Andy Wyenandt

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

April 23, 2015

Damping-off: Important Early-season Pathogens

It is extremely important to know which pathogen is causing damping-off problems and which fungicide to properly apply. The key to controlling damping-off is being proactive instead of reactive. Always refer to the fungicide label for crop use, pathogens controlled, and application rates.

Damping-off is caused by a number of important vegetable pathogens and is very common during the 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.

Control of damping-off depends on a number of factors. First, is recognizing the conditions which may be leading to the problem (i.e., weather/greenhouse growing conditions) and second, identifying the pathogen causing the problem.

Conditions Favoring Damping-off

Although all four pathogens are associated with damping-off, the conditions which favor their development are very different. In general, Phytophthora and Pythium are more likely to cause damping-off in cool, wet or overwatered soils that aren’t allowed to dry out due to cloudy weather or cooler temperatures. Conversely, Rhizoctonia and Fusarium are more likely to cause damping-off under warmer, drier conditions especially if plug trays are kept on the dry side to help reduce transplant growth. [Read more…]

Filed Under: Organic Production, Vegetable Crops
April 22, 2015

Controlling Septoria Leaf Spot in Parsley

Septoria leaf spot in parsley can cause significant losses in fields where it has become established. Like other Septoria’s, the leaf spots produced on parsley look much like the leaf spots produced on tomatoes and other crops.

Parsley SLS

Parsley: Septoria Leaf Spot

Septoria leaf spot overwinters from year to year on infected debris so long crop rotations of 2 or more years are important to help reduce disease pressure. During the season, SLS will spread rapidly with each subsequent rainfall and/or overhead irrigation event. Therefore, early detection and preventative fungicide applications are keys to successfully controlling SLS. Unfortunately, very few fungicides are currently labeled making control difficult.

Parsley growers who have significant septoria leaf spot issues every year and have seen poor control in fields where FRAC code 11 fungicides have been used considerable in the past should consider no longer using them due to potential resistance issues. Fungicide programs should include Fontelis at a high rate (16.0 to 24.0 fl oz/A) tank mixed with a copper rotated on a weekly basis with Merivon (5.5 fl oz) plus copper. Fontelis has a 3 day PHI and a 72.0 fl. oz season max. Merivon has a 1 day PHI and 33.0 fl. oz season max. Organic farmers should use an OMRI-approved copper fungicide on a regular basis to help suppress septoria leaf spot.

Filed Under: Organic Production, Vegetable Crops Tagged With: ,
April 22, 2015

Growers Guide to Protectant Fungicides
(FRAC groups M1 – M11)

Protectant (contact) fungicides, such as the inorganics (copper, FRAC group M1) and sulfur (FRAC code M2); the dithiocarbamates (mancozeb, M3), phthalimides (Captan, M4), and chloronitriles (chlorothalonil, M5) are fungicides which have a low chance for fungicide resistance to develop. Protectant fungicides typically offer broad spectrum control for many different pathogens.

Why wouldn’t fungi develop resistance to protectant fungicides? Protectant fungicides are used all the time, often in a weekly manner throughout much of the growing season.

[Read more…]

Filed Under: Vegetable Crops Tagged With:
April 22, 2015

Spear Damage in Asparagus

Spear damage in asparagus can be caused by diseases such as Phytophthora spear and crown rot and purple spot. However, other environmental factors during the spring can damage spears as they emerge from the soil.

Fig. 1. Wind damage of asparagus spears. Notice how all spears are pointed in the same direction

 Wind – Periods of heavy winds during emergence will cause spears to bend.Winds can cause one side of the spear to dry out quicker than the other causing the spear to bend and point in the direction of the prevailing wind. An asparagus planting is suffering from wind damage if most of the bent spear heads in the bed are pointing in the same direction (Fig.1).

[Read more…]

Filed Under: Vegetable Crops Tagged With:
April 22, 2015

Vegetable Disease Briefs – 4/22/15

  • Quadris 2F from Syngenta, the first strobilurin (FRAC group 11) fungicide on the market, is coming off patent and a number of companies are expected to apply to manufacture and sell is under another name. Thus, in the 2015 Vegetable Recommendations Guide you will see references to Quadris (FRAC group 11) switched to azoxystrobin (FRAC group 11) much like we did with changing Bravo WeatherStik (M5) to chlorothalonil a few years ago. As more FRAC group 11 fungicides come off patent in the next few years we expect to do the same.
  • Cucurbit downy mildew is presently active on acorn, butternut, yellow summer, cucumber, cantaloupe, and giant pumpkin in southern Florida. To track the progress of cucurbit downy mildew in the US please visit (http://cdm.ipmpipe.org/)
  • Basil downy mildew is active in southern Florida.
Filed Under: Vegetable Crops
April 21, 2015

Vegetable Disease Update 4‑20‑15

This week in the Vegetable Disease Update:

  • Asparagus
  • Cabbage
  • Cole crops
  • Leeks
  • Lettuce

Note: The new 2015 NJ Commercial Vegetable Production Recommendations is available online.

Asparagus

Phytophthora crown and spear rot – In fields with low spots (poorly drained soils) or fields with a history of crown and/or spear rot apply Ridomil Gold 4SL (mefenoxam, 4) at 1.0 pt/A, or Ultra Flourish 2E/A (mefenoxam, 4) at 2.0 pt/A, or MetaStar 2E (metalaxyl, 4) at 2.0 qt/A over beds just before 1st harvest. For new plantings, apply the same after planting or after crown covering. Do not apply Ridomil or MetaStar one day prior to harvest or illegal residues may result. For more information please see 2015 New Jersey Commercial Vegetable Production Recommendations Guide.
[Read more…]

Filed Under: Vegetable Crops