Andy Wyenandt

This is an archive of Dr. Wyenandt's posts on the Plant and Pest Advisory.

April 10, 2017

Got humidity? Get rid of it!

Unfortunately, closed greenhouses retain heat and humidity which can spell problems if left unchecked.

Remember, high relative humidity equals wet leaves which favor the development of fungal diseases such as Botrytis or bacterial diseases such as bacterial leaf spot. To avoid potential problems, do your best to vent out as much humidity as possible in the late afternoon and/or early morning. Turn on circular fans to promote air movement and finish watering earlier enough in the day so leaves have enough time to dry out before nightfall.

As a side note, stressed transplants where water and/or fertility have been withheld are also more prone to disease development. A light fertilizer application may go a long way in improving transplant health before setting in the field.

Please see Table E-14 and pages E52-E54 of the 2016-2017 Commercial Vegetable Recommendations Guide for a list of control options for important diseases in greenhouses.

Filed Under: Vegetable Crops
March 24, 2017

Best management practices for managing Dickeya dianthicola in potato – 2017

Using PCR test results and North American Certified Seed Potato Health Certificates to track Lot no., Dickeya dianthicola was reported in 22 states (ME, DE, FL, MD, MA, MN, NJ, NY, NC, PA, RI, VA, WV, WI, OH, IN, MO, MI, TX, ND, ID, and NM) on at least eleven potato varieties in 2016. Some of these varieties included: ‘Reba’, ‘Superior’, ‘Vivaldi’, ‘Norwis’, ‘Snowden’, ‘Yukon Gold’, ‘Beacon Chipper’, ‘Kennebec’, and ‘Atlantic’.  Known sources of infested seed found in potato fields on the East Coast have originated from WI, at least two suppliers in New Brunswick, Canada, and a number of seed suppliers in Maine this past growing season. To better understand the scope and breadth of the pathogen affecting potato production on the East Coast and elsewhere, information on known varieties and lot numbers that tested positive for Dickeya this past summer have been collected. Information on suspect varieties and lot numbers based on FL tests results from this past winter have also been collected. This information is now widely available. Of importance to all NJ potato growers, is that there have been NO CHANGES in the current policy or Blackleg tolerance levels for mitigating Dickeya dianthicola in seed production. All growers are encouraged to follow best management practices for buying seed and best management practices for Dickeya in field production. If you suspect Dickeya dianthicola in potato seed during cutting or planting please contact your county Extension agent or Extension Specialist. All suspect potato samples should be PCR tested to confirm the presence of Dickeya dianthicola.

 The best method for keeping your potato operation Dickeya-free is to adopt your own 0% Dickeya-tolerance policy.

Filed Under: Vegetable Crops Tagged With:
March 24, 2017

Understanding Damping-off Pathogens in Transplant Production

Damping-off is caused by a number of important vegetable pathogens and is very common during transplant production and early-spring. Damping-off can kill seedlings before they break the soil line (pre-emergent damping-off) or kill seedlings soon after they emerge (post-emergent damping-off). Common pathogens that cause damping-off include Pythium, Phytophthora, Rhizoctonia and Fusarium spp.

It is extremely important to know which pathogen is causing the damping-off problem and which fungicide to properly apply.

[Read more…]

Filed Under: Vegetable Crops Tagged With:
March 24, 2017

Greenhouse Disease Management: Transplant Production

Proper greenhouse sanitation is important for healthy, disease-free vegetable transplant production. Efforts need to be made to keep transplant production greenhouses free of unnecessary plant debris and weeds which may harbor insect pests and disease.

  • All equipment, benches, flats, plug trays and floors should be properly cleaned and then disinfested prior to use and efforts need to be taken throughout the transplant production season to minimize potential problems.
  • Any weeds in or around the greenhouse structure should be removed prior to and after any production.
  • Any transplant brought into the greenhouse from an outside source needs to be certified ‘clean’, as well as visually inspected for potential insects and diseases once it reaches your location.

Remember, disinfestants, such as Clorox, Green-Shield, or hydrogen dioxide products (Zerotol – for commercial greenhouses, garden centers and Oxidate – commercial greenhouse and field), kill only what they come into direct contact with so thorough coverage and/or soaking is necessary. The labels do not specify time intervals for specific uses, only to state that surfaces be ‘thoroughly wetted’. Therefore, labels need to be followed precisely for different use patterns (i.e., disinfesting flats vs. floors or benches) to ensure proper dilution ratios. Hydrogen dioxide products work best when diluted with water containing little or no organic matter and in water with a neutral pH. There are a number conventional and organic products labeled for disease control during transplant production in the greenhouse. Please see Table E-14 in the 2016-2017 Mid-Atlantic Commercial Vegetable Production Guide.

Filed Under: Vegetable Crops Tagged With:
November 9, 2016

Sources of Dickeya dianthicola in potato in 2016

Using PCR test results and North American Certified Seed Potato Health Certificates to track Lot no., Dickeya dianthicola has been reported in 16 states (DE, FL, MD, MA, NJ, NY, NC, PA, RI, VA, WV, OH, IN, MO, MI, and TX) on at least nine potato varieties to date in 2016. These varieties include: ‘Reba’, ‘Superior’, ‘Vivaldi’, ‘Norwis’, ‘Snowden’, ‘Yukon Gold’, ‘Beacon Chipper’, ‘Kennebec’, and ‘Atlantic’.  Known sources of infested seed found in potato fields on the East Coast have originated from at least two suppliers in Canada and a number of seed suppliers in Maine this past growing season. To better understand the scope and breadth of the pathogen affecting potato production on the East Coast, information on known varieties and lot numbers that tested positive for Dickeya this past summer have been collected. This information is now available. It’s important for potato growers using this information to know that this list is a working document and not all Dickeya dianthicola test results are known or have been made public or available by the Maine Potato Board or the Maine Department of Agriculture (or Canada). Dickeya testing is being done in Maine by the Maine Potato Board/Maine Department of Agriculture and independently by the University of Maine and other Universities and laboratories. Potato growers with any questions or concerns about Dickeya-infested varieties and seed lots in 2016 and sources of seed for 2017 should contact the Maine Department of Agriculture; or Potatoes New Brunswick, if purchasing seed from these regions.

Dickeya dianthicola has been detected in the US in the past, and because of this, APHIS  has designated the pathogen as a non-reportable/non-actionable pathogen despite its potential to cause 100% crop loss. A link to best management practices for managing Dickeya dianthicola in the Northeast (and mid-Atlantic region) can be found here. Importantly, there is no current policy in place designed specifically for regulating and/or controlling Dickeya dianthicola in seed potato coming into the US from Canada. The Maine Potato Board’s Executive Seed Council adopted their own Blackleg-tolerance policy last winter which is followed by the Maine Department of Agriculture. For more information on this policy please contact the Maine Potato Board or the Maine Department of Agriculture.

The best method for keeping your potato operation Dickeya-free is to adopt your own 0% Dickeya-tolerance policy.

 

Filed Under: Vegetable Crops Tagged With:
October 14, 2016

Best management practices for Dickeya in potato production fields in the Northeast

Potato seed tubers harboring Dickeya dianthicola are the only confirmed source of this pathogen. It does not appear to be able to survive in soil (including in crop debris) from one growing season to the next. Consequently, rotating with a non-susceptible crop is not a necessary component of the management program. Best management practices listed below are encouraged to minimize potential losses from Dickeya.

  1. Select certified seed with negligible potential to be contaminated with Dickeya. This is best determined by talking with the seed grower about past occurrence on the farm and what is being done to manage it. There are growers who have not had Dickeya develop from their seed.
    • Select seed from farms where the pathogen has not been detected and seed marketed in previous years was not associated with Dickeya developing where the seed was planted. Check Certificates before purchase to determine if the seed was increased in previous years on a farm where Dickeya has been detected and so is at risk for being contaminated.
    • Select seed from farms where zero tolerance is being implemented.
    • Select seed with zero blackleg levels reported on the North American Seed Potato Health Certificates or the Winter Grow Out Test results for presence of Dickeya in ANY seed lot from ANY source. Seed lots with field readings of blackleg present should have reports that suspect plant samples were taken for testing and found to be Dickeya free. Check Certificates before purchase and require a copy be provided for your records.
    • Select seed that tested negative for Dickeya. Note that not detecting a pathogen in a sample of seed does not mean the pathogen is not present in the seed lot.
    • Ask for ‘references’ to contact: potato growers who purchased their seed in 2016.
    • Avoid seed lots that tested positive for Dickeya in previous years.
    • Avoid seed if its Certificate is unavailable. All certified seed has a Certificate.
    • Avoid seed from fields where symptoms of Dickeya were observed, even if affected plants were rogued out.
  2. Request from supplier (directly from grower or broker) PCR testing for Dickeya dianthicola using an independent laboratory.
  3. It is recommended that each truckload brought to a farm operation be sampled and re-tested for Dickeya once delivered. All results should be reported to your State Dept. of Agriculture or Potato Growers Association.
  4. All equipment during seed piece cutting should be disinfected on a regular basis (at least daily), and also between lot numbers.
  5. While it is recommended to rotate where potatoes are grown to manage most pathogens that can survive in unharvested tubers, this practice is not considered important for Dickeya because this pathogen does not readily spread in fields (thus a few tubers with Dickeya will not result in significant disease outbreak as can occur with late blight) and infected tubers are likely to rot while in soil.
  6. Inspect fields for symptoms regularly, starting when skips and affected plants are readily visible. Examine the crop for unevenness (erratic growth) and plants that are unthrifty. Dickeya can be present in a plant affecting growth but not causing its typical blackleg symptom.
  7. Avoid excess irrigation that results in standing water as Dickeya can move in this water. Note that surface irrigation water is not considered to be a possible source of Dickeya.
  8. Do not apply copper or other fungicide for Dickeya. They are ineffective being unable to reach the pathogen, which is inside stems.
  9. Growers are encouraged to submit suspect samples for testing promptly to their local extension office.
  10. All growers are requested to share information about Dickeya occurrence and absence in their production fields. This information is needed to improve understanding about this disease. Include variety, lot number (North American Seed Certificate), field location, and testing results.
  11. Dickeya has not been observed to continue developing in storage, which is as expected considering high temperatures are favorable, thus there are no management steps to implement after harvest for table-stock potatoes. However, it is prudent to make sure storages and pile temperatures remain cool, also reduce condensation and encourage airflow and exchange.

Prepared by Meg McGrath and Andy Wyenandt with assistance from Steve Johnson, Kate Everts, Beth Gugino, and Nate Kleczewski.

Filed Under: Vegetable Crops Tagged With: ,