by Gary Knox | Nov 6, 2017
Crown gall symptoms on roses caused by the bacterium Agrobacterium tumefaciens (Rhizobium radiobacter) – Photo credits: Kamil Duman
A plant with a mature gall that is potentially releasing the crown gall bacterium into the potting media. Photo credits: Susannah Wright
For gardeners, rose enthusiasts and rosarians, each of the many rose diseases is as important as the others. But we can say for sure Crown Gall is one of the most unsightly of the many rose diseases that can been seen currently.
The disease got this name from the large tumor-like swellings (galls) that typically occur at the crown of the plant, just above the soil level. The cause of crown gall disease is a bacterium that resides in the soil, Agrobacterium tumefaciens (updated scientific name Rhizobium radiobacter).
SYMPTOMS
Galls or overgrowth (1/4 inch to several inches in diameter) of host plant tissue typically form at the soil line but also can form on branches or roots. Galls are initially white, spherical, and soft but darken with age as outer cells die. It can either be almost entirely on the surface of the plant and easily detached or can be almost indistinguishable from normal plant tissue except for its greatly enlarged appearance.
The bacterium that causes Crown Gall disease survives and persists in the soil for up to 3 years. It can invade recent wounds on the branches or roots. Swelling can be seen as early as 14 days following entry of the bacterium into the plant. The tissue near the gall can be crushed due to rapid cell enlargement. If vascular tissue is crushed, wilting can result from the restricted water movement.
Early stage symptom of Crown Gall on roses can be noticed as the small white galls. Photo credits: Susannah Wright
The galls can enlarge to a quarter size in a short period of time from the initial small galls. Photo credits: Mathews Paret
ABOUT THE BACTERIUM
Agrobacterium uses its genes as a weapon to attack plants. It enters the plant mostly from the soil through wounds on the roots or lower stem or from the branches during plant pruning. Symptoms are caused by the insertion of a small segment of DNA (known as the T-DNA), from a plasmid, into the host plant cell, which is incorporated into the plant genome. When the plasmid links up with the plants own DNA, the altered plant cells start dividing rapidly and uncontrollably, and the root or stem develops a tumor-like swelling.
Galls can range from pea size to softball size. Tiny cracks from freezing temperatures or wound sites can be the site of gall formation. Once the wound compounds are generated, the bacteria detach from the xylem cell walls and are carried upward with water during evapotranspiration to the wound site where they initiate galls. One of the common ways of the spread of the disease is by pruning infected plants and moving the bacterium accidentally while pruning nearby healthy plants.
The crown gall bacterium is a soil pathogen, which means main inoculum source is soil. The bacterium can overwinter in infested soils, where it can live as a saprophyte for several years. The bacterium can easily during field preparation, pruning and irrigation. Insects, nematodes and grafting materials, can also transfer the bacterium.
The galls will turn dark in color as they age. Photo credits: Kamil Duman
HOW CAN YOU MANAGE ROSE CROWN GALL DISEASE
- Plant only disease-free roses. Check very carefully before you buy plants for any kind of galls in the crown or branches. Use good sanitation practices in handling roses.
- Plant in clean soil. Avoid areas with a history of crown gall infestation.
- Avoid fields with heavy infestations of root-attacking insects and nematodes.
- Select well-drained soil and irrigate from clean water sources.
- Keep grafts and buds well above the soil line.
- Destroy diseased plants as soon as you notice them to avoid cross-contaminating other plants, or pruning equipment. Also, do not keep infected plants with healthy plants, as the likelihood of accidental transmission through pruning is high.
- Avoid mechanical injury to plants from tillage and hoeing. Provide winter protection so that the bark does not crack.
- Disinfect pruning tools between plants. disinfect budding/grafting tools before and after use. Bleach (10%; equivalent to 0.6% sodium hypochlorite), or quaternary ammonium-based sanitizer are effective as disinfectants. Make sure to prepare fresh stock routinely.
- If crown gall plants are noted, please let your local county extension agent know about it and they will be able to contact us for additional site-specific management plans if needed.
Gall formation at pruning sites indicating contamination of the plant during pruning. Photo credits: Kamil Duman
Authors: Kamil Duman, Susannah Wright, Fanny Iriarte, Barron Riddle, Gary Knox and Mathews Paret, University of Florida – NFREC, Quincy, FL
by Matt Lollar | Oct 2, 2017
Over the last month or so, home gardeners and commercial growers alike have noticed what look to be large dust particles floating through the air. It’s probably not uncommon to have inhaled a few or even a few hundred of these mysterious particles. Most likely, these “particles” aren’t dust at all but whiteflies instead. Whiteflies are small (less than a tenth of an inch long), white, soft-bodied insects. They aren’t flies but are considered ‘true bugs’ by entomologists. The most common whitefly species in Northwest Florida is the silverleaf whitefly, also known as the sweetpotato whitefly. Whitefly numbers have exploded exponentially this year because of last years’ mild winter. These irksome insects feed on a variety of annuals, shrubs, vegetables and trees.
Magnified whitefly adults and eggs. Photo Credit: James Castner, University of Florida/IFAS.
Whiteflies typically feed on the underside of leaves. Initially, disturbed leaves will become pale in color, then a sticky substance may develop on the surface of the leaves. This sticky substance is called honeydew. Honeydew is actually a sugary substance excreted by the whiteflies as part of their elimination process, similar to what aphids and scale insects produce. After honeydew is deposited, sooty mold develops to feed on this readily available sugar source. Sooty mold is a fungus that forms a gray to black colored coating on plant leaves. It normally grows on leaves that were previously covered with honeydew. Sooty mold hinders the ability of leaves to absorb light and ultimately limits photosynthesis.
Pale squash leaves due to feeding from whiteflies. Photo Credit: University of Florida/IFAS.
So what should be done to control whiteflies? It depends on what is being grown. If whiteflies are present, the role of beneficial insects should be taken into consideration. Plenty of predatory insects such as lady bugs and green lacewings are around to feed on whiteflies. In fact, leaving the whiteflies alone on your trees and shrubs will attract more predatory insects. Below are some whitefly control methods that produce minimal damage to beneficial insect populations.
Whitefly Control in Vegetables
- Sticky Traps – Yellow sticky traps are a good way to monitor whitefly populations and can help determine when insecticide application is appropriate.
- Insecticidal Soaps – Insecticidal soaps are usually applied as a 1 to 2 percent solution (2½ to 5 tablespoons per gallon of water). It is important to follow the application directions on the label. Insecticidal soap should be applied in the evening, when the sun is low in the sky and the temperature is below 85°F. Some insecticidal soaps available at local lawn and garden centers include: Bonide Insecticidal Soap, Bonide Insecticidal Soap, and Bayer Advanced Natria Insecticidal Soap.
- Horticultural Oils – Horticultural oils should be handled like insecticidal soaps. Like the soaps, they should be applied in the evening. Some horticultural oils available at local lawn and garden centers include: Bonide All Seasons Spray Oil, Southern Ag Parafine Oil, and Garden Safe Neem Oil.
- Other Insecticides – Harsher chemicals are not recommended for the home gardener, because whiteflies have become resistant to most products on the market. Use of broad spectrum insecticides may also contribute to an increase in whitefly populations because they kill beneficial predatory insects.
Hopefully winter will be cooler this year and the profuse whitefly population will be knocked back. Until then, we wish all home gardeners the best of luck with fall gardening!
by Matthew Orwat | Aug 24, 2017
On Saturday, September 16th, 2017, from 9AM to 12PM, UF / IFAS Extension Washington County will be providing a rose gardening workshop for gardeners across the Panhandle. Many roses are hard to grow in the Florida Panhandle without investing considerable time and energy into spraying for insect and disease problems. This workshop will teach attendees how to select and sustainably grow roses adapted to the hot-humid conditions of the Southern Gulf Coast. There will be opportunities for outdoor learning and hands-on activities.
Topics include:
- Selection of disease resistant rose cultivars adapted to the lower South
- Resources to obtain hard to find easy care rose cultivars
- Soil and Nutrient Management
- Disease and insect management
- Irrigation
- Rose Propagation
Participants will be given the opportunity to propagate their own rose and take home their own propagation assembly to grow their own roses from scratch.
Refreshments will be provided and a door prize will be available.
Address: Washington County Ag Center Auditorium, 1424 Jackson Ave, Chipley FL 32428.
Pre Registration required for count: Contact Nikki or Cynthia at 850-638-6180 or email Matthew Orwat at mjorwat@ufl.edu
or register online at eventbrite HERE !
by Daniel J. Leonard | Aug 11, 2017
Growing in containers can be one of the most versatile ways to add color, texture and mobility to the landscape. However, gardeners generally reach for finicky annuals to fill their pots with pizzazz. The problem with this strategy is that most annuals and perennials need to be watered constantly, fertilized regularly, and changed out with the seasons. That sounds like a little bang for a whole lot of buck! I and most of the real plant people I know fall squarely in the school of lazy gardening and believe there is an easier, less intensive, and ultimately less expensive way to get the same result. This can be accomplished by thinking outside the box and using an alternative class of plants that can fit the same bill of providing color and texture in pots without the headaches and have been sitting on the shelves right in front of us the whole time, the shrubs.
It is beyond me why shrubs aren’t used as container plants more often. Maybe the reason for the lack of use is pure perception; after all, no one with any sense would plant a giant, coarse green meatball or an enormous antebellum azalea in a decorative pot on their front walk. Recent innovations by plant breeders have left this argument moot though as new introductions of old species have revived interest in the entire group. Many of the best of these new cultivars sport traits perfect for container culture (dwarf growth habit, increased flowering, and interesting texture and form) while preserving the ironclad, undemanding nature of their parent plants. The following are a few of my favorite new shrub introductions for container growing!
- ‘Purple Pixie’ Loropetalum
Purple Pixie loropetalum is a low-growing shrub that can spill beautifully out of a container. (Photo by MSU Extension Service/Gary Bachman)
If interesting architecture is what you require in a plant, ‘Purple Pixie’ must be on display in your yard. This dwarf cultivar of the wildly overused purple shrub Loropetalum chinense has taken the horticultural world by storm. The unique combination of true purplish foliage that only greens slightly in the hottest summer sun, ribbon-like pink spring flowers, and a graceful weeping habit make ‘Purple Pixie’ a winner. Give this plant a medium sized container (at least 12” in diameter), water when the soil begins to dry, fertilize infrequently with a slow-release formulation, site in full sun to partial shade, and enjoy for many seasons to come.
This is definitely not your granddaddy’s Ligustrum. Gone are the rampant growth, sickly sweet smelling flowers, and the aggressive nature of ‘Sunshine’s’ parent Chinese Privet (Ligustrum sinense). ‘Sunshine’ is a sterile cultivar with dwarf characteristics (growing 4-5’ with infrequent light pruning), vivid yellow-chartreuse foliage, and most importantly, no flowers. All ‘Sunshine’ asks of us is plenty of sun, occasional fertilizer and a light haircut once or twice a season! Use this plant to frame a dark flowerbed or in a container as a companion to the previous plant, ‘Purple Pixie’ Loropetalum for an extremely striking combination!
‘Sunshine’ Ligustrum. Photo courtesy of JC Raulston Arboretum.
A new take on a landscape standard, ‘Baby Gem’ is an exceptionally compact and slow growing cultivar of Buxus microphylla var japonica. All the same features gardeners love about traditional “full-size” boxwoods remains (tight, formal growth habit, ability to prune into many different shapes and ironclad constitution) but with ‘Baby Gem’ are delivered in a perfect package for a pot. This little “gem” of a plant is perfect for use in a smallish container to frame a formal landscape or to give a sense of order to an informal container garden or border!
So if you’re ready to stop replacing all of your potted plants each and every season, reach for one of these shrubs the next time you are at a garden center. You’ll likely be rewarded with compliments on your creativity, four season interest from the plants themselves, and more time to enjoy being in your garden instead of laboring in it! As always, if you have any questions about this or any other horticultural topics please contact your local UF/IFAS Extension office! Happy Gardening!
by Julie McConnell | Jul 12, 2017
Coontie (Zamia floridana) planted at the same time but growing at different rates. Photo: J_McConnell, UF/IFAS
When designing landscapes, it is popular to create lines and masses of plants for high visual impacts. Plants are carefully selected to be similar in size and shape at the time of installation. They are all grouped together, so they must be getting the same care, but why do they look different years later? There are several factors to consider when we are trying to figure out why a perfectly matched set no longer looks like a uniform planting.
Although plants may be in the same bed, shadows cast at certain times of the day may reduce sunlight to some sections and not others. This can be caused by structures or trees that have grown over time and changed light patterns.
Supplemental irrigation may also be variable even with the best system design. Over time plants grow and may block sprinkler emitters from reaching some sections of landscape beds. Even if the landscape relies on natural rainfall, there can be still be dry/wet spots in the landscape due to drainage off of hard structures, low areas, or wind direction during storms.
It might be possible to adjust some lighting and watering issues, but there is one factor that many gardeners have not considered – genetics. If plants were grown from seed, than variation is not only possible, but likely. This might be displayed as differences in height and width, foliage color, flower color, speed of growth – all may be influenced by parentage despite best efforts to care for each plant similarly.
Many landscape plants are cultivars. This means they are grown from cuttings or divisions which make them identical to the original plant. When a plant is grown from seed, however, there is no guarantee it will have the same specific qualities as the mother plant.
To combat this phenomenon, landscapers should check sunlight and watering for irregular growth patterns and adjust if needed. If a landscape design requires uniform plants, use named cultivars rather than seedling grown plants in lines or masses.
by Matt Lollar | Jun 29, 2017
Algal leaf spot, also known as green scurf, is commonly found on thick-leaved, evergreen trees and shrubs such as magnolias and camellias. It is in the genus Cephaleuros and happens to be one of the only plant parasitic algae found in the United States. Although commonly found on magnolias and camellias, algal leaf spot has a host range of more than 200 species including Indian hawthorn, holly, and even guava in tropical climates. Algal leaf spot thrives in hot and humid conditions, so it can be found in the Florida Panhandle nearly year round and will be very prevalent after all the rain we’ve had lately.
Symptoms
Algal leaf spot is usually found on plant leaves, but it can also affect stems, branches, and fruit. The leaf spots are generally circular in shape with wavy or feathered edges and are raised from the leaf surface. The color of the spots ranges from light green to gray to brown. In the summer, the spots will become more pronounced and reddish, spore-producing structures will develop. In severe cases, leaves will yellow and drop from the plant.
Algal leaf spot on a camellia leaf. Photo Credit: University of Florida/IFAS Extension
The algae can move to the stems and branches in more extreme cases. The algae can infect the stems and branches by entering through a small crack or crevice in the bark. The bark in that area cracks as a canker forms that eventually can girdle the branch, killing it.
Algal leaf spot on a sycamore branch. (Platanus occidentalis). Photo Credit: Florida Division of Plant Industry Archive, Bugwood.org.
Management
In most cases, algal leaf spot is only an aesthetic issue. If only a few leaves are affected, then they can just be removed by hand. \It is important that symptomatic leaves are discarded or composted offsite instead of being left in the mulched area around the trees or shrubs. If symptomatic leaves are left in the same general area then irrigation or rain water can splash the algal spores on healthy leaves and branches. Infected branches can also be removed and pruned.
Preventative measures are recommended for long-term management of algal leaf spot. Growing conditions can be improved by making sure that plants receive the recommended amount of sunlight, water, and fertilizer. Additionally, air circulation around affected plants can be increased by selectively pruning some branches and removing or thinning out nearby shrubs and trees. It is also important to avoid overhead irrigation whenever possible.
Fungicide application may be necessary in severe cases. Copper fungicides such as Southern Ag Liquid Copper Fungicide, Monterey Liqui-Cop Fungicide Concentrate, and Bonide Liquid Copper Fungicide are recommended. Copper may need to be sprayed every 2 weeks if wet conditions persist.
Algal leaf spot isn’t a major pathogen of shrubs and trees, but it can cause significant damage if left untreated. The first step to management is accurate identification of the problem. If you have any uncertainty, feel free to contact your local Extension Office and ask for the Master Gardener Help Desk or your County Horticulture Agent.
