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: May 18th

The latest edition of NC Pest News is now available.  You can find it and all other archived editions here.

In this edition vegetable and fruit growers may find these articles of interest:

1. Brown Marmorated Stink Bugs
2. Thrips in Cucurbits
3. Squash Bugs
4. Soil Insect Management in Sweetpotato

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.

NC Pest News for June 3

Squash bug adults feeding on the stem of squash. Squash bugs love to hide below plastic!

Squash bug nymphs just hatched from bronze eggs.

This week's issue of NC Pest News is now available. It includes a review of strawberry disease issues from 2011 and the vegetable insect update. The insect update discusses the pest in the photo above, the squash bug. We have been seeing many squash bugs in WNC as of late, as well as cucumber beetles, a few stink bugs and thrips.

You can receive vegetable pest updates from North Carolina State University via Facebook (NCSU Vegetable Entomology) and Twitter (ncsuveg).

Check out these cucumber beetles feeding on summer squash! (below).


To view past issues of NC Pest News click here.

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.

Cantaloupe Recall- Linked to Salmonella

For those interested in the dynamic world of fresh produce safety and fruits and vegetables, Del Monte Fresh Produce N.A., Inc. of Coral Gables, FL has voluntarily recalled nearly 5,000 cases of cantaloupe (read the company's News Release). The cantaloupe is believed to be linked to 12 cases of Salmonella. The cantaloupes were available from March 10-21 at warehouse clubs in Alaska, Colorado, California, Montana, Idaho, Oregon and Washington and were grown in Guatemala.

To read more about the recall, visit Food Safety News for the article Cantaloupes Linked to 12 Salmonella Illnesses.

Insect Pests Plaguing Vegetable Growers

This article is from the latest edition of NC Pest News from Entomology Extension Specialist, Dr. Mark Abney.

"A variety of insects are currently plaguing vegetable growers across North Carolina. Armyworms and corn earworms have been abundant and moth flights are continuing. European corn borers have been abundant in many of our research trials this year after several years of low numbers. Heavy European corn borer infestations occurred in sweet corn at the Central Crops Research Station in Clayton and large numbers were seen in bell pepper trials near Kinston and in the mountains near Fletcher.

Melon growers have not been immune to insect problems, and there have been a couple cases recently of corn rootworm larvae feeding on the undersides of cantaloupes. We do not see this on a regular basis, but it seems to happen somewhere every year. Larvae feed on the undersides of fruit, usually after a heavy rain, and there is no technology currently available to effectively control the problem.

As we approach late August, home gardeners and commercial growers alike will be faced with managing pickleworms in cucumber and squash. Commercial growers are forced to rely on preventative insecticide applications as tolerance for pickleworms in harvested produce is essentially zero. Home gardeners are faced with an uphill battle against this pest as management options available are not likely to provide good control. The best advice for gardeners is usually to plant early and harvest before pickleworms arrive from the south each year.

Another perennial foe of the cucurbit grower, the squash bug, is making its presence known in backyard gardens, commercial organic production, and in research trials. Large populations recently moved into research plantings of squash and cucumber at the Horticultural Crops Research Station near Clinton. It only takes a couple squash bugs to kill a young squash plant, so scouting and timely management are critical. These bugs can be difficult to kill, and the adult stage is particularly tough to control. Targeting the nymphs is important.

Scouting vegetables is absolutely essential to prevent losses due to insects and to maximize the effectiveness of insecticide applications. For control recommendations in specific crops, please refer to the North Carolina Agricultural Chemicals Manual (http://ipm.ncsu.edu/agchem/5-toc.pdf)."

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.

Cucumbers and Pollinators: (Some) Questions Answered

When I first started my job in WNC in 2008, I was so excited to see that vegetable producers were growing cucumbers. Cucumber was the crop I worked with in my graduate work, so it was the only crop I felt mildly comfortable talking about (though it was still awkward at first).

To my surprise, in many of these production fields, I never saw a beehive. The areas that I had experience with in eastern NC, brought in at least one strong hive per acre of production. To learn more about bees, read Beekeeping and Cucumber Pollination.

How were these folks getting cucumbers? A cucumber flower must be visited multiple times by a pollinator to optimize fruit set. The answer was wild populations on pollinators and the nice sunny, warm weather that promotes activity and foraging of pollinators.

But, in 2009, growers noticed that yields were reduced and that fruit formation was off. The same varieties were grown and there was not downy mildew or other diseases in their early season crops. So what was different?

We were cool, cloudy and wet. How could you forget? The fact is, bees don't aggressively begin to forage until temperatures reach 70 F and they prefer dry conditions.

Could this lack of fruit also be due to a reduced population of wild pollinators? At this point we don't know, but it was obvious that the growers needed to do something. That something was to bring in some honey bee hives.

Here are some pictures of a female cucumber (top) and male cucumber flower (bottom), courtesy of Pollinator.com.


Below is an improperly pollinated fruit.

To see more pictures, visit pollinator.com's Cucumber Pollination: Visual Aids.

But, the growers were concerned. Bringing bees into their production was new and they had many questions - especially in regards to applying pesticides.

Here are a few of the questions that I received. Most answers are from NCSU Beekeeping Note 2.12.

• Where can I find honey bee hives to rent?

The NCDA&CS Apiary Services and NCSU Apiculture Program have developed Bee Linked, an online market for beekeepers and growers. www.ncagr.com/beelinked
You can also find local beekeepers through the North Carolina Beekeepers Association Website. www.ncbeekeepers.org.

• When should I apply pesticides to protect the bee hives?

Pesticides that are considered toxic to bees should be applied in the late afternoon (after 3:00 pm) or in the evening. Most honey bees have stopped foraging and have returned to the hive by 3:00 pm. This precaution will allow maximum time for the pesticide to break down before the bees come into contact the next day.

• What other considerations are important when applying pesticides?

Do your best to minimize drift. Drifting of the pesticide from the target pest and/or crop to areas frequented by bees should be minimized and pesticide formulation is the key to this problem. "Dusts" are prone to drift and are generally more dangerous to bees that sprays or granular applications. For more specifics, read Beekeeping Note 2.12.

Aerial applications are generally more dangerous than ground equipment. This is directly related to drift. Air-blast sprayers are more dangerous that pressurized pump sprayers. Never apply pesticides when wind velocities exceed 8 miles per hour.

Never apply any pesticide directly over a beehive.

Notify beekeepers who have beehives near an area to be treated, so that they may attempt to protect their bees from inadvertent exposure.

• Are there pesticides that are less toxic to honey bees?

Most pesticides are at least somewhat toxic to honey bees; however, the degree of toxicity varies considerably from product to product. Insecticides are generally the most likely to cause a bee kill. Below are some common pesticide active ingredients listed based on their toxicity to honey bees for a more complete list, see Beekeeping Note 2.12.

1. Highly Toxic: Severe bee losses may be expected if these products are used when bees are present. Abamectin, aldicarb, avermectin, azinphos-methyl, carbaryl, carbofuran, chlorpyrifos, dimethoate, imidacloprid, malathion, methomyl, pemethrin, spinosad...
2. Moderately Toxic: These pesticides can be used in the vicinity of bees IF dosage, timing, and method of application are correct. Bifenazate, disulfoton, endosulfan, fluvalinate, oxamyl, propamocarb, pyrethrum, tartar emetic, temephos, terbufos, thidicarb, zephyr...
3. Relatively Non-Toxic: These pesticides cam be used around bees with a minimum injury IF dosage, timing and method of application are correct. Bacillus thuringiensis, chlordimeform, cryolite, cymiazole, dicofol, dinobuton, esfenvalerate, methoxychlor, myriproxyfen, nicotine, Nosema locustae, pyrethrum, rotenone, tebufenozide, trichlorfon.

Visit the NCSU Apiculture Website for more details on honey bees.

To learn about cucumber production in NC: Fresh Market Production Cucumbers and Commercial Production of Pickling & Slicing Cucumbers in North Carolina.

To learn more about Bee Colony Collapse Disorder, read a scholarly article about the problem in Colony Collapse Disorder: A Descriptive Study.

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!***