CORN
Crop Observation and Recommendation Network

Mid-March, 2001
C.O.R.N. 2001-5

In This Issue:

A) Weed Control In Wheat
B) Weed Control In Alfalfa
C) Status Of First Year Corn Rootworm In Ohio
D) Dr. Jay Johnson Retires

A) Weed Control In Wheat - Mark Loux CORN Questions

Wheat as a rule is very competitive with weeds and some wheat fields do not require herbicide treatment. However, other fields can benefit greatly from herbicide application. Failure to scout fields and take the appropriate measure can result in yield loss and harvesting problems. The weeds that appear above the wheat canopy late in the season, such as ragweeds and Canada thistle, can often be easily controlled with a spring herbicide treatment.

The most common weeds observed in wheat fields at this time of year are winter annuals, such as chickweed, purple deadnettle, field pennycress, shepherspurse, and marestail. These weeds can interfere with the early spring development of wheat, and should be controlled as soon as possible to avoid interference with wheat growth. Winter annuals are more easily controlled when small and still in the rosette stage, before the stem has bolted. 2,4-D will control most mustard species and marestail adequately, and can be mixed with dicamba to broaden the spectrum of control somewhat. Harmony Extra will generally be a more effective choice for control of deadnettle and chickweed.

Many wheat herbicides have some activity on Canada thistle and can suppress it enough to prevent harvest problems. Effectiveness often depends upon the size of the thistle at the time of application - regrowth is more likely when thistles are very small at time of application. Best products for thistle control are Stinger, Curtail, and Express. Best products for wild garlic are Harmony Extra, Harmony GT, and Peak.

When wheat has not yet reached the jointing stage, any herbicide labeled can be safely applied. As wheat growth stage advances past jointing and then past boot stage, herbicide choices become much more limited. Most herbicides can be applied in nitrogen fertilizer solution when the wheat is top-dressed. This may increase injury somewhat, and some labels recommend adjusting surfactant rates to minimize injury. Where nitrogen is split-applied, risk of herbicide injury may be reduced if applied in a mix of nitrogen solution and water. Some key herbicide limitations are listed below - these are also shown in a figure on page 100 of the 2001 OSU Weed Control Guide and in the text on pages 93-99 or http://ohioline.ag.ohio-state.edu/b789/index.html.

2,4-D: all 2,4-D products are labeled for application before jointing. A few are labeled up to early boot stage. 2,4-D is generally safe up to early boot, but the risk of injury increases after jointing. To minimize the risk of injury after jointing, use water as the carrier and do not apply more than 1/2 pint of ester or 1 pint of amine. 2,4-D will not control chickweed or henbit, and can be weak on smartweed and deadnettle. MCPA products have characteristics and labeling similar to 2,4-D products.

Banvel: Apply before jointing. Not as effective as 2,4-D on mustard species, but more effective on smartweed. Weak on chickweed, deadnettle, henbit, and wild garlic. Can be tank mixed with 2,4-D.

Buctril/Moxy: Apply before the boot stage. Applying in fertilizer solution increases leaf burn. Weak on most winter annuals, dandelion, and wild garlic. For best results apply before weeds reach the 4-leaf stage or a height of 2 inches.

Curtail: premix of 2,4-D plus Stinger. Apply until jointing. Excellent control of ragweeds and Canada thistle. Weak on chickweed, henbit, and wild garlic. Do not plant double crop soybeans in fields treated with Curtail.

Harmony Extra: Apply before flag leaf is visible and when weeds are less than 4 inches tall or across (rosette). Apply with nonionic surfactant. Effective for wild garlic and most winter annuals. Weak on ragweeds.

Harmony GT: Similar to Harmony Extra, but less effective on Canada thistle, chickweed, and a few other winter annuals.

Express: Apply before the flag leaf is visible when weeds are less than 4 inches tall or across (rosette). Not as broad spectrum as Harmony Extra, but more effective on Canada thistle. Apply with nonionic surfactant.

Peak: Apply before 2nd node is detectable in wheat stem elongation, and when weeds are 1 to 3 inches tall. Do not plant double crop soybeans in fields treated with Peak. Apply with crop oil concentrate or nonionic surfactant.

Stinger: Best suited for spot treatment due to high cost. Effective for Canada thistle and ragweeds, primarily. Apply up to early boot.

B) Weed Control In Alfalfa - Mark Loux CORN Questions

Like wheat, alfalfa and other forages compete well with weeds, and proper establishment and management go a long way toward keeping weeds under control. Some general reminders on weed management in forages (from the Penn State Weed Control Guide):

Establishment and seedling year:

- weeds that emerge with the crop are generally most destructive
- maintain the forage relatively weed-free for the first 60 days
- weeds that emerge beyond the first 60 days will not influence that year's forage yield
- later-emerging weeds may still influence forage quality
- winter annual weed competition in early spring is most damaging to forages
- broadleaf weeds are generally more competitive against legumes than grassy weeds

Established stands - factors that should influence decision to use a herbicide:

- thin or irregular stands do not thicken once weeds are removed. Be sure there are sufficient desirable species to fill in the gaps. A minimum of five alfalfa plants per square foot should be present (another way to look at this is that yield will not be limited by stand if there are at
least 55 stems per square foot - stands with 40 to 55 stems can still be productive). Weeds tolerant of the herbicide may invade the space left by more susceptible species, ultimately creating a more severe weed problem.
- treat only well-established, vigorous stands with herbicides.
- if the forage stand is at least 2 years old and 25 to 30% of the plants are weeds, removing them with an herbicide is of questionable value.
- if 50% or more of the plants are weeds, it is time to rotate to a different crop.

At this point in time, winter annuals are the predominant weeds in many forage fields. Examples are chickweed, deadnettle, pennycress, etc., which will increase in size as temperatures increase. New forage growth has occurred in many fields also, which limits herbicide choices for winter annual control. Do not apply Gramoxone, Sencor, or Sinbar to fields where new growth has started. Velpar can be applied to established stands with no more than 2 inches of new growth (take note of the long recrop restrictions before using Velpar). Pursuit and Butyrac are probably the best options for winter annual control in fields where new forage growth has occurred.

Butyrac is weak on chickweed and henbit, but is effective on small weeds in the mustard family (pennycress, shepherds purse, mustards). Weeds should be no more than 2 to 3 inches tall, and rosettes should be no more than 2 inches in diameter for best results. Butyrac can be used on established or new stands of alfalfa, clover, and birdsfoot trefoil. Do not use on sweet clover. Butyrac should not injure grasses in the stand, but is not labeled for mixed grass/legume stands except in set-aside land.

Pursuit should be applied when alfalfa is in at least the 2nd trifoliate stage, but before alfalfa growth exceeds 3 inches to allow for adequate spray coverage on weeds. Apply when weeds are 1 to 3 inches tall, or before rosettes exceed 3 inches in diameter. Pursuit is effective on most small winter annual weeds. Pursuit may cause injury to small forage grasses - we do not have data on grass tolerance.

Buctril is less effective for winter annuals than Butyrac and Pursuit, but can be effective on mustards if small (rosettes less than 1 inch in diameter). Alfalfa should have at least 4 trifoliates. Buctril can cause crop leaf burn. Do not apply when temperatures will exceed 70 degrees on the day of and for three days following application.

Select and Poast/Poast Plus can be applied later in the spring when annual grasses are several inches tall. Both herbicides are effective on most annual grasses, but Select is more effective on quackgrass and other perennial grasses.

Unfortunately, while Sencor and Velpar have activity on dandelion and curly dock, none of the herbicides that can be used on actively growing alfalfa control these weeds. Where these weeds are a problem, winter application of Sencor or Velpar when alfalfa is dormant is by far the best option. It is too late in most fields to apply these herbicides, but plan on their use next winter. Canada thistle is another weed that cannot be controlled with alfalfa herbicides. Control is limited to spot application of glyphosate, or just timely cuttings.

C) ) Status Of First Year Corn Rootworm In Ohio - Dr. Hal Willson (Extension Entomology, in 2001 Regional Agronomy Meeting Proceedings) CORN Questions

At one time, rootworm injury to corn was primarily regarded as a continuous corn problem since egg laying of either the northern corn rootworm or the western was usually limited to corn fields from which the eggs hatched the following season and the larvae fed on root systems of the continuous corn. In the 80s, the extended diapause behavior causing injury to 1st year corn by northern corn rootworm populations became recognized. In the 90s, the development of a new biotype of western corn rootworm resulted in egg laying in soybeans and injury to 1st year corn.

During the past decade, the presence of first year corn injury in Ohio by both northern corn rootworm and western corn rootworm has been established. To facilitate risk prediction of first year corn rootworm problems, a cooperative effort to monitor adult rootworm activity in Ohio soybeans has been implemented by OSU Extension, independent consultants and agri-business personnel during the past three years.

Monitoring data for 2000 represents collections of adult western corn rootworm (WCR) beetles on Pherocon AM yellow sticky traps in soybean fields adjacent to first year corn fields. The data represent the average number of WCR collected from four traps serviced on a biweekly schedule from mid-August to late September. An average catch of one to two WCR per trap per day would be regarded as relatively high catch in Ohio. County WCR collection averages approaching 0.5 indicate a potential for first year corn rootworm (FYCRW) problems at some sites within the area monitored. County WCR collection averages around 0.2 indicate a presence of FYCRW, but most of the sites monitored in 2000 are expected to have minimal risk of a FYCRW problem.

In general, regions of FYCRW activity in Ohio are averaging 0.2 WCR per trap per day. In counties bordering Indiana, average WCR activity in soybeans has declined over the past three years. WCR activity in counties in the 2nd tier from the Indiana has been moderate with the exception of Putnam County. WCR activity in the 3rd tier of counties has increased and indicates a dispersal of FYCRW activity. In central Ohio counties, WCR activity in soybeans remains very low indicating an absence of FYCRW activity.

Complete insect catch data from the 1998, 1999 and 2000 trapping seasons can be found at http://www.ag.ohio-state.edu/~corn/library/articles/fycrw.html

D) Dr. Jay Johnson Retires - Dr. Don Eckert CORN Questions

Jay W. Johnson, Extension State Specialist in Soil Fertility, and Professor in the School of Natural Resources retired from OSU on January 31, 2001. He is currently enjoying his retirement on the Johnsons' new property outside London, Ohio.

"Jay grew up in Henderson, Tennessee, and became Volunteer at the University of Tennessee, graduating with a Master's degree in 1969. He later left his home state and received his Ph.D. in soil fertility at the University of Illinois in 1972. After spending two more years at Illinois he joined OSU as an Assistant Professor in 1974, with responsibilities for teaching a course in radioisotope methodology and conducting research in nitrogen management in crop production. Within a few years, however, Jay had his appointment changed to from resident instruction to extension, and continued with an extension/research split until his retirement earlier this year.

"Jay is known throughout North America for his work in practical fertility management for agronomic crops. His recognition of the importance of denitrification as a major mechanism for N loss focused attention on the need for extremely diligent management of this nutrient on poorly-drained soils, and led to development of many of the N-management strategies that are commonplace today. He was also responsible for much of the work that led to recognition that potassium was a critical nutrient for soybean production in Ohio and across the midwest. In addition, Jay was one of the pioneers in computer usage in the College, developing microcomputer-based fertilizer recommendation approaches, and creating a program to refine and customize manure applications.

"Jay was a major influence on Ohio agriculture in the 80s and 90s. His contributions were many and he will be missed. We all wish him the best in his retirement."

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Past versions of C.O.R.N. can be found on the World Wide Web at: http:/www.ag.ohio-state.edu/~corn/archive/

C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.

Editor: Greg LaBarge        Web Editor: Tom Rosati

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