Compiled by: John Gavloski, Extension Entomologist, Manitoba Agriculture and Food, Phone: (204) 745-5668; Fax: (204) 745-5690;  and David Kaminski, Plant Pathologist, Manitoba Agriculture and Food Phone: (204) 745-5656; Fax: (204) 745-5690

To report observations of insect or disease activity or control that may be of interest or importance to others in Manitoba, please send messages to be above contact addresses.

To be placed on an E-mail list to be notified when new Manitoba Insect and Disease Updates are posted, please contact John Gavloski at the address or numbers listed above.

Broadleaves

Canola

Flea beetles
Spraying and reseeding canola because of flea beetle damage continues. Reports over the past week include widespread foliar spraying for flea beetles in canola in the Pilot Mound district. Some fields only had the headlands sprayed, while in other fields the whole field was sprayed. Some canola fields that had insecticide treated seed had a second foliar application of insecticide to control flea beetles. A canola field near Mather, and 2 canola fields near Crystal City were reseeded because of flea beetle damage. All 3 fields were seeded in the first 4 days of May, and all had a seed treatment containing an insecticide.

The Somerset district reports that flea beetle damage has been severe enough in early-planted fields that canola damage warranted reseeding some fields. One particular field seeded by May 5th with insecticide treated seed had areas seeded deep and took a long time to emerge. High pressure from flea beetles resulted in about 200 out of 500 acres being reseeded. Another canola field near Somerset was reseeded due to a combination of flea beetle and cutworm feeding.

Some foliar spraying of canola near Plumas was reported. Flea beetles are also reported to be in high levels in the Northwest, and some spraying for flea beetles has been reported in the southwest.

In recent years farmers have been advised to seed their canola early, with some advising to seed as early as possible. One of the reasons is to avoid having the canola flowering during the hot weather and suffering heat blasting. But there are tradeoffs when canola is seeded too early. Many of the fields of canola that had an insecticide in the seed treatment and are now being reseeded or receiving foliar sprays were seeded in April or the first week in May. Canola seeded this early will take longer to make it to the more flea beetle resistant 3rd or 4th true leaf stage then canola that was seeded later. With the canola staying in the susceptible seedling stage for so long the insecticide component of the seed treatment is getting to levels that will not provide adequate control of flea beetles before the canola gets big enough to tolerate the feeding. Growers who seed canola early may still need to scout for and be prepared to use a foliar spray for flea beetle control, particularly if a lower rate of insecticide has been used in the seed treatment.

After the rain last Thursday night, a rumor seemed to be going around that the flea beetles would drown from a hard rain. There is no evidence that this is the case. Flea beetles will not be feeding while it is raining, and appear not to feed much when the relative humidity is high. But as soon as the rain stops and the favorable feeding conditions return, experience has shown that flea beetle will be back on the plants continuing their feeding.

Cutworms
A canola field near Shoal Lake was sprayed for cutworms, and a field near Elie was reporting heavy damage from a combination of cutworm and flea beetle damage.

Alfalfa

What causes an alfalfa crop that is only one year old to nearly die out over the course of one winter? Certainly NOT crown rot. That disease is easily found in heavily cut or grazed stands of three years or more. Jane Thornton, Grassland Specialist for the southwest region, has been following the story of brown root rot (aka. winter root rot) on three fields. The first sample to be diagnosed by the Crop Diagnostic Centre came from a field established in 2002. Mardi Desjardins alerted us to the fact that this was an unusual situation. brown root rot (l), healthy root (r)

click to expand brown root (l), healthy root (r)

Brown root rot is caused by a fungus called Plenodomus meliloti. As the Latin name suggests, this disease could also infect sweet clover (Melilotus). The part of the story that "fits" is when the infection took hold, during the winter while the plants are essentially dormant under a good snow cover. The part that doesn’t fit is the age of the stand. Jane’s background checking came up with these details:

" . . . light sandy to sandy loam soil. Part of the field was grass pasture for many years but had been sprayed out in 1998 and cropped for 5 years previous to alfalfa seeding. The farm has poultry barns and manure from these barns has been spread on the fields yearly. The farmer seeded the alfalfa in the spring of 2002 without a cover crop. He cut it once for weed control mid-summer and then again in early September just before a killing frost. At that time he said the stand was well established and looked good.

. . . The worst areas were north facing slopes and areas that caught lots of snow."

Soil tests from 2000 show very high levels of phosphorus (no doubt from the manure) moderate N-fertility, slightly alkaline pH (7.4) and no evidence of salinity. Thus the addition of manure has NOT put undue stress on the alfalfa. The management choices, however, HAVE placed an abiotic (i.e. non-pathogenic) stress on the crop that has allowed this non-aggressive pathogen to take hold. Two cuts, in the establishment year, is not a wise choice, especially when the later cut is after mid-August. Roots need time to re-stock their reserves before a killing frost. There is no remedial measure that can turn things around. After Crop Insurance ruled that the stand was excessively weakened the grower elected to interplant new alfalfa seed to rejuvenate the stand.

Pulse Crops

High cutworm populations have been reported in peas and beans in Southwest Manitoba.

Cereals

Wheat

The big question is – "Seeing leaf disease so early, does it pay to spray?", especially considering the time saving of combining herbicide and fungicide. Although hard evidence of cost-benefit is lacking for this practice, it may be warranted when:

1. infective stubble is abundant
2. there have been frequent showers and more are expected
3. the temperature will remain cool

If, on the other hand, the disease has been made worse by abiotic factors (excessive depth, frost, etc.), it is probably better to wait until a later stage to consider foliar fungicide. Warm, dry weather and good conditions for growth can make the symptoms appear to vanish – just because the new growth overtops the diseased lower leaves. But keep a close eye on the field for further symptom progression. Certainly consider scouting again at the 6-leaf stage.

Wireworms
Wireworm damage in a wheat field near Holland was reported.

Barley

Cutworms
Cutworm damage over the past week has resulted in some insecticide applications and reseeding. Reports include insecticide treatment of a barley field south of Eden, reseeding of a barley field south of Oakville, and reseeding a patch of 80 acres (out of a half section) of tame oats. Cutworms are reported to be in high numbers in many fields in the Arborg area.

Rye

This is a relatively disease-free crop, amazing for its winter hardiness (compared to winter wheat). We’ve seen crops that are headed and about to flower. For the sake of such crops, a week of sunny growing weather should take care of any real concern over ergot. There might always be some in rye, particularly where native grasses grow next to or within the field. Even quackgrass serves as a "leapfrog" host.

Corn

A corn field between Carman and Elm Creek was sprayed for cutworms. When using insecticides in corn, note that there is the potential for injury to the corn when an organophosphate insecticides and sulfonylurea herbicide are applied within a week of each other.

General

Ornamental

High levels of forest tent caterpillars have been reported near Swan River.

Grasshoppers

The hatch of our grasshopper species of economical concern is continuing and the number of first and second instar grasshoppers is increasing in the overwintering sites. Although number are increasing along many field edges and ditches, it is still early to be thinking of controlling these populations in most instances. The hatch is still in the early stages, and the grasshoppers are too small to be moving too far. At this point farmers and agronomists should be scouting the major overwintering sites (areas that would have had lush vegetation late last summer) and determining what the levels are like. Note that newly hatched grasshoppers are not much better than a grain of wheat. The pictures below show what you are looking for this time of year. Also, be careful not to confuse leafhoppers for small grasshoppers when scouting field edges and roadside ditches.