Agronomist Notes

We’ve had the second coldest spring in five years and now we might see endless weeks above thirty degrees. Crop maturity on average may only be slightly behind normal with flag leaves emerging last week. At the same time, disease pressures have increased with the cool weather and high humidity. This week I’ll be continuing my leaf disease checks, post herbicide checks and begin insect sweeping on canola.

I hear that many producers are deciding to spray a fungicide regardless of whether it’s warranted. I’ve recommend fungicide applications on only a small percentage of fields so far. The majority of high risk fields are wheat on wheat or barley on barley which demonstrates the effectiveness of crop rotation. In some cases and depending on variety, I’ve sprayed wheat on canola stubble because disease pressure was high. The crops I’ve found to be at the highest risk for disease are winter wheat and CPS wheat. Next week I’ll have an update on canola insect pressures as well as wheat midge.

In this week’s newsletter we’ll look at fungicide decision making tools and information to help you with disease scouting. We’ll discuss the risks of spraying herbicides on canola after the plants have begun to bolt. Next, we’ll briefly discuss cabbage seedpod weevil scouting and control and then we’ll look at how we can distinguish between leaf diseases and physiological leaf spot. Finally, we’ll see what’s going on around the world for weather.

Crop Staging Area (Calgary to Drumheller to Three Hills)

Date Seeded	April 23-31	May 1-7	May 8-15
Wheat	Flag leaf	Early flag	1st node
Canola	4% bloom	Bolting	Bud stage
Barley	Flag leaf	Early flag	1st node
Peas	Early flower	12th node	10th node

 

This Week in Scouting

Monitor cereal leaf disease pressure in wheat and barley planted during the first two weeks of May.
Continue 10 to 14-day post-herbicide application checks to analyze herbicide efficacy.
Begin sweeping canola for cabbage seedpod weevils.

Agronomy

Spraying Canola at Bolting Can Be Risky

Over the years I’ve noticed a few things about spraying canola at certain stages. I’ve seen canola sprayed with RoundUp Transorb at 30% bloom without any effect on yield. I’ve also seen RoundUp Ready canola sprayed at late bolting and the yield was cut in half. In Liberty Link fields sprayed at bolting I’ve counted upwards of 4 to 5 aborted pods on the main stems of about 5% of the plants. Spraying herbicides at bolting can set back maturity and terminate the first few flowers on what usually are the strongest plants. I find plant genetics play a large role in herbicide tolerance and whether one can safely spray at later stages of growth. It’s best to follow herbicide label recommendations to be safe. SL

How to Scout for Leaf Diseases

This risk of diseases like tan spot, septoria, net blotch and scald spreading to the flag leaf is greater this year than in other years. The cool weather has reduced plant height allowing a shorter distance for diseases to travel upward. In fact, most fields of wheat have barely reached my kneecap! Those of you who know me would agree I’m not a tall man. When determining the risk of disease moving up the plant, take plant height into consideration. The difference from top to bottom leaves may only be 12 inches. Also, monitor morning dews and their duration. Hot days and cool nights can promote disease as well when leaves are kept wet for extended periods of time. 

1. Review the field history. Identify any fields that have had chronic disease problems.
2. Check the most disease-prone locations first. Foliar diseases tend to be worse in thick growth. Row ends, where seeding and fertilizer rates are inadvertently high, often have the heaviest disease pressure.
3. Scouting requires examination of 5-10 randomly selected sites that represent the character of plants within the field. Closely examine the leaves of each of the plants selected.
4. Estimate the percentage of disease pressure in the bottom, middle and top 1/3rd of the plants. Identify all diseases present as soon as possible. Some diseases increase quickly (e.g. stripe rust) and must be dealt with promptly. Multiple diseases sometimes require different control measures.
5. Map the areas where diseased plants are found to determine where treatments should be applied, to monitor any disease increase, and to assist in planning future crop rotations.

Reference: Manitoba Agriculture

Factors Promoting Leaf Disease Development

1. Seeding wheat after wheat or barley after barley.
2. Abundance of over-wintered straw and stubble (result of zero- or min-tillage).
3. Above-normal levels of precipitation in early- and mid-season.
4. Lush, dense crop stands (elevates humidity within the canopy).
5. Production of varieties susceptible to leaf diseases.

For detailed information on crop diseases follow these links:

Diseases of Cereal Crops: http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/prm8707?opendocument
Diseases of Oilseed Crops: http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/prm8840?opendocument
Diseases of Field Peas: http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/prm7819?opendocument

Which Leaves Do You Protect From Disease?

In wheat, the flag leaf is the most important to protect as it is at the top of the canopy where it receives significant sunlight. The flag leaf does the bulk of the photosynthetic work for the wheat plant, and is responsible for 55% of the grain fill. In barley, the penultimate leaf (2nd leaf from the top) and the flag leaf are the most important leaves to protect. They are responsible for 80% of head fill.

Predicting Flag Leaf Emergence for Fungicide Timing

Barley (2-row): When the third node is about half an inch above the ground; the penultimate leaf (one just below the flag) is visible, and the next leaf to appear is the flag. If only one node is visible, then it will be about 10-14 days till flag leaf; if two nodes are visible it will be about 5-7 days until the flag leaf is out.

Barley (6-row) and wheat: When the second node is half an inch above the ground, the penultimate is visible and the next leaf is the flag. If only 1 node is visible, the next leaf will be about 5-7 days. The flag leaf is usually the seventh or eighth leaf in cereals. In wheat, the flag leaf is large and contributes to 45% of the yield. The penultimate leaf contributes another 10%. In a barley crop, the flag leaf is smaller so the penultimate and flag together contribute 65% of the yield.
Source: Syngenta

Fungicide Decision Making

1. Does the crop show good yield potential?
2. Must the crop meet defined quality criteria (ie. plumpness, bushel weight)?
3. Does the crop show lush growth and a heavy canopy?
4. Is there moisture due to rainfall, dew or humidity?
5. Is there disease infection on the lower leaves?
6. Is there infection on the middle leaves?

If you’ve checked three or more items off this list, a fungicide application is likely beneficial. Use the following link to help you choose registered fungicides to control fungus problems in your crop.

Fungicide selector: http://www.agric.gov.ab.ca/app23/pesticides/fungicides/getcrop.jsp

Cabbage Seedpod Weevil

The early seeded canola is now anywhere from bolting to early bloom. This is the time to begin scouting for cabbage seedpod weevils. The adult weevils are an ashy, charcoal gray colour approximately 3 mm long with a pronounced snout. The adults feed on buds, flowers, stems and pods. The adult weevils lay their eggs inside developing pods where the eggs hatch and larvae begin to feed on the seeds. Each larva can consume up to 5 seeds during its development, which can equate to a 15-20 % yield loss. The tiny exit holes left in the pods after the weevils emerge cause early shattering, and provide an entry point for disease.

The threshold for cabbage seedpod weevil is 1 to 2 weevils per sweep. The proper technique to sweep for weevils is to do ten 180-degree sweeps in four locations. Be sure to move away from the headlands and pick areas that are representative of the field. Weevils are typically higher in number along field edges. Sweeping should take place from bud stage through flowering. The best time to apply an insecticide is the 10-20% bloom stage if possible to avoid harming the beneficial insects in canola. SL

For additional information and pictures:
Link: http://www1.agric.gov.ab.ca/$Department/deptdocs.nsf/all/agdex2538

Photo: Adult cabbage seedpod weevil, Source: Canola Council of Canada

Is it Stripe Rust or Physiological Leaf Spot?

Recently, physiological leaf spot (PLS) has been showing up in some winter and spring wheat fields. Some people may misdiagnose PLS as stripe rust and try to use fungicides to reduce PLS symptoms. Because PLS and stripe rust are controlled by different methods, it is important to distinguish the two. Similarly, it is important to tell PLS from other spot/blotch diseases caused by fungal pathogens.

Physiological leaf spot is a complicated disorder and is sometimes used to describe problems of which the causes are not known. However, a typical PLS is a physiological and genetic disorder that expresses spot symptoms on leaves in fields with a deficiency of chloride.  Physiological leaf spot symptoms start with tiny chlorotic (mosaic) spots, which can grow up to spots of a quarter inch in diameter. The early symptoms resemble those of the early infections of rust and some other pathogens. Early spots sometimes have a halo pattern, but mature spots usually have a distinct margin. PLS spots are usually round to oval in shape, but in severe situations, spots connect to each other, appearing to be irregular. 

Strategies to manage PLS include growing tolerant varieties, rotation with other crops or fallow and the application of chloride. When the crop is growing, application of chloride is the only way to reduce PLS symptoms. Fungicides, such as Tilt, Quilt, Quadris, Headline, and Stratego, which control stripe rust and other fungal diseases, do not control PLS.

As shown in Figure 1, it is easy to differentiate PLS symptoms from the typical symptoms of stripe rust (Figure 2). It is also easy to differentiate PLS from resistant reactions of wheat to stripe rust. After the stem elongation stage, stripe rust produces white necrotic stripes without or with limited rust pustules as shown in Figure 3. Wheat crops showing resistant reactions to stripe rust usually do not need to be spayed with fungicide while those showing susceptible reactions should be sprayed with a registered fungicide such as Tilt, Quadris, Quilt, Headline, Folicur or Stratego when stripe rust develops to 5-10% severity. Unlike PLS, stripe rust cannot be reduced by the application of chloride.

It is more difficult to distinguish PLS from spot/blotch diseases caused by fungal pathogens. For comparison, pictures showing symptoms of fungal spot/blotch diseases are shown in Figure 4. The major difference between PLS and these fungal diseases is that PLS does not spread from field to field while the latter group of diseases spread because they produce infectious spores. These fungal spot/blotch diseases are not as common as PLS and stripe rust in the Pacific Northwest. Fungicides that control rusts usually control the fungal spot/blotch diseases.
Source: Xianming Chen and Richard Koenig

Market News

International Crop and Weather Highlights

United States: Record setting heat is promoting rapid crop development in the Northwest. On the Plains, cool, dry weather prevails, except for unusual warmth spreading into Montana. Drought remains a significant threat to rain-fed summer crops across the southern half of the High Plains. In the Corn Belt, showers are gradually diminishing across the Ohio Valley. Dry weather prevails elsewhere, but below-normal temperatures are slowing crop development. Meanwhile, flooding continues to subside in the middle Mississippi Valley.

Europe: In northeastern Europe, showers further improve moisture supplies for reproductive winter wheat. In central Europe, wet weather continues to benefit filling winter grains and vegetative summer crops. Following last week’s rain, drier weather in southern Europe favors winter grain maturation.

Former Soviet Union: In Ukraine and western Russia, widespread, light to moderate showers favor winter grains and spring sown crops. In major spring wheat producing areas of eastern Russia and Kazakhstan, increasing heat and dryness lowers topsoil moisture.

East Asia: Rain boosts soil moisture for emerging to vegetative corn and soybeans in Manchuria.

Southeast Asia: Typhoon Fengshen cuts across the Philippines, bringing flooding rains to central rice and corn areas.

South Asia: Heavy monsoon rain in northern portions of India worsens flooding in cotton, rice, and soybean areas.

Australia: In New South Wales, much-needed rain boosts soil moisture for germinating to emerging winter grains and will likely encourage additional winter grain planting in the wake of drought-induced delays. In Queensland, Victoria, and South Australia, mostly dry weather favors fieldwork. In Western Australia, light showers aid winter wheat and barley development.

South America: Rain improves planting prospects in key winter wheat areas of central Argentina, although pockets of dryness linger in some locations. Cold weather slows vegetative growth of winter wheat in southern Brazil, while raising concern for possible freeze damage to winter corn.

Canada: Lingering showers accompany a warming trend across the Prairies, promoting early growth of spring grains and oilseeds following last week’s timely rain.

Mexico: Warmer, drier weather spurs corn planting across the southern plateau.
    
CWB 2008-09 PROs Increase for Wheat, Durum and Barley

The CWB released its June 2008 Pool Return Outlook (PRO) for the 2008-09 crop year. Wheat values are up by $9 to $10 per tonne, except for non-select soft white spring wheat, which remains unchanged from last month's projections. The durum PROs have increased by $8 to $10 per tonne. Designated barley is up $6 per tonne, while feed barley Pool A values have increased by $10 per tonne from the May PRO.
June PRO: http://www.cwb.ca/dom/db/contracts/pool_return/pro.nsf/WebPRPub/2008_20080626.html?OpenDocument&CropYr=2008-09