Disease Management for Greenhouse Strawberry in Kentucky

 

Disease Management for Greenhouse Strawberry

 

Plug production, Greenhouse:

·         Drench or dip: Aliette/Rampart (33) for Pythium root rot

·         Drench: for fungal root and crown rots

o   Switch (9+12)

o   Captan (M)

 

 

Crop production, Greenhouse:

·         At Planting (Fall)

o   Dip/drench: Aliette/Rampart (33) or LalStop K-61* or
RootShield PLUS* for Pythium root rot

o   Dip: Switch anthracnose crown rot

·         Vegetative, apply on 14-day intervals, rotate among at least 3 of fungicides listed below, adhere to maximum applications for each FRAC group.

o   Captan (M) + Elevate (17)

o   Fontelis (7)

o   Luna Sensation (7+11)

o   Luna Tranquility (7+9)

o   PhD/OSO (19)*

o   Quadris Top (3+11)

·         Vegetative phase, as needed

o   Powdery mildew, as needed: Torino (U6)

o   Pythium root rot, as needed: Aliette/Rampart (33) or LalStop K-61* or RootShield PLUS*.

·         Fruiting (mid-late Spring), apply on 7-to-14-day intervals, adhere to maximum applications per season for each FRAC group.

o   Captan (M) + Elevate (17)

o   Fontelis (7)

o   PhD/OSO (19)*

o   Quadris Top (3+11)

 

FRAC groups in parentheses.

OMRI approved with asterisk*
Biologicals that are living organisms (LalStop K-61 and RootShield PLUS) can be deactivated by fungicides. Do not apply with Switch or other fungistat.

Limited options for Pythium root rot in greenhouses; maintain strict sanitation.

Refer to efficacy guide and other information in ID-232 Midwest Fruit Pest Management Guide.

UK Plant Pathology disease management resources can be found at https://plantpathology.ca.uky.edu/extension/publications#SMALLFRUIT 

Using Resistant Cultivars to Manage Strawberry Diseases

From the Midwest Small Fruit Pest Management Handbook
http://www2.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/MwSmFruitPMHandbook.pdf


In any IPM program, the use of resistant cultivars is an important consideration.  Many commercial cultivars have resistance and/ore tolerance to leaf spot, leaf scorch, red stele, and powdery mildew.  The more resistance within a program, the better.  Table 21 (page 27) lists ratings for disease resistance in several of the more commonly grown strawberry cultivars.

 

Two New Strawberry Viruses Detected in Kentucky.

Two New Strawberry Viruses Detected in Kentucky. The viruses (strawberry mottle virus, abbreviated SMoV; and strawberry mild yellow edge virus, abbreviated SMYEV) originated from a plug producer in Nova Scotia. In the aforementioned case,... three growers shared a shipment of plants, but only one of the growers has seen symptoms. The other two growers have not.

We encourage strawberry growers to contact their brokers to determine the source of his/her plants. Those with high risks may need to take some of the precautionary steps outlined below.

An article describing the two viruses in more detail is available at http://extension.psu.edu/plants/tree-fruit/news. Briefly, SMoV and SMYEV are transmitted by aphids. SMYEV infects only strawberry, but SMoV can also infect the weed common lambsquarters. Therefore, we encourage high-risk growers to scout for aphids and to implement a solid weed management program.  

 

 

 Finally, remember that virus diseases cannot be cured. We recommend that symptomatic plants be destroyed to prevent spread to healthy plants. If you determine that your plants originated from the Nova Scotia area, please do not hesitate to contact me for more specific information.

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

Crown Rot of Strawberry

Strawberry growers in KY have reported losses of up to 25% in new strawberry plantings this month due to crown rot issues.  Incidentally, last month a commercial strawberry supplier announced possible shipments of transplants and plugs infected with the pathogen that causes Phytophthora crown and root rot.   Several Kentucky strawberry growers submitted plant samples UK Plant Pathology Diagnostic Labs for diagnosis of this crown rot disease. Meanwhile, many growers applied the Phytophthora-specific fungicide Ridomil to their fields.  In spite of the assumptions, diagnosticians confirmed that all of the samples had Anthracnose crown rot. 

Various pathogens can cause rapid loss of new transplants, and as we saw in this example, the diseases may have very similar symptoms.  Correct diagnosis is critical for effective control.  Below are brief descriptions of some common diseases of strawberry transplants.

 

1.       Anthracnose Crown Rot – caused by the fungus Colletotrichum fragariae.  Dormant spores can remain on plant tissue until ideal conditions arise.  Warm, rainy/irrigated, humid conditions cause the fungus to begin growing again.  Upon reinfection of plants, the fungus produces new growth and sporulates.  These spores splash up and infect crowns, as well as petioles, leaves, and fruit.  As crowns are infected, plants wilt and die suddenly.  If crowns are cut lengthwise, crowns are firm, and red streaking or marbling is apparent.   Roots usually appear healthy.  Abound (azoxystrobin), Cabrio (pyraclostrobin), or Pristine (boscalid + pyraclostrobin) are effective fungicides.  Control of this pathogen is important to reduce disease incidence in spring.  Apply fungicides as foliar sprays, through drip irrigation, or as a transplant dip according to label instructions.

2.       Crown Rot, Phytophthora Crown Rot – caused by the water mold Phytophthora cactorum.  Warm wet conditions, as well as poorly drained soil encourage infection. This pathogen causes crown and collar rots, leaf blights, and fruit rots in strawberry and various other plants.  Symptoms begin in the upper part of the crown, with youngest leaves wilting first.  Above ground symptoms appear before roots are affected.  Upon splitting the crown, inner tissue is extensively soft, brown, and necrotic.   Ridomil (mefenoxam) may be applied as a drench application, while Aliette or ProPhyt (phosphite) can be applied as foliar spray or transplant dip according to label instructions. 

3.       Red Stele – caused by the water mold Phytophthora fagariae.  This water mold requires wet conditions to establish and infect.  Cool wet conditions are ideal for this pathogen, at which time it can extend throughout root systems quickly.  Water runoff and farm implements can spread the pathogen from plant to plant or from field to field.  Roots begin rotting from the ends, infecting upward toward the crown.  Cutting roots lengthwise reveals the red-colored stele.  Do not plant strawberry where Red Stele occurred in the past.  When conditions become hot and dry, this pathogen can produce survival structures that are heat and fungicide resistant.  Applying Ridomil (mefenoxam) to soil before planting can eliminate a significant amount of inoculum.  Alternatively, Ridomil can be applied through drip irrigation systems shortly after planting.  Phosphites such as Aliette or ProPhyt are effective as transplant dips or as preventative foliar applications only.  Follow label instructions for rates and other application regulations. 

Disease management begins with prevention.  Purchase disease-free transplants.  In the event of disease, consider field conditions and symptoms, then contact your county agent for advice.  Keep in mind that proper diagnosis is critical for disease control.  Your agent can assist with submission of plant samples to the UK Plant Disease Diagnostic Lab.  More information on strawberry disease control can be obtained from PPFS-FR-S-05 and ID-44.