C.O.R.N. Newsletter 2004-31

YieldGard Rootworm in Ohio

Authors: Ron Hammond, Bruce Eisley

We conducted several trials this year to evaluate YieldGard Rootworm hybrids compared to their isolines for rootworm larval efficacy. We had two trials at the Western Agricultural Research Station comparing a YieldGard Rootworm hybrid, Dekalb DKC60-05 YGRW, to its nontransgenic isoline, Dekalb DKC59-08 (treated and untreated), for rootworm larval efficacy and yield. The plots were planted in areas that had been planted to a corn trap crop in 2003. A trap crop area is planted later than usual, in this case late June, 2003 and thus it is the last area on the farm that has green silks and pollen and should attract all of the rootworm beetles into the area resulting in heavy rootworm egg laying.

Trial one was planted 28 April in an area that was in a sweet corn trap crop in 2003 and trial two was planted 7 May in an area that was in a field corn trap crop in 2003. Plots were evaluated for rootworm damage by randomly digging 5 roots per replicate for each treatment. Roots were washed, examined for corn rootworm larval feeding injury and rated in accordance with the 1-6 “Traditional” scale (1 = no damage and 6 = roots severely damaged) and the 0-3 Node Injury Scale (0 = no damage and 3 = roots severely damaged). Plants in were evaluated for rootworm on 6 July for trial one and on 8 July for trial two. Results from trial 1 in the 1-6 scale had check plots with a root rating of 4.2 while the YieldGard Rootworm hybrid had a root rating of 2.30. The lowest insecticide treated root rating was 2.40. Results from trial 2 in the 1-6 scale had check plots with a root rating of 3.05 while the YieldGard Rootworm hybrid had a root rating of 1.95. The lowest insecticide treated root rating was 2.05. In these two cases the YieldGard Rootworm hybrid performed like we would have expected even under the heavier rootworm pressure that we saw in trial 1. These plots will be machine harvested later this fall. Complete root rating results from these trials can be found on the web at: Trial 1; http://entomology.osu.edu/ag/reports/04si1.pdf and trial 2; http://entomology.osu.edu/ag/reports/04si2.pdf.

Another trial compared two YieldGard Rootworm hybrids, Dekalb DKC60-05 YGRW and Dekalb DKC60-13 YGRW, to their nontransgenic isolines, Dekalb DKC59-08 and Dekalb DKC60-15. The hybrids were planted at the Western and Northwest Stations and also at eight on farm trials throughout Ohio. The hybrids were planted following corn in all cases except one where the hybrids were planted following soybeans. Roots were rated in July at each location using both the 1-6 and the 0-3 scale. Root ratings were lower in this trial than the above trial with the highest check plot at 2.70 and most of the other check plots at 2 or less. This is the type of root injury we expected to see in Ohio when corn follows corn. These plots will be machine harvested later this fall. Root rating results from this trial can be found at: http://entomology.osu.edu/ag/reports/04ygrw.pdf.

Getting That Last Cutting of Alfalfa

Authors: Mark Sulc

Early September is ideal for taking that last yearly cutting of alfalfa. The timing of this cutting can be very important to the long-term health of the stand. It is best for alfalfa to not be cut during the 5 to 6 week period before a killing frost. During this critical period, cold resistance and energy reserves for winter survival are built up.

A killing frost for alfalfa occurs when temperatures drop to 25F or less for several hours. So the period from mid-September through October is the critical fall rest period in our region. Harvesting during this period disrupts accumulation of energy reserves and development of cold hardiness.

Producers often harvest alfalfa during the critical fall period despite the increased risk of winter injury. Research shows that often the tonnage gained by cutting during the critical fall period is lost in the first cutting the following year. Plus there is the increased risk of winter injury and ultimately shorter stand life by stressing alfalfa in this way.

This year rainy weather has delayed cutting schedules throughout the growing season, pushing back the time when the crop will be ready for a last harvest. The tonnage expected from a fall cutting and the need for the forage should be high before considering a cutting during the critical fall period.

When harvesting alfalfa during the critical fall period, several factors can help reduce the risk of winter injury:

* Young, healthy stands are less susceptible to winter injury from fall harvesting than older stands. On the other hand, more future production potential is lost if a younger stand is injured from fall cutting.

*Forages in well-drained soils will be at lower risk of injury than those with marginal drainage. Fall cutting should not be attempted on soils prone to heaving! Removal of the topgrowth cover increases the potential for heaving injury.

*Length of harvest interval during the growing season is often more important than the actual date of fall cutting. Making a 3rd cutting during the fall is less risky than making a 4th cutting in the fall, because a 3-cut schedule allows longer intervals for plant recovery between cuttings compared with a 4-cut schedule. Likewise, a growth interval of 45 days BEFORE a fall harvest will reduce the risk of injury compared with a pre-harvest growth interval of 30 days. The longer growth period allows more energy buildup before the fall harvest, lessening the amount of energy reserves needing to be built up after harvest.

* Fields with optimal soil fertility levels (pH, P, K) are at less risk than where fertility levels are lower.

* Disease resistant and winter hardy varieties lessen the risk of injury from fall cutting.

* Alfalfa that was not under stress during the summer will be at lower risk. Any stress (wet soils, potato leafhopper injury, etc) that weakened the crop during the year can increase the risk of damage from fall cutting. This is the case in many of our alfalfa fields this year.

* Cutting AFTER a killing frost (25 F for several hours) in late October or early November can be an option for well-drained soils. Leave a 6-inch stubble after late fall cutting. Cutting this late in the year prevents regrowth that burns up energy reserves; however late removal of plant cover increases the risk of frost heaving! Fall cutting should not be practiced on soils prone to heaving.

Use a Burndown Herbicide Program in No-Tillage Winter Wheat

Dandelions and winter annual grasses, such as downy brome, cheat, and annual bluegrass are becoming more of a problem in no-tillage winter wheat. The excessive moisture in most of the state in the last month has allowed dandelion and winter annual weeds to germinate quite well.

To control dandelions and quackgrass apply glyphosate at least at 0.75 pounds acid equivalent/acre (lbs ae/A), 22 ounce/acre (oz/A) of Roundup WeatherMax, 24 oz/A of Touchdown Total, or 32 oz/A of a 3.0 lbs ae/gallon glyphosate formulation. To control winter annual grasses apply at least 0.38 lbs ae/A of glyphosate. To control purple deadnettle and most any other winter annual broadleaf species apply 0.56 lbs ae/A.

The glyphosate should be applied as late as possible for maximum control of all targeted weeds, although it must be applied before the wheat emerges. The later the application the more likely the dandelion is sending photosynthates to the tap root and moving the glyphosate along with it and the greater emergence of winter annual species. This burndown application, if done late enough, may control most of the winter annual weeds threfore eliminating the need for an herbicide application next spring to control winter annual weeds.

The only other way to control winter annual grasses in wheat in Ohio is to apply Maverick at 0.67 oz/A when grasses are in the 2-3 leaf stage. Maverick will only control the brome species and some winter annual broadleaf species. Double-crop soybeans cannot be planted next season unless an STS variety is planted.

Resistant Weed Demonstrations at Farm Science Review

Examples of marestail with multiple resistance to ALS and glyphosate herbicides will be one of the highlights in the Agronomics Crops Team tent at Farm Science Review, Sept. 21-23. The Agronomic Crops Team display tent is located on Friday Avenue, across from the Bailey and Firebaugh Buildings.