Tuesday, January 31, 2012

Fungicide Resistance Found in Strawberry

Strawberry gray mold resistance to fungicides appears widespread

The fungal organism that causes gray mold in strawberries has become completely resistant to some fungicides that Southeastern growers have been relying upon for years.

Should spring weather be cool and wet, strawberry producers may experience the "perfect storm."
With that in mind, Guido Schnabel, a research and Extension plant pathologist at Clemson University, says growers should carefully choose and rotate fungicides.

His research group collected samples from
  • four counties in North Carolina and from
  • eight in South Carolina. 
They found resistance to certain chemical classes in all of the sample areas.

The fungicide classes with the greatest levels of resistance were QoIs, SDHIs and benzimidazoles, he says.
  • QoI fungicides include strobilurins, fenamidone and famoxadone.
  • SDHIs include fluopyram and boscalid.
  • Benzimidazole include benomyl and thiabendazole.

But the resistance wasn't uniform, Schnabel says.
"In some areas, benzimidazoles are still active, while in other areas SDHIs are still active," he says.
What has him more concerned is how widespread the resistance is.
"We didn't expect to see that much resistance so widespread," he says.
The resistance is caused by mutation at the fungicidal target site in the fungi.
"The fitness of the resistant isolates compares to the sensitive isolates," Schnabel says. "Even though you back off with one chemical, there's a good chance that the resistant ones will outcompete the sensitive ones."

As a result, it may take several years of not using a fungicide before the fungal organism regains sensitivity to the product.

The fungus, Botrytis cinerea, causes crown rot, tissue blight and fruit rot.
During wet, cool weather, untreated plants can lose up to 90 percent of flowers and fruit.
Growers may be unaware of the resistance problem because they have not experienced total product failure, he says.
In addition, recent dry weather has minimized fungal pressures.
Growers may be spraying regularly, but the dry weather—and not the fungicide—is keeping gray mold in check, Schnbabel says.

To help growers determine whether they have resistant gray mold isolates in their fields and to which chemical or chemicals, Schnabel is part of a team developing field test kits.
These are similar to test kits he helped develop for Southeastern peach growers who had resistant fruit rot isolates in their orchards.
The idea is growers test the gray mold organisms, then avoid using any product to which the organism is resistant.
Schnabel, as well as Natalia Perez, a University of Florida plant pathologist in Balm, will field test the kits with growers this spring.
"We tested them in the lab, and they worked great," he says.

Their work is part of a a four-year, $2.9 million U.S. Department of Agriculture grant project to develop a forecasting system for two strawberry fungal diseases.
Managing fungicide resistance is part of the research project

Monday, January 23, 2012

Weather Review from UK Ag Weather Center

Compliments of Tom Priddy, UK Agricultural Weather Center:

Review of the year's Weather across Kentucky provided by NWS Weather Offices:

Take some time to check out their website, also.  There's a wealth of weather-related information for growers across the region.  http://wwwagwx.ca.uky.edu/

Friday, January 13, 2012

Disease-Resistant Apple Cultivars

Selecting the Best Apples for Backyard Orchards

Apples, the most popular of the pomme fruits, are a treat for gardeners and hobby orchardists.  Although backyards do not have the immense disease pressure experienced in commercial orchards, a proactive disease-control program is still essential.  Apple production requires a dedicated gardener and often a preventative spray schedule.  An effective disease-management program can include 10 or more fungicide applications, and without some type of program, disease loss will be extremely high. 

Some of the most destructive diseases affecting apple include fire blight, apple scab, cedar apple rust, and powdery mildew.  Their prominence makes organic apple production in Kentucky extremely difficult.  Thus, gardeners desiring low-pesticide fruit should begin with disease-resistant cultivars.  Those included in the table below produce high-quality fruit and exhibit resistance to a variety of diseases.  Incorporation of these and other cultivars can greatly reduce fungicide applications in the home orchard.  However these cultivars have no resistance to the insects that find apples particularly enticing.   Alternatively, bagging individual fruit when they are roughly an inch in diameter significantly reduces fungicide and insecticide spray requirements. http://www.ca.uky.edu/entomology/entfacts/ef218.asp

Additional information can be obtained by accessing publications ID-21 Disease and Insect Control Programs for Homegrown Fruit in Kentucky, ID-92 Midwest Fruit Tree Spray Guide, or other UK Plant Pathology Extension publications (http://www.ca.uky.edu/agcollege/plantpathology/extension/pubs.html) .

Wednesday, January 11, 2012

Resistant Fire Blight in Apple

Strep-Resistant Fire Blight Found In New York

A strain of streptomycin-resistant fire blight has been detected in New York apple orchards.

Cornell plant pathologists have issued a warning to New York apple and pear growers after discovering a strain of fire blight that is resistant to such traditional treatments as the antibiotic streptomycin.
For 50 years, the disease has been kept at bay using the antibiotic, but streptomycin-resistant strains of the disease were recently found in four locations in Wayne and Ontario counties.
“This is a serious situation that we need to manage effectively. The rapid identification of this outbreak positions us to implement a coordinated plan leading up to next year’s growing season,” said Herb Aldwinckle, professor of plant pathology and plant-microbe biology at Cornell’s New York State Agricultural Experiment Station (NYSAES) in Geneva.
In coordination with colleagues at NYSAES and Cornell Cooperative Extension, Aldwinckle is developing guidelines growers can follow to reduce the threat. Upcoming sessions at the Fruit and Vegetable Expo and CCE Fruit Schools in several counties will also provide growers with opportunities to learn more about the outbreak and possible solutions.
Fire blight is caused by the bacterium Erwinia amylovora, earning its name from the scorched appearance of infected leaves and branches. Its symptoms include blackening of flowers and young leaves, resulting in crop loss and even death of trees.
This current infection was first spotted in Wolcott, NY, where a persistent suspected fire blight infection evaded a streptomycin spray regime. Samples were immediately brought to Aldwinckle’s lab.
Sampling was necessarily limited in late fall, so the full extent of the outbreak will be unclear until additional samples are studied, but the latest results indicate there are several outbreaks of strep-resistant fire blight in Wayne and Ontario counties.
Aldwinckle said the fact that one of the sites is a nursery does complicate the management plan. Fortunately, that nursery has a strict rogueing program — in which infected plants are removed from the soil and destroyed — that should minimize the chance of spread, he added.
However, Aldwinckle noted that some infections might not be immediately visible, so there’s a possibility that a small number of trees with the strain were inadvertently shipped to growers.
He advises all growers to examine their trees carefully for any symptoms of fire blight that may develop after planting. These recommendations apply to all trees purchased, with particular attention for those from New York and Michigan nurseries, where strep-resistant fire blight is known to occur.
He is also exploring other ways to eradicate the blight.“The antibiotic kasugamycin is as effective as streptomycin, and in some ways it is a more appropriate antibiotic because it is not used in human or veterinary medicine,” said Aldwinckle. “Kerik Cox, an assistant professor of plant pathology at Cornell, is leading an application for a Section 18 emergency registration from the EPA for growers to use Kasumin [commercial kasugamycin] next spring.”
Source: Cornell University College of Agriculture and Life Sciences