Wednesday, June 29, 2011

Japanese Beetles Out in Full Force This Season

Robber fly eating Japanese beetle (Photo D. Stephan) 
Barbara Shew, our clinic director, said that she observed the cardinals in her yard putting on quite a show a few days ago.  They were knocking Japanese beetles from her crape myrtle flowers and then chasing the beetles as they tried to fly away.  I guess sometimes cardinals delight in chomping down some beetles in addition to their usual diet of seeds.  Cardinals are not the only animals that enjoy the occasional beetle treat.  My cat, Slinky, loves eating Japanese beetles.  She catches them, knocks them out with her paws, and then carries them to the hood of the car.  After letting them cook all day in the sun, she goes back and eats them! Predatory insects, like robber flies, assassin bugs, and others will feed on the adults.  Unfortunately, humans do not get the same satisfaction from finding these beetles in their yards. 

Japanese beetles emerge once per year to feast on a variety of ornamental and crop plants.  Their favorite ornamental hosts include roses, rosaceous trees, shrubs such as crab apple, crape myrtle and linden, grape, and fruit trees. 

Typically, Japanese beetles feed on the upper leaf surface eating the tissue between leaf veins.  This gives the leaves a lacy appearance, a type of damage called skeletonizing.  

Japanese beetle and skeletonizing damage (Photo: B. Shew)

They generally consume entire petals of roses and other flowers. Beetles aggregate on plants in response to chemicals (odors) released by damaged plants and pheromones released by female beetles.  The resulting hungry masses of beetles can rapidly devour trees, shrubs, vines, and flowers.

Japanese beetle damage (Photo: B. Shew)

 After they have fed for a while, the female beetles burrow into soil to lay their eggs.  Grubs (larvae) hatch from the eggs and feed underground through the rest of the summer and fall. Female beetles and the grubs prefer moist soils, so a damp summer means more beetles the following year.

The beetle grubs may be serious pests of the roots of grasses and shrubs, especially on turf farms and golf courses.  They burrow through the soil feeding on roots.  This can result in areas of dead grass.  The grubs overwinter deeper in the soil, and in the spring, they move just below ground level, complete feeding, and pupate.  New beetles emerge from pupae in late spring to start the cycle again.

Japanese beetles can fly long distances, so beetle traps do not offer any protection to landscape plants.  They may actually attract more beetles to your yard! Likewise, treating a lawn for Japanese beetle grubs will not reduce damage from incoming beetles.

Long-term protection for landscape and nursery plants can be achieved through the use of neonicotinoid insecticides such as imidacloprid (e.g., Merit, Marathon II) or acetamiprid (Tri-Star).  Acelepryn (chlorantraniliprole) is a new product with extremely low vertebrate toxicity but good efficacy against a number of pests, including Japanese beetles.

Japanese beetle on flower (Photo: B. Shew)

For more information on the biology and management of adult Japanese beetles in nurseries and landscapes, consult Ornamentals and Turf Insect Information note No. 146 at:

Special thanks to Steve Bambara and Dave Stephan for their help with this post!

Tuesday, June 14, 2011

It Looks Like a Dog Threw Up in My Mulch: Slime Molds - Harmless but Ugly!

Fuligo Septica in Mulch
Photo by Donna Steinbach (Submitted to PDIC)

Every year, we receive image samples depicting the “dog-vomit” slime mold. 

People see this ugly growth on their mulch and immediately want to get rid of it! The culprit is a slime mold known as Fuligo septica.  In spite of their names, the slime molds are not true fungi, but are related to amoebas, algae, and paramecia. These fascinating organisms spend part of their lives inconspicuously creeping through mulch, leaf litter, etc., engulfing bacteria and bits of organic matter.  Through some sort of environmental or chemical signal, they switch to the spore-producing phase of their life cycle.  In the case of Fuligo septica, the spore-producing fruiting body appears as a bright yellow froth that quickly forms a pinkish crust covering the dark powdery spores inside.  These spores will blow away and start the cycle over again.  The fruiting body can simply be raked out of the mulch or washed off with a hose. It is not toxic, although some people are allergic to the spores.  
Fuligo Septica Slime Mold
Photo by Donna Steinbach (Submitted to PDIC)

The dog vomit slime mold is not a plant pathogen. However, slime molds sometimes will grow on plant parts that touch the affected mulch, as seen on the end of a gardenia branch in the picture below.
Slime Mold on Gardenia
Photo by Mike Munster

Fuligo septica is often seen in hardwood mulches. It is less of a problem in pine bark or cedar mulches.  It is usually worse the first year mulch is applied than in subsequent years.  

While dog vomit is one of the most noticeable slime molds, many other types can be found in most back yards. 

Here are some other slime molds we have seen lately.  

Physarum Slime Mold
 On Annual Ryegrass and a weed (Carolina geranium)
Photo by Mike Munster

Physarum Slime Mold
On Cucumber
Photo by Anne Edwards

Slime molds can be startling, but up close they can be startlingly beautiful.  See the collection of images by Georgia resident Ray Simons here.

Special thanks to Mike Munster for helping with this blog idea!

Friday, June 10, 2011

Attack of the Killer Tomato (Spotted Wilt Virus)

TSWV fruit symptoms
Photo by F. J. Louws
Lately, we have seen a lot of tomato samples with tomato spotted wilt  (TSWV) come through the clinic.  TSWV is a virus that is spread by at least seven different kinds of tiny insects known as thrips.  It takes only 15 minutes of feeding for a tomato plant to become infected, and once TSWV is acquired, there is no cure.  TSWV is sporadic in nature with heavy disease pressure in some years relatively little disease pressure in others.  Due to this unpredictable nature, and the broad host ranges of thrips, controlling TSWV can severely challenge traditional pest management practices. 
TSWV can be a major problem both in greenhouses and in the field and can affect field crops like tomato, peanut, and pepper, tobacco along with many ornamental plants.  On tomatoes, symptoms may be expressed on leaves, petioles, stems, and fruit.  Early symptoms include cupping and off-colored bronzed foliage.  Later, leaves may show small, dark spots and eventually die.  Dark brown streaks can be seen on stems and petioles.  Plants may be severely stunted and new growth can be deformed.  Sometimes the plant may exhibit one-sided growth.  The tops of the plants may turn yellow and wilt.

TSWV foliar symptoms
Photo by E. C. Lookabaugh

Fruit symptoms are very distinctive.  Immature fruit have mottled, light green rings with raised centers.  Mature fruit has a unique red/orange mottling that can make the fruit unmarketable.

TSWV immature fruit symptoms
Photo by F. J. Louws 

TSWV mature fruit mottling
Photo by E. C. Lookabaugh

In North Carolina, tobacco thrips (Frankliniella fusca) and western flower thrips (F. occidentalis) are the two most common vectors.   Tobacco thrips are able to spread the virus from nearby weed hosts before they can be killed by insecticides applied to the crop.  Early infections usually result in the greatest impact on yield because early infections can prevent flowering and fruit set.   Secondary spread within fields is very uncommon but may occur by large populations of western flower thrips.  Western flower thrips are extremely difficult to control because they are highly tolerant to insecticides and prefer to reside deep within the blossoms where it is difficult to reach with insecticides.  In addition to spreading TSWV, thrips alone can be damaging to crops because of how they feed.  Thrips feeding causes the collapse of plant cells which leads to deformed plant growth, flower deformation, and silvery areas and flecking on expanded leaves. 

Two common TSWV vectors
Photo UGA

Controlling this disease is very difficult.  In home garden settings, there is usually little secondary spread after the first wave of infections in the spring when virus-bearing thrips are moving from winter weeds to garden plants.  You may wish to remove infected plants, especially those that were infected before fruit set, because they will not recover.

TSWV field symptoms (left plant showing severe stunting)
Photo by F.J. Louws
In a field setting, it is important to manage weeds adjacent to the field because these weeds harbor both the thrips vector and the virus during the winter.  Infected plants should be removed and destroyed as soon as symptoms appear.  TSWV resistant varieties are available and can be effective.  Organic growers and other larger acreage growers may want to consider reflective mulches to cover their beds rather tha the traditional black mulch.  In greenhouses, thrips populations should be eliminated so they, along with TSWV, are not spread to the field when seedlings are transplanted.  

More information on managing this disease can be found here, under "Viral Diseases"

Special thanks to Dr. Louws for helping put together this post and for supplying images!

Friday, June 3, 2011

Now That's Just Peachy!

My favorite time to visit the local farmers market is during peach season.  To me, there is nothing tastier than slicing open a juicy peach on a hot summer day.  Right now, there are three major peach diseases that you can be on the lookout for: bacterial spot, peach scab, and brown rot.  The next time you visit the local market or if you have a peach tree in your backyard, try and see if you can spot some of these diseases for yourself! 

Bacterial Spot
Dr. David Ritchie, the peach “disease” guy here at NCSU, says that, this year, bacterial spot is the worst he has seen since 2003 and the most damaging it has been in the past 20 years on highly susceptible cultivars.  Bacterial spot is caused by the bacterium Xanthomonas arboricola pv. pruni.   The most obvious leaf symptoms are yellow, chlorosis of the leaves with angular lesions at the leaf tip, mid-rib, and along the leaf margin.  Premature leaf drop is common in infected leaves.  Foliar lesions appear water-soaked and sometimes grayish in color.  As lesions age, centers may become dark or purple in color and necrotic, eventually dropping out to result in a shot-hole appearance. 

Bacterial Spot Symptoms
(Photo by D.F. Ritchie)
Twig symptoms consist of cankers on either side of leaf and flower buds on the previous year’s growth.  These cankers are called “spring cankers” because they are first visible during bloom.  “Summer cankers” can be seen on current-season growth and are visible early to mid-summer.  

Bacterial Spot Twig Symptoms
(Photo by D.F. Ritchie)
Bacterial Spot Twig Symptoms
(Photo by D.F. Ritchie)
The earliest fruit lesions are normally seen about three weeks after petal all.  Fruit infection is favored by moist and warm conditions with fruit being very susceptible from shuck split to pit-hardening. Developing lesions have a water-soaked appearance with small necrotic centers that become black in color and enlarge as the lesions mature.  Early infections result in lesions that expand down the pit before harvest.  Infections later on in the season result in shallow lesions that cause skin cracking.  Attempts to control bacterial spot at this time in the season (June) are of little to no value because once the bacteria have infected, the “path” to damage has occurred. 

Bacterial Spot Fruit Symptoms
(Photo by D.F. Ritchie)
Bacterial Spot Fruit Symptoms
(Photo by D.F. Ritchie)

Peach Scab

Peach scab occurs every year in North Carolina.  This disease is caused by the fungus, Cladosporium (syn. Fusicladosporium) carpophilumC. carpophilum is an asexual fungus that produces conidia and chlamydospores.  The conidia are wind or water splashed dispersed and infect shoots, leaves, and fruit during the season.  Chlamydospores are thick-walled survival structures that form on infected twigs during the winter.  Usually the leaf infections are less noticeable and least important.  The twig infections are ecologically important because they serve as the site for the production of the overwintering chlamydospores.  Fruit infections result in considerable yield losses because of grade reductions or culling of affected fruit that would be less desirable in the marketplace.  First fruit infection occurs during the 4-week period after bloom. The fungus has a long latent period of approximately 6 weeks before the scab lesions are observed, usually by the end of May to early June.  Greenish-gray to olive circular spots form on the fruit and these spots expand in size as the disease progresses. 

Peach Scab
(Photo by D.F. Ritchie)
The fungus sporulates on the fruit lesions, producing conidia that can cause secondary infections of fruit and twigs.  Fruit scab lesions often have a raised, corky appearance, whereas bacterial spot lesions are often sunken in appearance.  Severe infections may lead to cracking of the fruit skin, which can serve as entry points for fruit-rotting organisms like the brown rot fungus.  There are no resistant varieties or cultural control options for managing peach scab.  Control relies exclusively on well-timed fungicide applications starting at petal fall and making 2-3 applications during the following 4-5 weeks. Once scab is observed, fungicide sprays will have little if any controlling effect of scab on the fruit.

Brown Rot
Brown rot is most risky in warm, humid climates.  Brown rot is caused by the fungus, Monilinia fructicola.  This disease occurs in two phases: a twig and blossom blight phase and a fruit rot phase.  Twig and blossom blight phase occurs in early spring when the trees are blooming.  Infected blossoms wilt, turn brown, and usually cling to the twigs.  The infections can then spread into the twigs resulting in twig cankers. Fruit susceptibility to brown rot increases during the 2 to 3 week period prior to harvest because of the increased sugar content in the fruits.  Initially, tan-brown circular spots can be seen on the fruit. 

Brown Rot
(Photo by D.F. Ritchie)
Under humid conditions, ash-gray-brown spore masses are visible on infected tissue.  There can be thousands of spores on each lesion and each spore is capable of initiating a new infection.  If conditions are wet and warm during fruit ripening, the entire crop can be destroyed overnight! Controlling this disease relies primarily on good sanitation practices combined with judicious use of fungicides.  Fungicides are most effective when applied just before the blossoms open and then again during the 2-3 week period leading up to harvest. 

More information on peach production and diseases can be found in the "Peach Growers Handbook"

Hopefully these diseases won't keep too many peaches from ending up in your basket at the local martket! Enjoy!

Special thanks to Dr. David Ritchie for providing his peach disease expertise and photos!