Manitoba Insect and Disease Update

June 7, 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

• Aster leafhoppers are starting to show up in Manitoba.
• Diamondback moth counts continue to increase in traps in southern Manitoba, with highest counts in eastern Manitoba.

Weed Management Update

Optimizing weed control under delayed herbicide application conditions.

It’s again that time of the year when, after planting, we look forward to getting the best out of our weed control options. We have experienced another not so “normal” start to the growing season. The early warm spring got us going and we have some early plantings. However, the rains got too frequent and many fields are still too wet for herbicide applications. Some weeds have overtaken the crops. It is well documented that delayed herbicide applications results in yield losses. In such situations, selecting the right herbicide is very important. Some points to keep in mind are:
    • Do extensive scouting to identify the weeds correctly and determine the stage of growth (number of leaves or height).
    • Make sure the herbicide label of the product(s) you choose matches with the stages of weeds. If the weeds have passed the last recommended stage, check with your agronomist or company reps to assess whether that herbicide will work or not. In most cases however there will be reduced efficacy.
    • Check with your agronomist for alternative herbicides to get the best results when herbicide applications are delayed and weeds are more advanced.
    • With herbicide-resistant crops (like Roundup Ready, Liberty Link or Clearfield varieties), if the weeds are too advanced you may have to go with the higher recommended rates.

Recent Insect and Plant Pathogen Activity

Aster leafhoppers: While checking sticky traps for flea beetles, we noticed a lot of aster leafhoppers (20 to 30 per trap) on some of our traps from the Lowe Farm area. They seemed to have arrived relatively early this year. Aster leafhoppers can spread a plant pathogen that causes a condition known as aster yellows, and can be a big concern for vegetable growers. Although aster yellows can affect field crops as well, it is generally less economical. Aster leafhopper is sometimes called the six-spotted leafhopper: note the 6 spots (which actually look like 2 spots and 4 dashes) between the eyes of the leafhopper in the photo below

aster leafhopper

Our horticultural entomologist, Brent Elliott, annually monitors levels of aster leafhoppers and provides data on whether or not the population is highly infected with the pathogen for aster yellows. So we will keep you posted as this data becomes available.

Flea beetle update: Flea beetle numbers have generally not been high this year. Numbers are low on sticky traps that have been put up as part of a research project, and canola in many fields is getting to the stage (3 to 4 true leaves) where it becomes more tolerant to flea beetle feeding.

Surveys and Forecasts

Diamondback moth: The heavy rains in late-May appears to have not reduced the levels of diamondback moth adults. Some traps in eastern Manitoba continue to catch high levels; in the past week alone a trap near Landmark had 89 moths and a trap near Oakville had 77. Some of the higher counts after 4 weeks of trapping are 226 from a trap near Landmark, 137 from a trap near Kleefeld, 123 from a trap near St. Jean Baptiste, and 92 from a trap near Oakville. Larvae are starting to be seen but only in small numbers and are still quite small. The first stage mines the leaves, so you would see narrow white markings where they have tunneled in the leaves.

Data for the diamondback moth monitoring program is updated at the beginning of every week on the MAFRI website at: Diamondback Moth Forecasting Program

Bertha Armyworm Monitoring: A reminder to anyone involved in monitoring adults of bertha armyworms that traps can now be set up. A protocols for setting up the traps can be found at: Trap Assembly and Monitoring Protocol for Bertha Armyworm

Grasshopper Development: A new bio-climate model of development of our pest species of grasshoppers enables us to determine approximately what % of the grasshopper eggs should have hatched, and what instar these grasshoppers should be in. On May 31st, which is right after the weekend we got our deluge of rain, the model predicted the following

Location	% Hatch	% 1^st Instar	% 2^nd Instar
Carman	33.0	23.0	6.2
Dauphin	33.0	23.8	6.2
Melita	16.3	10.3	5.9
Swan River	16.3	10.6	5.5

So anywhere between 15 and 33% of the eggs of our potential pest species of grasshoppers may have hatched before those heavy rains. These grasshoppers would have been very susceptible to the excessive moisture over those few days. However, the model predicts that we were early enough in the hatch that there would still be a high percentage of grasshopper eggs yet to hatch.