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									Volume 12 Ontario Ministry of Agriculture, Food & Rural Affairs Agriculture Development Branch (Field Crops Unit) Issue 07 Editor: Albert Tenuta - Plant Pathologist (519) 674-1617 June 6, 2007 www.omafra.gov.on.ca/croppest ISSN 1203-2204

Inside Issue 07 (2007): Pg. Gearing Up for Soybean Aphids this Year 1 4 No Nodal Roots? 6 Winter Wheat Update as of June 6, 2007 7 Eastern Ontario Crop Diagnostic Day 8 Evaluating Soybean Emergence 10 Soybean Crop Staging and Herbicide Application Timing 13 Gambling in the Tractor Seat

Gearing Up for Soybean Aphids this Year
Tracey Baute, Field Crop Entomologist, OMAFRA, Ridgetown Reports of sightings of soybean aphids on soybeans have started to come in from fields across the Midwest US and Ontario and Quebec. Aphid numbers are very low but this does indicate that the aphid season has officially started. Though these sightings are a few weeks earlier than past years, it may be more of an indication that we are getting better at finding soybean aphids or that the crop was planted earlier this year and is up and available for the soybean aphids that are currently looking for their summer host. Regardless, it means that we need to be prepared for what this season could bring. Unfortunately Ontario is challenged every year with the possibility of soybean aphids reaching threshold as we are geographically positioned to receive aphids from any location in the Midwest anytime in the season. Despite the US predicting it will be an aphid year based on the abundance of overwintering eggs they found last fall, what will truly determine if 2007 is a bad soybean aphid year is the 1

weather conditions at the time that the aphids hit the field, the stage and condition of the crop when they do and whether the natural enemies present are up for the task of keeping the populations below threshold. The threshold for soybean aphids is to “take action if populations are actively increasing above 250 aphids per plant on 80% of the plants from the R1 up to and including the R5 stage of soybeans”. More aphids per plant are needed once the soybeans are in the R6 stage and once beyond the R6 stage, economic return from any insecticide application is not likely. Research from multiple locations across North America has shown this threshold to work well while helping to avoid misapplications of insecticide on the helpful natural enemies We play an important role too. By scouting regularly, properly identifying the natural enemies of soybean aphids and determining if

the soybean aphid populations are being kept below threshold by them is critical. To determine if the natural enemies are doing their job requires a minimum of two field visits to confirm if aphid populations are increasing above threshold or not. By scouting only once and making a management decision based on the aphid population you see at that one time puts you at risk of spraying and killing off a natural enemy population that was doing an effective job for you. Any aphids that survive the spray will then multiple potentially above threshold in the absence of their natural enemies thus resulting the need for a second application. To help Ontario soybean growers stay informed of what is going on in fields across Ontario, OMAFRA and our scouting partners will be monitoring fields across the province again this year and will be reporting these results on both the Ontario Soybean Growers website (www.soybean.on.ca) and on the soybean aphid webpage of the USDA PIPE network (www.sbrusa.net). Weekly scouting maps and current provincial recommendations, as shown below (Figure1) from 2006 season, are posted to indicate when you need to start scouting in your own fields and determine what is going on.
Figure 1. Example of the weekly scouting map and Ontario commentary to be posted on the USDA PIPE website.

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The Canadian Soybean Aphid Working Group involving experts from provincial governments, federal government, universities and industry has developed new reference material to use in the fields this year to help with natural enemy identification and soybean aphid management decisions. Thanks to funding provided by the Ontario Soybean Growers, the Agricultural Adaptation Council, the Pesticide Risk Reduction Program of Agriculture and Agri-Food Canada, and Syngenta Crop Protection Canada, we will be providing you with the first installment of a series of soybean aphid reference materials this year. Be on the lookout this spring for “Soybean Aphid Scouting Cards” (Figure 2) and “Soybean Aphid Threshold Postcards” (Figures 3 and 4) available in Ontario, Quebec and Manitoba in

both English and French. And finally, for those interested in more of a hands-on lesson in how to scout for soybean aphids, identify their natural enemies and proper insecticide application, two sessions will be held at the SouthWest Crop Diagnostic Days being held at the University of Guelph, Ridgetown Campus on July 11th and 12th. More information about the event can be found at: www.diagnosticdays.ca Happy Scouting!

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Figures 2, 3, and 4: Introducing the “Soybean Aphid Scouting Card” and “Soybean Aphid Threshold Postcard” made available this season by the Canadian Soybean Aphid Working Group

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No Nodal Roots?
Bob Nielson, Corn Agronomist, Purdue University

Excessive drying of the upper soil profile can be conducive for the development of what some of us affectionately call the “rootless corn” or “floppy corn” syndrome. The problem illustrates a classic example of the importance of the timing of stress and plant development. The permanent (nodal) roots of a corn plant develop initially from near the crown area of the plant (Nielsen, 2007a). They develop sequentially in sets or “whorls” from individual nodes of the stalk. The growing point or meristem of a root lies near the root tip and must remain alive in order for the root to develop normally. Contrary to popular opinion down at the coffee shop, roots do not grow toward moisture on purpose. They grow downward in response to gravity (i.e., a gravitropic response). If nodal roots begin development in bone-dry surface soil but elongate into soil moisture at deeper depths prior to desiccation of the root tip, then the root will survive and proliferate. If the root tip (and accompanying meristem) desiccates prior to reaching soil moisture, the entire young nodal root will likely die. This is particularly true if the axillary meristems along the length of the root (that eventually produce the branch roots) have not yet differentiated or become active.

The appearance of such a desiccated root is what one would imagine; shriveled and discolored. This symptom is unlike that of any other lethal root stress, including salt injury from fertilizer. These symptoms are NOT like any associated with herbicide injury or insect feeding. Because several sets

Figure 1. Broken Mesocotyl

Figure 2. Example of "floppy corn" syndrome of roots may not have formed below ground, the crown may “appear” to be at or above the surface. That appearance is an optical illusion except in a few cases (Nielsen, 2004). Entire sets or “whorls” of nodal roots sometimes die in this manner and 4

the plant essentially survives on what’s left in the kernel reserves and what the seminal roots offer in terms of moisture and nutrient uptake until the next set of nodal roots develop and become established. If subsequent sets of nodal roots die in the same manner, the plant continues its dependence on the kernel and seminal root support.

root development if moist soil is thrown around the base of the plants. However, if the soil is dry enough to be causing the problem in the first place, there’s probably very little moist soil shallow enough to be brought up by row cultivation. The ultimate solution to the problem is a good soaking rain or at least enough of a rain to sustain new nodal root

Figure 3. Desiccated, dead nodal roots In fact, it is amazing to me how the aboveground appearance of a plant affected with the “rootless” syndrome can remain fairly normal up until the windy day when the mesocotyl simply can no longer support the plant and it flops over to the ground. “Floppy” corn plants are NOT technically root-lodged; they are simply broken over at the mesocotyl below the crown area of the plant. Obviously, the health of the mesocotyl and the seminal roots determine whether an affected plant can “hang on” until a decent soaker occurs to replenish soil moisture levels. What Can Be Done? Unfortunately, very little can be done to prevent the situation from becoming worse. Row cultivation may encourage new nodal

Figure 4. “Normal” Nodal root Development development long enough to allow the roots to reach deeper and hopefully wetter soil conditions before the upper soil dries again. A “Hindsight” Reminder. “Rootless” corn can also be aggravated by extremely shallow seeding depths that result in nodal root initiation beginning near the soil surface rather than at the usual 3⁄4 inch depth. This is one of several reasons that growers should avoid choosing seeding depths shallower than about 1 to 11⁄2 inches. Related References Elmore, Roger and Lori Abendroth. 2007. Rootless Corn Syndrome. Integrated Crop Management Newsletter, Iowa State Univ. [OnLine]. Available at http://www.ipm.iastate.edu/ipm/icm/2 5

007/5-21/rootless.html>. (URL verified 5/23/07). Nielsen, R.L. (Bob). 2004. OverExtended Mesocotyls and Floppy Corn Syndrome. Corny News Articles, Purdue Univ. [On-Line]. Available at <http://www.kingcorn.org/news/articl es.04/FloppyCorn-0624.html>. (URL verified 5/23/07). Nielsen, R.L. (Bob). 2007a. Root Development in Young Corn. Corny

News Articles, Purdue Univ. [OnLine]. Available at <http://www.kingcorn.org/news/timel ess/Roots.html>. (URL verified 5/23/07). Nielsen, R.L. (Bob). 2007b. Variable Emergence Due to Variable Seedbed Moisture. Corny News Articles, Purdue Univ. [On-Line]. Available at <http://www.kingcorn.org/news/articl es.07/VariableEmergence0520.html>. (URL verified 5/23/07) Leaf disease levels remain very low in many fields but be on the look-out for leaf rust which has begun to appear in the province. Powdery mildew has continued to advance in about 20% of fields, with lesions just beginning on upper leaves. Short periods of high temperatures over the last two weeks do not seem to have been sufficient to stop mildew development on these varieties. Control is warranted in these fields. Physiological fleck is evident at high levels in some fields. Barley Yellow Dwarf Virus (BYDV) symptoms continue to develop, particularly in the southwest where significant aphid numbers were present in May. Aphids are now being found in spring cereals in this region. With the higher levels of BYDV in winter wheat, spring cereals may be even more at risk. Scout! If control is warranted, (15 aphids/stem pre-heading, 50 aphids/stem post-heading) please contact Jen (519 272 4268) or Peter (519 318 7769) to set up some trials, and validate threshold levels. There is little Ontario data on the impact of aphid control in cereals.

Winter Wheat Update as of June 6, 2007
Jen Mullen, Assistant, and Peter Johnson, OMAFRA Cereal Specialist, Stratford Winter wheat fields continue to advance rapidly. Earliest harvest will begin the first week of July. Fields in Essex/Lambton have pollinated and are moving beyond the Folicur window. In Huron/Bruce, much of the crop is heading now (June 6/7). Rainfall over the weekend (June 2/3/4) held many growers out of the field with Fusarium control products, while increasing the Fusarium risk. Optimal timing for Folicur or Proline is Day 2 (Day 0 is when 75% of heads have cleared the flag leaf). However, applications up to Day 5/6 can reduce Fusarium somewhat, and other leaf and head diseases will still be controlled. Check the website for your fusarium risk. http://www.weatherinnovations.com/ DONcast.cfm

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Eastern Ontario Crop Diagnostic Day
Tuesday, July 17
2007
8:30 am to 3:30 p.m at the

Winchester Research Station Kemptville College, University of Guelph

Pre-registration by Friday, July 6, 2007 for the Eastern Ontario Crop Diagnostic Day and save $20.00. Preregistration of $50.00 includes lunch and materials. After July 6th, registration is $70.00 per person. Certified Crop Advisor (CCA) continuing education credits will be available. Topics such as timing of herbicide application, soybean seed treatments, perennial forage and weed identification, and alternative crops will be part of this year’s day. For further information contact the Kemptville OMAFRA Resource Centre at 613-258-8295.

Ministry of Agriculture, Food & Rural Affairs

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Evaluating Soybean Emergence
Horst Bohner, Soybean Specialist, OMAFRA, Stratford

2 - Insufficient moisture for germination Seed planted to a depth of 2.0” was planted into moisture. Seed planted at 1.0” was not planted in moisture

The spring of 2007 has been one of the best planting seasons in recent memory. Dry conditions have made timely planting possible and emergence has been excellent in most fields. The majority of soybeans were planted by the 25th of May. So far most of the crop is in good condition. However, there have been some emergence problems especially on clays soils and fields planted between May 8 and 15th. There are numerous reasons for poor stands. The most common reasons this year include: 1- Soil crusting Clay soil planted on May 15th

2.0 Inch Planting Depth

1.0 Inch Planting Depth

3 - Insect and slug feeding.
Seed corn maggot feeding in a field where manure was applied.

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Make sure that all the beans are up before making a decision. Fields with a plant reduction of up to 50% do not need to be replanted, if plant loss is uniform and the remaining stand is healthy. Numerous studies and field experience have demonstrated that keeping an existing stand is often far more profitable than replanting. If the stand reduction is due to slugs or insects remaining damaged seedlings are often weak and will not perform well. If the problem is due to seed corn maggots consider using Cruiser insecticide seed treatment if replanting is required. Yield results will depend on the remaining plants being healthy and distributed evenly throughout the field. It's also important that plants be kept free of weed competition, or yield reductions will occur. On lighter soils, fields with a plant stand of more than 100,000 plants/acre should not be replanted, while heavier clay soils may require more plants per acre for success -- a minimum of 100,000 - 120,000 plants/acre. Graph 1 shows the effect of plant stand on soybean yield.

Graph 1 shows the effect of plant stand on soybean yield. Results from 28 Ontario soybean population trials conducted in 2005 and 2006. Source: Bohner, Earl.

50 40 30 20 10 0 0 50 100 Plants / acre (X 1000) 150 200

Yield (bushels / acre)

One of the quickest ways to determine a soybean stand is the “Hula Hoop” method. For example for the hoop below 15 plants = 100 000 plants/acre. Once the number of plants per hoop has been calculated to plants per acre from Table #1 write these numbers on the side of the hoop for future reference. (ie. 15 = 100 000, etc) Take at least 10 hoop counts and average the results.

Figure 4. “Hula Hoop” method can help determine your soybean plant stand population.

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Table 1 – Plant Populations Using the “Hula Hoop” Factor by Which to Multiply the Number of Plants within the Hoop to Equal: Inside Diameter of Hoop in cm (in) 91 (36) 84 (33) 76 (30) 69 (27) 61 (24) Plants per Hectare 15 385 18 182 22 222 27 027 34 483 Plants per Acre 6 165 7 334 8 874 10 956 13 865

The alternative method is to measure the length of 1/1000th of an acre, count the number of plants and multiply by 1000 to get the number of plants per acre. Table 2 – Length of Row Required for 1/1000th of an Acre Row Width cm (in) 38 (15) 51 (20) 56 (22) 76 (30) Length of Row Required for 1/1000 of an Acre: Metres Feet 10.6 34’ 10” 8.0 26’ 1” 7.3 23’ 10” 5.3 17’ 5”

For more details on replanting please see last year’s article entitled “Thickening Thin Soybean Stands”http://www.omafra.gov.on.ca/english/crops/field/news/croppest/2006/05cpo06a3.htm

Soybean Crop Staging and Herbicide Application Timing
Mike Cowbrough, Weed Specialist, OMAFRA, Guelph What happens when there is an abundance of weeds at or near the maximum leaf-stage for effective control with an herbicide, yet your soybean crop is not at the growth stage specified on the product label? As a producer you are now faced with the ultimate risk/benefit analysis. Do I sacrifice the level of weed control, or risk possible crop injury?

Is there any risk in applying an herbicide before its specified label stage? In general, yes. The application stage specified on the label is there because: 1. There is an increased chance of crop injury when the product is applied outside the application window, or 2. Research on the product was conducted at the stages specified on the label. Therefore crop tolerance to applications outside those stages is unknown. In any case, there is a level of risk to applying an herbicide before the recommended crop stages Refer to Table 1 for a breakdown of ideal crop application stages. The decision 10

to “pull the trigger” will ultimately come down to what growth stage the weeds are at. For example, lets assume you scout your field and the soybean crop is at the cotyledon stage, yet common lamb's-quarters is at the 4-6 leaf stage and at extremely high densities. In this situation, it is probably more

advantageous to spray a suitable herbicide as soon as possible versus waiting until the specified crop stage. Refer to Table 2 for a list of maximum weed leaf stages where a specific herbicide will still be effective.

Table 1. Soybean application stages for a number of post-emergent herbicides.
Critical Weed-Free Period in Soybean

Basagran Forté, CleanSweep

Blazer, Classic, Firstrate Pinnacle, Reflex

Assure II, Excel Super, Poast Ultra, Pursuit, Select, Venture L

Bottom Line: Don't make the decision on your own If you are in a situation where there are advanced weeds in a soybean crop not yet at the labeled application stage, have your agronomist and territory sales representative scout the field with you so that you can make the best decision together.

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Table 2. Maximum weed leaf stage whereby the herbicide is still effective according to the product label.
Broadleaf Herbicides Product Maximum Weed Leaf Stage 4 leaf 6 leaf Weeds Controlled

Basagran Forté (0.9 L/ac)

8 leaf 10 leaf

giant ragweed, velvetleaf common ragweed, hairy galinsoga, hairy nightshade, purslane, shephard's-purse, stinkweed lamb's-quarters cocklebur, flower-of-an-hour, lady's-thumb, wild mustard lamb's-quarters cocklebur eastern black nightshade, redroot pigweed common ragweed, lady's-thumb jimsonweed, wild mustard velvetleaf common ragweed dandelion, redroot pigweed, yellow nutsedge annual and perennial sowthistle jimsonweed, velvetleaf giant ragweed cocklebur, common ragweed redroot pigweed, lady's thumb, wild mustard velvetleaf lamb's-quarters cocklebur*, eastern black nightshade, ragweed*, old witchgrass, wild buckwheat, wild mustard green foxtail, yellow foxtail barnyardgrass* velvetleaf redroot pigweed

2 leaf 4 leaf Blazer (1 L/ac) 6 leaf 8 leaf 10 leaf 4 leaf 6 leaf Classic (14 g/ac) 8 leaf bud stage 4 leaf Firstrate (8.5 g/ac) 6 leaf 8 leaf Pinnacle (2.2 g/ac) 8 leaf 4 leaf Pinnacle (3.2 g/ac) 6 leaf Grass and Broadleaf Herbicides 2 leaf Pursuit (125 mL/ac) 4 leaf 6 leaf 8 leaf 12 leaf

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Grass Herbicides Product Assure II (150 ml/ac) Assure II (200 ml/ac) Assure II (300 ml/ac) Excel Super (268 ml/ac) Poast Ultra (130 ml/ac) Poast Ultra (190 ml/ac) Poast Ultra (450 ml/ac) Select (50 ml/ac) Select (50 ml/ac) Maximum Weed Leaf Stage 6 leaf to early tillering to early tillering 6 leaf 6 leaf 6 leaf 6 leaf 3 leaf 4 Leaf 6 Leaf Weeds Controlled volunteer corn green foxtail, volunteer cereals barnyard grass, fall panicum, old witchgrass, proso millet, yellow foxtail quackgrass barnyard grass, crabgrass, fall panicum, green foxtail, yellow foxtail, witchgrass, proso millet, volunteer corn barnyard grass, crabgrass, fall panicum, green foxtail, yellow foxtail, witchgrass, proso millet volunteer cereals quackgrass (supression) green foxtail, yellow foxtail, volunteer cereals barnyard grass, fall panicum, witchgrass, proso millet, volunteer corn volunteer cereals, quackgrass (supression) quackgrass barnyard grass, volunteer corn (only needs 240 ml/ac rate for control of volunteer corn) crabgrass, green foxtail, yellow foxtail, fall panicum1, old witch grass1, proso millet1 quackgrass (supression) quackgrass, wirestem muhly

Select (75 ml/ac) 6 Leaf Select (150 ml/ac) 6 leaf Venture L 4 leaf (320 ml/ac) Venture L 4 leaf (400 ml/ac) Venture L 5 leaf (800 ml/ac) *Use the 168 ml/ac rate when targeting this species. 1 Can be controlled up to the 5 leaf stage.

Gambling in the Tractor Seat
Helmut Spieser, Agricultural Engineer, OMAFRA, Ridgetown It looks like it’s time to talk about farm safety. Most of the newer tractors that we see moving through the fields and on the roads have cabs with built-in “Roll Over Protection”. These new cabs, in addition to being sleek and comfortable can also save your life in the event of a roll over accident.

Seeing a new tractor without a cab going down the highway, catches my eye. What makes me angry is when I also see the tractor driver holding a young child on his lap. What were you thinking? Give your head a shake! Children and other passengers should never be taken on the tractor unless there is a seat and seatbelt for that individual. Accidents happen quickly and unexpectedly. Don’t become a farm fatality statistic. PLEASE!

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