Andy Wyenandt

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

May 4, 2016

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.

Filed Under: Vegetable Crops
May 4, 2016

Wet Weather Ripe for Strawberry Fruit Rots

Anthracnose fruit rot of strawberry

Anthracnose Fruit Rot of Strawberry

Fruit rots in strawberry can cause significant losses if not recognized early and controlled. The use of good cultural practices such as: keeping fields weed-free and promoting good drainage; long crop rotations, and preventative fungicide applications are critical.

Pathogens such as anthracnose, gray mold (Botrytis), and leather rot can become systemic problems in strawberry plantings once established. All three fungal diseases are soil-borne and once in fields can be difficult to manage over the lifetime of the planting.

For growers new to strawberry production and/or those just looking for valuable resource(s), please visit Cornell University’s strawberry production website here. An Organic Strawberry Production Guide is also available.

The use of mulch (matted rows) to prevent/reduce soil splashing and keeping fruit from coming into direct contact with the soil surface can be beneficial in organic production systems where conventional fungicides cannot be used. Use of long crop rotations and staying away from areas of the farm with known instances of any of these pathogens is also important. Remember that same species of Colletotrichum that causes fruit rot in pepper and other crops can also infect strawberry.

[Read more…]

Filed Under: Organic Production, Vegetable Crops Tagged With:
May 1, 2016

Vegetable Disease Briefs – 5/1/16

  • Dickeya sp., an aggressive form of Black leg, has been confirmed on potato in New Jersey in 2016. Symptoms of Dickeya infection look similar to Black leg infection and can cause significant rot above ground (stems and foliage) and below ground (tubers). All potato growers should scout on a regular basis and report any suspect plants or fields.
  • There have been no new reports of cucurbit downy mildew.
  • With the cool, prolonged wet weather, basil downy mildew may become active in greenhouses or high tunnels that have been closed up to retain heat. Appropriate venting to keep relative humidity low and leaf wetness to a minimum is critically important to keep the pathogen from sporulating and spreading rapidly.
Filed Under: Vegetable Crops
May 1, 2016

Vegetable Disease Update – 5/1/16

Cabbage

Damping-off – To help control losses due to damping-off pathogens apply Ridomil Gold (mefenoxam, FRAC code 4) at 1 to 2 pt/A, MetaStar (metalaxyl, 4) see label, or azoxystrobin at 0.40 to 0.80 fl oz 2.08SC/1000 row ft (for Rhizoctonia only), or Ridomil Gold at 1.0 to 2.0 pt/A 4SL plus azoxystrobin at 0.40 to 0.80 fl oz 2.08SC/1000 row ft. in a band up to 7 in. after seeding. To help control damping-off pathogens in Collards and Kale only: Apply Uniform (mefenoxam +  azoxystrobin, 4 + 11) at 0.34 fl oz 3.66SE/1000 ft row. For more information please see 2016 New Jersey Commercial Vegetable Production Recommendations Guide.

[Read more…]

Filed Under: Vegetable Crops
April 19, 2016

Damping-off: Identifying and Controlling 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 15, 2016

Vegetable Disease Briefs – 4/15/16

  • Late blight has been reported in Florida and South Carolina on tomato. To track the season-long progress of Late blight in the US please visit (http://usablight.org/)
  • There has been isolated reports of cucurbit downy mildew on watermelon and cucumber in southern Florida. To track the season-long progress of cucurbit downy mildew in the US please visit (http://cdm.ipmpipe.org/)
Filed Under: Vegetable Crops