Late July- Pest News for WNC Fruit and Vegetable Growers

FRUIT AND VEGETABLES

From: Hannah Burrack, Extension Entomologist

End of Harvest Concerns in Blueberries

As blueberry harvest nears the end in some areas of North Carolina, a few important insect related issues require some attention.  

Spotted wing drosophila in processing fruit

Rainfall makes spotted wing drosophila (SWD) management more challenging (http://strawberries.ces.ncsu.edu/2013/05/swd_in_rain/), as growers have discovered in the last two months.  As we move into the end of blueberry harvest, fruit being picked for processing is at higher risk for SWD infestation for several reasons: It is often softer than fruit picked for the fresh market and SWD prefer soft fruit (http://news.ncsu.edu/releases/wms-burrack-suzukii-2013/). Processing fruit may be harvested less frequently than fresh market fruit, increasing the time ripe berries are exposed to SWD. Finally, because processing fruit is often machine harvested, all the fruit in the field (good and bad) may be picked.

There are some strategies that growers can employ post harvest to decrease the likelihood that SWD infested fruit will be sent off for processing:

1. Hold fruit at cool temperatures. Work in our lab suggests that SWD eggs and larvae cease development at temperatures less than 41F. They will not necessarily die at cool temperatures, but they likely will not cause further damage to the fruit. The longer fruit are stored and the cooler the temperature of storage, the more likely that small SWD larvae will die. Holding fruit at cooler temperatures also give growers the added benefit of determining how significant the infestation, as large larvae will exit fruit as it cools.

2. Sort out soft fruit. Soft fruit is the most likely to be infested with SWD for two reasons – egg laying SWD are more attracted to soft fruit and blueberries become softer as SWD feed. If growers can remove soft fruit before sending fruit for processing, this will further decrease risk of infestation being present. I suspect our aggressive soft sorting standards for fresh market blueberries are one of the reasons that SWD has been a less significant issue in this crop than some other hosts.

3. Sample collection timing. When receiving fruit, processors can either collect samples before or after fruit are sorted/de-stemmed. Samples collected before fruit has been soft sorted are not necessarily representative of the status of the fruit that will be processed. Samples of fruit after chilling and sorting, prior to processing/freezing, are likely more representative.

Post harvest leafhopper treatments

Treatments to manage sharpnosed leafhopper (http://ipm.ncsu.edu/small_fruit/hopper.html) vectors of blueberry stunt disease typically begin post harvest (http://pemaruccicenter.rutgers.edu/assets/PDF/Blueberry/iSharp-nosed_Leafhopper.pdf). Blueberry stunt disease is caused by a phytoplasma, and symptoms include "bushy" growth due to short, stunted branches and yellowed leaving during the growing season which may prematurely turn red and fall off in late summer. Most importantly, plants infested with stunt-causing phytoplasma do not produce. 

Aerial applications of ULV (ultra low volume) malathion has been used in the past for leafhoppers due to effectiveness and ease of application. However, many growers have also used this material for SWD management during the season, and careful attention must be paid to label restrictions on the number of applications that can be made of materials when selecting tools to manage sharpnosed leafhopper. Application limits apply to the entire growing season, not just harvest season, so label limits on the number of applications also apply to leafhopper treatments. Application limits apply to the amount of active ingredient, not the trade names of those active ingredients. Sources for updated labels with current use restrictions include CDMS (http://www.cdms.net/Home.aspx) and Agrian (http://www.agrian.com/home/label-lookup/overview).

Alternatives to malathion that are effective against sharpnosed leafhopper include Assail (acetamiprid) and Asana (esfenvalurate).  Imidaclorprid and thiamethoxam are also options for sharpnosed leafhopper. The North Carolina Agricultural Chemicals Manual (http://ipm.ncsu.edu/agchem/agchem.html) has recommendations for the use of these materials. It's important to note, however, that all these materials pose some risks to pollinators. While blueberries are not in bloom, some of our most efficient blueberry pollinators (http://repository.lib.ncsu.edu/ir/handle/1840.16/7822) are ground nesting bees that may remain near fields after bloom. Therefore, any insecticide treatments should be timed to leafhopper flights, ideally determined through trapping, to provide maximum efficacy against target pests and limit unnecessary applications. See http://ncsmallfruitsipm.blogspot.com/2011/04/practicing-what-we-preach-implimenting.html for information on trapping and the following for images, http://ipm.ncsu.edu/small_fruit/hopper.html, to aid in sharpnosed leafhopper identification.

From: Lina Quesada-Ocampo, Extension Plant Pathologist

Cucurbit Downy Mildew Moves Towards Western North Carolina

Cucurbit downy mildew has been reported in Haywood, Polk, Ashe, Henderson and Chatham counties (http://cdm.ipmpipe.org/scripts/map.php) during this past week. Now that cucurbit downy mildew is present in several regions of North Carolina and surrounding states, it’s important that growers scout for the disease and keep up with preventive sprays to protect their crop and avoid yield loses.

If you are not familiar with cucurbit downy mildew symptoms on different cucurbits please see our previous alert (http://plantpathology.ces.ncsu.edu/2013/07/do-you-know-how-to-diagnose-cucurbit-downy-mildew-in-different-cucurbit-crops/) to assist you in diagnosing this foliar disease. If you think you have cucurbit downy mildew in your cucurbits please contact your local Extension agent (http://www.ces.ncsu.edu/local-county-center/) and send photos and/or physical samples to the Plant Disease and Insect Clinic (http://www.cals.ncsu.edu/plantpath/extension/clinic/submit-sample.html).

For more information about the disease and how to control it, see our factsheets in English and Spanish (http://projects.cals.ncsu.edu/veggiepathology/disease_factsheets). Control recommendations are also available in the cucurbit downy mildew IPM pipe website (http://cdm.ipmpipe.org/index.php), where you can also register to receive text, e-mail and/or phone alerts when new disease outbreaks are reported. We have also compiled previous cucurbit downy mildew alerts athttp://plantpathology.ces.ncsu.edu/tags/cdm/.

Follow us on Twitter (https://twitter.com/QuesadaLabNCSU) and Facebook (https://www.facebook.com/QuesadaLabNCSU) for more veggie disease alerts.

Cucurbit Downy Mildew in Western NC

Cucurbit downy mildew has been identified on cucumbers in Buncombe and Haywood Counties.  Growers are urged to scout their fields and begin preventive management.

Review control measures and previous posts on this major disease issue - Cucurbit downy mildew

Water soaked lesions, caused by Pseudoperonospora cubensis (causal agent of cucurbit downy mildew), visible on the underside of cucumber leaf.

Also, please visit the Cucurbit Downy Mildew Forecasting site to see more pictures of the disease, review control measures, report disease outbreaks in your area and more.

Pest News June 1, 2012

Though this week's NC Pest News does not contain anything specifically about vegetable or fruit pests (though kudzu bugs may be a problem for folks growing edamame), I did want to draw your attention to some possible issues to be on the lookout for.

Cucurbit downy mildew and late blight of potato and tomato are very devastating and rapid moving diseases.  Though we do not have any reports of these diseases in WNC or our immediate surrounding areas, they have been reported in other parts of NC.  Weather has been ideal for both of these diseases in our area, cool and wet.  Also, because weather has been unsettled (many storms moving throughout the east coast) there is a chance that the spores of these pathogens could travel to WNC.

In fact, the Cucurbit Downy Mildew Forecasting site issued WNC a low risk warning on Friday.  Cucurbit downy mildew has both been detected in eastern and central NC.  On June 1, new reports of the disease were confirmed as close as Franklin, Nash and Wake Counties in NC.  Cucurbit downy mildew is also tracking up the east coast into New Jersey.  To view a map of current Cucurbit Downy Mildew outbreaks visit the CDM IPM Pipe website.  Growers are advised to scout for this disease and to report to their local cooperative extension office if they need assistance or to report an outbreak. 

 

Symptoms of cucurbit downy mildew on cucumber are angular lesions that start a pale green and progress to bright yellow and then finally brown (above).  The best way to identify cucurbit downy mildew is to turn the leaf over to look for the downy growth of the pathogen's spores (below). 

 

Late blight on potatoes has also been detected in Camden County, NC and various other states on the east coast.  To view a current map of these outbreaks, visit the USABlight website.  Growers are urged to scout for this disease as well, as we know this can be a deal breaker for organic producers especially.

 

Late blight on a tomato leaf.

  Again, these diseases have not been reported in WNC.  If you suspect you have these diseases in your planting, please contact your local Cooperative Extension office for assistance.  It is reporting and early detection that can save a planting!

Cucurbit Downy Mildew and Powdery Mildew Early

There have been unusually early reports of both downy mildew (Pseudoperonspora cubensis) and powdery mildew (Podosphaera xanthii and Erysiphe cichoracearum) on cucurbits in the southeast this season.


Growers are encouraged to be on the lookout for these diseases and to call their local cooperative extension office if they need identification help, management recommendations and to report disease.

DOWNY MILDEW
Southeast Farm Press. May 11. 2012: Downy mildew showing up early in cucumbers.

Cucurbit Downy Mildew Found in NC, Rapid Response and Implications for Local Growers.

Frank J. Louws (1), Wendy Britton (1), Peter Ojiambo (1) and Billy Little (2). (1) Department of Plant Pathology, NCSU; (2) Cooperative Extension, Wilson NC.

There was a confirmed report of cucurbit downy mildew (CDM) in a hoop house in Wilson County, NC on May 3, 2012.  The house contained 2 rows of trellised cucumbers and about 20 vines had early symptoms.  The infection was about 5% and with actively sporulating lesions.

Wilson Cooperative Extension, the NCDA, NCSU specialists, and the CDM ipmPIPE team actively worked to contain this outbreak as soon as possible. Discussions with the grower, industry representatives, and state/University employees reached a quick consensus that the best course of action was to destroy all cucumber vines. The vines were cut, roots extracted, all debris swept up and placed in plastic bags. The contained plant material was carried from the greenhouse and buried at the edge of a field that will not be cultivated this season. This was completed and verified as of 2:00 pm Friday May 4, 2012.

CES and industry knowledge about the area suggested field cucumbers were not present in the vicinity and the inoculum from the hoop house presented a zero to low risk to the industry as a whole. The CDM ipmPIPE subsequently changed the status of this outbreak from "confirmed" to "no longer found".  The county in NC will remain on the map but will not be forecasted as an active source. This data is available at http://cdm.ipmpipe.org.

The only other recorded incidence of CDM is in south Florida. Based on recent weather patterns, there is no evidence the inoculum originated from south Florida and there are no field reports of CDM north of south Florida. A thorough examination suggested the grower used optimum best management practices regarding sanitation, removal of all volunteers and other standard practices. Thus, the source of inoculum remains unknown. However, early detection, rapid destruction and historical weather patterns provide high confidence the problem was contained and does not represent a threat to the industry. At this time, we would not recommend implementation of spray programs to manage CDM in cucumber fields in NC. Monitoring of local fields and forecasting spore dispersal from known sources in south Florida will continue and observations will be posted at the CDM ipmPIPE website.

For further information or questions do not hesitate to call Dr. Frank Louws 919-515-6689 or email frank_louws@ncsu.edu (use subject line Downy Mildew).  

To view previous posts on cucurbit downy mildew click here


POWDERY MILDEW
Dr. Tony Keinath, Clemson University Extension Plant Pathologist, sent out a Timely Talk Update about the presence of powdery mildew on watermelons already this season.  To learn more go to Early Outbreak of Powdery Mildew on Watermelon in South Carolina.

To learn more about cucurbit powdery mildew click here.

Downy Mildew Confirmed in Buncombe County

Downy mildew has been confirmed at very low levels in a 2-acre cucumber field in Buncombe County. Growers are encouraged to begin treatment.

Review this post from June on the current recommendations: Pest News June 24

Don't forget to review the Cucurbit Downy Mildew Forecasting website for more information.

Pest News June 24

The latest edition of the NC Pest News is now available.

In this latest edition:

1. Cucurbit downy mildew recommendations for 2011
2. Cucurbit powdery mildew recommendations fro 2011

Cucurbit downy mildew has been found in NC in more eastern counties. It has not been found in WNC, yet. We are actively scouting as afternoon thundershowers and storms from the south could provide inoculum and suitable conditions for disease development. There have been no forecasts on the Cucurbit Downy Mildew Forecasting Website for disease development in our area. However, if you think you have this disease, please visit your local extension office for confirmation.

Downy mildew symptoms on cucumber leaf.

Downy mildew sporulation on the underside of a cucumber leaf.

The fungus that causes cucurbit powdery mildew is a very different pathogen than the water mold pathogen that causes cucurbit downy mildew. Cucurbit powdery mildew likes warm, humid conditions (the humidity within a plant canopy provides ideal conditions). The pathogen does not like wet conditions, but water will spread the pathogen spores to other plants.

Powdery mildew on a squash leaf.

Powdery mildew on the stem of a squash plant.

South Carolina: Downy Mildew Found on Cucurbits in Home Garden Center

**No cucurbit plants infected by downy mildew have been identified in NC big box stores, but growers and home owners should always inspect transplants before purchasing**

Earlier this week, Dr. Anthony Keinath at Clemson sent the following report to agents:

"My technician found cucurbit downy mildew (CDM) on yellow summer squash and zucchini plants at a Home Depot store in Charleston, SC on Wed. 4/6/11. There were several plants at bloom stage in 1-gallon pots with spots of downy mildew on about 25% of the leaves. Several CDM spots had begun to sporulate. (The plants also had powdery mildew, which was more severe than CDM.) The plants were grown in Miami, FL, and labeled with Home Depot tags. The garden manager pulled all of the remaining plants. However, it appears that some diseased squash plants were purchased between Wed. and Sunday, when I confirmed CDM.

Please check your local Home Depot store to see if they also had a shipment of diseased squash plants. These plants could be the start of an early epidemic of CDM in your area! If you find any diseased plants, please let me know. (Squash plants with powdery mildew only also should not be sold.)"

Dr. Keinath put together an informational fact sheet on this problem including control recommendations. Timely Talk: Cucurbit Downy Mildew.

Please revisit my blogpost from April 22, 2010 on diseases in home garden centers entitled "Don't Bring Problems in With Transplants! "

Use the "Search WNC Veggies" application at the top of the right hand menu to find pictures and descriptions of cucurbit downy mildew.

Downy Mildew on Cucumber in WNC

Well, this has been a very exciting week to be a plant pathologist! First, downy mildew on basil, now downy mildew on cucumbers.
*These are two different disease problems, just because they have the same name DOES NOT mean that these two disease are caused by the same organism and will cross-infect one another!*

Cucurbit downy mildew, caused by pathogen Pseudoperonospora cubensis, has been confirmed on pickling cucumbers in Henderson County. Growers are advised to scout their cucurbit plantings which include cucumber, squash, melons and other gourds. Last year we found the downy mildew in Henderson County late in July.

Symptomatic downy mildew cucumber leaf. Angular lesion are first light green and then turn brown with age.

The underside of a downy mildew infected cucumber leaf. You can see the dark spores of the pathogen as they arise from the angular lesions which are bound by the leaf veins.

Downy mildew of cucurbits has the potential of spreading very quickly. Its wind-borne spores can spread easily throughout the region - especially on cloudy days. The pathogen prefers cool temperatures and wet conditions, which we certainly have not had in WNC as of late! I believe that recent hot, dry and sunny conditions are the reason that the downy mildew on cucurbits is not widespread at this time. For example, large cucumber plantings just miles away from where I initially found the disease are unaffected at this time.

With rain possible this weekend, it is very important to prevent downy mildew from infecting your cucurbits, especially cucumber. Growers are advised to protect their plants using fungicides. For conventional producers, review the June 4th North Carolina Pest News or review my blogpost from June 2009 for control recommendations.

Management of downy mildew on cucurbits is tricky for organic producers. There are a number of OMRI-listed products that are labeled for the control of downy mildew on cucurbits, including copper, OxiDate, Serenade and neem. In research studies, copper products were proven to be the best option (only option, really) for managing downy mildew on cucurbits. Copper is only efficacious in plants that are not yet infected or exhibit only mild symptoms.

Visit the Cucurbit Downy Mildew Forecasting Website to see where the disease is currently located and where the team predicts it to show up next.

If you need help diagnosing a problem on your cucurbits, please contact your local NC Cooperative Extension Office.

To see more pictures of the downy mildew on cucurbits and to learn more about the disease, visit my previous posts.

Downy Mildew on Cucumber Confirmed in Eastern NC!

Downy mildew has been confirmed on cucumbers in Columbus County (May 27) and Duplin County (June 1). Both of these counties are located in eastern NC.

Downy mildew has not been found on cucurbits in WNC yet this season and current forecasts do not indicate risk to our production. If the forecasts show risk for our area, or downy mildew is found in our region, I will update the blog.

The Cucurbit Downy Mildew Forecasts can be found at http://cdm.ipmpipe.org/.

Current recommendations for cucurbit downy mildew can be found in the latest issue of North Carolina Pest News.

Recommendations for powdery mildew on cucurbits can be found in this issue, as well as information on late blight of tomatoes.

Downy Mildew Confirmed in Henderson County!

Downy mildew has been confirmed at 2 locations in Henderson County, NC.

• July 20 - The first incidence of cucurbit downy mildew in WNC was reported from the Mountain Horticultural Crops Research Station in Mills River. The hosts were butternut squash and cucumber. Disease incidence and severity is very low at that site.

• July 24 - Cucurbit downy mildew was confirmed this morning in Zirconia (just south of Hendersonville, NC). This was a larger planting, about 8 acres. Spaghetti squash is the most severely diseased, about 65% of plants are showing early (top picture) - more advanced (second picture) symptoms. Sporulation (noticeable on the underside of the leaf) was very heavy on the spaghetti squash (third picture). Cucumber (cv. Jackson) is also affected, though less severely overall (bottom picture). The summer squash (cv. Destiny III) is showing only very early and mild symptoms.

Moral of the story, cucurbit downy mildew is in WNC and growers need to start treating now!

Review a previous post for control recommendations.

Visit the Cucurbit Downy Mildew Forecasting site for more updates.

If you feel you have downy mildew on your cucurbits, bring a sample to your local county cooperative extension office for positive identification. It is important that the outbreaks get reported to the forecasting site.

Downy Mildew Confirmed on Cucumber in Franklin County, NC

We have had our first report of the year of downy mildew on cucumber in NC. The outbreak is in Franklin Co, NC, located in the northeast of Wake County (Raleigh).

This disease favors the cool, wet weather we have been experiencing here in NC. Though we have not had any confirmed cases in WNC, it would be worth your time to scout your fields. Also, follow the Cucurbit Downy Mildew Forecasts for updated information.

Downy mildew of cucurbits is a disease that is very difficult to control once it becomes established in your field and can spread very quickly (see pictures below- Top picture = healthy cucumber field, Bottom picture = same field a few weeks later). Research has shown that by delaying fungicide sprays to cucumber just one week after the disease has become established in the field, yield losses of greater than 50% can occur (especially in cool, wet weather).



The disease spreads via wind currents from downy mildew infected areas. It can also be spread throughout a field by water splashes.

Symptoms on cucumber, squash and melon begin as yellow spots on the leaf. The spots are bound by the leaf veins and, as a result, appear angular. On the underside of the leaf, the spots may appear water-soaked, especially in early morning when moisture is still present in the plant canopy. You may also see a light gray to dark almost black, downy growth. Those are the spores (zoosporangia) of the pathogen, Pseudoperonospora cubensis. Eventually these lesions, and then the entire leaf, will become necrotic and turn brown. The leaf may appear crispy, like it has been burned. Because of rapid onset and crispy leaves, this disease has been referred to as "wild fire:


The following products* have proven very effective for the control of downy mildew:

Presidio 4F (fluopicolide)
Ranman 400 CS (cyazofamid)- must use with non-ionic surfactant
Gavel 75DF (zoxamide + mancozeb)
Curzate 60DF (cymoxanil)

Chlorothalonil and mancozeb products can be sprayed as protectants, but when downy mildew is detected in a field growers need to take a more aggressive approach. *The label on some of these products require that they be tank mixed with a fungicide of a different mode of action. Chlorothalonil and mancozeb products make excellent mixing partners.

A sample spray program might look like this:

Curzate 60DF (3.2 oz/acre) + Manzate Pro-Stick 75DG (3 lb/acre) alternated with Previcur Flex 6F (1.2 pt/acre) + Manzate Pro-Stick 75DG (3 lb/acre)

OR

Presidio 4F (3 fl oz/acre) + Bravo Weather Stik 6SC (2 pt/acre) alternated with Gavel 75DF (1.5 lb/acre)

These treatments can be rotated on a 7-day schedule when downy mildew pressure is great.

To read more about this disease visit the NCSU Factsheet.
In addition, look for updates in the latest NCSU Pest News.

***As always, follow the product label for instructions!***