Rutgers University | New Jersey Agricultural Experiment Station | Pesticide User Responsibility

Andy Wyenandt

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

May 10, 2015

Vegetable Disease Update – 5/10/15

Cole crops

Downy Mildew and Alternaria – Symptoms of downy mildew include purple to yellowish-brown spots on upper leaf surfaces. A grayish-white spore mass will develop and cover the underside of leaves under ideal temperatures (night temperatures of 46 to 61°F and day temperatures below 75°F. Downy mildew can kill young plants. Heavily infected leaves may drop providing entry points for bacterial infections (black rot and soft rot). Symptoms of Alternaria on infected leaves include small, expanding circular lesions with concentric rings that may have a ‘shot-hole’ appearance as lesions age.  Heavily infected seedlings may result in damping-off. Control of Downy mildew and Alternaria begin with preventative fungicide applications. Please refer to pages F34-35 of the 2015 NJ Commercial Vegetable Production Recommendations to determine which fungicides are labeled for each specific crop and disease. [Read more…]

Filed Under: Vegetable Crops
May 4, 2015

Angular Leaf Spot in Strawberries

Often considered a minor pathogen, angular leaf spot caused by the bacterium, Xanthomonas fragariae, can cause serious leaf and calyx infections ruining the marketability of fruit if left uncontrolled. Like all bacterium, the pathogen will infect leaves and the calyx through natural openings or wounds.

Fig. 1. Water-soaked lesions caused by angular leaf spot on infect strawberry leaf. Photo by P. Nitzsche

Infections can often start in production operations and come in on infected bare root transplants or cuttings. Symptoms on leaves include initial small, irregular water-soaked lesions (Fig. 1).
[Read more…]

Filed Under: Organic Production, Vegetable Crops Tagged With: ,
May 4, 2015

Strawberry Fruit Rots 2015

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.

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 3, 2015

Vegetable Disease Briefs – 5/3/15

Basil downy mildew has been found in potted greenhouse-grown basil. All growers producing basil should scout on a regular basis. Basil downy mildew is seed-borne and can cause significant losses.

Late blight has been found in FL and CA. To track the movement of Late blight in the US please visit USAblight.

Cucurbit downy mildew has been found on yellow summer squash, acorn, cucumber, and giant pumpkin in FL and on watermelon in TX. To track to progress of cucurbit downy mildew in the US please visit the downy mildew forecasting website at NCSU.

Filed Under: Vegetable Crops
May 3, 2015

Vegetable Disease Update – 5/3/15

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 2015 New Jersey Commercial Vegetable Production Recommendations Guide. [Read more…]

Filed Under: Vegetable Crops
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