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Originally posted on onspecialtycrops:

Over the last few weeks, we have had numerous calls from homeowners and growers wondering why their basil is turning yellow and defoliating.  The reason in most cases is downy mildew.  Basil downy mildew seems to be particularly common this summer, likely due to the rainy weather and the fact that the disease first appeared in the field in mid-July rather than August which has been more typical.

In Ontario, the fungicides cyazofamid (Ranman and Torrent), mandipropamid (Revus) and phosphorous acid (Confine) are registered for control of downy mildew in commercial field basil.   All of these products are preventative, and will have limited effect on the disease once symptoms are widespread in the field.  It is important for growers to also be aware that once leaves are infected with downy mildew, it takes at least a week for symptoms to develop. Consequently, seemingly healthy leaves at harvest may develop symptoms…

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Late blight update

Previous 2014 late blight updates: August 8July 29July 25July 13, July 3.

Late blight has been confirmed on tomatoes in Elgin County, Chatham-Kent, and the Regional Municipality of Waterloo. Credible reports have also been received from other areas, including the United Counties of Stormont, Dundas and Glengarry, Middlesex, and Perth County.

Recent weather has been conducive to the development and spread of late blight.  Commercial growers should scout often and ensure they are using fungicides with good late blight activity in their fungicide program.  When late blight is in the area, spray intervals should be shortened.

Know the symptoms. See the Tomato Late Blight Photo Gallery and refer to Late Blight Look-Alikes for photos of late blight and possible look-alikes on tomato.

See the late blight post from July 29 for fungicide recommendations for tomatoes in Ontario.

Contact OMAFRA at 519-674-1690 or janice.leboeuf@ontario.ca if you suspect you have found late blight in Ontario.

Marion Paibomesai, Vegetable Crops Specialist, OMAFRA

Michael Celetti, Plant Pathology Lead – Horticulture, OMAFRA

Onion downy mildew has been found on onions in Waterloo and York Regions (updated 18 Aug 2014).  In Ontario, this disease is common in July and August and if left uncontrolled, the size, quality and quantity of yield can be significantly reduced. The neck tissue of the affected onions may not ‘cure’ properly at harvest and is thus open to secondary fungal and bacterial pathogens which can further reduce yield quality. When cool, humid conditions are present particularly when the canopy of the crop is advanced, the risk of downy mildew increases. Foliar symptoms first appear as pale light green patches on infected leaves (Figure 1).

Figure 1. A purple-grey downy growth often appears in the lesions after a period of wet weather or when conditions favour dew formation.

Figure 1. A purple-grey downy growth often appears in the lesions after a period of wet weather or when conditions favour dew formation.

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Cucurbit Downy Mildew has been identified in a cucumber field in Chatham-Kent, Ontario.  Levels were very low (< 1% of the field). The infection likely occurred within the past few days.  However, this does indicate that all area cucumber and melon fields are at a high risk of developing downy mildew at this time.

Continue to use a preventative fungicide program, rotating between the targeted downy mildew fungicides.  For more information on fungicide selection, see the Downy Mildew Report – July 11, 2014.

Previous 2014 late blight updates: July 29July 25July 13, July 3.

Although OMAFRA has not yet confirmed late blight in tomatoes in Ontario, credible reports of the disease in tomatoes are coming in from the United Counties of Stormont, Dundas and Glengarry and from Perth County. Once samples are examined, further updates will be available.

We do know, however, that is has been confirmed in tomato and potato in neighbouring states, where it is spreading.  It has also been confirmed in potatoes in Simcoe County.

Recent weather has been conducive to the development and spread of late blight.  Commercial growers should scout often and ensure they are using fungicides with good late blight activity in their fungicide program.  When late blight is in the area, spray intervals should be shortened.

See the late blight post from July 29 for fungicide recommendations for tomatoes in Ontario.

Contact OMAFRA at 519-674-1690 or janice.leboeuf@ontario.ca if you suspect you have found late blight in Ontario.

While downy mildew has still not been confirmed in Ontario, recent report from Michigan indicate that levels are starting to increase in the Saginaw Bay area.  At this time growers should maintain preventative downy mildew fungicide programs, especially for the late harvested crop.

Phytophthora has been identified in a pumpkin field in Norfolk county.  This disease thrives under wet soil conditions.  For more information, see: Phytophthora Blight of Cucurbits – August 7th, 2014.

Angular leaf spot, a bacterial disease, is present in many pumpkin fields at this time.  While this is a sporadic disease of cucurbits in Ontario, under the appropriate weather conditions, it could spread a cause premature defoliation of the crop.  Infections may also predispose the fruit to bacterial soft rot at harvest or in storage.  Copper fungicides, such as Copper 53W and Copper Spray, will help to control the spread of this disease.

Angular Leaf Spot on Pumpkin

Angular Leaf Spot on Pumpkin

 

Phytophthora symptoms include stunting, crown rot and fruit rot depending on the cucurbit species and the time of infection. The crown rot phase is the most destructive. Dark-green, “water soaked” lesions form on the crown or vines, girdling it and causing the entire plant to turn yellow or brown and die. (Figures 1 and 2).

Water-soaked lesion on the stem and necrosis of the crown tissue

Figure 1. Stem Lesion (L) and Crown Rot (R)

Yellowing of the foliar, followed by necrosis and widespread croploss

Figure 2. Foliar Symptoms in Pumpkins (L) and Zucchini (R)

Fruit infections begin as a large water-soaked lesion. Under humid conditions, a thin layer of white spores develop on the surface of the fruit. These spores resemble a fine dusting of powdered sugar (Figure 3). In pumpkins, the lesions frequently are circular in shape, while in cucumbers the spores often cover the entire fruit.

White spores on the fruit surface of zuchinni and pumpkin.

Figure 3. Fruit Rot in Zucchini (L) and Pumpkin (R)

Phytophthora is a water mould. It thrives under wet soil conditions caused by excessive rainfall, poor drainage or even compaction. Fields with short rotations are at high risk of developing phytophthora. The spores survive in the soil for long periods of time. Other host crops include the solanaceous crops (peppers, eggplant, tomatoes and potatoes.)

Products registered for phytophthora in cucurbits include Zampro (ametoctradin/dimethomorph) and Presidio (fluopicolide)[1]. Apply fungicides before disease symptoms appear, when the risk of infection is high based on local soil and weather conditions.

In Michigan, phytophthora spores have been found in irrigation ponds and streams. See: The Potential for Spread of Phytophthora Blight of Cucurbits and Peppers in Irrigation Water

The most effective way to manage this disease is through early identification and crop rotation. While a 3-yar rotation is normally sufficient for most cucurbit diseases, fields infested with phytophthora may require a longer (4-5 year) rotation. If you suspect phytopthora in a cucurbit crop field, contact OMAFRA or your local agri-business.

[1] Suppression only. Refer to the product label for rotational crop restrictions.

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