Andy Wyenandt

The weather has been a double-edged sword of late throughout most of the mid-Atlantic region. The extremely hot weather with temperatures at or above 90 these past few days have been good for slowing disease development down. At those temperatures, its even too hot for pathogens to develop!

Unfortunately, the weather has also brought with it a lot of wind and rain these past few days and weeks. We all know what this leads to. Remember that bacteria need a wound or natural opening to enter a plant and cause an infection. The heavy winds and driving rains that beat up plants also help create the wounds that allow this to occur so its not unlikely to see an uptick in bacterial problems across a number of crops, such as in the case of bacterial leaf spot in tomato and pepper, after the weather we’ve had this past week.

Growers need to be proactive with copper applications and/or disinfestant applications prior to and/or after such events. Growers should also avoid working in fields when foliage is wet, if possible. This is extremely important if a bacterial problem is already present in the field!

The wet weather, along with the high humidity and prolonged leaf wetness also makes nice for many fungal pathogens, both leaf and soil-borne. Phytophthora blight in cucurbits, pepper, eggplant and tomato;  Early blight in tomato;  Alternaria and Anthracnose in cucurbits; and downy mildews just to name a few are favored by our current weather conditions, especially after temperatures cool down after todays weather front passes through the region.

During these conditions, all growers need to remain diligent and keep up with their protectant fungicide programs as long as field conditions allow and be proactive instead of reactive. After today, we get a few hours of dry weather before potential rains return on Thursday night into Friday.

• Basil downy mildew has been reported in Northern New Jersey this past week. All basil growers should continue to scout and be proactive.
• Late blight has been reported on potato as far north as North Carolina near the Virginia border. There have been no reports of late blight in the region to date. To track late blight in the US please visit http://usablight.org/
• Cucurbit downy mildew has been reported on cucumber, butternut, acorn, and yellow summer squash as far north as central South Carolina. To track the progress of CDM in the US please visit http://cdm.ipmpipe.org/
• Bacterial leaf spot are coming in on pepper and tomato.
• Black leg has been reported in potato in southern New Jersey.
• Phytophthora blight on pepper and cucurbit crops has been reported. The heavy rains that have come into and remain in the region have been ideal for P. capsici. All growers need to scout on a regular basis and be proactive.
• Early blight has been reported in tomato.

Potato

Black Leg – Black leg is caused by Erwinia spp. which also cause ‘soft rots’. The bacteria which lead to the aerial phase of Blackleg are soil-borne (originate from old crop debris) and spread by rainfall, overhead irrigation and wind. The aerial phase of Blackleg does not originate from decaying seed pieces. The bacterium can enter the plant through wounds created by cultivation or through stems damaged by blowing wind, sand or hail. Dense canopies, warm weather and prolonged periods of leaf wetness favor the spread of aerial Blackleg. Fortunately, the disease rarely extends below ground and only causes dieback of stems over time. Symptoms of the aerial phase of Blackleg first appear as an irregular, water-soaked ‘green’ decay on stems that turns light-brown to black over time. Hot, dry weather will cause infected areas to dry out and become brittle. Do any cultivating when plants are dry, cultivating in the presence of dew or wet plants may help to spread the bacterium around.

• Basil downy mildew has been reported in New Jersey. All growers should be scouting on a regular basis and applying protectant fungicides.
• Late blight was reported on potato in northern North Carolina near the Virginia border on this past week. There have been no reports of late blight in the region to date. To track late blight in the US please visit http://usablight.org/
• Cucurbit downy mildew has been reported on cucumber, butternut, acorn, and yellow summer squash as far north as central South Carolina. To track the progress of CDM in the US please visit http://cdm.ipmpipe.org/
• The first reports of bacterial leaf spot are coming in on pepper and tomato.
• Black leg has been reported in potato in southern New Jersey.