Summary

Aphid control in peas continues in some areas. White heads from wheat stem sawfly are visible in many fields. Sunflower bud moth larvae are present in sunflower stems and buds in many fields in Central Manitoba.

Recent Insect Concerns and Observations

Wheat Stem Maggots

White heads from feeding by wheat stem maggot are noticeable in a lot of fields. Some reports are of up to 10% of heads affected. This is much higher than we normally see. The 2 most common questions on this are how bad will it get, and is there anything that can be done.

My guess is that we will not see many more white heads from wheat stem maggot feeding than we are seeing now. When larvae can be found in the stem they are near fully grown, so we are probably finishing the first generation for this season. There is usually a second generation in Manitoba, but this should not be as noticeable in cereal crops.

There is nothing that can be done this growing season to prevent further damage; as mentioned the damage is probably almost complete. Insecticides are not registered for management of wheat stem maggot. In fields where wheat stem maggot was a concern this year, management options include rotating to a non-susceptible crop for next year, and stubble cultivation. Host plants of wheat stem maggot include wheat, barley, oats, rye, timothy, and millet; and other native and introduced grass species including quack grass, green foxtail and yellow foxtail.

Wheat Staging and Susceptibility to Wheat Midge

A lot of wheat has now flowered. So it is no longer susceptible to damage by wheat midge. Wheat changes chemically when it flowers, and produces a chemical that acts like an insecticide to wheat midge. So it would be pointless to be applying an insecticide to control wheat midge after the plants have already flowered. Some later seeded fields may still be susceptible and in need of scouting to determine if wheat midge is a concern, but many fields are now advanced beyond this stage. As a rough guideline, if about 75% of the heads have flowered, it is too late to be controlling wheat midge. You will still see wheat midge flying in the field, but they are no longer a threat to the crop. Also recall from last weeks update that in the long term more harm than good can occur by applying insecticide for wheat midge that are below economic thresholds, or where the crop is already too far advanced.

Sunflower Bud Moth

There are a lot of sunflower bud moth larvae in stems and buds of sunflowers in Central Manitoba. Although the larvae are hidden in the stems and buds of the plants, their presence is conspicuous by the piles of black faeces that are in the leaf axils or on the buds where they have tunneled in. Very little research has been done on the economics of sunflower bud moth, but the few studies that have been done suggest that larvae in the stem result in very little yield loss. Some growers are concerned, however, because they are seeing quite a few buds with the larvae in them. This may cause some distortion to the heads, but the overall effect on yield has not been well researched. There are no insecticides registered for sunflower bud moth. Some have asked whether spraying an insecticide now, or if they had sprayed earlier in the season, would control them. Once they are in the stems, as they are now, you will not reach them with an insecticide. Spraying earlier in a hope of targeting the adults seems pointless since we don’t know a lot about their emergence and flight habits. So this is an insect where insecticides are not really an option.

Aphid in Peas

Control measures for pea aphids in field peas continue in some area. Recent control has occurred near Swan Lake, Pilot Mound and Crystal City. Refer to the July 3rd update for information on economic thresholds and scouting tips for aphids in peas.

Surveys and Forecasts

Bertha Armyworm Trap Results: Results from monitoring adults of bertha armyworm continue to climb. The highest cumulative trap counts are as follows:

As mentioned in earlier updates, the early indication is that potentially economical populations could be found a lot further east in the province than last year. This data should be used as a guide to help prioritize field scouting for the larvae. In many areas of the province it will be critical that canola fields are scouted frequently from about mid-July to mid-August to know what the bertha armyworm levels are.

Trap data, a risk map, as well as a table indicating how to interpret the trap data can be found at:

• http://www.gov.mb.ca/agriculture/crops/insects/bertha/index.html

You will notice in the raw data that counts from some traps have peaked and are now declining, while counts from other traps are still not declining.

Insect Identification Quiz

Question: While collecting grasshoppers for our House of Hoppers at the Crop Diagnostic School, we came across several grasshoppers with these red things on their thorax. What mite these be?

(click to enlarge)

Answer: These are red velvet mites. The immature stages of these mites are parasitic on grasshoppers and other insects. The adults prey on insect eggs and other small arthropods. They seem to be quite abundant on grasshoppers this year. This particular grasshopper was the heaviest infested one that we saw, with 6 or 7 tucked into the area where the wing buds were developing.