Hillsborough Extension Garden Blog

Solutions you can use for your gardening problems.

It’s Phytophthora, Not a Lichen December 31, 2013

Filed under: Uncategorized — Hillsborough County Residential Horticulture @ 6:59 pm

Lichens often get a “bad rap.” They are a common “mistaken identity” and blamed for tree and plant death and decline.

A lichen (pronounced lī-ken) is a relationship between an algae and a fungus, but the fungi do not exist independently and therefore are not capable of causing disease.  Lichens have structures called rhizoids, or fungal hyphae, and the rhizoids attach to rocks, bark, branches, and soil. As with Spanish moss, lichens do not parasitize the structures they are living on. They obtain minerals from atmospheric moisture such as rainwater, fog and dew, plant leachates and organic debris.

Examples of common lichens mistaken as disease. Photo credit: Nicole Pinson

Examples of common lichens mistaken as disease. Photo credit: Nicole Pinson

If your tree appears diseased, consider other contributing factors such as stress, drought, disease, insects and water. For example, if your citrus tree is declining and you see a gummy sap, the problem may be phytophthora, not a lichen.

Lichen on citrus tree.

Lichen on citrus tree.

The UF/IFAS Citrus Research and Education Center provides a website for management and field diagnosis of phytophthora and other citrus diseases. You can access the site at this link: http://www.crec.ifas.ufl.edu/extension/plant_pathology/phytophthora.shtml

Phytophthora is a soil-borne disease. Signs and symptoms of phytophthora include yellow veins, shoot dieback and leaf/fruit drop, trunk damage (often from mechanical equipment), gummosis, sloughing off of roots (root rot) and bark peeling in the crown roots and trunk located near the soil level (foot rot).

Causes of phytophthora or foot rot include poor drainage or soils with hard pans or clay layers, areas with a high water table, overirrigation, tree damage, planting too deep and mulching around the base. Use of mulch under citrus trees can make your tree prone to infection by limiting air circulation. Be sure to maintain a grass and weed free zone beneath your tree.

Phythophthora, also known as foot rot. Photo credit: UF/IFAS

Phythophthora, also known as foot rot. Photo credit: UF/IFAS

You can try to scrape off the discolored bark until you reach healthy wood, and apply a copper fungicide to affected areas. Treatment with a copper fungicide may help, but foot rot is very serious and your tree may not recover. In addition, disease occurs when three conditions favor disease development: susceptible host, environment and pest or pathogen. All three need to be present for disease to occur. If you treat with fungicides or replant, and do not address conditions such as poor drainage, the problem may continue to occur.

The UF/IFAS Extension Hillsborough County provides information about citrus diseases. Contact our office if you have questions about how to care for your dooryard citrus.

Nicole Pinson
Extension Agent – Urban Horticulture
Master Gardener Coordinator
UF/IFAS Extension Hillsborough County
5339 County Road 579
Seffner, FL 33584-3334
p: (813) 744-5519 X 54145
nicolepinson@ufl.edu
pinsonn@hillsboroughcounty.org

http://hillsborough.ifas.ufl.edu

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Indian Hawthorne Spots

Filed under: Uncategorized — Hillsborough County Residential Horticulture @ 5:55 pm

Have you noticed spots on your Indian Hawthorne plants?

Leaf spots on Indian Hawthorne can be evidence of Entomosporium leaf spot, Cercospora leaf spot or anthracnose. All are caused by fungi that spread by spores.

Temperatures between 59°F and 77°F favor Entomosporium leaf spot. Warm temperatures and wet conditions favor anthracnose and Cercospora leaf spot. Dry conditions are less conducive to disease development.

Although it is difficult to control the weather, you can reduce disease potential by:

  • replacing overhead irrigation with drip irrigation (which also helps conserve water).
  • watering in early morning, or close to dew point, to reduce the amount of time moisture remains on leaves.
  • changing irrigation practices when weather (for example, rainfall) favors disease development.
  • improving air circulation around plants.
  • pruning and removing dead and diseased branches.
  • collecting leaves with symptoms and disposing them in the trash (not in the compost pile).
  • following the 3rd Florida-Friendly LandscapingTM principle and fertilizing appropriately, to discourage disease development.
  • following the 4th Florida-Friendly LandscapingTM principle and applying a two to three inch layer of mulch.
  • selecting disease resistant cultivars.
  • using and rotating fungicides when appropriate.
  • learning what is normal in your garden and scouting regularly for pests and diseases.

The UF/IFAS Extension Hillsborough County provides information about plant disease and can assist you with symptom identification. Contact our office if you have questions or need assistance with sample submission. In some cases, sample analysis by a laboratory may be necessary to determine the exact cause of disease.

 

Nicole Pinson
Extension Agent – Urban Horticulture
Master Gardener Coordinator
UF/IFAS Extension Hillsborough County
5339 County Road 579
Seffner, FL 33584-3334
p: (813) 744-5519 X 54145
nicolepinson@ufl.edu
pinsonn@hillsboroughcounty.org

http://hillsborough.ifas.ufl.edu

 

Identifying Citrus Greening

Filed under: Uncategorized — Hillsborough County Residential Horticulture @ 4:16 pm

A Hillsborough County resident contacts the Extension office, asking how to tell if her citrus trees are infected with citrus greening. She mentions over the past few years, her trees have declined and some of the leaves look similar to pictures she has seen online.

Citrus greening, also known as Huanglongbing (HLB) disease, is one of the more recent diseases affecting citrus trees. Confirmed in Florida in 2005, the disease has spread to all citrus producing counties in the state.

All citrus are susceptible to greening, and the disease is caused by the bacterium Candidatus Liberibacter spp. and the bacterium is spread by a tiny insect vector called the Asian citrus psyllid. When the Asian citrus psyllid feeds on infected citrus trees, it can pick up the disease-causing bacterium and move the disease from tree to tree.

This bacterial disease affects the vascular tissue of the plant (the phloem) and inhibits nutrient transport. When phloem transport is disrupted, signs such as twig dieback occur. Citrus greening causes smaller fruit, inferior fruit quality and taste, less fruit production, increased fruit drop and twig dieback.

To determine if citrus greening disease may be causing your tree to decline, please consider the following symptoms:

  • The early symptoms of citrus greening on leaves are vein yellowing and an asymmetrical “blotchy mottle.”
  • Trees may show twig dieback, causing productivity to decline within a few years.
  • Fruit are often few in number, small, may be lopsided with a curved central core and fail to color properly. You can often cut the fruit in half and notice the lopsided, central core.
  • Fruit drops prematurely from afflicted trees.
  • The fruit may contain aborted seeds and have a salty, bitter taste.
Asymmetrical fruit with lopsided central core and aborted seeds. Photo credit: JoAnn Hoffman

Asymmetrical fruit with lopsided central core and aborted seeds. Photo credit: JoAnn Hoffman

Leaf showing blotchy mottle. Photo credit: Mongi Zekri

Leaf showing blotchy mottle. Photo credit: Mongi Zekri

If your citrus trees are healthy, take care of them by following a routine fertilizer and irrigation schedule. Avoid planting and neglecting citrus trees in the landscape. If trees no longer produce fruit, homeowners must decide to remove them and whether or not to invest in replanting.

Florida oranges supply about 90% of the United States’ orange juice. Citrus greening impacts our lives because it reduces juice quality, decreases revenue and employment opportunities and affects Florida’s culture, as citrus trees and fruit are a sentimental, inherent part of Florida’s landscape and history. There is a lot we don’t know about this disease, but coordinated research efforts focused on psyllid control, tree nutrition, mapping genomes, biological control and disease-resistant trees may provide insight into this disease.

The UF/IFAS Extension Hillsborough County provides information about citrus greening and can assist you with symptom identification. Contact our office if you have questions about citrus greening or sample submission.

Nicole Pinson
Extension Agent – Urban Horticulture
Master Gardener Coordinator
UF/IFAS Extension Hillsborough County
5339 County Road 579
Seffner, FL 33584-3334
p: (813) 744-5519 X 54145
nicolepinson@ufl.edu
pinsonn@hillsboroughcounty.org

http://hillsborough.ifas.ufl.edu

 

 
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