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Manitoba Agriculture, Food and Rural Initiatives

Manitoba Insect and Disease Update

August 9, 2010                   

Compiled by: John Gavloski, Entomologist, Manitoba Agriculture, Food and Rural Initiatives
                    Phone: (204) 745-5668; Fax: (204) 745-5690, and
                    Vikram Bisht, Plant Pathologist, Manitoba Agriculture, Food and Rural Initiatives
                    Phone: (204) 745-0260; Fax: (204) 745-5690

To report observations on insects or plant pathogens that may be of interest or importance to farmers and agronomists in Manitoba, please send messages to the above contact address.

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

Summary

• Some canola fields are showing sclerotinia and blackleg infections, although incidence is generally very field-specific.
• Lygus bug remains a concern in some fields of confection sunflowers.
• Incidence of fusarium head blight is high in some fields of spring wheat

Recent Insect and Plant Pathogen Activity

Canola

Sclerotinia: A disease survey recently conducted in canola indicates that:
    • Sclerotinia is more a field specific problem. The fungicide spray may have been mis-timed in some fields, or the inoculum   may have been higher than normal in some areas.
    • Petal tests later in July showed less infection than June petals
    • Southwest in general has low infection, as in other years. For example, in the Boissevain area even some unsprayed fields have low infections.

Figure 1. Sclerotinia in canola

Blackleg: Blackleg ratings are being done close to swathing time. Blackleg is in general very low. However, there appear to be a few fields with higher ratings. Root maggot damage appears to have increased the blackleg readings in some fields that have been in canola in consecutive years.

Sunflowers

Insects on sunflower heads: This time of year it is common to find small brown pupal cases on the heads of sunflower plants (see figure 2 below), and there have been several recent enquiries about what these are. These are the pupae of an insect called the sunflower seed maggot (Neotephritis finalis). Larvae feed on the florets and the first generation pupates in the head. They are generally considered to be not economical to sunflower seed production, however studies on the economics of this insect are being conducted in North Dakota.

Figure 2. Pupa of sunflower seed maggot

Lygus bugs continue to be the biggest concern in confection sunflowers. Where economical, insecticides should ideally be applied between the R4 to R5.1 stage.

Pheromone-baited traps for banded sunflower moth continue catching adult moths. Weekly counts have generally ranged from about 150 to 300 moths per trap over the last three weeks. This tells us the moths are flying, but this data can not be used to predict levels of larvae. There have still been no reports of seed weevils in sunflowers.

Pathogens in sunflowers: There have been a few samples of sunflower plants badly infected with downy mildew, although generally the incidence has been low. Low levels of rust have been reported.

Pulse Crops

Soybean aphids: Soybean aphid populations generally remain low and well below the economic threshold. However, populations have been noted to be increasing in some fields in the Beausejour area, with reports as high as 100/plant. This is something to pay attention to when scouting soybean fields. The economic threshold for soybean aphids is when there are on average at least 250 aphids per plant and the population is increasing, and the plants are in the R1 (beginning bloom) to R5 (beginning seed) growth stages.

Sclerotinia in dry beans: Petal tests on dry bean crops showed much lower sclerotinia infections than canola petals, and the disease appears to be lower than feared. There are some fields that have had 2 fungicide applications. Now that the rows have closed there is more sclerotinia rot showing within the canopy.

Root rot in soybeans: Some soybeans have had root rotting problems which were apparently Rhizoctonia infections, and a few fields have had Phytophthora root and stem rot.

Cereals

Fusarium: Fusarium head blight incidence seems to be high in some fields of spring wheat. For example,
an unsprayed field in the Boissevain area had a 15% incidence, with rating of 1 to 8 on a scale of 0-9 (9 being highest). Other areas of Manitoba have had a 1-2% incidence of infected heads in fusarium head blight sprayed areas, to >30% in unsprayed patches.

Figure 3. Fusarium in spring wheat.

Note in figure 3 the browning of the stem (peduncle) immediately below the head of the stem to the left, and 50% head blight in the head on the right.

Crown Rust in Oats: Some fields with oats and wild oats have been showing crown rust. In many canola fields, wild oats are showing a very high severity of infection.

Armyworms: Adult moths of the next generation of armyworms (Pseudaletia unipuncta) are emerging. This second generation is not likely to be as damaging to crops as the first generation, because many of the crops will be mature or harvested by the time larvae get large. Below is a picture of an adult moth of an armyworm. These moths are quite distinctive; light brown and with a white dot in the centre of each forewing. They are active only at night.

Figure 4. Adult moth of armyworm

 

Surveys and Forecasts

Grasshopper Survey: A reminder that counts for the grasshopper survey are done during August, when the majority of grasshoppers are in the adult stage. Agronomists and farmers who would be interested in estimating grasshopper numbers in the fields they are in and have this information included in the survey are encouraged to see the survey protocol for more details of the survey and where to send data. Estimates of grasshopper levels can be collected during regular farm visits. The grasshopper survey protocol is located at: https://www.gov.mb.ca/agriculture/crops/insects/fad95s00.html

Insect Identification Quiz

Question:
What are the insects clustered at the top of this canola plant?

Answer:
The insects clustered near the tip of this canola plant are a species of aphid known commonly as the turnip aphid (Lipaphis pseudobrassicae). If we look hard enough it is likely that there will be aphids in most crops that we scout, but in most cases the population will not be economical. Aphid populations are often heavily regulated by natural enemies such as predators, parasites, and pathogens, as seen here where a seven-spotted lady beetle (Coccinella septempunctata) is among the aphids. A study in Manitoba found that the number of aphids eaten by one adult lady beetle in a 24 hour period varied from about 60 to 180 depending on the species of aphid and species of lady beetle (The Manitoba Entomologist: 1971: 89- 95).