by Matthew Orwat | Aug 19, 2013
Cercospora in Pepper
Image Credit Matthew Orwat
This summer’s rainy and humid weather has created a perfect environment for the proliferation of a variety of fungal diseases. In particular, Cercospora is a genus of fungus of which there are over 1,200 different species. Because there are so many species of this fungus, many different plant species are affected including many garden vegetables and ornamentals.
Cercospora leaf spot in Pepper
Image Credit Matthew Orwat
Cercospora causes purple, brown or black spots on a variety of garden vegetables and ornamental shrubs. The spots usually include a grey dead area in the center and a yellow “halo” or “ring” surrounding the entire spot. This disease usually starts at the base and interior of the plant, where there is more moisture and less air circulation, and moves outward.
Severe Cercospora infections have the ability to defoliate entire plants within a season and kill garden annuals, such as pepper, within a season. On shrubs, turf and perennials, Cercospora ranges from minor annoyance to major disease depending on the resistance of the cultivar or species. Serious infections can kill some ornamentals, such as Indian Hawthorn or Rose, in three years.
Several methods exist to limit the spread and severity of Cercospora outbreaks. It is a good practice to remove all dead plants and leaf litter from the garden. If Cercosproa infection occurs, remove and dispose of dead plants and pick up all leaf litter from the garden immediately upon drop. This will limit the fungal spore’s ability to reproduce. Another preventative strategy is to reduce water splash on leaves. Splashing water spreads Cercospora spores and allows them to take hold on a leaf. Irrigate the vegetable garden or landscape with drip irrigation to avoid wet leaves. Additionally, irrigate in the morning, so plants will not remain wet overnight. Cercospora requires 16 hours of moisture to reproduce. Specifically, infection of Indian Hawthorn has proven to be reduced by switching from overhead to drip irrigation.
Cercospora Infection on Rose
Image Credit U-Scout (Mathews Paret)
If fungicides must be used, be sure to follow label directions since some products labeled for the home ornamental garden, such as Chlorothalonil, are not labeled for turf. Be sure to use fungicides with more than one mode of action, since resistance may develop if only one type of fungicide is used.
For more information, please consult the following UF / IFAS publications regarding Cercospora:
Also, contact your County Extension Office for additional assistance.
by Larry Williams | Jul 22, 2013
Gray Leaf Spot is a common fungal disease of St. Augustinegrass. Recent wet conditions have promoted this disease. This includes high humidity, heavy dews and particularly frequent afternoon and evening rains.
Gray leaf spot symptoms on St. Augustinegrass. Photo credit: UF/IFAS Extension
The individual spots or lesions are first seen as tiny brownish spots smaller than a pinhead. As they become larger, they will be circular and then begin to elongate lengthwise along the leaf. The spots will become brown to grayish in appearance. Numerous spots or lesions may be found on an individual leaf. Heavily infected leaves begin to turn brown and wither, usually beginning at the tip of the blade.
Gray leaf spot can move rapidly during prolonged warm, wet periods. Over watering or irrigating in the evening provides the prolonged period of wetness required for disease infection. For more information on how to correctly water a Florida lawn, visit the UF / IFAS Lawn Watering Website.
According to the Florida Lawn Handbook, “Severity of the disease is enhanced by application of readily available nitrogen fertilizer and is proportional to the amount of nitrogen applied.” Select fertilizers that are low in nitrogen or that have slow release nitrogen. Be careful to not overdo it in fertilizing your lawn and do not apply a high nitrogen fertilizer on top of an already infected lawn. Also, some lawn weed killers such as atrazine will increase the susceptibility of the grass to gray leaf spot.
Irrigate during early morning hours to minimize the period in which the grass is wet and water only on an as needed basis, watering less often but deeply. Avoid frequent, shallow watering and don’t irrigate when the lawn is already wet from rain. With the recent frequent rains, very little to no supplemental irrigation has been needed on most lawns in our area. Avoid leaving irrigation timers on when adequate rainfall has occurred. It’s best to operate irrigation controllers on manual so that the lawn can be monitored and irrigation provided during dry times.
If the disease outbreak is severe, fungicide may be needed. Look for products containing propiconazole, triadimefon or thiophanate-methyl. Always follow the product’s label directions and precautions.
For more information on maintaining a Florida lawn, contact your County UF/IFAS Extension Office or visit the YourFloridaLawn Website.
by Julie McConnell | Jul 22, 2013
When you contact your local extension office for pest control recommendations you will likely hear “follow the label” over and over again. So, why do we emphasize the pesticide label so strongly when talking to both homeowners and landscape professionals?
There are many important reasons why you should always read and follow label instructions.
- The Label is the Law – using a pesticide in a manner that is inconsistent with the label is a violation of the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA). Using a product inconsistent with the label includes, but is not limited to: rate of application, use on site not labeled for control, use on plants/lawns not labeled, frequency of application, method of application, distance from water sources, etc.
- Safety of Humans – using a product incorrectly can cause harm or even lead to death
- Safety to Non-target Organisms – this includes non-target insects, reptiles, birds, fish, mammals, and plants which can lead to negative impact on environment and economy
- Effectiveness of Product – millions of dollars are spent to figure out the most effective way a product works best, follow their instructions! (remember the manufacturer wants the product to be effective so that you’ll recommend to others and buy it again)
- Increased Resistance Decreases Control – improper application and a failure to rotate products as part of an integrated pest management program can increase likelihood of resistant pest populations
Before shopping for any pesticides, do some research:
- Has the pest been identified properly? What life cycle stage is the pest at? Most pesticides have different levels of efficacy depending on life cycle of target. For example, glyphosate works best on young plants that have not yet flowered. Your local extension office can help with identification and timing of control methods
- Can you control the pest with cultural practices such dethatching, irrigation, fertilizer, or mowing height changes? Start with the least toxic method of control and only work up if ineffective
- Read the label before you buy to be sure that it is labeled for your plant /lawn, target pest. The label will also tell you what equipment you’ll need to mix and apply and safety equipment. If product is not ready to use, be sure you can follow mixing and application procedures safely
- Are there particular environmental precautionary statements that are relevant to your site?
- How much do you need? Have you measured the area for treatment? Just as you don’t want to make multiple trips to the store, you also do not want a lot of excess chemicals on hand. They have to be stored or disposed of according to label instructions, too
For more information about pesticide labels read EDIS PI-34 Interpreting Pesticide Label Wording.
by | Jul 1, 2013
This summer parts of the Florida Panhandle have been blessed with ample rain, but coupled with high temperatures, this can be both a blessing and a curse.
Adequate moisture is critically important to landscape plants during hot weather, but too much rain or excessive watering also can bring problems. Wet soil combined with high temperatures can create stressful conditions for bedding plants, vegetables, shrubs and even trees – especially those just planted this year.
When the soil is saturated with water, pore spaces in the soil, which normally hold air, are filled with water. Since the roots of plants get the oxygen they need from the air in those spaces, the roots can literally drown in a soil that stays waterlogged over an extended period.
In turn, a sick root system leads to a sick plant. Plants in such situations often lose vigor, look wilted, turn yellow, are stunted and often die.
Symptoms of Root Rot on Azalea
Wet soil conditions also encourage fungus organisms that live in the soil to attack the roots or crown of a plant, thus causing rot. The crown is the area where the stem of a plant enters the soil. These disease organisms can cause die-back, inflict severe damage or even kill plants. Worse yet, once infection occurs, little can be done to help a plant affected by these disease organisms.
Plants with succulent stems such as impatiens and begonias, those that like cooler temperatures such as geraniums and dianthus and those that prefer drier, well-drained soils such as Indian Hawthorns are particularly susceptible.
Gardeners can take steps to help alleviate the situation. First , it is critical to adjust irrigation systems that are on automatic timers. Often seen are sprinklers unnecessarily watering at homes or businesses the day after or during a heavy rain simply because the timer turned them on. Turn off the automatic timer if the weather is wet, and turn the system on only when drier conditions occur.
Home Irrigation Timer
Beds should always be well mulched, at 2-4 inches, to control weeds and maintain soil moisture. If garden beds are staying too wet, however, the mulch can be pulled back from around plants or removed entirely to allow the soil to dry faster. Just make sure keep weeds are kept under control while the mulch is off.
Plants affected by wet soils or root rot may look wilted even though the soil is moist. A plant showing these symptoms immediately after a period of prolonged heavy rain may benefit from soil aeration in its root zone. Using a garden fork by driving the tines straight down into the soil and pulling straight out in numerous places around the plant is helpful. This provides air to the roots and encourages the soil to dry faster. Just be sure you don’t dig with the fork.
Gardening Fork
Fungal diseases that attack the foliage of many plants also are encouraged by rainy weather. Black spot on roses is prevalent even on fairly resistant varieties, and control is nearly impossible if it rains every afternoon. Cercospora leaf spot and Powdery mildew on crape myrtles can cause the leaves to turn yellow or red and drop off. The disease is not fatal, and the trees will recover without sprays, but flowering may be diminished.
Powdery Mildew on Crape Myrtle
Cercospora Leaf Spot on Crape Myrtle
Other pests such as snails and slugs thrive and reproduce rapidly during rainy weather. These pesky critters chew holes in the leaves and flowers of plants and are particularly fond of soft-leaved plants such as impatiens, begonias and hostas. Try not to let their populations get out of control. Note that Toads should be left alone because they feed on slugs. There also are numerous baits on the market that will help control snails and slugs. You can even place a bowl up to its rim in the ground and fill it half full of beer to attract and drown many snails and slugs.
Frequent rains can leach available nutrients from the soil in the landscape. Landscape plantings should be evaluated with this in mind and be fertilized, if needed. If possible, controlled release fertilizer should be used in this situation. Plants rapidly growing now such as lawn grasses, summer bedding plants and tropicals like ginger and hibiscus are especially vulnerable.
by Mary Salinas | Jun 21, 2013
We love our native magnolias in part because they are tough, easy to care for trees. The mainstay of southern gardens, they grace us with attractive thick, waxy leaves year round and sublimely fragrant and graceful blooms.
However, this past spring brought conditions that encouraged a fungal leaf disease known as anthracnose, most noticeably on the southern magnolia, Magnolia grandiflora. Affected leaves develop large irregular dead patches with a clearly defined border. The dead patches are a brownish gray and will flake and eventually deteriorate and fall away from the rest of the leaf. Fortunately it is rare for the disease to affect all branches of the tree and infection is somewhat spotty as you can in the photograph below.
Credit: Mary Derrick, UF/IFAS Extension
Conditions that favor the development of anthracnose in magnolia are the cooler, moister conditions that the panhandle experienced this early spring. Spores overwinter on affected branches and in leaf litter and travel to their new hosts through rain, wind and splashing water.
View this article to learn more about the Southern Magnolia
[important]The good news is that this disease is rarely a serious threat to the long term health of the magnolia. [/important]
Credit: Mary Derrick, UF/IFAS Extension
But in order to avoid another infection next spring, remove and dispose of as many affected leaves as possible from the tree and certainly those that have fallen. Avoid irrigation that wets the leaves because the consistent presence of moisture on the leaf is a perfect incubator for anthracnose. Ensure that there is sufficient air flow around the trees. Fungicidal treatment is generally not warranted.
by Matthew Orwat | Jun 17, 2013
Although black or white streaks are shocking when they appear on an otherwise healthy lawn, the incidence of slime mold is rarely harmful.
Closeup: Slime Mold in Centipedegrass. Image courtesy Matthew Orwat
Slime mold is actually caused by the reproductive structures of an array of different organisms, classified as plasmodia or Protista, which are regularly present in the soil. They are often mistaken for fungi. The different types are referred to as myxomycetes or dictyosteliomycetes. They usually appear on warm humid days in late spring or early summer after extended periods of rain. This extended period of heat and humidity, as is currently being experienced in the Florida Panhandle, initiates the perfect climate for slime mold development.
Slime Mold in Centipedegrass. Image Courtesy Matthew Orwat
As depicted in the picture above, slime mold makes the lawn look like it was just spray-painted with black or grey paint. The round fruiting bodies, called sporangia, carry the spores which will give rise to the next generation of the “mold”. After a few days the sporangia will shrivel up, release the spores and leave no noticeable trace on the lawn.
Slime Mold Sporangia. Image Courtesy Matthew Orwat
Currently, no fungicide exists to control slime mold because chemical control is not necessary. An excellent method to speed up the dissipation of slime mold is to mow or rake the lawn lightly. This will disturb the spores and hasten their departure. Another effective removal method is to spray the lawn with a forceful stream of water. This process washes off the slime mold sporangia and restores the lawn to its former dark green beauty.
Excessive thatch accumulation also increases the probability of slime mold occurrence.
For more information consult your local county extension agent or read the Alabama Cooperative Extension publication Slime Mold on Home Lawns.
