Southeast - Spring 2021

Joe Willis, Singh, Raghuwinder, Strahan, Ronald E., Fontenot, Kathryn, Kirk-Ballard, Heather, Fields, Jeb S.

HH banner SOUTHEAST-01.jpg thumbnail

Past Issues


Upcoming Events:

2020 LSU AgCenter Citrus Symposium
8:00 AM
Saturday, February 20th
Docville Farm (Virtual)
Link TBA
atimmerman@agcenter.lsu.edu to RSVP


Get Your Soil Tested!

Get your soil testedjpg

www.lsuagcenter.com/soiltestingkits


Never miss an issue of Horticulture Hints from the LSU AgCenter!

Visit the Horticulture Hints website at
www.lsuagcenter.com/HortHints

Then click on the Subscribe button!

Sweet Basil Downy Mildew

Downy mildew of sweet basil, a disease caused by Peronospora belbaharii, has been known in Louisiana home gardens since 2009. Symptoms include irregular yellowing of leaves, beginning with the older leaves first and progressing to the new growth. The yellowing is initially restricted by the major leaf veins, but the entire leaf eventually yellows. Irregular black spots appear on the leaves as the disease develops. Gray, fuzzy growth appears on the undersides of the leaves as the disease develops. This fuzzy growth is the reproductive stage of the pathogen, with the color coming from the spores produced. Entire leaves may eventually turn black and the plant eventually dies.

Spores are produced in darkness before sunrise and occurs at 50 to 78 degrees Fahrenheit and greater than 85% relative humidity. The spores are dispersed by wind and splashing water. On wet leaves at temperatures from 41 to 83 degrees, spores germinate within two hours and infect plant tissue within four hours. From the time a spore lands on a wet leaf, new spores can be produced in as little as seven and a half hours. Five to 10 days may elapse between infection and the appearance of symptoms, depending upon environmental conditions, such as temperature and light. The disease has also been shown to be seed-borne.

The most effective control measures on conventional sweet basil varieties are disease prevention.

Begin with disease-free seed and plants. Only purchase from reputable dealers and never save seed from infected plants or from plants in the vicinity of infected plants.

Leaf wetness and high humidity are essential for infection. To reduce these, grow basil in areas with good air movement and space plants to facilitate air movement through the canopy. Avoid overhead watering. Water using drip irrigation or directing water to the base of the plants. Use mulch around plants to reduce splashing. Water early in the day so the plants dry quickly and to help reduce relative humidity in the plant microclimate.

Some fungicides are labelled for use on basil. Conventional fungicides include: Ridomil Gold, Orondis Ultra, Revus and Presidio. OMRI listed products include: Actinovate AG, Aviv, Triology, Milstop Carb-O-Nator and Oxidate. Some bio-pesticides include phosphorous acid-based products and hydrogen peroxide-based products.

Another great development, especially for home gardeners, is the release of four resistant varieties developed at Rutgers University and one resistant variety developed at Genesis Seeds. The four Rutgers varieties are:

  1. Rutgers Obsession-DMR: An excellent sweet basil for field or potted plant production It will also make an excellent edible landscape plant. It is more compact. While also quite vigorous and high yielding, it starts off slower growing than the Rutgers Devotion-DMR and the Rutgers Thunderstruck-DMR. This line has a high leaf-to-stem ratio, which is good for small bunches or small clamshells and dark green, thick, glossy leaves. This new variety is slower to flower than the Rutgers Devotion-DMR and Rutgers Thunderstruck-DMR and flowers form late. It regrows prolifically after cutting, allowing many harvests over the growing season, and it is highly resistant to Fusarium wilt disease.
  2. Rutgers Devotion-DMR: An excellent aromatic sweet Genovese-type basil for potted, greenhouse and field production for fresh markets; establishes faster than the Rutgers Obsession-DMR with uniform, upright growth, dark, green color with flat to cup-shaped leaves and also allows for many harvests over growing season.
  3. Rutgers Thunderstruck-DMR: An excellent sweet basil with high yields needed for processing. Establishes quickly with fast, upright growth and medium-sized, bright green, ruffled leaves. This line does show some leaf variation, particularly when young. Some consider this as an ornamental sweet basil.
  4. Rutgers Passion-DMR: A beautiful sweet basil for potted plant and field production. Exhibits vigorous growth with a high leaf-to-stem ratio; Has ability to regrow after many harvests over a season and slightly cupped leaf of a greater size compared to Rutgers Obsession-DMR.

The resistant variety developed by Genesis Seeds is:

  1. Prospera: Fast growing, large leaves, and resistant to downy mildew and Fusarium. Plants produce high yields of 4-inch-long leaves. Highly uniform plants have a sweet aroma with notes of anise. Suitable for field and greenhouse production. Very similar to Nufar but with downy mildew resistance. Height of 24 to 30 inches.

All varieties are readily available to commercial growers. Seed companies offering one or more of these varieties are: Siegers Seeds, VDF Specialty Seeds, Genesis Seeds, Johnny’s Seeds and High Mowing Organic Seeds.

For homeowners, the best source of seeds is Johnny’s Seeds or High Mowing Organic Seeds. High Mowing Seeds currently offers Prospera, Devotion and Obsession varieties. Johnny’s Seeds offers Prospera, Devotion, Obsession and Passion.

Another downy mildew-resistant variety is available as a plant only – Amazel. This is a sterile basil variety that can only be vegetatively propagated. It is currently available from Proven Winners and from JungSeed.

  1. Amazel: Downy mildew resistant and sterile so you can enjoy more of the fresh basil taste you love. Keep harvesting and pinching and this amazing basil will keep producing sweet, fresh leaves all season because it doesn’t produce seed. The flavor remains excellent even if plants produce a few flowers. Best when grown in the landscape or large containers.

Dr. Joe Willis
Horticulture specialist

Amazel basilpng

Amazel basil. Picture from Proven Winners

Devotion basiljpg

Devotion basil. Picture from Johnny’s Seeds Catalog

Obsession basiljpg

Devotion basil. Picture from Johnny’s Seeds Catalog

Passion basiljpg

Passion basil. Picture from Johnny’s Seeds Catalog

Prospera basiljpg

Prospera basil. Picture from Johnny’s Seeds Catalog


The 2021 Spring Louisiana Super Plants

The Louisiana Super Plant program is an LSU AgCenter educational campaign that identifies superior plant material for Louisiana Landscapes. Any plant that is selected as a Louisiana Super Plant has gone through rigorous trials at multiple AgCenter locations across the state of Louisiana. Moreover, they are supported by the Louisiana nursery garden center industry. As such, Louisiana Super Plants are touted as “university tested, industry approved.”

The 2021 Louisiana Super Plant selection process was a very competitive year with so many amazing choices. With the voting completed, the Louisiana Super Plant committee has selected the winners for the 2021 Louisiana Super Plants. We are happy to introduce you to our two new warm-season inductions. Both winners will bring a vivid splash of color to any Louisiana landscape while thriving in the hot and humid Louisiana summers.

Starting the year off, we have Beacon impatiens. One of the top performers in the LSU AgCenter Hammond Research Station Trials over the last few years, the aptly named Beacon impatiens serve as a beacon of light in shady garden areas. Impatiens have long been a staple crop for shady Louisiana landscapes; however, with our high heat and humidity that extends throughout the night, some impatiens can develop mildew issues. Not the Beacons. They provide mounds of color and pop in the shade without the disease issues. They come in a wide variety of flower colors that look great against their deep green foliage. Flower colors include Bright Red, Violet, Salmon, Coral, Orange, Rose and White. With this much variety, there is sure to be a Beacon for every taste and theme.

The second 2021 warm-season Louisiana Super Plant is the Suncredible yellow sunflower. Another of our top performers for the last few years in the Hammond Trials, Suncredible provides nonstop flower power. Quite the opposite from Beacon, Suncredible yellow sunflowers thrive in full sun and take the heat as well as any flower out there. Excellent for pollinators, these indeterminate sunflowers steal the show with perpetual mounds of bright, vivid color. Unlike most other sunflowers, Suncredible keeps blooming and branching, providing color into fall. These will not only make a statement in the landscape, but they will make your neighbors jealous.

Look for these new Louisiana Super Plants and all the previous Louisiana Super Plants at your local garden center today. Watch for the announcement of the fall 2021 Louisiana Super Plants later this summer. For more information on the Louisiana Super Plants Program, please visit www.LSUAgCenter.com/SuperPlants.

Dr. Jeb Fields
Commercial and Ornamental Horticulture Specialist

Beacon Rose ImpatiensJPG

Beacon Rose Impatiens

Bright Red Beacon ImpatiensJPG

Bright Red Beacon Impatiens.

Coral Beacon ImpatiensJPG

Coral Beacon Impatiens.

Suncredible Yellow Sunflowerjpg

Suncredible Yellow Sunflower


Lawn Weed Control

Herbicides can be effective tools for reducing weeds in your yard, but the best way to manage weeds is to grow a thick, healthy lawn. Lawns that are managed properly are lush and healthy with few weed problems.

Visit www.LSUAgCenter.com and search for the keywords “lawn BMP” for more information on growing a beautiful lawn.

Pre-emergence herbicides

Weed preventers or pre-emergence herbicides can be helpful in preventing the emergence of several summer annual grasses and broadleaf weeds. Pre-emergence herbicides may be applied safely in late winter to early spring to all established Southern lawns.

Most pre-emergence products for home lawns are granular and should be applied with drop or broadcast spreaders and “watered in” soon after application. These types of herbicides kill weeds as they germinate, so application timing is extremely important. You have to apply before the weeds, such as crabgrass, germinate. They will not kill any existing winter weeds.

Residents in the New Orleans area and southernmost areas of the state should apply pre-emergence herbicides in late January or early February (definitely before Valentine’s Day) and then follow up with another application in mid-April. From Alexandria to Baton Rouge, residents should apply around Feb. 10, with a follow-up application in late April. If you live in north Louisiana, try to get these herbicides applied in late February to early March, with a follow-up application by mid-May. Some pre-emergence herbicide trade names to look for are Scotts Halts, Barricade, and Hi-Yield Crabgrass Preventer with Dimension. Consult product labels concerning rates and application techniques. When it comes to the successful use of pre-emergence herbicides, going a little early with your applications is better than applying too late. Winters over the last few years have been nearly nonexistent. Lack of cold weather has caused an earlier emergence of summer weeds. Let’s get those pre-emergence herbicides out on time.

Post-emergence herbicides

Post-emergence herbicides are used to kill weeds that already have emerged in the lawn. Winter broadleaf weeds usually are prevalent in the late winter to early spring throughout the state. MSM Turf (metsulfuron) and Celsius (theincarbazone-methyl + dicamba + iodosulfuron) are two highly effective broadleaf-killing herbicides that have consistently performed well in LSU AgCenter evaluations on winter broadleaves. MSM is effective on wild onion, false garlic and blue-eyed grass (actually an iris) as well as most winter broadleaves. These are low-use-rate herbicides, especially MSM. Follow the product labels very carefully so that lawns and trees are not injured. Do not use Celsius on carpetgrass.

More widely available broadleaf weed killers include “trimec-type” herbicides formulated with the active ingredients 2,4-D; dicamba; and mecoprop. Some examples of trade names to look for with these active ingredients include Trimec Southern, Ortho Weed B Gon for Southern Lawns, and Ferti-lome Weed Free Zone. Product manufacturers will often recommend a follow-up spray two or three weeks after the first application. Broadleaf weed killers such as these are widely available and can be used on most southern grasses. Injury can occur, however, when using them on St. Augustinegrass and centipedegrass as the weather gets warmer in late spring.

Atrazine is a herbicide that is effective on winter broadleaves and also controls annual bluegrass, especially when applied before the annual bluegrass flowers. Most garden centers have a good supply of atrazine on their shelves. Weed and feed products labeled for St. Augustinegrass and centipedegrass contain atrazine as their active ingredient. However, liquid atrazine sprayed on weeds in the yard has worked better in LSU AgCenter trials than atrazine weed and feed products impregnated on a fertilizer granule.

What about weed and feed products?

Weed and feed herbicides can be used at the times recommended for the first fertilizer application of the year. Apply weed and feed in the New Orleans area from mid-to-late March. For north Louisiana, mid-April is the time. Just be aware that applying weed and feed too early (late February to early March) may encourage outbreaks of large patch disease.

Clean your sprayers thoroughly with an ammonia solution if the same sprayer is used for applying insecticides or fungicides on landscape plants. It is best to buy a sprayer specifically dedicated for weed killers, however, to avoid accidental injury to desirable plants. As always, be sure to read and follow product label recommendations before using any pesticide.

Fertilizing the lawn

Lawns vary in the amount of fertilizer required during the growing season. See the table to the right for information regarding the number and timings of fertilizer applications recommended for lawn species grown in Louisiana. Bermudagrass and St. Augustinegrass require the most fertilizer compared to other lawn grasses. Centipedegrass and zoysia only require one to two applications of fertilizer per year.

Lawn Number of fertilizer applications/year Recommended months
Bermudagrass 3 March/April, June, August (optional September)
Centipedegrass 1 to 1.5 April and possibly June at half fertilizer rate
St. Augustinegrass 2 to 3 April, June, August
Zoysiagrass 2 April and July

Which fertilizer should I use during the growing season?

A spring application of weed and feed could serve as your first fertilizer application. For future applications during the growing season, consider using 3:1:2 or 4:1:2 ratios of N-P-K (nitrogen-phosphorus-potassium) as a guide for the analysis of fertilizers to choose for the lawn. For example, a fertilizer with an analysis of 21-7-14 is a fertilizer with a 3:1:2 ratio. You would be better off getting your soil tested. Soil tests would be most helpful to determine exactly what nutrients are needed to make your lawn beautiful. Contact your parish extension office concerning soil sampling your yard today.

Ron Strahan
Weed Scientist and Turfgrass Specialist

blue eyed grass is actually an iris that often infests lawns in the early springJPG

Blue eyed grass is actually an iris that often infests lawns in the early spring.

indian mock strawberry is infests thin lawnsJPG

Indian mock strawberry is a perennial weed that can infest thin lawns.

spotted burclover is a common weed seen early in the springJPG

Spotted burclover is a common weed seen early in the spring.


Checklist for March, April, May

March

  1. In the vegetable garden: Work compost and a preplant complete fertilizer, such as 13-13-13, at seven to 21 days before planting or laying mulch cloth. In south Louisiana plant beans, cantaloupes, collard greens, sweet corn, eggplants, herbs, mustard greens, okra, Southern peas, peppers, pumpkins, summer squash, tomatoes and watermelons. North Louisiana gardeners should wait until the beginning of April.
  2. In the lawn: Make your first mowing at a low setting and remove grass clippings. Continue to treat weeds in the lawn. You may start fertilizing lawns this month after March 15 in south Louisiana and after April 1 for north Louisiana.
  3. In the landscape beds: To revive your cool-season flower plantings, pinch off old flowers on bedding plants after their first flower cycle is completed this spring. Start planning your warm-season annual beds while you continue to enjoy the end of the cool-season annual plants as seasons transition. Look for Louisiana Super Plant selections at local nurseries for planting this spring.
  4. Trees and shrubs: Spring is a great time to plant new trees and shrubs. Consider whether you want them to be evergreen or deciduous and consider the trees and shrubs’ size, fall foliage change and flowers when selecting new plants. Apply dormant oils to control scales, whiteflies and other sucking insects on trees and shrubs that may be affected. Fertilize this month if you missed it in February. Begin your preventative rose spray program in early March. Alternate fungicides to control blackspot and powdery mildew. Treat in the early morning or late evening every week. Copper is a great organic alternative to other traditional fungicides.
  5. Fruit: Apply fertilizer to fruiting trees that were not fertilized in winter now at the recommended rate. Spring is a great time to plant both fruit trees and shrubs.

April

  1. In the vegetable garden: Apply pine straw mulch to prevent weeds in the vegetable garden. The last week of April is a good time to side-dress vegetables planted in late March with ammonium nitrate, ammonium sulfate, calcium nitrate or potassium nitrate. Be sure to apply several inches away from the base of the plant and water in immediately to prevent burning. Plant flowers such as zinnias and marigolds in your vegetable garden to encourage pollinators for crops that require cross-pollination, such as cucumbers, beans, and squash.
  2. In the lawn: Fungal diseases are common this time of year. Keep an eye out for large patch and gray leaf spot. St. Augustinegrass is susceptible and centipedegrass is more resistant. Use fungicides containing maneb, myclobutanil, PCNB, propiconazole, thiophanatemethy or triadimefon every 10 days as the fungus persists.
  3. In the landscape beds: You can begin planting warm-season annuals, perennials and caladium bulbs this month. Thin border plants and clumping ground covers, such as monkey grass, liriope, and hostas, this month.
  4. Trees and shrubs: Prune spring-flowering shrubs, such as azaleas, camellias, viburnum and spireas, after they have finished flowering. Fertilize after pruning. Powdery mildew can be a problem on the foliage of ornamentals. Control with fungicides containing one of the following active ingredients; azoxystrobin, copper sulfate, myclobutanil, trifloxystrobin or triforine.
  5. Fruit: Thin fruit on your fruit trees this month. Thinning fruit improves the size and quality of the remaining fruit and can help reduce the spread of diseases.

May

  1. In the vegetable garden: Stake tomato plants. Now is a critical time to scout vegetable plants for immature stink bugs and leaf-footed bugs. If you see them spray soon. When they turn into adults they are much more difficult to control. Continue to plant warm-season vegetables.
  2. In the lawn: If your weeds are under control, you can encourage vigorous turfgrass growth by aerifying your lawn. Plug removal is the best method to provide air to roots. If you fertilized in March, you may go ahead and fertilize again late this month. Lay sod or sprig your lawn this month and throughout the summer, if needed.
  3. In the landscape beds: Install a microirrigation system. Home installation kits and timers are homeowner friendly and readily available online and in stores. Next month is National Pollinator Month. Plan and plant native plant species for pollinators, such as native milkweeds, Louisiana phlox, passion vine, purple coneflower, cardinal flower, sunflowers, bee balm, coral honeysuckle, rose mallow and irises.
  4. Trees and shrubs: Prune spring blooming shrubs now through no later than July to encourage new growth. Be careful not prune summer blooming shrubs, such as hydrangeas, butterfly bush, crape myrtles and others.
  5. Fruits: Bird netting may be necessary for fruit trees and shrubs this month. Once the word gets out, the birds will come back day after day. It is harvesting time for mayhaws, loquat, mulberry, peach, sweet orange, blackberries and blueberries this month.

Dr. Heather Kirk-Ballard
Consumer Horticulture Specialist

Vista Bubblegum Supertunia in 25-gallon containersJPG

Vista Bubblegum Supertunia in 25-gallon containers.

Water early in the morning between 2 am and 8 amjpg

Water early in the morning between 2 and 8 a.m.


Warm Weather — and Spring Gardens — Have Returned

Welcome, spring! And welcome back into the garden! January and February can be so cold and uninviting that when March, April and May come around, we do not just start gardening. No, we jump back with open arms into the garden. Moreover, warmer months indicate that red, ripe juicy tomatoes; bright, cheerful squash; and fun little pops of flowers are just around the corner. Read on for a few tips to make this spring season a great garden season.

Before Planting:

Prepare your garden as soon as possible. Louisiana springs are warm but also rainy. So, at the first chance of dry weather, make up your rows and get your fertilizer incorporated into the soil. After soil, preparation and planting both seeds and transplants, consider how you are going to prevent weeds. I hate it when my garden starts so nice and clean and then BAM! One or two days without visiting and weeds are popping up everywhere. As hobby gardeners, we do have options to help us control the weeds, beyond hand-picking.

  • The first option is cultivation. Cultivation not only pulls out weeds but also loosens soil and helps roots grow. Check out the photo of my new hand cultivator put together by my friend Bobby Williams. I cannot wait to use this tool. I had one a few years back that mysteriously disappeared. Whoever has it now knows that this is a great tool. Cultivate once a week on the side of rows to keep weeds down.
  • The second option for weed control is mulch. I love mulching. In traditional in-ground gardens put 4 to 5 inches of mulch between the rows where you walk. In raised beds mulch over the entre top of the bed. Use leaves and pine straw, not wood chips. In vegetable gardens, the wood chips tie up valuable nutrients and leave vegetable crops looking sad and yellow.
  • The third option is herbicides. Make sure the herbicide you choose has vegetables on the label. Herbicides with the active ingredient sethoxydim will kill only grasses. Spray this right over the top of all broadleaf vegetable crops without injury. Use trifluralin or corn gluten meal as pre-emergent herbicides to keep small-seeded broadleaf weeds from emerging in our garden. Willing to spend a little more money and really hate weeds? Go for Dual. The active ingredient is S-metolachlor. It is labelled for so many vegetable crops and really does a nice job of keeping weeds out of the garden.

Now … start planting!

March

Direct-plant snap beans, Swiss chard, radish, lettuce, collards, mustards, turnips, cabbage, broccoli and sweet corn seeds. Remember sweet corn is wind pollinated, so full ears require a good layer of preplant fertilizer and at least three rows side by side for filled out ears. Plant tomatoes, peppers and eggplant transplants midmonth in south Louisiana and later in the month for north Louisiana. Plant cantaloupes, squash, cucumbers and watermelons well after danger of frost is over; this is usually after March 15 in south Louisiana and closer to April 1 in north Louisiana. The cucurbits can be planted from seedlings or directly seeded into the soil this month.

squashjpg

Yellow squash are a popular summer vegetable.

April

Plant snap bean and butter beans. Butter beans or lima beans require little more heat to germinate and grow nicely, so April is a great month to get them growing. Radishes, collards, cucumbers, eggplants, cantaloupes, okra, Southern peas (field peas), peanuts, pumpkins, winter squash, summer squash, sweet corn, sweet potatoes (late April), tomatoes (transplants), peppers (transplants) and watermelons are also great to be planted this month. Like butter beans, okra really needs warm soil to germinate, so you may need to wait until the middle of the month or even later. If the soil is cold, the growth will be slow, and the plant will be more susceptible to insect and disease attacks. Well-fed, well-watered plants planted at the right time can withstand a lot more insect and disease pressure, so patience is key for warm weather and excellent okra germination. Many gardeners also recommend soaking okra seeds for a few hours in water or scratching the surface of okra seeds with sandpaper just to help with uniform germination.

k4297-14jpg

Plant peanuts in April and May for a late summer harvest.

May

Most spring vegetables can be planted in May because the soil has warmed, and danger of frost has passed. Plant sweet potatoes (transplants), okra, Southern peas, pumpkins, peanuts, sweet corn, watermelons, cucumbers, butter beans, squash, cantaloupes, collards and eggplants (transplants). Snap beans, butter beans, sweet corn, tomatoes and peppers (transplants) should be planted in the early days of May to prevent poor fruit set because of high temperatures. If you have not had a chance to plant tomatoes yet, you can still do so, but the LSU AgCenter recommends planting heat-set tomatoes at this time of year, especially if it is late in May. Heat-set varieties include, but are not limited to, solar set, sun gold, Phoenix, Florida 91 and more. If the name sounds hot, it is probably heat-set. Heat-set simply means that when night temperatures are above 75 degrees Fahrenheit, pollination and fertilization will still occur.

Watermelon 1JPG

Watermelons are a fun and easy crop to grow in the summer.

Okra SHjpg

Okra grows best when seeds are planted after the soil warms in May.

After Planting:

Once your spring plants begin to flower, fertilize some more. This is called side-dressing because the fertilizer is not placed at the base of the plant but about 6 or so inches to the side of the plant. Side dressing allows your plants to size up. Sizing up equals better harvests. When side-dressing, the nutrient we most care about is nitrogen. Nitrogen sources include bone meal, calcium nitrate, nitrate of soda, potassium nitrate, ammonium sulfate etc. Because each source has a different percentage of nitrogen, you really need to read the bag for the proper rate. Identify insects before you spray. Some insects are good and others are bad. There is no use in spraying the good ones, and there is no use in spraying the bad ones with insecticides that will not work. There is no one-size-kills-all, so make sure to talk to your local extension agent when identifying both insects and disease. Have fun and eat well.

Dr. Kiki Fontenot
State Vegetable Extension Specialist


Lichens

Lichens are fascinating creatures. They are composed of two different organisms — a fungal partner and a pho­tosynthetic partner living in a symbiotic relationship.

The photosynthetic partner is either a green alga or a cyanobacterium (blue-green bacterium). Lichens get their nutrients from the food prepared by the photosyn­thetic partner, and the fungal partner provides the body and shape.

Lichens grow successfully in different environments and geographical areas ranging from arctic to desert. They can grow on almost any surface, including the roofs and walls of buildings, rocks and trees and even on iron fence posts as epiphytes (Figures 1 and 2).

Figure 1 lichens growing on an iron fence postjpg

Lichens growing on an iron fence post.

Lichens have several different growth habits. Some grow flat like a crust (Figure 3) or filamentous like hair (Figure 4), while others are leafy or branched. They come in some of the most vibrant colors, ranging from lime green to bright orange (Figure 5). Lichens grow slowly and may live long. Actively growing lichens are an indica­tion of good air quality because air pollutants can adversely affect them.

So the question is: “Are lichens plant pathogens?” And the answer is: “No!” Lichens are not plant pathogens. They use a tree or another surface as a substrate to grow epiphytically. Lichens are not parasites and do not derive any nutrients from the host on which they are growing.

Lichens may grow on healthy as well as stressed trees. They are more noticeable on stressed trees because of the open or thinner canopy. Stressed trees with open canopies allow sunlight to penetrate deep into the canopy, which results in increased growth of lichens. Drought stress, improper fertilization, compact soils, disease or insect pressure, or other poor cultural practices may result in poor growth and stressed trees.

Generally, no chemical control is recommended to manage lichens, but residents should avoid any biotic (insects, diseases, nematodes and weeds) or abiotic (nutrients, drought, water logging and compaction) stresses to their trees. Good cultural practices that promote vigorously growing, healthy trees with dense canopies may reduce lichen growth.

Dr. Raj Singh
Plant Pathologist and Director of Plant Diagnostic Center

Figure 2 lichens growing on a wooden fence postJPG

Lichens growing on a wooden fence.

Figure 3 flat crust like lichen growing on a citrus branchjpg

Flat crustlike lichen growing on a citrus branch.

Figure 4 filamentous lichen growing on a blueberry branchjpg

Filamentous lichen growing on a blueberry branch.

Figure 5 bright orange colored lichenjpg

Bright orange-colored lichen.

2/2/2021 5:28:00 PM
Rate This Article:

Have a question or comment about the information on this page?

Innovate . Educate . Improve Lives

The LSU AgCenter and the LSU College of Agriculture

Top