Andy Wyenandt

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

May 30, 2024

Edema development in brassica crops

Edema is often expressed as off-color swellings or galls that appear on leaves and stems. Edema develops when epidermal cells hold excessive water due to a slowing of evapotransporation when hot, muggy days are followed by cooler, wetter weather. Edema develops because the plant takes in more water (due to a high soil moisture content) faster than it can get rid of it through evapotranspiration causing cells to rupture which results in the blistering of the leaves. Edema is strictly caused by environmental factors and can appear whenever these conditions are met. Properly monitor soil conditions, irrigation cycles, and the weather to avoid over irrigating on warm, hot early spring days, especially when quick cold fronts/temperature drops and cloudy weather are expected.

Symptoms of edema on collard leaf. Note the off-color appearance of leaf surface.

Symptoms of edema on top side of
collard leaf.
Note the off-color appearance of leaf surface.

Edema, bottom side of collard leaf. Note the irregular, 'corky appearance caused bythe rupture of leaf cells.

Edema, bottom side of collard leaf.
Note irregular, “corky” appearance due to leaf cell rupture.

Filed Under: Vegetable Crops Tagged With:
May 29, 2024

Controlling Phytophthora blight in cucurbit plantings

As the summer heats up in New Jersey, the control of Phytophthora blight in cucurbit plantings can be extremely difficult (even with the use of fungicides) as hot, wet weather finally sets in. Mitigating losses to Phytophthora blight in cucurbit crops begins with long crop rotations,  where recommendations suggest crop rotations longer than 5 years if possible. Other cultural practices include avoid planting in low areas of the field where water may persist after rain or overhead irrigation, rogueing out infected plants as soon as possible, cutting the plastic to help dry out the soil, proper weed control, and proper preventative fungicide programs.

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Filed Under: Vegetable Crops Tagged With: , ,
May 27, 2024

Controlling Septoria Leaf Spot and Bacterial Leaf Blight in Parsley

Septoria leaf spot (SLS) 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. 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 key to successfully controlling SLS. There have been a few new fungicides labeled for SLS control in the past few years.

Parsley SLS

Septoria leaf spot of Parsley

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Filed Under: Vegetable Crops Tagged With: , ,
May 26, 2024

Diagnosing Verticillium Wilt in Eggplant

Verticillium wilt has been reported in eggplant this summer. It is a common soil-borne fungal pathogen that once it has infested soil can remain for a very long time. Verticillium wilt is caused by either Verticillium albo-atrium or Verticillium dahlia and has a wide host range (over 200 plant species). Both pathogens can survive (overwinter) as microsclerotia in the soil. Verticillium wilt prefers cooler weather and drier soils and can be more severe in neutral to alkaline soils. Solanaceous weeds such as Nightshade may harbor the pathogen. [Read more…]

Filed Under: Vegetable Crops Tagged With: ,
May 25, 2024

Phomopsis fruit rot in eggplant

Phomopsis blight is caused by the fungal pathogen, Phomopsis vexans. It survives between seasons in the soil on infested plant debris. Although the pathogen can infect stems and older leaves, fruit infections are most prominent. Cankers that develop on stems and branches can cause the entire plant to collapse and die. Circular, grayish spots may develop on infected leaves. On fruit, the pathogen causes brownish-black spots that can quickly enlarge causing flat spots that can produce black pycnidia (e.g., fruiting bodies) that produce masses of conidia (spores) which are rain dispersed onto healthy plants and fruit. Phomopsis blight is favored by hot, wet weather (85 – 90 F). Spores germinate in free water on leaves and fruit causing infections. The pathogen can survive on solanaceous weeds such as nightshade, so good weed control is necessary. Crop rotations of 3 to 4 years are recommended. If possible, infected fruit should be harvested and removed from the field to help reduce to inoculum and the spread of the disease. Fields should be scouted on a regular basis, especially fields with a history of Phomopsis blight. Fungicide applications include Quadris Top (difenoconazole + azoxystrobin, 7 +11) or Priaxor (fluxapyroxad + pyraclostrobin, 7 +11) rotated with chlorothalonil every 7 to 10 days. For more information please see the 2024/2025 Mid-Atlantic Commercial Vegetable Production Recommendations Guide.

 

Filed Under: Vegetable Crops Tagged With: , ,
May 24, 2024

Controlling Phytophthora blight in eggplant

Phytophthora blight, caused by Phytophthora capsici, can cause crown and fruit rot in eggplant. Unfortunately, most of New Jersey has been plagued by heavy rains and pop-up thunderstorms these past few weeks making conditions ideal for pathogens such as Phytophthora blight on pepper, eggplant, tomato, and cucurbit crops.

Control of Phytophthora blight is extremely difficult (even with the use of fungicides) in the very hot, wet weather conditions that most of New Jersey has been through during the month of July. In the past few years a number of new fungicides, with new active ingredients, have become commercially-available for use on multiple crops. Mefenoxam and metalaxyl, both once widely-used to effectively control Phytophthora blight have been hit by resistance issues around much of Southern New Jersey. Growers with a known history of mefenoxam-insensitivity on their farm should use Presidio or Ranman plus a Phosphite fungicide in rotation in their drip application programs for the control of the crown rot phase of Phytophthora blight. Importantly, if mefenoxam has not been used in particular fields on any crop for a number of years (more than 5+) the fungus may revert back to being mefenoxam-sensitive and control with these products may return. Mefenoxam, metalaxyl, and the phosphite fungicides are the most systemic of the group and should readily be taken up the by plant via application through the drip. Orondis Gold (OXTP + mefenoxam) is also systemic. Presidio is locally systemic, and Ranman has protectant activity and can also be applied via drip.
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Filed Under: Vegetable Crops Tagged With: ,