Wheat Management: 

Getting it Right

Getting It Right wheat production management workshops, held in four locations across western Minnesota earlier this year, focused on virtually all facets of wheat production.  Following is some of the information presented by University of Minnesota Extension Service personnel.  The workshops, the research data on which the workshops were based, and the dissemination of this information are all funded in part by the Minnesota Wheat Checkoff, directed by the Minnesota Wheat Research and Promotion Council.

Managing excess water
Crop producers (and researchers) in the Red River Valley have been learning more about how tile or subsurface drainage can remove excess water from their fields. U of M extension educator Hans Kandel pointed to research in Canada, Ohio, and Iowa which all clearly demonstrate a yield advantage to properly drained fields compared to fields with poor drainage.  Research conducted near Brooks and Crookston, Minn., from 2001-03 also indicated a yield advantage to wheat (11%) and sugarbeets on tiled fields versus those that weren’t tiled.

Kandel said drained soils allow for increase root development because “if you dry out layers of soil, oxygen will replace the space occupied by the excess water.” Other benefits of drainage include earlier planting, better stand establishment, reduced soil compaction, reduced fuel, improved fertility and better competition against weeds.

U of M small grains specialist Jochum Wiersma stressed that drainage tile doesn’t remove more water than field capacity, but stops when the field is at its water holding capacity.

Information on tile drainage can be found online at www.smallgrains.org .  Under the “Production & Research Info” link, click on “Tile Drainage.”

No varietal yield response to N
Should nitrogen fertilizer be adjusted for new wheat varieties?  That is the question U of M soils specialist George Rehm addressed with research conducted in 2003. Rehm evaluated four varieties (Alsen, Oxen, Knudson, 2375) with varied applied nitrogen rates (0, 40, 80, 120, 160 lb N/ac) and found no response to yield by variety.

The applied rate of 120 lb N/ac appeared to be optimum at two test sites where wheat followed wheat.  The optimum rate at a site where wheat followed soybeans was about 100 lb N/ac, illustrating the N credit from a previous crop of soybeans.

Grain protein did vary by variety, however all varieties in the study had at least 14% protein with the 120 lb N/ac treatment. 

While the study indicated no yield difference by variety, the common yield response of all varieties to N demonstrated that the return on investment in fertilizer N is substantial. For example, if wheat is valued at $3.25/bu and the cost of the nitrogen fertilizer is 22 cents/lb of actual N, the value of the added yield response in this study after subtracting the cost of the N ranged from about $60 to over $80/ac.  Since the rate of N needed to reach optimum yield did not change with variety, this return could be expected for most commonly-grown spring wheat varieties grown in the region.

Properly drained soils allow for better root development.

Seeding Rates and Depth
According to Wiersma, seeding rates to obtain 1.25 million live plants per acre have been the standard recommendation for spring wheat. However, Wiersma conducted a three-year study (1996-98) to see if this initial plant population is still appropriate for newer varieties that are generally shorter and have higher yield potential than varieties used decades ago. He evaluated nine varieties, and found that the plant population that maximized grain yield differed by variety (see table). In addition, he found that the corresponding seeding rates needed to attain this optimum plant population were substantial higher than commonly used.

It’s best to do a seed count for the most accurate seeding rate by variety. The simplest method to determine the number of kernels per pound of seed is to count and weigh one hundred kernels four or five times. Calculate the average weight of the five samples. Divide 454 (in grams per lb) by the average weight. Multiply this answer times 100 and this gives you the number of kernels per pound of clean seed.

Example: 100 seeds weigh 2.89 grams

 (454 g per lb) ÷ (2.89) x 100 seeds = seeds/lb

(157.09) x (100) = 15709 seeds/lb     

When planting is delayed producers should increase the initial plant population by one or two plants per square foot for each week planting is delayed. Increasing the initial plant population will partially compensate for the yield losses that result from the delay in planting. Wiersma says producers can determine stand loss by counting live plants in a square foot at the two to three leaf stage before plants start to tiller.

Seed should be placed 1.5” in the soil; deeper seeded plants will emerge up to one week later and result in maturity differences within a field.  “Slowing down the seeder and getting good seed placement is critical,” he emphasizes, adding that one setting will not work all spring under different soils and residue. He stressed checking drill calibration at and within each field.

Most of these varieties are not grown anymore since this study was conducted in the 1990’s. However, it still illustrates how optimum seeding rate can differ by variety.

Table 1: The optimum seeding rate and corresponding expected and realized stand for nine HRSW-cultivars to attain maximum yield when planted early.

			Stand
	Seeding Rate		Expected	Realized	Loss
Variety	(# x 106/acre)	( lbs/acre)	(#/ ft2)	(#/ft2)	%)
Bacup	1.96	128	45	33	27
Marshall	1.89	119	43	30	30
Kulm	2.05	136	47	30	36
Grandin	1.94	134	44	32	27
P2375	2.20	170	51	37	27
Nora	1.89	107	43	31	28
Gunner	2.10	132	48	35	27
Hamer	2.06	152	47	36	23
Verde	1.98	120	41	31	23
Average	2.01	133	45	33	28

Table 2: The optimum seeding rate and corresponding expected and realized stand for nine HRSW-cultivars to attain maximum yield when planted late.

			Stand
	Seeding Rate		Expected	Realized	Loss
Variety	(# x 106/acre)	( lbs/acre)	(#/ ft2)	(#/ft2)	(%)
Bacup	2.16	141	50	36	27
Marshall	2.08	131	48	33	30
Kulm	1.98	132	45	29	36
Grandin	2.25	155	52	37	27
P2375	2.08	160	48	35	27
Nora	2.02	115	46	34	28
Gunner	1.98	125	45	33	27
Hamer	2.58*	190	59	46	23
Verde	2.16*	146	50	38	23
Average	2.14	144	49	36	28
* Contrast not significant.

Early Fungicide Application
U of M small grains extension plant pathologist Charla Hollingsworth discussed the early season leaf diseases, tan spot and Septoria. Tan spot is a residue-borne disease that needs extended periods of wet leaves to develop. During optimum conditions, the fungus can cause lesions in as few as seven days. Cool, wet weather favors development of Septoria (tritici blotch), producing lesions 10 to 20 days after infecting the plant. Dry conditions can greatly reduce the spread of tan spot and stop Septoria. 

Although no variety is completely resistant to leaf diseases, she lists Knudson, NorPro, Verde, Parshall, and Reeder as moderately resistant, Dandy and HJ98 as moderately susceptible, and Alsen, Mercury, Walworth, Ingot, and Oxen as susceptible.  She notes that Knudson and NorPro appear to exhibit a “hypersensitive response” to help in stopping the fungus from spreading across the leaves. This type of response is noted by scattered, very small dark lesions that lack the yellow “halos” characteristic of tan spot lesions.

Hollingsworth recommends foliar fungicide applications for leaf diseases when wheat is planted into wheat stubble, a susceptible variety is used, sustained wet weather exists, and the lower leaves have lesions.

North Dakota State University has small grains disease forecasting models which can be found online at www.ag.ndsu.nodak .edu/cropdisease/cropdisease.htm.

N Timing: Wheat, Casselton, ND, 2003

	Time of Application
Preplant	5th Leaf	Boot	Yield
	lb. N/ac.		bu./ac
125	0	0	66.8
65.5	65.5	0	69.6
42	42	42	68.5

N Timing: Irrigated Wheat, Carrington, ND, 2003

	Time of Application
Preplant	5thLeaf	Boot	Yield
	lb. N/ac.		bu./ac
150	0	0	84.3
75	75	0	92.3
50	50	50	92.0

Weed Control
Hoelon, Tiller, and Fargo will not be available in the market this year, Bronate will only be available as Bronate Advance, and Cheyenne is in limited supply, according to Bev Durgan, U of M extension weed scientist.

Wild oat is the number one weed problem in spring wheat, and the most competitive weed, she said.  “If you have wild oat, you need to concentrate on it.”  Wild oat germinates in soil temperatures from 40 to 70 degrees. Durgan said reduced rates of Puma and Discover have given good to excellent wild oat control but lower rates should not be used if it is warm or dry, or if wild oat infestations are greater than 40 plants per square foot. She added that reduced rates are legal but the herbicide manufacturer has no obligation to support herbicide failures under reduced rates.

Foxtails are warm-season weeds that germinate at soil temperatures from 50 to 85 degrees.  Durgan said yellow foxtails are the most difficult to control as they tiller early, and later applied herbicides only kill main stems and not tillers. Yellow foxtails can be differentiated from green and giant foxtails as they have hairs at the base of the leaf. Durgan said low populations of foxtails at 50 or less plants per square foot may not need to be controlled if the wheat stand is good and foxtails emerge after the crop. But she added, “don’t let yield loss be your only decision” about spraying for foxtails.  She said harvest problems, dockage, and seed bank control are other considerations for justifying treatment.

In-Season Fertilizer
With increased discussions of split applications of nitrogen in wheat, Rehm suggested using in-season nitrogen when conditions favor a yield potential higher than the original yield goal, or when weather patterns favor nitrogen loss.  This includes sandy soils with increased water for nitrogen leaching, and under heavy soils with high temperatures and reduced denitrification.  Rehm’s research, and other studies as well, have indicated no consistent increase in yield from an in-season application of N if enough was present at the beginning of the season.  In-season or split applications may have a place where N loss is known, in irrigated sandy soils or sandy soils with high yield potential, or where there is higher yield potential, otherwise there is no advantage to routinely include split applications of N in a fertility management plan, said Rehm.

Resident and immigrant insects
Insects that affect spring wheat can be classified into two groups: “residents” that over-winter, and “immigrants” that travel to the region each year.  Ian MacRae, U of M extension entomologist, said we have some warning of resident insect population, as they can be monitored to whether they build up or decline over years.  These include wireworms, grasshoppers, Hessian fly, wheat stem maggots, and wheat stem sawfly. 

But he said the immigrant insects such as cereal aphids, aster leafhoppers, armyworms, and cutworms migrate in on southerly winds in spring and early summer, and are thus more difficult to predict. 

Spraying for insects at a pre-determined date, which MacRae called “calendar application,” is not a feasible management practice.  He asserted that applying insecticides as insurance, without regard to what insect populations are actually present, leads to the overuse of pesticide, unnecessary expenses, and possible treatment resistance over the long -term.  Instead, MacRae stressed the use of good scouting.  Research indicates better economic return from treating only when populations require control.  

Yield Factors
Zach Fore, U of M extension cropping systems specialist, listed factors identified by one farm in northwest Minnesota which had been yield mapping for numerous years:  the number one most yield limiting factor was poor drainage, followed in order by crop variety, pest problems, crop rotation, tillage, herbicides, fertility placement, fertility levels, and plant population.  He pointed out that the importance or impact of each factor will change by field and by crop year.  Fore said farmers need to list their limiting factors and “manage them in priority order.”  Yield maps, Fore suggested, allow growers to determine their yield limiting factors in each field, and provide a historical data set to establish yield limiting trends.

Weed Competition in Wheat
Left unchecked 10 wild oats or wild mustard plants per square foot will reduce wheat yields 10-20 bushels per acre or 35%. Two to three kochia plants per square foot can reduce yields 30%. Canada thistle patches often reduce yields by 60% and green foxtail can reduce yields 10-15% when wheat is planted late. Below shows wheat yield reduction from foxtail and wild oats. Information is compiled from research performed at NDSU.  In the wild oat example, a 9% reduction in wheat yield from 10 weeds per sq yard would be 3.6 bushels lost from a 40-bu yield, or a loss of about $12.60/acre assuming a price of $3.50/bu

	Foxtail	Wild Oat
Weeds/sq.yard	% wheat	Yield reduction
10	0	8-9%
50	4-5%	18%
75	6-7%	25%
100	8-9%	34%
150	15%	40%

Below is a global positioning satellite (GPS) image of a sunflower field prior to bloom near Crookston, Minn. The blue lines are open field drainage waterways. The red and lighter colors in the field illustrate low reflectance values, or less plant biomass growth.  The green and darker colors illustrate higher reflectance values, or better, more dense plant biomass growth.  The differences help with crop scouting, and to key in on management practices needed to improve field productivity.