A number of onion fields in the Winkler area were damaged by hail since the last report, a result of the intense thunderstorms that hit the area on June 23rd. Onions near the Miami area were free of damage as were those in Portage la Prairie. Damage varied with the crop stage of the plants.
Onion Smut (Urocystis cepulae) was found in one field near Portage. This disease is soilborne, and once a bulb is infected, it is no longer marketable. It has the appearance of soil trapped between the leaves of the bulb, and gives the bulb a striped appearance(The image below has a healthy onion at the top and a smut infected onion at the bottom).
The leaves appear fattened as they become filled with spores of the smut fungus and often split, releasing the dark brown spores (See picture below). Infected young seedlings often begin to yellow and die. The spores are capable of surviving in soil for as long as 15 years. Systemic seed treatments, if plants are grown from seed and disease free onion sets are recommended to reduce the impact of future outbreaks.
In general bulb development still looks good throughout the scouting area. See the photos below for the typical sizes of seeded and transplanted onions collected on June 26th and June 28th, 2006.
No insect activity was observed this week though there is strong potential for pests to be about.
Potatoes:
The Potato Hotline Recording is currently operating. The Manitoba Potato News website at www.gov.mb.ca/agriculture/news/potato/ is updated weekly to provide information on potato production.
Colorado potato beetle (CPB) adults are active in the fields and abundant in some areas. As indicated last week, eggs of the CPB have begun hatching in many areas.
Staging of beetles remains quite variable, but less dependent upon geographic area than previously. Larger larvae in the fourth and fifth larval instars (stages) are now present in most regions. Egg laying is continuing as well with late emerging adults, so everything from unhatched eggs to larvae close to pupation are present in all growing areas at this point. Potato flea beetle activity is currently minimal.
There are some reports of potato flea beetle activity from the Portage la Prairie area. In table potatoes, flea beetles are seldom a problem unless they are combining with Colorado potato beetle to contribute to considerable defoliation.
Cole Crops:
No diseases have been observed on cauliflower or cabbage to date.
Flea beetle activity has been fairly minimal to this point in the year. The population was set back considerably by the cool, wet weather of the past two years. Some shot holing was observed on older foliage and an occasional beetle was seen, but new foliage was largely untouched.
Some larger holes in cabbage and cauliflower were observed this week as well. We had quite a time finding the culprits responsible but were able to determine that the insects responsible are larvae of the diamondback moth.
Early damage results in just the lower layer of the foliage being removed, as seen in the picture above. As the leaf grows, this will often open up and leave a hole in the foliage. Larger larvae will also chew right through the entire leaf creating a hole immediately.
The larvae do not get very large, unlike what happens with cabbage looper and imported cabbageworm larvae. Generally these are found on the underside of the leaves as well and often they wriggle rapidly off the plant to get away from prying eyes. They remain attached to the plants via a silken thread and will work their way back onto the plants after the disturbance is over.
Pheromone trap monitoring in canola crops has just ended and the indications are that we will not be having a bad year with diamondback moth. They are present in low numbers, but shouldn¿t reach outbreak proportions this year. Still a good idea to watch for substantial holes in the leaves of your Cole crops as localized outbreaks may still occur.
Sweet Corn:
Sweet corn development is variable with plants in the 3 to 6 leaf stage as of June 28th. A typical plant is below.
Sweet corn diseases have not been observed to date. A plant with genetic stripe was observed (see below), a condition that results when a dominant gene is expressed, which alters chlorophyll production. This plant likely will not be very productive, but due to the dramatic pigmentation the symptoms are easily observed. Plants like this pose no threat to other plants, simply remove them.
In about a week or two European corn borer (ECB) moths will become active with egg laying following shortly thereafter. The first egg masses are often observed in the last week in June, so scouting for should commence shortly.
Cucurbits:
Reports continue to come in from various regions of the province. We had previously mentioned that the beetles are usually quite patchy in their distribution from year to year, but this year is proving to be the exception. Reports are coming in now from all the main growing regions including Portage la Prairie, Otterburne, Beausejour, Winkler and smaller areas as well. We continue to suggest active scouting every couple of days for the pest. Adult beetles are not very large, only about 10 mm in length but they are brightly coloured in yellow with vertical stripes along the elytra (back wing covers).
Adult beetles are not very large, only about 10 mm in length but they are brightly coloured in yellow with vertical stripes along the elytra (back wing covers).
Feeding damage from the beetles resembles that of flea beetles, with a shot hole appearance, though as leaves grow they holes often merge with each other to give the appearance of larger holes. When the plants are young, beetles can cause plant death. Later they feed on the flowers and may skeletonize the leaves, resulting in considerably lower yields. The most important issue with the beetles is that they transmit bacterial wilt disease which results in losses much higher than those caused by direct feeding damage.
General thresholds are as follows: scout five locations within each field. Control is warranted if two or more beetles are found at three of the five sites examined.
Carrots:
Carrot development continued at an excellent pace with taproots lenghthening and beginning express the orange pigments. Most plants were in the three to five leaf stage and fields seem in general to be in good condition.
No diseases were observed on carrots this week.
No insects have been determined to be causing problems at this point. Sweeps did not yield any aster leafhoppers at this point but it is likely they are present in the area in small numbers. Aster leafhopper moves into Manitoba on southern winds and we have had a considerable number of days with the wind blowing from the south.
Based on reports from the U.S. the infectivity seems to be around 4% this year, so that is the value we will be using to calculate the Aster Yellows Index (AYI) once the leafhoppers start showing up in sweep samples.
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
Prepared by:
Brent Elliott Entomologist Ph. 204-745-5669 Philip Northover Pathologist Ph. 204-745-5694 Manitoba Agriculture, Food and Rural Initiatives Soils and Crops Branch, Carman
