by Larry Williams | Apr 15, 2020
Did you know that the first virus discovered was in plants, not in humans? As early as 1857, tobacco farmers in the Netherlands recognized a new disease of tobacco. It wasn’t called a virus at the time as the causal agent was unknown. In 1886, Adolph Mayer, a German agricultural chemist, determined that the “tobacco mosaic” disease could be transmitted to healthy plants by rubbing them with infected leaf sap.
Tomato leaf with tobacco mosaic virus. Photo credit: UF Plant Pathology Department
When taking a plant pathology course in college, it amazed me that viral organisms were ever discovered. They are extremely small. So small that it was not until the development of the electron microscope in the late 1930s that scientists were able to see the structure of the tobacco mosaic virus. Viruses are 20 – 250 nanometers in diameter, about 100 times smaller than bacteria.
The discovery of fungi and bacteria came before the discovery of viruses as the cause for plant diseases. In most cases, we have many chemical options for control of fungal and bacterial diseases in plants. But there are few to no chemical options to control viral organisms in plants. By the nature of how a virus operates in a plant cell, chemical control results in death of the host cell, surrounding tissue and possibly the whole plant.
Control of viruses in plants involves eliminating the source of the virus such as nearby weeds, control of insect vectors that transmit the disease such as aphids and thrips and use of resistant plants.
Historically, plant diseases have caused major impacts on humans. In 1845, the Potato Famine in Ireland was caused by the fungus Phytophthora infestans. This disease was responsible for the death of more than 1 million people as it devastated the production of the potato as a major food source at the time and is credited for the beginning of plant pathology as a science. Cryphonectria parasitica, an introduced fungus, essentially wiped out the American chestnut as the dominant tree in the eastern U.S. forests during the early 1900s. The excellent wood was used to build homes and the nutritious nuts were eaten by humans and fed to livestock. Currently, UF/IFAS plant pathologists are working to solve Citrus Greening, a bacterial disease that has severely damaged the citrus industry and has the potential to completely eliminate citrus production in Florida.
If it were not for the land-grant university system, of which Extension Agents are a part, there would be few to no plant pathologists in the United States. It is these land-grant universities, like the University of Florida and others, that provide plant pathology courses, training, research, development and ultimately that graduate with degrees those who go on to careers in the field of plant pathology, discovering new diseases and developing controls for these diseases.
by Larry Williams | Mar 20, 2020
Ground-dwelling bees get a lot of attention in late winter and spring as they create large numbers of small mounds in local lawns and landscapes.
Many people become concerned as they see these bees hovering close to the ground out in their lawns and landscapes. But these bees are interesting, docile, beneficial and are unlikely to sting.
These bees are known as andrenid bees or mining bees. Andrenid bees are solitary. As the name implies, they live alone. However, they may nest in close proximity to one another but they do not form a colony or hive. They produce individual mounds with a small entrance hole. The bees are approximately ½ inch in length with a black body.
Richard Sprenkel, retired UF/IFAS Entomologist, explains their biology in today’s article.
“After mating in late winter and early spring, the female selects a site that has dry, loose soil with sparse vegetation. She excavates a vertical shaft in the soil that is approximately the diameter of a pencil and up to eighteen inches deep. Off of the main shaft, the female will construct several brood chambers that she lines with a waterproof material. The female bee provisions each brood chamber with pollen and nectar on which she lays an egg. The pollen and nectar sustain the larva until fall when the overwintering adult is formed. Early the following spring, adult bees emerge from the ground to begin the cycle again. There is one generation per year.”
The small mound of soil that is excavated from each burrow brings additional attention to the activity of the bees. As males continue to hover in the area of the burrows looking for unmated females, the bees appear more menacing than they actually are. Andrenid bees have a tendency to concentrate their nests in a relatively small area. The openings to the underground burrows may be no more than three to four inches apart.
The threat of being stung by these bees is usually highly overrated. The males cannot sting and the females are docile and not likely to sting unless stepped on, handled or threatened. While entrances to the tunnels and excavated soil may appear disruptive to the lawn, they usually are not damaging. It may appear that the grass is thin because of the bees but it is more likely that the bees are in the area because the grass was already thin. Control is usually not necessary. Because the andrenid bees forage to gather pollen and nectar, they are actually beneficial. They serve as pollinators this time of the year.
**** Photo Credited to UF / IFAS Extension Jackson County courtesy of Josh Thompson****
by Larry Williams | Jan 27, 2020
Q. I have a camellia plant that is about 25 years old. It forms flower buds but the buds never fully open. The plant otherwise looks healthy. Is there something that I’m doing or not doing that causes this?
Sasanqua camellia bloom, Photo credit: Larry Williams
A. I have seen this happen over the years. There are a number of possibilities for why this happens. If the camellia cultivar is otherwise known to do well in the area, the problem could be caused by one or more of these factors.
- Stress (primarily drought stress could inhibit buds from opening)
- Freeze damage
- Too many buds on the plant to allow each and every bud to open
However, with this being the norm for your camellia plant for that many years, it may be the wrong camellia variety in the wrong place.
Camellias have been so common in our Southern landscapes that some people think they are native to our area. However, camellias are native to Asia. They were first brought to America during the latter part of the 1700’s.
Years ago, people planted any camellia they could get their hands on because camellias weren’t as common or available and definitely had a more limited selection.
Some camellia cultivars are simply not well adapted to the Gulf Coast and, as a result, will not flower well even though they may grow well here. This is why some varieties are favored in Seattle, some do better in California, some do better in New England and others perform well here in the South.
Even though camellias are a common sight in shady Southern gardens now, not all camellias will perform well here. So, it is important to do some homework before purchasing and planting just any old camellia.
As stated in the UF/IFAS Extension publication Camellias at a Glance, “There are numerous species of Camellia, but the types commonly grown as landscape shrubs in Florida are Camellia japonica, Camellia sasanqua, and hybrids of these.” This publication is available online at https://edis.ifas.ufl.edu/pdffiles/EP/EP00200.pdf or from the UF/IFAS Extension Office in your County.
Sasanqua and japonica camellias come in whites, pinks, reds, double and single flowers and sizes from four to twenty feet tall.
The sasanqua types bloom as early as October while the japonica types begin flowering later.
It is possible to select a few different varieties, instead of just one, to extend the color in your landscape from weeks to months. Selecting camellias for staggered flowering times can provide color all fall and winter long.
When purchasing camellias, research the bloom times of varieties for your area.
by Larry Williams | Dec 4, 2019
Fall oak tree leaves abound and can be recycled as landscape mulch. Photo credit: Larry Williams
Weed control is not top on my list as a reason to use mulch. There are weeds that can push through mulch such as nutsedge (nutgrass) or that can germinate and grow in the mulch. But done correctly, mulching plant beds and gardens can help inhibit some weeds. Tree leaves can be used as a mulch.
In addition to weed control, mulch provides other benefits. It can make landscapes look more attractive. It keeps roots evenly moist, acts to insulate roots from extreme heat and cold and can help decrease loss of soil from wind and water erosion. Mulch serves as a barrier to some soil-borne diseases, especially in the vegetable garden. And, as organic mulch breaks down, it improves the soil’s fertility, aeration, structure and drainage.
Tree leaves make good mulch. They can be placed on the soil surface beneath and around shrubs, trees, perennials, annuals and vegetables.
Fall leaves are abundant. Some people feel overwhelmed by the volume. One resident reported raking more than 100 large bags of leaves from his half-acre property. One large oak tree can contain over 250,000 leaves!
Tree leaves can be placed in landscape beds or around vegetables “as is” or chopped up with a shredder or mower into smaller pieces and then spread around vegetables, shrubs and trees. Mixing leaves from several different species of trees can make better leaf mulch. Leaves of the same size tend to mat together and produce a shingling effect that can shed water and reduce gas exchange in the soil. Shredded leaves stay seated better on the landscape than whole leaves.
A mulch layer three inches deep after settling is enough for most plants. If possible, extend the mulched areas out to the outermost leaves (called the drip line) and beyond. And be sure to pull the mulch back a few inches from the main trunk. Never pile mulch around the trunk.
Using those fallen tree leaves as mulch recycles a natural resource and saves you money, enriches your soil, fertilizes your plants and keeps them out of the local landfill.
So, instead of putting all those leaves curbside in plastic bags to be hauled off, use them to benefit your landscape, which may include less weeds.
For additional information on landscape/garden mulch, contact the UF/IFAS Extension Office in your County or access the following sites.
http://gardeningsolutions.ifas.ufl.edu/care/planting/mulch.html
http://edis.ifas.ufl.edu/topic_mulch
by Larry Williams | Dec 4, 2019
Fire ant control options in some situations include doing nothing.
Fire ant colonies consist of the brood (eggs, larvae and pupae) and adult ants. The adults include winged males, winged females, one or more egg producing queen and workers. The winged males and females mate in spring or early summer after a rainy period. Males die shortly after mating. Newly mated females can fly as far as twelve miles from the nest (or farther carried by wind). After landing, mated females shed their wings and begin digging chambers in which they lay eggs to start a new colony.
A single queen can lay over 2,000 eggs per day! She can live an average of six to seven years. A mature fire ant colony may contain 100,000 to 500,000 workers. Fire ant mounds/colonies can reach densities of 200 to 800 per acre.
You should now begin to understand why fire ants are difficult to control. Where they don’t present a direct threat to human health, the best management practice may be to leave them alone.
Homeowners may have to find a tolerable level. Waging war on this insect can be expensive and requires a long-term commitment. There is no single, universal solution to controlling fire ants. A one-time treatment may make the problem worse. In areas where native ants and fire ants have been reduced or eliminated with insecticides, reinfestation by fire ants into these treated areas is rapid.
A balanced approach to fire ant management is recommended. Those mounds that pose no threat to humans should be left alone. Instead target specific mounds such as those close to buildings and walkways.
When treating single mounds with contact insecticides, it’s critical to treat when the queen and brood are close to the surface, which is between 70ºF to 85ºF. When using fire ant baits, it’s important to apply the bait when the ants are foraging for food. They are most actively doing that between 70ºF to 85ºF. Actively foraging ants will pick up the bait and carry it into the nest within minutes. That’s important because baits tend to quickly go rancid and then are no longer attractive to ants. When using season-long control products, it’s a must to achieve uniform coverage of the area. Always read and follow the label precautions and directions when using any insecticide.
Where fire ants create no threat in out-of-the-way areas on your property, consider the option of leaving them alone.
The following link to a UF/IFAS Extension publication provides options for fire ant control in lawns, gardens and landscapes. http://edis.ifas.ufl.edu/lh059
