogwood (Cornus florida), Taiwan cherry (Prunus campanulata), saucer magnolia (Magnolia X soulangiana), parsley hawthorn (Crataegus marshallii), redbud (Cercis Canadensis) and silverbell (Halesia diptera).

Picture of a mature tree with a rounded canopy. The picture was taken in the fall and the tree is covered in bright orange fall foliage.
Chinese pistache is an excellent medium sized decidous tree for excellent fall foliage.

Other deciduous trees with outstanding fall foliage change are the American hornbeam or ironwood (Carpinus caroliana), hop-hornbeam (Ostraya virginiana), swamp red maple (Acer rubrum Drummondii), Japanese maple (Acer palmatum), southern sugar maple (Acer barbatum), green ash (Fraxinus pennsylvanica), sweetgum (Liquidambar styraciflua), Chinese pistache (Pistacia chinensis) and many oak species, such as shumard oak (Quercus shumardii), nuttall oak (Quercus nuttallii), white oak (Quercus alba) and post oak (Quercus stellata).

Planting trees is a great way to leave a lasting legacy for generations to come to enjoy. In my humble opinion, trees are the key to combating climate change by conserving energy, sequestering carbon and reducing the overall concentration of greenhouse gases in the atmosphere.

Consider this proverb: “The best time to plant a tree was 20 years ago. The second-best time is now.”

Heather Kirk-Ballard, Ph.D.
Consumer Horticulture Specialist

Checklist for December, January and February


December

  1. In the vegetable garden: Plant onions sets, such as leeks and shallots, this month. Harvest bunching onions. Store vegetable seeds in the refrigerator to keep them viable (able to germinate). Store in tightly fitted plastic or glass containers.
  2. In the lawn: Soil tests should be conducted every so often to check soil nutrient levels. If your soil tests indicate the need for lime, this is a good time of year to add it.
  3. In the landscape beds: Keep winter weeds out of beds. Transplant alyssum, columbine, daffodil, dianthus, foxglove, hollyhock, larkspur, lobelia, narcissus, pansy, snapdragons and sweet William this month. Protect the roots and rhizomes of tropical plants by spreading a 4-to-6-inch layer of mulch around the base of the plant.
  4. Trees and shrubs: Heavily mulch cold-sensitive trees and plants and cover them in extended periods of below-freezing weather. Winter is a good time to plant trees and shrubs. Water-in newly planted trees, but established trees will not need to be watered this month.
  5. Fruits: Heavily mulch citrus trees to protect them from freezing temperatures. Cover young, tender citrus trees by constructing a simple frame extending above the leaves and cover with clear plastic. Make sure the cover does not touch tender leaves, and place the cover during the day to trap radiant heat coming up from the ground.

January

  1. In the vegetable garden: Cool-season vegetables and herbs tolerate freezing temperatures but small seedlings can be affected. Cover tender growth if you are expecting freezing temperatures with frost cloth, also known as reemay. If your vegetables need a boost of fertilizer, side-dress with a teaspoon of complete fertilizer placed a couple of inches from the base of the plant.
  2. In the lawn: If you over-seeded with annual ryegrass, mow regularly to keep the lawn looking tidy. If winter weeds are bad, it is safe to apply broad leaf weed killer following label directions, or hand pull them.
  3. In the landscape beds: Keep winter weeds in check by applying mulch at a 2-to-4-inch depth. Pine straw, leaves and pine bark are all excellent choices. Plant chilled tulips and hyacinths into the garden this month.
  4. Trees and shrubs: This is a great time to plant trees and shrubs while temperatures are down. This is also a good time to relocate established trees and shrubs that you want moved elsewhere in the yard. Be sure to go out a foot or more from the trunk of the tree or shrub to get an adequate root ball. Water newly transplanted trees in well to help encourage new root growth.
  5. Fruit: Cover tender fruit trees, such as citrus, when temperatures are set to drop into the mid-20s overnight. Wrap or drape the plants with canvas or another type of fabric extending all the way to the ground. Place the cover on trees during the day to trap radiant heat coming up from the soil. Fertilize citrus at the end of January to early February. Apply 1 to 1 ½ pounds of 8-8-8 or 13-13-13 per year of tree. Year one equals 1 to 1 ½ pounds, year two equals 2 to 3 pounds and year three equals 3 to 4 ½, and so on.

February

  1. In the vegetable garden: Plant warm-season vegetables late this month to decrease the chance of disease and insect problems. Be prepared to cover plants in freezing temperatures. Cut seed potatoes with a couple of eyes about the size of a golf ball and plant 4 inches deep and 12 inches apart. Corn planted in late this month will have few earworms.
  2. In the lawn: Time to relax and rejuvenate. Perform lawn equipment maintenance this month in preparation for the spring and summer. Dormant sodding can be done this month if you have new construction or need to stabilize bare patches in the lawn. The warm-season turf is dormant and will be brown but will green up in spring.
  3. In the landscape beds: Fertilize Louisiana irises and calla lilies and other fall-planted spring-flowering bulbs and cool-season annuals with a slow-release granular fertilizer this month. Prune repeat-blooming roses.
  4. Trees and shrubs: Prune your roses on or around Valentine’s Day and begin a preventative spray program, alternating fungicides for blackspot and powdery mildew. Fertilize spring-blooming trees and shrubs.
  5. Fruit: Time to fertilize fruit trees and shrubs, including apples, peaches, citrus, figs, blueberries and blackberries. Dormant cuttings from fig trees can be taken from 1-year-old growth and stored at 40 degrees for a month or so before rooting in moist media.

Heather Kirk-Ballard, Ph.D.
Consumer Horticulture Specialist

04_Leek_02jpg
Leeks

Low ornamental blushes with green leaves and small orange and yellow blossoms, surrounded by light brown pine straw mulch.
Pine straw mulch

General Winter Vegetable Planting Tips


Let’s make the most of December’s garden and start the New Year off right by following best management practices to get the most out of our fruit and veg crops.

December is the last month I think of as actual winter. January and February to me are very early spring. So, in this last month of winter here are a few to-do items to help keep the garden active!

December

  • Scout lettuce, strawberries and all cole crops for insects. Aphids, slugs, snails and worms tend to cause problem in the winter garden. Insecticides such as horticulture oil, insecticidal soap and Bifenthrin products (Ortho Bug –B-Gon Max) work great for aphid control. Insecticides that kill worms and loopers include Sevin, Bt (Dipel) and Spinosad. Snails and slugs are best controlled with baits. Iron phosphate baits are safest for pets. Early evening is when these pests feed. You want the baits to smell strong, so apply baits in the early evening for best results. If you have a lot of slug and snail problems, remove mulch from around the base of plants. This gives them fewer hiding spaces.
  • Till and hip rows in the garden now for January-planted crops. Early January can be very wet.
  • Plant onion sets. Choose sets that are thin, the size of a pencil or thinner. Thicker plants tend to bolt in cold weather and set seed rather than forming bulbs.
  • Cover blooming strawberry plants when temperatures drop below 32 degrees Fahrenheit. Plants not in bloom? No need to cover.
  • Order spring vegetable seed now if you want first pick of the great varieties. Wait too long and other gardeners will order all the good varieties.

January

  • Onions can be planted from mid-December to early January. In early January, continue to plant onions sets. Bulbing onion varieties that perform well include but are not limited to: Texas Grano, Mr. Buck, Texas 1015Y, Pinot Rouge, Red Burgundy and Miss Megan.
  • Mid-January through the end of February: Transplant broccoli, cabbage, cauliflower, chard, kale and lettuce into the garden. You can also direct-seed carrots, radishes, turnips and other rooting vegetable crops.
  • Mid-January through mid-February: Plant Irish potatoes into the garden. Cut the potatoes a few days before planting. Cut larger potatoes in quarters and smaller potatoes in half. This larger size helps reduce rot. It doesn’t matter if the potato pieces face up down or sideways. They will grow.
  • Vegetable growers in south Louisiana should start their tomato, eggplant and pepper transplants mid-January. North Louisiana vegetable growers should wait until the end of January or the beginning of February. It takes between eight and 10 weeks to germinate and grow into a decent-sized tomato, pepper and eggplant seedling for the garden. Keep seedlings in a warm and BRIGHT area. One week prior to transplanting, move the seedlings outside to harden off.

February

  • Continue to transplant broccoli, cabbage, cauliflower, chard, kale and lettuce transplants into the garden. Successive planting, or planting a portion of a row or a new row, every two weeks ensures a steady harvest.
  • Direct-seed beets, turnips, mustard, parsley, radishes, lettuce, snap beans and Irish potatoes.
  • Pull winter weeds. Hand-pull them or cultivate with a tiller or hoe. Get weeds out of the garden. Small insects like thrips like to hide here and get your spring crops later. Pre-emergent herbicides like Dual and Treflan are wonderful technology that can make gardening easy, especially in larger gardens. To control grasses in the garden use Poast or other herbicides with the active ingredient sethoxydim to kill grass and not broadleaf weeds.
  • Leave space for spring crops, which will go into the garden in March and April. If you have not pulled up rows, be sure to get it done at the first chance of dry weather. Spring is here!

Enjoy the Garden,

Kathryn “Kiki” Fontenot, Ph.D.
Associate Professor
LSU AgCenter School of Plant, Environmental and Soil Sciences

Several rows of strawberry plants covered in white and black plastic in a field.
Strawberry plants covered to protect them from below freezing temperatures.

A bushel of purplish red onions sitting on a shelf.
Red Burgandy onions

General Winter Vegetable Planting Tips


The dormant season for turfgrass begins in December

Most lawns should be dormant or at least close to this stage by Christmas. Because lawns are not actively growing, fertilizer applications are not needed during the winter. Most lawn fertilization for growth should have stopped on home lawns by late summer (late August to very early September for St. Augustinegrass and centipedegrass).

Nitrogen fertilizer on dormant to semidormant St. Augustinegrass, centipedegrass and zoysiagrass lawns can lead to increased brown patch and winter kill. Also, nitrogen applications during this time have a greater potential for leaching or movement into nontarget areas.

Soil sampling and pH adjustments

I’m a big believer in soil testing. If your lawn did not perform well last growing season or you just want to get a quick check on soil pH, get the soil tested. Winter is an excellent time to collect soil samples and submit them for analysis.

Samples should be a composite of soil collected from 3 to 4 inches deep at various places around the lawn. Mix well and reduce the sample to about a pint of soil and take it to the LSU AgCenter Extension Service office in your parish or to a participating garden center. Make sure to specify the type of grass you are growing on the soil test form.

Soil samples submitted to the LSU AgCenter result in a wealth of information concerning the overall fertility of your soil. If results of the soil test indicate the soil pH is too acidic, lime will be prescribed in the soil test recommendations. Sulfur may be prescribed for soils that are too alkaline. Winter is the best time to apply lime or sulfur so that it can be activated by for the growing season next spring and summer. The correct soil pH is extremely important and has everything to do with nutrient availability and fertilizer performance.

Turf establishment

Postpone any permanent warm-season turfgrass seeding until next spring. Soil and air temperatures will be too cold for germination and growth.

Sod, such as St. Augustinegrass and centipedegrass, can be laid during winter and established successfully during the spring. But remember to maintain good moisture to prevent the sod from dying. Establishment of sod is easiest, however, when sodding is delayed until the middle of spring, well after spring green-up.

Large patch disease (formerly brown patch)

Large patch disease can come and go throughout the winter if the weather is mild. Treatment with fungicides containing myclobutanil, propiconazole, pyraclostrobin, and triticonazole and azoxystrobin will reduce the spread of large patch. Damage from large patch will slow spring green-up, and diseased areas will remain unsightly until warmer spring weather conditions help with turfgrass recovery. These diseased areas become more prone to weed infestations.

Winter weed management

Broadleaf weeds, such as clover and lawn burweed (sticker weed) and annual bluegrass infesting St. Augustinegrass, centipedegrass and zoysiagrass and dormant bermudagrass, can be suppressed with a late fall followed by a winter application of atrazine herbicide. The window for these atrazine applications is from October to early March. Herbicides containing a three-way mixture of 2,4-D plus dicamba plus mecoprop (trimec-type herbicides) can be used for winter broadleaf control on the same lawns that were sprayed with atrazine. MSM (metsulfuron) works well on lawn burweed and is highly effective on clovers and false garlic. Weed-and-feed products can be substituted as your first application of fertilizer during the early spring.

When it comes to managing lawn burweed specifically, don’t wait until the stickers show up in April to treat. It’s too late then. Spray burweed in early November with products mentioned previously. Repeat these applications in February and March.

When should you resume fertilizing your lawn

Lawns may show signs of green-up in southern Louisiana in late February. Do not push turfgrass growth with fertilizer at that time! Fertilizer applied too early will feed winter weeds and will result in lush turfgrass growth that is more susceptible to injury from late frosts and increased levels of large patch disease. Lawns may be fertilized in the New Orleans area by late March, but delay fertilizing central Louisiana lawns until April. Consider fertilizing lawns in north Louisiana around mid-April.

Ron Strahan, Ph.D.
Associate Professor
Turfgrass and Weed Science

Plant with fine textured foliage that will eventually develop spiny seed heads
Lawn burweed germinates in lawns fall and produces painfull stickers in the spring.

Seed head has alternate seed structures. Seed head is wide at the bottom and narrows at the top.
Annual bluegrass seedhead

A light green plant with long stems with thin and narrow leaves whorled around the stem. Beneath the catchweed bedstraw is a dark green turfgrass.
Catchweed bedstraw is a sticky winter weed that attaches to pants and pets.

The plant is surrounded by loose pine straw. The leaves are grouped in small leaflets and there is a red mature fruit on the mock strawberry.
Wild geranium is a common winter broadleaf infesting lawns.

Round shaped plant with thin red stems with one leaf at the end of each stem. Leaves are deeply lobed.
Mock strawberry

Sooty Molds


Sooty molds are a result of nonplant pathogenic fungi that grow superficially as a thin black layer on leaves, fruit, twigs and stems of various crop plants or trees. The fungi grow on the honeydew produced by insects with piercing-sucking mouthparts. The insects, including aphids, leafhoppers, mealy bugs, psyllids, scale insects and whiteflies, pierce the plant tissue with their stylets and feed on plant sap. While continuously feeding, these insects ingest a large volume of sap fluid into their bodies, which is not entirely digested. After extracting nutrients from the sap, these insects excrete excess water and sugars from their bodies in the form of a sticky, sugary substance called honeydew. Most of the time, these insects feed on young, tender new growth and the honeydew drops below on all plant parts, including leaves, fruit, twigs and stems. Additionally, the honeydew covers understory vegetation, concrete surfaces, sidewalks, furniture, parking lots, etc., under host plants infested by sap-sucking insects.

Sooty molds are saprophytic fungi with dark, powderlike spores that break down honeydew. Abundance of sooty molds lead to formation of a thin, black layer. There are several species of sooty molds, but the most common ones are Capnodium spp. and Fumago spp. Sooty molds do not directly affect the host plant on which they reside but can inhibit the photosynthetic ability of the plant by covering leaves, twigs, fruit and stems. Under extreme conditions plants entirely covered with sooty mold may lose vigor and be predisposed to other plant pathogens. Plant growth may also be retarded, and yields can be significantly reduced. The aesthetic value of the plants covered with sooty mold is greatly reduced.

All plant species that are hosts for sap-sucking insects with the piercing and sucking type of feeding are affected with sooty molds. Some of the common landscape plants heavily affected by sooty mold are azaleas, camellias, citrus, crape myrtles, magnolias, oleander, pears, pine, roses, sago palms and viburnum. Hedges, small bushes or other plants, such as boxwoods, Indian hawthorn and ground covers, get sooty mold if the trees under which they are planted are infested with these insects. This happens when the honeydew from insects high in the canopy of trees drops on the vegetation underneath.

Managing sooty molds is very simple. Keep insects, such as aphids, mealy bugs, scale insects and whiteflies, in check. Once the insect problem is solved there will be no new sooty mold occurrence. The existing sooty mold infestation dries out after some time and easily sloughs off the infested areas.

Pressurized water can be used to wash off the sooty molds. Care should be taken while using pressurized water because it may damage the plant parts.

Insect infestations are generally controlled with insecticides, insecticidal soaps or horticultural oils. Before applying any kind of chemical pesticide, it is very important to identify the insect properly. Samples of plants infested with insect pests may be taken to your extension agent for identification. Consult with your local extension agent on the use of chemicals for managing insects. The LSU AgCenter Plant Diagnostic Center is also available to diagnose your plant health problems.

Raghuwinder (Raj) Singh, Ph.D.
Horticulture Pathology Extension Specialist

Small red insects cover the new growth foliage of a plant. The insects are on the top and bottom of the leaves.
Figure 1: Aphids feeding on a weed host.

Underside of a leaf showing several small white bodied insects. Their two white wings cover most of their body. Also visible are their small legs and antennae.
Figure 2: Whiteflies feeding on the underside of a holly leaf.

Small bodied scale insects on a tree branch. The insects are grouped tightly together and cover a large patch of the bark.
Figure 3: Crape myrtle bark scale on a crape myrtle trunk.

Black film on crape myrtle leaf's surface. The black film is thicker in places and thinner in others. This is called sooty mold.
Figure 4: Crape myrtle leaves covered with sooty mold.

Black film on citrus leaves and a citrus fruit.
Figure 5: Citrus fruit and leaves covered with sooty mold.

A group of crape myrtle leaves that are shiny because there is a substance called honeydew on the leaves.
Figure 6: Honeydew present on the upper surface of crape myrtle leaves.

Close up of a rose leaf with a shiny liquid on the leaf's surface. This liquid is called honeydew. There are several tiny bodied aphid insects on the leaf's surface.
Figure 7: Honeydew present on the upper surface of a rose leaf.

Picture of the side of a shrub with several leaves having a black film on leaf's surface. Some leaves are losing their green color and turning yellow. There are small red berries attached to the shrub.
Figure 8: An Indian hawthorn covered with sooty mold planted under a large tree infested with aphids.

A picture looking at the ground below a crape myrtle tree. The mulch surrounding the tree has a black tint because of sooty mold.
Figure 9: Mulch covered with sooty mold under a crape myrtle tree heavily infested with crape myrtle bark scale.
12/23/2021 5:53:21 PM
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