Citrus Greening (HLB) A Troublesome Bacterial Pathogen

Citrus Greening (HLB) A Troublesome Bacterial Pathogen

Small Fruit vs Normal

If we look at the big picture when it comes to invasive species, some of the smallest organisms on the planet should pop right into focus. A microscopic bacterium named Candidatus Liberibacter asiaticus, the cause of Citrus Greening (HLB), has devastated the citrus industry worldwide. This tiny creature lives and multiplies within the phloem tissue of susceptible plants. From the leaves to the roots, damage is caused by an interruption in the flow of food produced through photosynthesis. Infected trees show a significant reduction in root mass even before the canopy thins dramatically. The leaves eventually exhibit a blotchy, yellow mottle that usually looks different from the more symmetrical chlorotic pattern caused by soil nutrient deficiencies.

One of the primary vectors for the spread of HLB is an insect called the Asian citrus psyllid. These insects feed by sucking juices from the plant tissues and can then transfer bacteria from one tree to another. HLB has been spread through the use of infected bud wood during grafting operations also. One of the challenges with battling this invasive bacterium is that plants don’t generally show noticeable symptoms for perhaps 3 years or even longer. As you would guess, if the psyllids are present they will be spreading the disease during this time. Strategies to combat the impacts of this industry-crippling disease have involved spraying to reduce the psyllid population, actual tree removal and replacement with healthy trees, and cooperative efforts between growers in citrus producing areas. You can imagine that if you were trying to manage this issue and your neighbor grower was not, long-term effectiveness of your efforts would be much diminished. Production costs to fight citrus greening in Florida have increased by 107% over the past 10 years and 20% of the citrus producing land in the state has been abandoned for citrus.

Classic blotchy mottle in Leaves

Many scientists and citrus lovers had hopes at one time that the Florida Panhandle would be protected by our cooler climate, but HLB has now been confirmed in more than one location in backyard trees in Franklin County. The presence of an established population of psyllids has yet to be determined, as there is a possibility infected trees were brought in.

A team of plant pathologists, entomologists, and horticulturists at the University of Florida’s centers in Quincy and Lake Alfred and extension agents in the panhandle are now considering this new finding of HLB to help devise the most effective management strategies to combat this tiny invader in North Florida. With no silver-bullet-cure in sight, cooperative efforts by those affected are the best management practice for all concerned. Vigilance is also important. If you want to learn more about HLB and other invasive species contact your local UF/IFAS Extension office.

Asymmetrical Fruit

 

 

 

 

 

 

 

 

 

 

Typical nutrient deficiencies observed in leaf, on trees with heavy fruit load. Not related to Citrus Greening (HLB)

 

Article by: Erik Lovestrand, UF/IFAS Franklin County Extension Director/Florida Sea Grant Agent

 

 

Plan Carefully with Indian Hawthorn

Plan Carefully with Indian Hawthorn

One of the most commonly used shrubs in landscapes is the Indian hawthorn, Rhapheolepsis indica. Although not native to Florida, it can be a very attractive shrub when used properly in landscapes. Plants offer spring flowers in pinks and whites followed by berries that are a food source for birds.

Indian hawthorn

Indian hawthorn as a single planting can be attractive.

 

Indian hawthorn plants in landscapes are susceptible to a couple of pests that create unattractive and unhealthy plants. A leaf spot fungus called Entomosporium leaf spot easily spreads from infected plants through irrigation and rainfall leading to leaf discoloration, leaf drop, and dieback of limbs. Scale insects can also be common on leaves causing yellowing and dieback. The fungal problem is difficult to manage on heavily infected plants but the scale can be managed with a low toxicity pesticide choice such as a horticulture oil.

Indian hawthorn disease

A heavy infection of leaf spot fungi is often too difficult to manage when plants are routinely irrigated.

 

Most often the problems on Indian hawthorn, especially fungal, are the result of poor management. This shrub likes sun, well-drained soil, and no overhead irrigation. Once established, plants should need little supplemental irrigation and water should only be applied to the base of plants. Since plants normally form a rounded mound, there is also little need for pruning if planted in a correct spot and spaced appropriately when planting. Most landscape installations of Indian hawthorn space plants based on the gallon pot size and not the mature size of the plant which is about 3-5 feet in height and spread.

Indian hawthorn can still be a good selection for homeowners. Buy healthy plants without any signs of spots on leaves and don’t plant a monoculture of these plants in the landscape. If one plant does have serious pest issue it is easier to either treat or remove one plant versus a mass planting.

Get an Early Start on Spring Veggies

Get an Early Start on Spring Veggies

 

Raised bed spring vegetable garden in NW Florida

Raised bed spring vegetable garden in NW Florida – photo credit: Blake Thaxton

Growing spring vegetables in northwest Florida can be challenging!  Sometimes failures seem more numerous than successes.  Extreme cold events in the winter and blistering hot summer days make it tough on vegetables.  One suggestion is to get the garden started earlier than usual!

The climate in northwest Florida challenges the gardener due to very high insect pest pressure and it being the perfect environment for fungal and bacterial diseases to grow.  Hot and humid summers with moderate winters can be disastrous because diseases will be very active and the insects are not eliminated by extreme cold temperatures.  Random cold temperatures in the spring make it hard to know when to plant the vegetable garden.

[important]Because insects and diseases become more active as it gets warmer in the spring, getting a head start may aid the success of your vegetable garden.[/important]

How can a gardener get a head start?  Here are a few suggestions:

  • Start Vegetable Transplants Inside

Seems simple, but just getting seed started in a temperature controlled environment can help the vegetable plants get a leg up on the insect pests and diseases that are eminent.  If you have a greenhouse structure, that would work perfectly.  If not, consider starting your plants in a room with as much possible natural light.  On warm days take the plants outside to get some sunshine.

  • Use Black Plastic Mulch

Tomato Plant grown with black plastic mulch - photo credit: Blake Thaxton

Tomato Plants grown with black plastic mulch – photo credit: Blake Thaxton

Black plastic mulch is commonly used in commercial vegetable production.  One of its main functions is to help warm the soil to encourage root growth of the vegetable plants.  Other benefits include good moisture and weed control.

Learn more from this Penn State Extension website: Plastic Mulches

  • Use Row Covers

Row Covers protect vegetable plants in the ground when temperatures drop lower than expected in the early spring.  Row covers are transparent or semitransparent flexible materials used to cover a row of plants to help insulate the air around the plant from the colder temperatures and wind.  If you can not find this kind of material you can always use black plastic nursery pots, Styrofoam cups, or other materials to protect individual small plants.

Learn more from this UF/IFAS publication: Row Covers for Growth Enhancement

  • High Tunnel Structures

High Tunnel with end walls and side walls removed for cooling warmer teperatures - photo credit: Blake Thaxton

A High Tunnel with end walls and side walls removed for cooling warmer temperatures – photo credit: Blake Thaxton

Another method of protecting your vegetable garden from cold early spring temperatures is to construct a high tunnel, also known as a hoop house.  A high tunnel is a structure that looks very much like a greenhouse but the crops are planted in native field soil and the structure lacks an active temperature control.  The temperature is passively controlled by rolling up end walls and side walls on warm days and closing the walls when cool temperatures are expected.

Learn how to build a high tunnel from this video from Utah State Extension: How to Build a High Tunnel

For more information on any of these topics please contact your local UF/IFAS Extension Agent or email Blake Thaxton: bthaxton@ufl.edu