Andy Wyenandt

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

April 19, 2020

Understanding The Differences Between FRAC Group 11 and FRAC Group 3 Fungicides

FRAC Group 11 Fungicides

The strobilurin, or QoI fungicides (FRAC group 11) are extremely useful in controlling a broad spectrum of common vegetable pathogens.

You may know some of strobilurins as azoxystrobin (Quadris), trifloxystrobin (Flint), pyraclostrobin (Cabrio), or Pristine (pyraclostrobin + boscalid, 11 + 7). For example, FRAC group 11 active ingredients such as azoxystrobin are also now available generics or in combination products as Quadris Top (azoxystrobin + difenoconazole, 11 + 3), Quilt (azoxystrobin + propiconazole, 11 + 3), or Quadris Opti (azoxystrobin + chlorothalonil, 11 + M5).

All strobilurin fungicides inhibit fungal respiration by binding to the cytochrome b complex III at the Q0 site in mitochondrial respiration. Simply said, the fungicide works by inhibiting the fungi’s ability undergo normal respiration. The strobilurin chemistries have a very specific target site, or mode-of-action (MOA).

Although highly effective, fungicide chemistries like those in FRAC group 11, with a very specific MOA, are susceptible to fungicide resistance development by some fungi. Why is that? In the strobilurin’s, a single nucleotide polymorphism of the cytochrome b gene leads to an amino acid substitution of glycine with alanine at position 143 of the cytochrome b protein.

For us, knowing the specifics on the technical jargon isn’t so important, it’s understanding what is at stake. So, if we hear someone speak about G143A resistance development to the QoI fungicides (where resistance is already known in cucurbit Powdery mildew and Downy mildew), we know what they are talking about and how important it is! So much so, if cucurbit powdery mildew develops resistance to one strobilurin compound it may develop what is known as cross resistance and become resistant to all chemistries in FRAC group 11, even if only one chemistry has been used!

[Read more…]

Filed Under: Commercial Ag Updates, Vegetable Crops Tagged With: , , , , , ,
April 19, 2020

Preparing for Pepper Anthracnose

Pepper Anthracnose

Pepper Anthracnose

In recent years, pepper anthracnose caused by Colletotrichum spp. has become a significant problem on some farms in southern New Jersey.

Unlike in tomato, where symptoms are only present in mature (red) fruit, pepper anthracnose can infect pepper fruit at any growth stage. Currently, there are no commercially-available bell or non-bell peppers with known resistance to anthracnose. [Read more…]

Filed Under: Vegetable Crops Tagged With:
April 18, 2020

Anthracnose and Alternaria Leaf Blights in Cucurbit Crops

Anthracnose and Alternaria leaf blight can become problematic in cucurbit crops during long periods of wet, humid weather. Both can cause significant losses if not controlled properly. With the production season quickly approaching, now is a good time to review a few of these important diseases.

Symptoms of anthracnose on infected cucumber leaf.

Symptoms of anthracnose on infected cucumber leaf.

Alternaria leaf blight on cantaloupe

Alternaria leaf blight on cantaloupe (NCSU – G. Holmes)

 

 

 

 

 

 

 

 

 

Anthracnose, caused by Collectotrichum orbiculare, and Alternaria leaf blight (Alternaria cucumerina) produce distinct spots on infected leaves, and in most cases, symptoms begin on the older leaves. With Alternaria, diagnostic concentric black rings will be develop within the spots on infected leaves, often there is a chlorotic (yellow) halo around margins. With Anthracnose, spots always develop on veins on the underside of infected leaves. Often, black setae (hair-like projections) will develop on the veins of infected tissue. These symptoms make for easily diagnosing which disease might be present.

Both pathogens can overwinter on infected plant tissue in the soil for 1 to 2 years, thus extended crop rotations are important. Conidia (spores) develop from dormant mycelium in the soil and are splashed into the canopy causing primary infections during prolonged periods of humid, wet weather causing extended leaf wetness. Secondary infections and spread of both diseases can occur during the production season under favorable conditions for disease development.

Deep plowing debris or the removing of plant debris after harvesting, avoiding overhead irrigation during the production season, and most importantly, choosing cucurbit varieties with resistance are important cultural practices all conventional and organic growers should consider.

Anthracnose and Alternaria are easily controlled with weekly protectant fungicides such as chlorothalonil and mancozeb as long as they are applied prior to the arrival of the pathogen and on a regular basis during favorable disease development. Organic growers can apply copper and other labeled products to help suppress development of these diseases. Complete foliar coverage is critically important for the control of these diseases.

For more information on the control of anthracnose and Alternaria leaf blight in cucurbit crops please see the 2020/2021 Mid-Atlantic Commercial Vegetable Production Recommendations Guide.

Additional Resources:

University of MN Extension: https://extension.umn.edu/diseases/alternaria-leaf-blight

University of Florida: https://plantpath.ifas.ufl.edu/u-scout/cucurbit/alternaria-leaf-spot.html – Images of Alternaria

University of Florida: https://www.growingproduce.com/vegetables/aim-to-keep-anthracnose-out-of-your-cucurbit-crops/ – Additional information on anthracnose

University of MN: https://extension.umn.edu/diseases/anthracnose-cucurbits – Additional information on anthracnose of cucurbits

 

Filed Under: Vegetable Crops Tagged With: , ,
April 17, 2020

Avoid Sunscald Injury in Transplants

Now that the weather is beginning to cooperate and temperatures are warming up, be cautious about sunscald developing on the stems of transplants, especially those being set onto black plastic mulch. With a little planning ahead potential losses to sunscald injury can reduced significantly.

Sunscald

Sunscald injury on stems of newly transplanted pepper seedlings caused by stems laying against edges of black plastic mulch on hot, sunny days.

A transplant coming straight out of the greenhouse and directly into the field has not been exposed to much direct sunlight. Add that with black plastic mulch and you have a lot of heat aim directly at the tender tissue of the transplant. All transplants should have some time to harden-off outside the greenhouse before going into the field, a day or two, is better than none at all, the longer the better if time and space allow.

Sunscald typically appears as the slow bleaching out of the stem that will typically appear only on one side. Often this starts to appear right where the stem meets the black plastic mulch. In many cases if the stem is touching the mulch, the sunburn will start there and the transplant will begin to fall over as if the stem was broken.

When transplanting, make sure the holes in the plastic are wide enough to keep the stem from coming into contact with it. In some cases growers will fill in the transplant hole with soil to help keep the transplant upright before between-row herbicides are applied. ‘Leggy’ transplants that lay across plastic mulch and even those transplanted onto bare ground are prone to sunscald injury.

Filed Under: Vegetable Crops Tagged With: ,
April 17, 2020

Take-Home Extension Talk: Updates on important vegetable diseases.

The following video includes a review and update on important diseases for vegetable farmers in New Jersey.

Covered in this presentation are:

  • Bacterial leaf spot in pepper and tomato
  • Phytophthora blight
  • Cucurbit downy mildew
  • Pepper Anthracnose
  • Cucurbit powdery mildew

Take-Home Extension Talk: Updates on important vegetable diseases.

Please click here: Take Home – PPA 4-17-20

For commercial growers, fungicide recommendations can be found in the 2020/2021 Mid-Atlantic Commercial Vegetable Production Recommendations Guide. The new guide available FREE on-line or can be purchased in hardcopy form through your county agricultural office in New Jersey. The complete 2020/2021 Vegetable Production Recommendations guide or specific sections can be downloaded depending on your production needs.

Filed Under: Vegetable Crops
April 17, 2020

Vegetable Disease Update – 4/17/20

  • Bacterial leaf blight in Cilantro was reported this week in southern New Jersey.
  • Common leaf spot was reported in strawberry this past week. For more information click here.
  • White rust and anthracnose have been reported in spinach over the past few weeks. For more information click here.
  • Damping-off has been reported in pepper transplants this past week. For more information click here.
Filed Under: Vegetable Crops