The 2007 Manitoba Vegetable Insect and Disease Situation
Philip Northover and Brent Elliott, Crops Knowledge Centre, Manitoba Agriculture, Food and Rural
Initiatives, Box 1149, Carman, MB R0G 0J0
Introduction Aster Leafhopper/Aster Yellows Sweet Corn
The Manitoba weekly vegetable report is a multimedia web based report published
Monitoring in 2007 Observations regarding corn are made from sweet corn fields but
may be applied broadly to what is happening in field and silage
weekly during the vegetable growing season by MAFRI. It compiles the results of corn as well. Scouts look for disease or insect issues during
the weekly scouting program of commercial vegetable fields in Ma nitoba. Reports The aster or six-spotted leafhopper (Macrosteles quadrilineatus) is a tiny, pale green weekly visits to select fields.
from carrots, onions, cucurbits, cole crops, sweet corn, rutabaga, potatoes, and insect that arrives in Manitoba from May to July on southerly wi nds (Figures 8,10). It feeds
other crops (tomatoes, red beets, parsnips, and peppers) are made weekly to by piercing plant tissues and sucking out fluids. During this process it may transfer the There were few disease and insect concerns in sweet corn in 2007.
inform producers of what developments in insect pests and disease pathogens are aster yellows phytoplasma. European corn borer (Ostrinia nubialis), corn leaf aphid, corn rust
Figure 12: Corn leaf aphids
occurring within Manitoba fields from Winkler and Portage la Prairie. Though (Puccinia sorghi ), corn smut (Ustilago maydis) and fusarium root
2007 was a year in which very high levels of aster yellows were reported in a variety of on sweet corn.
developed for commercial producers the report can be accessed on the web by rot (Fusarium graminearum) were observed in 2007. None of these
anyone at: http://web2.gov.mb.ca/agriculture/mwvr/index.php. crops. The most important aspect we need to recognize from 2007 is that leafhopper appeared to cause any significant damage (Figures 12-15)
populations were ten times higher than have been recorded previously. The reason for
The report incorporates text, audio files, and numerous photographs to assist in the such high populations was an unusually high proportion of migrating leafhoppers were
education of producers, and decision makers in the vegetable industry. deposited in Manitoba. It is generally believed that the aster leafhopper does not
overwinter in Manitoba, so all aster leafhoppers present in Manitoba arrive on southerly
winds or are offspring of those migrants. This means that the population level is a direct
result of the migration and one year’s population has no relationship to the following year’s
Figure 14: Corn root
Figure 15: European Corn
Figure 13: Corn rust (Puccinia showing characteristic pink
Symptoms of aster yellows in carrots, squash, and cabbage are shown below sorghi) symptoms. to purple discolouration Borer in a corn stalk.
attributed to Infection by
For several years now, carrot crops have been monitored for leaf hopper levels, an index Fusarium graminearum.
In 2007, Pink root (Phoma terrestris, figure 4) was the has been developed to give producers an idea of when they should spray for carrots. In
most widespread disease, observed in fields in Winkler 2007 this economic threshold was exceeded in one field by almost 35 times.(Figures 9,
and Portage la Prairie. After first being detected in mid- 11)
July, it continued to be found throughout the season, in a
number of fields and cultivars. Reduced bulb size, Cole crops share the same pest guild as canola though many canola pests
attributed to destruction of the root system, is the chief Figure 1: Early symptoms cause far more serious damage in cole crops than they do in canola.
concern. Severity levels were not high, though the of Botrytis neck rot on a Cole crops pests of note in 2007 Several pests of Cole crops, notably cabbage
incidence level was. Increasing incidence levels raise red onion cultivar, note
looper (Trichoplusia ni), flea beetles and to a lesser extent, diamondback moth
concerns this could become a significant disease in the discoloured bulb
(Plutella xylostella) were of significance economically while the outbreak of
Manitoba. imported cabbageworm (Pieris rapae) subsided from 2005-06.
Symptoms of aster yellows (figure 2) were observed in a Symptoms of aster yellows were observed along the edges of a cabbage field
field in Portage. Aster yellows was not a big problem in Figure 8: Aster or six spotted in 2007, but did not appear to be widespread in the field or Manitoba in general
onions in 2007. leafhopper (Macrosteles quadrilineatus) Figures (16-20).
on corn leaf.
Botrytis neck rot (Botrytis allii figures 1,3) is an ongoing
concern to onion producers as the losses can be. In 2007,
this disease was observed first on red onions in an onion
storage in Portage la Prairie. A survey in mid-September 4000
of two other fields of red and yellow onions, revealed
levels of 2.3% and 11.5% respectively. This is a disease in
which infection occurs in the field and the symptoms do 3000
Figure 16: Aster Yellows Figure 17: Flea beetle on a
not show up until very late in the season or in storage. Figure 2: Aster Yellows 2500 cabbage leaf
symptoms on cabbage.
Reduced quality, and other economic losses often occur symptoms on onions (left 2000
due to the costs incurred in storing an economically two) compared to a healthy
unviable crop. onion (right).
Figure 18: Cabbage looper
Figure 19: Diamond back moth
(Trichoplusia ni) in final instar. (Plutella xylostella) larva.
Figure 4: Pink root (Phoma terrestris) symptoms on onion Figure 9: The change in Aster Yellows Index in five carrot fields in Manitoba in 2007.
roots. The picture on the left shows symptoms in which
Figure 3: Sclerotia of Botrytis allii the roots have been reduced, and broken off, the picture
on an onion with Botrytis neck on the right shows an early season infection, with the
rot. This onion can act as a entire root still intact.
Cucurbits crops are scouted weekly and typically there are few problems. On butternut
source of inoculum in subsequent squash in the Winkler area , pronounced distortions of the leaves and a marked reduction
in internode length were attributed to Squash Mosaic Virus (SqMV). Aster yellows
symptoms of shoot proliferation were also observed (Figure 21)
Sclerotinia stalk rot was also observed in spaghetti squash, in one field in 2007 (figures
Figure 10: The aster leafhopper
(Macrosteles quadrilineatus) on a cucurbit Both the striped (Acalymma vittatum) and the much less common spotted cucumber
leaf. beetle (Diabrotica undecimpunctata howardi) and were observed in 2007, an interesting
development, though of limited practical signficance at this point in time.
In addition to Aster Yellows which was a big concern in 2007,
(Figure 6) Sclerotinia mold/cottony rot was also observed in at least
one field in 2007 (Figure 5). Also monitoring for carrot weevil was Figure 21: Butternut squash
conducted. and determined that this pest is in Manitoba. 70% with symptoms of aster
Figure 23: Sclerotinia stalk rot on
30% Figure 22: Sclerotia of the fungus
Sclerotinia sclerotiorum in inside a stem
spaghetti squash. The gourd is
of a squash vine. drying out in advance of the
Figure 5: Sclerotinia cottony-rot
Figure 5: Aster yellows
symptoms on carrot.
symptoms on a carrot
Figure 11: The incidence of aster yellows symptomatic carrots in five fields The authors would like to thank the continued support of the Vegetable Growers
in Manitoba in 2007. Association of Manitoba for their years of support for the scouting program and the support
of Covering New Ground.