Blog: Agronomy & Extension

Management Tools for Spring Volunteer Weeds from an Overwintered Crop

Mallorie Lewarne – Agronomy Extension Specialist, Manitoba Crop Alliance

Jeremy Boychyn – Agronomy Research Extension Specialist, Alberta Wheat and Alberta Barley Commissions

With many unharvested acres across Western Canada in 2019, this spring will see a wide range of challenges. One common challenge may be management of high volunteer weed pressure. Unharvested or spring harvested crops can increase the amount of shelling out, and in turn, volunteers.

If you are considering seeding directly into an unharvested crop, high volunteer pressure is likely. An important point to consider is the potential impact volunteers can have on the grain quality of this season’s crops, especially if volunteers go to seed. It’s important to note that any management decisions around unharvested crop should first be discussed with your crop insurance provider.

Farmers should also consider increased disease risk that comes with crop residue left on the soil surface, especially if the unharvested crop and the crop being seeded host the same diseases. Unharvested crops have larger pieces of plant residue that take longer to break down and therefore have reduced amounts of disease breakdown, which can potentially increase disease presence. It should be noted that this is can be an issue even when an overwintered crop is not present. Although field options and rotations may be limited when harvesting crop in the spring, it is best to avoid sequential seeding of the same crop two years in a row, especially when heavy residue from the previous season is present and that residue was known to high heavy disease presence from the previous season.

If you expect to be dealing with increased volunteer pressure, here are some tactics to help mitigate the impact on this season’s crop.

Crop rotation. A diversified crop rotation is an effective strategy to help manage many issues, including disease, insects and volunteers. Planting a competitive rotational crop will ensure that you have diverse herbicide modes of action that can be utilized. This goes hand in hand with consideration of herbicide tolerance systems. For example, if the previous year’s crop was Round-Up Ready canola, it’s not a good idea to plant Round-Up Ready soybean unless it also has the dicamba trait.

Delayed seeding into spring harvested crops. This allows volunteers to germinate prior to seeding and be controlled with a spring burn-off herbicide pass. Keep in mind that multiple modes of action are recommended, and if a herbicide has soil residual activity, it will need to come in contact with the soil to be effective. There are some herbicides that can get ‘tied up’ in crop residue on the soil surface, reducing the efficacy of control. Delayed seeding will allow for summer annual weeds such as kochia, lamb’s quarters and wild oats to emerge, which can then be controlled with tillage or herbicides and can give the crop an early head start. On the downside, winter annual, biennial and perennial weeds may become large and hard to control in a delayed seeding situation. Examples include dandelion, narrow-leaf hawk’s beard, flixweed, stinkweed, cleavers and Canada thistle. To investigate pre-seed and pre-emergence control options, consult your province’s crop protection guide.

Keep in mind that this management strategy could lead to maturity issues later in the season. Delaying seeding to wait for volunteer germination will impact the available season length. If taking this management approach, consider shorter season crops or shorter season varieties to ensure your crop can reach maturity in the current growing season.

Harrow to promote volunteer seed germination. Weeds such as redroot pigweed and volunteer canola may be encouraged to germinate with early season light tillage. This is sometimes referred to as a “Stale Seedbed” – where early pre-plant tillage stimulates germination of weeds which are then controlled with herbicides or a second tillage operation immediately before seeding. This technique is most effective when the major weed species being controlled has a single large flush early in the season

Get out and scout early. Weed staging is always a primary concern. Some crops are more sensitive to certain herbicides, so checking product labels and manufacturer’s recommendations is important. Volunteers that emerge prior to the seeded crop will have a more significant effect on yield that those that emerge after the seeded crop. A one-pass system to control all weeds in a field may not be feasible, given the number of weeds that may germinate in flushes. A more likely scenario is that both a pre-seed and in-crop, or multiple in-crop applications, may be necessary for effective control.

Ensure proper water volumes to allow for adequate coverage. A contact herbicide requires thorough coverage to be effective, so cutting water volumes to save time will also result in less effective weed control. In situations where volunteers are very dense, adequate water volume to penetrate the canopy and contact every volunteer is very important to optimize control.

Other options include seeding with the intention of silaging, as well as forage chopping combined with removal of residue. These options may be more desirable in cases where volunteers will cause substantial issues such as barley for malt, and for producers that have a mixed operation. Intuitively, any management strategy that removes the crop/residue and prevents further seed set will aid in reducing volunteer pressure.

In summary, successful control of volunteers this spring will depend on early scouting, planning and timely decision making.

Acknowledgements to Tammy Jones- Weed Specialist with Manitoba Agriculture and Dr. Breanne Tidemann- Research Scientist with Agriculture and Agri-Food Canada for their contributions to this article

Seeding into overwintered/unharvested crop

Crop being seeded Wheat Barley Canola Field Peas
Wheat Cannot control volunteers Volunteers may impact field maturity and evenness which may cause greater FHB, disease and grain quality challenges Minimal control options in-crop. Barley more competitive that wheat; will likely have high volunteer grain contamination Likely plenty of shattering and volunteers If harvesting last seasons crop in the spring, consider allowing volunteers to germinate, followed by burn-off and seeding Pre-seed and pre-emerge options available Many in crop control options Hairpinning pea residue may be a concern depending on conditions and seeding system; could lead to stand quality issues and opportunities for weed growth
Barley Minimal control options for volunteer wheat in barley Silage opportunity Cannot control volunteers Volunteers may impact maturity and evenness which may cause greater FHB, disease and grain quality challenges Avoid this situation if aiming for malt (quality degradation is likely) Likely plenty of shattering If harvesting last seasons crop in the spring, consider allowing volunteers to germinate, followed by burn-off and seeding Pre-seed and pre-emerge options available Many in crop controls options Hairpinning pea residue may be a concern depending on conditions and seeding system; could lead to stand quality issues and opportunities for weed growth
Canola Round Up (RR) or Liberty Link (LL) systems will control volunteers easily – Round Up (RR) or Liberty Link (LL) systems will control volunteers easily Higher risk of Clubroot, Blackleg issues Increased risk of root rot and root maggot Round Up (RR) or Liberty Link (LL) systems will control pea volunteers easily in-crop
Field Peas Grass herbicide for in-crop control. Pre-emerge and pre-seed option available Grass herbicide for in-crop control Pre-emerge and pre-seed option available High risk of canola volunteers Can be managed with pre-seed, pre-emerge, and in crop herbicides Concern with volunteers if growing greens on yellows or vice-versa Increased risk of Ascochyta on residue as well as Aphanomyces and other rots

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 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