Beneficial Insects at Work in Your Cereals
Are those pests or beneficial insects at work in your fields? Sometimes the answer is just a phone call away. John Gavloski, entomologist with Manitoba Agriculture, received several calls in July from agronomists seeking information about clusters of silky-covered eggs spotted at the top of many cereal heads.
As he explains, the clusters were not eggs, but clusters of pupal cases of a parasitic wasp called Cotesia. “They’re actually a parasitoid of caterpillars such as armyworms, which were a problem in some cereal fields in Manitoba in 2019,” says Gavloski. Parasitoids lay eggs into other insects and eventually kill them.
For example, Cotesia wasps will lay 20 to 60 eggs into an armyworm (or other caterpillar) and inject it with a virus, which shuts down the pest’s immune response. Because the eggs develop at exactly the same time, Cotesia larvae emerge out of the caterpillar almost simultaneously. They then rapidly form their cluster of pupae, which can easily be misidentified as a cluster of eggs.
Gavloski assures agronomist callers that the only thing Cotesia larvae feed on is other insects, which can help reduce the pest population. For this reason, he likens them to “insect superheroes.”
Gavloski says growers and agronomist can protect Cotesia and other beneficial insects by following three practices. “Step one is only using insecticides if you’re above the pest’s economic threshold,” he says. “Second, use a more selective insecticide – one that protects parasitic wasps.” Finally, because parasitic wasps feed on nectar in the adult stage, there is value in having flowering plants around the farm site.
Visit FieldHeroes.ca or follow @FieldHeroes on Twitter for more about the benefits of protecting beneficial insects.
Content provided by Synthesis Network
As posted on Manitoba Wheat and Barley Growers Association Website
Wheat Fungicide Timing – Early vs Later?
The growing season is well underway, with many cereal crops in or nearing the stem elongation stage (growth stage 30). Many farmers may be wondering when they should apply fungicide to their crop. There isn’t a simple answer to when fungicide should be applied, however, depending on the year the decision to apply it earlier, later or at all may make a big difference.
As of the first week of June, most regions in Manitoba have received less than 70% of normal precipitation. The good news is that spring cereal crops are not yet suffering. It is important to note when considering fungicide application timing that dry situations do not favour leaf disease development. Sound economics necessitate timely weed control, since weed competition for scarce soil moisture is the principle competitive threat to crops withstanding ongoing dry conditions.
Reasons to consider an early fungicide application for wheat:
- You have planted wheat on wheat stubble, or immediately adjacent to last year’s wheat crop.
- You have selected a variety that is less resistant to the leaf spot complex than the current standards – Cardale, Faller and Carberry are listed as MS (moderately susceptible) while AC Domain is fully susceptible.
Reasons to consider later fungicide application for wheat:
- Even when symptoms of tan spot are present on the earliest emerging leaves, those leaves contribute very little to grain production and filling.
- By the time flag leaves emerge (and they are the principle contributors to yield), an earlier fungicide application will have disappeared from the plant and provides no protection against leaf rust, or the other leaf diseases, that predominate later in the season.
- Delaying herbicide, to maximize disease control with a fungicide/herbicide pass, is a poor compromise because early weed pressure is a bigger yield robber.
- Multiple applications of fungicides with the same mode of action in the same season (e.g. seed treatment, flag leaf timing and head blight timing) increases the odds of disease-causing pathogens developing fungicide resistance.
Article written by David Kaminski, Crop Industry Specialist (Plant Pathology) with Manitoba Agriculture.
As posted on Manitoba Wheat and Barley Growers Association Website
Have You Thought About Your Seedling Mortality?
You’ve chosen the variety or varieties you want to grow in 2019. You’ve decided on your target plant stand. And from your seed test results, you have the percent germination and thousand kernel weight (TKW). But have you given any thought to your seedling mortality?
When calculating the seeding rate needed to achieve your target plant stand, you often hear about TKW and percent germination. But remember when calculating seeding rates, you need to take into account the seedling mortality rate, i.e. what percent of viable seed will germinate but not produce a plant.
Seedling mortality can vary greatly from year to year, and field to field. For cereals, seedling mortality rates can range from 5 to 20%. Many farmers and agronomists have found a 5 to 10% mortality rate can be assumed. However, farmers may need to make adjustments to their seedling mortality based on factors such as available moisture, soil temperature, residue cover, seed quality, amount of seed-placed fertilizer, seeding depth, seeding date, and disease and insect pressure.
One additional factor you maybe should consider is the impact of seeding rate itself on seedling mortality or stand loss. Grant Mehring from North Dakota State University shared some recent work at the 2015 Manitoba Agronomists Conference looking at optimum seeding rates for hard red spring wheat. Across 23 environments from 2013 to 2015, his research showed increased stand loss as seeding rate increased (from a percent stand loss of 3% at the lowest seeding rate up to 21% at the highest seeding rate). His research suggests using a seedling mortality of 10 to 20%, even under good seed bed conditions.
Determining seedling mortality is not easy. Since mortality depends on the combination of conditions and management practices of individual farms, producers should keep records of emergence (and thus mortality) in their fields each year. The data collected will help in the future when calculating seeding rates.
As posted on Manitoba Wheat and Barley Growers Association Website