Manitoba Agriculture, Food and Rural Initiatives
Manitoba Weekly Vegetable Report
| Carrots | Cole Crops | Corn | Cucurbits | Daikon | Onions | Potatoes | Parsnips | Others |
Introduction
Sunny weather into the mid-high 20's, were experienced over much of the vegetable growing regions in Manitoba. Rainfall events on Tuesday have added more moisture to soils. Currently crop development appears to be anywhere from 2 weeks to a week behind, a year ago, which was a very warm growing season. There have been no diseases to report to date in any of our scouted fields, but on the insect side of things there have been some notable observations from scouting.
This year we will be incorporating a new type of crop staging rating system. These will have the plants on black backgrounds to give an approximation of what stage the growth is at. This will of course vary with cultivar, planting date, and local weather conditions in Portage la Prairie, Winkler, and Otterburne.
If you wish to have your name added to the mailing list to give you a reminder of when the report has been uploaded (please email Brent Elliott Entomologist) .
Carrots
Carrot development is well behind last year at this time (2 weeks), due to the cool temperatures in May and early June. Currently, growth is at the 3 true leaf stage (GS13--we will explain this system in upcoming reports).
Aster leafhoppers (Macrosteles quadrilineatus) have been detected in very small numbers to this point in the year, most samples coming from cereal fields which are preferred early season hosts for the leafhoppers and serve as hosts for the juvenile stages. We’re certain you’ll recall how bad last year’s populations were. At this time of year we often get questions asking us how bad the population will be. While we cannot give a definitive answer, we’re fairly comfortable stating that it is unlikely to be as bad as last year and we’ll explain why.
Most of the aster leafhoppers that we see in Manitoba arrive on southerly winds and are part of a migratory population that originates in the Gulf States in the southern US. Typically these arrive sometime in June in Manitoba and from that point on we have relatively significant populations in carrot fields. In years like 2007 we see very large migrations and tremendous numbers of leafhoppers arrive. This makes for very high populations and tremendous aster yellows pressure on carrot fields. In bad years like that other crops such as potato and canola are also adversely affected, though not always at an economic level. Aster leafhoppers may also over-winter here. There are some minor reports of adults over-wintering successfully but we don’t put much stock in those because everywhere there are known over-wintering populations the leafhoppers spend the winter in the egg stage. We do believe that a very small number of leafhoppers over-winter in Manitoba in the egg stage, much as they do in Michigan, Wisconsin, Nebraska and other locations. Those over-wintering eggs do not contribute much to the overall population of aster leafhoppers; the bulk coming from the migratory population.
So far this year we have been rather cool with temperatures well below normal. In addition, we have not experienced any strong, sustained southerly flows of air that would bring leafhoppers into the province in larger numbers. It is still likely that we will see some south winds during the summer, as we always do, but given that we are in the middle of ‘summer’ already, there will not be time for populations of leafhoppers to build up like last year. It is also unlikely that we will see such a large influx of migratory leafhoppers as we did last year. For those reasons we are not expecting a year like 2007. This does not mean that we won’t exceed the economic threshold in carrots, we have done so in every year since scouting has been done. But it does likely mean we won’t have a year as bad as last year and that we won’t hear the complaints from the other crops that we did last year.
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As is the tradition, we explain how to calculate the Aster Yellows Index (AYI): AYI is calculated by taking the number of leafhoppers and multiplying this by the infectivity level below. The migrating aster leafhopper population infectivity in Wisconsin is 4%. This is slightly higher than the normal 0-2%.
| Crop | AYI |
| Carrots | |
| Resistant (eg. Six Pak II) | 100 |
| Intermediate | 70-75 |
| Susceptible (eg. Spartan Bonus) | 40-45 |
| Celery, Romaine | 30-35 |
| Head Lettuce | 20-25 |
There are no observations of carrot diseases at this time.
Cole Crops
Cabbage and cauliflower are also behind the stage at this time last year, appearing to be approximately one week behind, again a result of the unseasonably cool May and June. Currently the crop is at the 9-12 unfolded leaf stage (GS19), which is just prior to the beginning of head formation.
Crucifer flea beetles (Phyllotreta cruciferae) were observed in moderate numbers on cabbage this week. At this point in the year we normally don't see much in the way of adult flea beetles as typically the only stage around is the larval stage that feeds underground and is not seen. With the delay in heat we've seen a delay in the life cycles of many insects, meaning they are around later than we'd normally see them.
There are no cabbage diseases to report at this time.
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Corn
Sweet corn is about two weeks behind last years growth. Seven leaves are expanded (GS17) at this stage. The hot sunny weather has helped development greatly from last week.
As we are at the end of June, it is time to keep an eye out for European corn borer or ECB (Ostrinia nubilalis). During scouting we did not find any egg masses or larvae, but we did see some leaves exhibiting symptoms that looked like early feeding damage, often referred to as 'window-paning'. If indeed this is early larval ECB feeding, it is because the larvae are very small and only are able to feed on the outer surface of the leaf at this time, making it thinner and allowing light to pass through. This is the time, when the larvae are outside the plant, that they are susceptible to applications of insecticide. Once inside the plant they are no longer susceptible to control measures. Remember though that we tend to see egg laying activities throughout the month of July, so larvae may be present at any time.
No diseases of corn were observed this week.
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Onions
Onions are about a week or less behind last year but this is quite variable as crops, have had a wide range of planting dates,
Scouting for onions did detect the presence of onion thrips in the Portage area this week. The fields scouted in the Winkler area did not have any thrips present, but the plants in the scouted fields were much younger and plants were smaller. Numbers did not approach the economic threshold in fields scouted in Portage.
Onion thrips (Thrips tabaci) are pale yellow to brown or black in color. They are very small (1-1.2 mm in length) and very slender in shape. They tend to prefer to hide in between the leaves and feed by piercing the plant tissue with their mouthparts and suck up the plant juices. We did not observe any feeding damage either, but were able to get a picture of the immature stages which resemble the adults, but do not have any fringed wings as the adults do. Thrips tend to thrive in hot, dry weather so in Manitoba tend to do the most damage in July.
No diseases of onions were observed this week.
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Others
We have been receiving reports of growers having difficulty with both cutworms (various species) and asparagus beetles (Crioceris duodecimpunctata) affecting Asparagus over the past week. The cutworms shouldn’t continue to be much of an issue as they typically are down their life cycle by this point in the year. The delay in warm weather seems to have delayed them or slowed their development, but they should be done by this week.
The asparagus beetles on the other hand are likely to be present for the remainder of the year. They are typically not found in all areas, so while some fields may experience significant populations, others and usually most fields will experience no problems at all. They are quite sporadic in their appearances from year to year and field to field. Adults will feed on the fern primarily at this time of year, but early in the season will feed on the spears. The larvae feed almost entirely within the berries and affect seed production. Control measures during the summer will not provide any economic benefit in the current year, but may reduce populations for the following season.
No diseases of asparagus were observed.
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Prepared by:
Brent Elliott Entomologist Ph.
204-745-5669
Philip Northover Pathologist
Ph. 204-745-5694 Manitoba Agriculture, Food and Rural
Initiatives, Crops Knowledge Centre, Carman
