C.O.R.N. Newsletter 2004-05

Timing Of Spring Nitrogen For Wheat

Authors: Edwin Lentz

For the past four years at the Northwestern Branch of OARDC, we have observed wheat yields from single applications of N applied at initial greenup and early stem elongation (Feekes GS 6) using ammonium sulfate, urea and urea-ammonium nitrate (28% solution). Differences were not observed between the two application timings three out the four years. Only in 2002 did N applied at Feekes GS 6 have significantly larger yields than greenup applications. Recall that in 2002, significant nitrogen losses occurred as a result of an abnormally warmer and wetter winter. Yields significantly dropped in three out of four years when nitrogen was applied later (Feekes GS 9) than initial stem elongation. One may be tempted to wait until early stem elongation to insure maximum yields; however, if weather conditions were unfit for several weeks at that time, the delayed application may cause a yield reduction. As a compromise, we would suggest that N be applied as soon as the ground is fit after initial greenup but before Feekes GS 7. In most years this would give a six week window between early March and mid April for southern Ohio and mid-March to late April for northern Ohio.

In this same study, yield response to nitrogen source was as follows: ammonium sulfate > urea > urea-ammonium nitrate. Yield differences among nitrogen sources were relatively small except in years of high nitrogen loss, such as 2002. As a result, 28% may be a poor choice for poorly drained fields and very early applications of nitrogen. Even though ammonium sulfate was more consistent, economics may make urea a better choice in these situations. In well-drained fields and as application time approaches Feekes GS 6, selection of nitrogen source becomes less critical. Supportive data showed that nitrogen loss caused yield differences between ammonium sulfate and other nitrogen sources and not sulfur. Actual http://west.osu.edu/agronomy/index.html are at http://west.osu.edu/agronomy/index.html.

Too late for dormant applications of Sencor or Velpar to alfalfa?

Authors: Mark Loux

Winter application of Sencor or Velpar to dormant alfalfa is one of the most effective tools for weed management. With the recent warm weather, be sure to check alfalfa to make sure that it is still dormant when applying Sencor. Velpar can be applied after alfalfa breaks dormancy but before new growth exceeds 2 inches in height. Sencor can be applied to mixed grass/alfalfa stands, while Velpar is labeled for pure alfalfa only. Either herbicide will be effective for most winter annual weeds and will suppress of control dandelion. Velpar can also be fairly effective at controlling undesirable perennial grasses.

Scout wheat for early-season weed problems

Authors: Mark Loux

Wheat fields should be scouted soon to determine how well the stand survived winter and the degree of infestation with winter annual weeds. Over-wintering winter annual weeds, including chickweed, purple deadnettle, and mustard species, compete with wheat in early spring and inhibit its further development. Control of these weeds as early as possible in spring allows for the most rapid development of wheat, which promotes its response to fertilizer and improves its competitiveness with later-emerging weeds.

Check the wheat herbicide section of the current http://ohioline.osu.edu/b789/index.html (pages 128-136) for effectiveness ratings and other guidelines. Harmony Extra and Express are among the most effective herbicides for winter annual weed control, but control of some weeds may be improved when combined with 2,4-D. Most wheat herbicides can be applied using fertilizer solution as the spray carrier. Surfactant recommendations for Harmony Xtra, Express, and Harmony GT vary with the spray carrier, and these herbicides can occasionally cause unacceptable crop injury when applied in fertilizer solution. Injury is most likely to be severe when wheat is stressed from saturated soils and cold temperatures. To avoid injury with these products, make separate applications of fertilizer and herbicide.

Predicting Flea Beetle Activity & Stewart's Disease On Corn

Authors: Bruce Eisley, Patrick Lipps, Dennis Mills

Stewart's bacterial leaf blight was negligible throughout Ohio in 2003, but it has caused significant problems in other years. The bacterium causing this disease is carried and spread by the Flea Beetle. During years with mild winter temperatures the flea beetle adults overwinter in large numbers. In the spring, as corn emerges from the ground, the flea beetles feed on the young plants and spread the bacterium which in turn causes seedling wilt and leaf blight. The incidence of Stewart's disease is related to the ability of the flea beetle to overwinter. http://www.oardc.ohio-state.edu/ohiofieldcropdisease/corn/stewarts.htm
http://www.oardc.ohio-state.edu/ohiofieldcropdisease/corn/stewarts.htm

Flea beetle adults become active in the spring when soil temperatures reach 65 F. Adults are most active on sunny, warm, windless days. They hide in cracks in the soil during windy, cool or cloudy periods. After feeding and mating, adult females lay eggs at the base of the corn plants. Larvae feed on corn roots and are full grown in about two weeks. There are at least two generations per year in Ohio. The beetle overwinters as an adult in the soil near corn fields. It prefers bluegrass sod, but may be found in fence rows, roadsides, and woods (OSU Extension Fact Sheet CV-1000-94, not available on the web). See also http://ohioline.osu.edu/b827/b827_31.html, Soybean, Wheat, and Alfalfa Field Guide, Bulletin 827 and http://ohioline.osu.edu/b631/b631_3.html on Field Crop Disease Management, Bulletin 631-98.

The occurrence of Stewart's bacterial disease is totally dependent on the level of flea beetle survival over winter. For may years, winter temperatures have been used to predict the severity of Stewart's disease because higher populations of the flea beetle survive during mild winters than during cold winters. The 'flea beetle index' is calculated as the sum of the average temperatures (Fahrenheit) of December, January and February. Index values of less than 90 indicate negligible disease threat, 90-95 indicate low to moderate levels, 95-100 indicate moderate to severe and values over 100 predict severe disease.

Table 1. Monthly average temperatures and Flea Beetle Index for predicting severity of Stewart’s Bacterial Leaf Blight for different location in Ohio, 2003-2004.

Location	December	January	February	Sum	PredictedSeverity
Hoytville	31.6	21.0	27.2	79.6	Negligible
Wooster	32.0	21.9	28.8	82.7	Negligible
S. Charleston	32.2	23.5	30.7	86.5	Negligible
Piketon	35.1	28.0	34.2	97.3	Moderate to Severe
Jackson	34.5	27.7	32.9	95.1	Moderate to Severe

These numbers indicate that flea beetle populations should be very low in northern and central Ohio and moderate to severe in southern Ohio. Stewart's bacterial disease could be a problem for southern Ohio this year. Time will tell if this prediction is correct. Although the flea beetle index has been a relatively good predictor over the years, we would still recommend that growers scout their corn fields for the presence of flea beetles. Growers should watch this CORN newsletter for up-dated information as the spring progresses.

Corn and Nitrogen Utilization-Thoughts from 2003

Authors: Peter Thomison, Edwin Lentz

With the return of warmer temperatures, many of us will soon think about planting corn and nitrogen utilization. Along this subject, the following is a response to several questions asked by a Henry County producer during the Crop Profit Program this winter.

Why didn't the corn run out of nitrogen in 2003?

Unlike some areas of the state, much of Henry County had conditions that maximized nitrogen availability and minimized losses, such as cool conditions in May followed by moderate temperatures and timely wet/dry cycles throughout the growing season. Cool May temperatures limited N loss and the wetting and drying throughout the summer promoted the release of organic N. Rains continued during the normally dry months of July and August allowing continual root growth (root hairs) to take advantage of residual N. In addition, plants had a good start from uniform emergence resulting from relatively warm, dry conditions in April. Soil conditions may have been improved by the previous cold winter, which allowed freezing and thawing activity at a greater soil depth. This loosen soil may have allowed better conditions for early root growth and improved nitrogen uptake. In summary, 2003 Henry county weather conditions improved the efficiency (utilization) of fertilizer N applied to the crop and also increased the release of N from the soil organic matter.

What is the current thought on how much nitrogen is needed for corn?

Follow the university recommendation found in the http://ohioline.osu.edu/e2567/index.html http://ohioline.osu.edu/e2567/index.html, utilize N credits from appropriate previous crops, and follow management practices that minimize N loss.

Performance of Bt hybrids in the 2003 Ohio Corn Performance Test

Authors: Peter Thomison

Most researchers agree that hybrids containing the European corn borer (ECB) Bt events provide effective control and reduce yield losses when these hybrids are subjected to economic ECB infestations. However, when Bt corn hybrids were first introduced in 1996, they were sometimes associated with yield “drag” or “lag”. Comparisons between the yield potential of ECB Bt hybrids and normal (non-Bt) hybrids were mixed. Most studies including OSU research by Bruce Eisley found that grain yield was similar for Bt and isoline hybrids under relatively low natural ECB infestations. However, other studies found that in the absence of ECB, elite adapted non-Bt hybrids had greater yield potential than Bt hybrids suggesting an initial yield lag associated with Bt hybrids.

A recent Penn State/University of Maryland study evaluated Bt hybrids, their near isolines, and leading non-Bt hybrids under natural infestations of ECB over a three year period across multiple locations. On average, Bt and lead hybrids performed similarly suggesting that isolines have similar yield potential as lead hybrids. Bt hybrids had higher grain moisture at harvest than isoline and lead hybrids.

In the 2003 Ohio Corn Performance Tests, Bt hybrids, as a group, consistently averaged higher yields than the non-Bt hybrids in each of the three testing regions (Table 1). Moreover, a Bt hybrid was the top yielding entry at several test locations in 2003. In the Southwest (SW) and Northwest (NW) test regions, the differences in average yield between the Bt and normal hybrid groups were generally small, but at the Wooster test site, which represented the Northeast region in 2003, the yield advantage to the Bt corn hybrids was about 21 bu/A. European corn borer injury to non-Bt hybrids was evident at Wooster, which may explain the markedly higher yields of the Bt hybrids, but at the other locations ECB damage was low or absent.

Although greater than in past years, the number of Bt hybrid entries in 2003, for both the early and full season trials combined within a region, comprised no more than 25% of the test entries (Table 1). Therefore, these comparisons of Bt and normal corn hybrids are confounded by the marked differences in numbers of hybrids (and possibly genetic backgrounds) associated with each of the groups. Nevertheless, the results suggest that as Bt events have been more widely incorporated into elite genetics, differences in yield between Bt and top yielding non-Bt hybrids have become less pronounced.

Table 1. Yields of Bt and Normal Corn Hybrids by Region, 2003 Ohio Corn Performance Test: Early and Full Season Trials.

Region	Type	Early	FullSeason
Southwest	Bt	185 (10)*	184 (18)
	Normal	181 (49)	180 (37)
Northwest	Bt	169(12)	155 (16)
	Normal	161 (53)	151 (41)
Northeast	Bt	223 (9)	219 (9)
	Normal	201 (30)	199 (28)
* Number of entries in parenthese