Despite the hot, dry conditions, levels of asparagus rust are increasing in young plantings. Foliar disease management is important in all asparagus plantings. However, fields are particularly susceptible to infections during the first few years of establishment, causing a reduction in productive crown development.
Even in established asparagus fields, rust can have a significant impact on both the spear weight and spear number.
Warm weather with heavy dew, fog, or light rainfall enhances rust development. Infection can occur with as few as 3-9 hours of leaf wetness.
All foliar fungicides are most effective when they are applied before symptoms begin to move into the upper crop canopy. Thorough coverage is essential for good control.
By Elaine Roddy, Vegetable Crops Specialist, OMAFRA
Do you ever just get completely overwhelmed by choices? I do. Especially when it comes to cucurbit fungicides. In a few short years, we have gone from having a very limited fungicide tool kit, to having over 20 distinctly different fungicides to choose from. In many ways, it is a nice problem to have; but it doesn’t make building a fungicide program any easier.
Fungicide product selection is extremely important, and the best choices will vary depending on the type of cucurbit crop grown. Each of the cucurbit crops is impacted by the various cucurbit diseases to a different degree.
Both rust and purple spot (stemphylium) thrive under cool, wet conditions. Scout fields regularly, at least 2 times per week under high disease pressure conditions. Inspect a minimum of 100 plants per field; looking closely at the bottom 24″ of each stalk. Foliar diseases often first appear in immature and newly planted fields. Continue reading Watch for Diseases in Asparagus→
Last week’s confirmation of downy mildew in both Kent and Elgin was unusually early. Recent reports have also been made in Michigan and Ohio. As a result, we are in the unfortunate situation of having to “stay ahead” of the disease this year. Here are a few additional thoughts to help manage this aggressive disease in what appears to be a high pressure year.
Rotate! Research at Ridgetown Campus has shown that the “best” product does vary from year-to-year, and that all of the products have had years where they did not perform as well. To rely on one or even two products puts the crop at risk should one of those products fail, or if resistance develops. Use at least 3 different products from different fungicide groups.
If at all possible, spray BEFORE aforecast rain event. While several of the products have a limited amount of curative properties, they all work best when used preventatively.
If downy mildew is present in your field, shorten the spray interval. Especially if rain is forecast in the immediate future (see above).
All leaf material is susceptible to downy mildew infection, even the cotyledons. Begin a preventative program in new plantings as soon as they emerge.
Scout fields regularly, especially fields in which downy has not yet been identified. And by regularly, I mean daily! The disease can progress significantly in just a few days. I have seen fields go from “watersoaked” lesions to spore producing brown lesions in less than one day.
Ranman 400SC/Torrent 400SC
In response to the issue regarding the use of Ranman 400SC the PMRA has issued this response: “The RANMAN 400SC AGRICULTURAL FUNGICIDE (Reg. No. 30716) was recently amended to remove all uses except potatoes. With respect to product bearing the previous label,(i.e. just prior to the latest amendment), the PMRA would have no issue with this previously purchased product being used on cucumbers for the 2015 use season. Any purchase of product bearing the newly amended label however, will need to be used in accordance with the new label.”
Moving forward, cucurbit growers are reminded that Torrent 400SC is now the registered formulation of cyazofamid for the control of downy mildew in this crop.
Trace amounts of downy mildew were found in a Kent County cucumber field today by the University of Guelph, Ridgetown Campus, scout.
All cucumber growers in Ontario are advised to begin a preventative downy mildew spray program using targeted downy mildew fungicides. For more information fungicide selection, see the Ontario 2015 Downy Mildew Control Strategy for Cucumbers. Growers are also encouraged to monitor their own fields for early signs of infection (see figure 1, below).
Current weather conditions are very suitable for the spread of this very aggressive disease. Under these conditions, with downy mildew in the area, a 7-day spray schedule is warranted.
By Elaine Roddy, OMAFRA and Cheryl Trueman, University of Guelph – Ridgetown Campus
Rhizoctonia belly rot has been identified in certain Southwestern Ontario cucumber fields since 2011. The pathogen, Rhizoctonia solani, thrives under hot, humid weather conditions and is more commonly associated with growing conditions in the Southern United States.
Under suitable conditions, symptoms appear in as little as 24 hours on the underside of the fruit, or where the blossom-end rests on the soil surface or on decaying plant material. Irregular-shaped, yellow-brown discoloured patches develop on fruit (Figure 1). These patches do not usually penetrate below the surface of the skin. Lesions later develop a scab-like appearance and fruit fly maggots may occasionally be found feeding on the damaged area.
Research at the University of Guelph Ridgetown Campus sponsored by the Ontario Cucumber Research Committee, is evaluating the efficacy of foliar fungicides applied at different crop development stages for reducing damage to this disease. Fungicides and biofungicides were evaluated in growth chamber screening trials over the winter months using greenhouse mini-cucumbers. Quadris Top and Fontelis, which are both registered for other fungal diseases on cucumber, reduced disease severity in the growth chamber studies. They are now being evaluated under field conditions along with one experimental product.
This disease may be difficult to control with standard foliar fungicides because protective sprays are unlikely to reach the lower surface where the fruit infection occurs. The field evaluation at Ridgetown includes a variety of fungicide application timings including the 1-3 leaf stage, vine tip-over, and different fruit development stages.
Since standard foliar fungicide applications may not be a silver bullet solution, the tolerance of different cucumber cultivars to belly rot is also being evaluated in two other trials at Ridgetown Campus. The incidence and severity of belly rot on five common pickling cucumber cultivars grown in inoculated field soil will be assessed in the first trial. In the second trial, healthy field-grown cucumber fruit from four cultivars will be collected and evaluated for disease development after exposure to inoculated media in a growth chamber.
We have had reports of asparagus rust in new plantings. Now is the time to get out and scout; especially in the two-year old fields and any volunteer asparagus near the production fields. These plants often act as source of inoculum for the commercial crop later in the season.
Severe rust infections cause the plants to die prematurely in the fall, impacting both the vigour of the crown and the following year’s harvest.
The early infections are slightly raised, light green lesions 10 to 20 mm in length. As they mature, the lesions turn cream-to-light orange (figure 1, asparagus rust aeciospores). Initial infections generally appear at the base of the stalks. Look for these lesions early in the season on volunteer asparagus or two-year old fields. As harvest concludes, scout all fields regularly during the fern development stage. Continue reading Get out and Scout for Asparagus Rust Symptoms→
Identification: Currently, bacterial leaf spot (Xanthomonas cucurbitacae) is not commonly found in Ontario. However, it is known to cause serious pumpkin crop losses in the Mid-western United States. Leaf lesions are dark and very small with yellow margins (figure 1). As the disease progresses they coalesce to form large necrotic areas. They are easily confused with several other foliar diseases including angular leaf spot.
Fruit lesions are circular in shape, small and slightly sunken. They often have a dark brown border (figure 2). As the lesions enlarge in size (up to 12 mm in diameter) they crack and become scab-like. Infected fruit often develop soft, watery rots in the field or in storage and collapse quite quickly.
Biology: Bacterial spot survives in crop residue. It is also seed-borne. It can tolerate high mid-summer temperatures. It spreads quickly within the field.
Management Notes: Use disease-free, certified seed. Follow a 2-3 year rotation away from all cucurbit crops. The bacteria are easily spread by splashing rain or irrigation and by machinery. Avoid working in the field when the foliage is wet.
The Ontario Ministry of Agriculture and Food, the Ministry of Rural Affairs and the University of Guelph, Ridgetown Campus are hosting a disease management workshop for growers of cucurbits and peppers.