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Managing Phytophthora Blight in 2012

August 7, 2012

From Margaret Tuttle McGrath, Department of Plant Pathology and Plant-Microbe Biology,
Long Island Horticultural Research and Extension Center, Cornell University, Vegetable MDOnline website.

Phytophthora blight was more severe in 2011 than it has been for many years, which raises concern that 2012 could be another bad year for this very destructive disease because of the quantity of pathogen spores left in fields at the end of last season to survive over winter. Blight was severe in areas where there were intensive rainfall events, which created unusually favorable conditions. A key to successfully managing this disease is managing soil moisture to avoid saturated conditions that favor pathogen development and infection. Achieving this is difficult when rainfall amounts are large. Another key has been fungicides registered recently with targeted activity for pathogens in this biological group (Oomycetes). Rain events in 2011 challenged maintaining a good spray schedule and thus achieving effective control. Once blight starts to develop in a crop, it can be difficult to stop, thus a management program will be most successful when initiated before symptoms begin to develop. This includes fungicide applications. An integrated program with cultural practices and fungicides is considered essential.

Symptoms of blight include seedling damping-off, leaf spots, die-back (collapse) of growing tip, root and crown rot, stem lesions, and fruit rot. The first step in managing Phytophthora blight in 2012 is avoiding fields where the disease was severe in 2011. This can be difficult to achieve because many crops are susceptible and there are space limitations for some crops on a farm, notably u-pick pumpkins. Susceptible crops (listed in order of importance) are all cucurbits, pepper, eggplant, snap bean, lima bean, and tomato. Also avoid moving soil on farm equipment from heavily infested fields. While a field with no history of blight occurring may seem an ideal location to grow a susceptible crop, additional management practices are still needed as blight has occurred in such situations.

Grow resistant varieties when possible. New resistant pepper varieties are being evaluated at Cornell's research facility on Long Island (LIHREC) this summer.

Physically separate plantings of susceptible crops such that there is no opportunity for water to move from one planting to another. Biofumigation with one of the mustard cover crop varieties developed for this purpose is a useful new management tool to consider. This can be done in spring or fall. Maximize activity by promoting good mustard growth, then chop it into small pieces 3-6 weeks after onset of flowering, and immediately incorporate the mustard then seal the soil surface with a culti-packer and irrigation or rain. An integrated program starting with biofumigation is being implemented at LIHREC in a field where blight was severe in 2011.

Reduced tillage has long-term potential to contribute to managing blight. Symptoms did not develop in 2011 on pumpkin in a research field at LIHREC where reduced tillage has been used since 2004. Blight did develop in other fields at LIHREC, including a field in its second year of reduced tillage. Improving soil health is expected to take time to achieve.

Use cultural practices that improve drainage to minimize the length of time soil is saturated with water, and especially to avoid standing water. Subsoiling is recommended between crops and also between rows after planting. Maintain records of where water drainage is poor in each field; avoid planting susceptible crops in these locations. Plant a cover crop instead. Raised, dome-shaped beds are recommended except with vining cucurbit types. Planting field driveways to annual ryegrass or another cover can improve drainage as well as minimize water movement across a field. Avoid over irrigating.

Apply fungicides with targeted activity. It is critical to use these fungicides in alternation and combined with broad-spectrum contact fungicides (chlorothalonil and copper) to minimize selection of fungicide resistant strains; many labels contain use restrictions that require this. Pathogen strains with resistance to Ridomil and Ranman have been detected in the US. Scout fields for symptoms routinely. Promptly destroy affected plants when found localized in a small area. Physically remove them when there are just a few, small plants. Otherwise disk beginning with a border of healthy-appearing crop around the affected area.

Fruit that look healthy should be removed from infested fields as soon as possible and checked routinely for symptom development so that fruit developing symptoms after harvest can be discarded before the pathogen spreads further. Asymptomatic affected fruit should develop symptoms within a week. It is especially important to harvest before rain. Growers have asked about disinfectants to use on fruit after harvest. None are registered for this use. Furthermore, applying a disinfectant to fruit will only kill pathogen spores on the fruit at the time; it will not stop the pathogen if it has already started to infect the fruit and it will not affect spores that land on the fruit after treatment. Cleaning fruit with water after harvest is recommended.

Carefully inspect fruit bought to re-stock u-pik pumpkin fields. Do not display pumpkin fruit for sale in a field where Phytophthora blight developed in previous years: healthy fruit have developed fruit rot in these situations.

Another important step to take after a disease is severe on a farm, is to critically examine the management program used in order to identify the reason(s) why the disease might not have been effectively managed. From this assessment means can be identified to improve the management program used this year.

Please Note: The specific directions on fungicide labels must be adhered to -- they supersede these recommendations if there is a conflict. Any reference to commercial products, trade or brand names is for information only; no endorsement is intended.

Targeted Fungicides for Phytophthora Blight

Phosphorous acid fungicides (Agri-Fos, ProPhyt, Phostrol and Fosphite)(Group 33) are labeled for use on pepper, all cucurbits, plus additional crops. They are thought to have greatest benefit when applied early in crop development and to the soil so that they can be taken up by roots. ProPhyt and Fosphite are labeled for use at planting and/or transplanting (specific directions differ). Phosphite ion, the active ingredient for these fungicides, affects fungal pathogens directly and promotes the plant's defense system. All fungicides in this group can be applied to foliage. There are also several phosphate fertilizer products that should not be confused with the fungicides as they do not have this active ingredient and it is illegal to use them for disease control because they are not registered as fungicides.

Ranman
(FRAC Group 21 fungicide). Apply at 2.75 fl oz/A for a maximum of 6 applications. Use an organosilicone surfactant such as Silwet L-77. The minimum interval is 7 days, REI is 12 hr, and PHI is 0 days (may be applied day of harvest). 

Presidio (Group 43). Apply at 3-4 fl oz/A for a maximum of 12 fl oz/A with no more than 2 consecutive sprays.  The minimum interval is 7 days, REI is 12 hr, and PHI is 2 days. Restricted-use pesticide. The rotational restriction is 18 month for corn and other crops that are not labeled.  Therefore only labeled crops can be grown in a field the year after Presidio was used.

Revus (Group 40). Apply at 5.5 to 8 fluid ounces for a maximum of 32 fl oz/A with no more than 1 consecutive spray. Label specifies that it must be tank-mixed with copper fungicide. REI is 12 hr and PHI is 0 days.

Forum (Group 40). Apply at 6 oz/A every 5 to 10 days, depending on disease pressure, beginning when cucurbit plants are 4-6 inches high for a maximum of 30 oz or 5 applications. Label specifies that it must be tank-mixed with another fungicide and applied no more than twice before alternating with another fungicide. REI is 12 hr and PHI is 0 days.

Ridomil Gold (Group 4). Apply at 1 pt/A in a banded or broadcast spray or injected through drip. REI is 0 hours (incorporated) or 48 hours if banded, and PHI is 7 days.

Ridomil Gold Bravo or Copper (Group 4). Apply at 2 lb/A for a maximum of 3 applications. The minimum interval is 14 days, REI is 48 hours, and PHI is 5 days (Bravo) and 14 days (Copper).

Tanos (FRAC Group 11 and 27). Apply at 8 oz/A for a maximum of 4 applications. It must be tank-mixed with a copper fungicide and a fungicide containing maneb or mancozeb.  Follow a strict alternation with no consecutive applications of Tanos.  REI is 12 hours and PHI is 3 days.

Gavel (Group M3 and 22). Apply at 1.5 - 2.0 lb/A every 7 to 10 days or when conditions are favorable for disease for a maximum of 8 applications. The FIFRA 2(ee) approved in 2004 for cucurbits was needed because the label has just fruit and stem rot without specifying the pathogen Phytophthora. REI is 48 hr and PHI is 5 days. Restricted-use pesticide.

Targeted Fungicides by Crop:
Beans: none.
Cucurbit crops: Forum, Gavel, Phosphorous acid, Presidio, Ranman, Revus, and Tanos.
Eggplant:  Forum, Phosphorous acid, Presidio, and Ridomil Gold.
Pepper:  Forum, Presidio, Phosphorous acid, Ridomil Gold, and Tanos.
Tomato (buckeye fruit rot): Gavel, Presidio, Ridomil Gold, and Tanos

Biofungicides (including Actinovate, RootShield, and SerenadeSoil) can be applied at planting to manage the blight pathogen, Phytophthora capsici, in the root and crown zone of pepper and cucurbit crops.  SerenadeSoil use directions for this application are as a soil drench (2-6 qt/A) for pepper or through drip irrigation or as a directed spray (2.2-13.2 fl oz/1000 row ft) in the furrow just before the seeds are covered for both crop types. Actinovate AG can be applied to seed as a spray or dry coating, or applied in-furrow or through drip at 1-12 oz/A. There are two RootShield formulations. The granular is labeled for use on pepper but not cucurbits. The WP can be applied as a drench to potting soil or field soil, or in furrow or broadcast.



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Upcoming Events

Ag Manager Webinar Series: Ag Tax Topics - Sales Tax and Property Tax Issues for Ag in NYS

August 27, 2019
12:30 - 12:50pm

Join Liz Higgins from the CCE ENYCHP every other Tuesday at 12:30pm throughout the summer as she discusses pertinent business topics for busy farm managers.
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Willsboro Farm High Tunnel Twilight Meeting

August 27, 2019
5:00pm - 7:00pm
Willsboro, NY

Join vegetable specialists Elisabeth Hodgdon, Jud Reid, and farm manager Mike Davis for a high tunnel and field tour at Cornell's Willsboro Research Farm, where they will share research results for the following projects: 
  • Striped cucumber beetle management suing netting and row cover
  • Varietal differences in cucumber susceptibility to striped cucumber beetle
  • Ground cherry and goldenberry production in field and high tunnel environments
  • Overwintered high tunnel spinach nitrogen fertility 

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Announcements

Resources from CCE ENYCHP!

We are developing new ways to connect with the CCE ENYCHP team this year! We have a Youtube page located at this link. Check out videos on Table Grape Production, Pest Updates and the 20 Minute Ag Manager - in 4 Minutes series

We have a Facebook Page here as well as an Instagram page. We keep these places updated with current projects, events, and other interesting articles and deadlines.

There are also text alerts available. Fruit and vegetable farmers in 17 Eastern NY counties can now receive real time alerts on high risk disease and pest outbreaks texted directly to their cell phone. The Eastern NY Commercial Horticulture program, which is supported by local Cornell Cooperative Extension associations, will now offer text alerts to those that enroll in our program in 2019. 

The text alerts will be reserved for important crop alerts that could impact management decisions immediately. For instance, if there were an outbreak of Late Blight in the area, this would be transmitted to vegetable growers.

Farmers can choose the crop for which they wish to receive updates. Additionally they can request that Ag Business Alerts be sent to them. These alerts might include due dates for crop insurance deadlines, market opportunities etc.

If you have questions, please contact enychp@cornell.edu


Podcasts

Biweekly Vegetable News Podcast - Episode 9 - 08/21/19

August 21, 2019
The August 21st, 2019 edition of the Eastern New York Vegetable News covers the following topics:

Changes to Worker Housing Regulations in the Farmworker Fair Labor Practices Act (1:25)
Managing Alternaria Leaf Spot and Head Rot on Broccoli (4:25)
Gauging Winter Squash Maturity for Harvest (10:05)
Insects in Hemp, especially European Corn Borers (18:33)
Guidance on the Dropped Covered Produce Provision of the Food Safety Modernization Act (22:53)
Cucurbit Downy Mildew Management Update (27:02)
Report from the BioControl Field Day and Weed Management Recommendations (31:07)
Day Neutral Strawberries (40:33)

Here are links to additional resources mentioned in the episode:

Current Housing Regulations for Seasonal and Migrant Farmworkers
(On January 1, 2020, these will now apply to farms housing any number of seasonal and migrant farmworkers)

Public Health Law, section 225, NYCRR Title 10 Health, Part 15, Migrant Housing: https://www.health.ny.gov/regulations/nycrr/title_10/part_15/

Managing Alternaria Leaf Spot and Head Rot in Broccoli

Sue Scheufele “Can Alternaria Leaf Spot Be Managed Organically?” http://www.hort.cornell.edu/expo/proceedings/2013/Cole%20Crops/Cole%20Crops%20Scheufele%20Alternaria.pdf

Christy Hoepting “Control of Alternaria head rot in broccoli featuring exciting results from 2018 on‐farm fungicide trial” http://www.hort.cornell.edu/expo/pdf/20190115-all-day-hoepting.pdf

Dropped Covered Produce:
FDA Factsheet on Dropped Covered Produce: https://www.fda.gov/media/129568/download

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