CORN
Crop Observation and Recommendation Network

For Week of April 13-19, 1998
C.O.R.N. 98-5

In This Issue:

A) Wheat Growth and Disease Update
B) Some Reminders on No-Till Burn Down
C) Black Cutworm and Common Armyworm Moth Collections
D) European Corn Borer and BT Corn
E) Early Planted Soybeans and Bean Leaf Beetle
F) Warrior Receives Label for Alfalfa

A) Wheat Growth and Disease Update - Pat Lipps CORN Questions

Warm daytime temperatures over the past week have pushed wheat growth forward, but cold nighttime temperatures have helped wheat plants maintain tolerance to freezing injury. Wheat growth stages in Ohio range from beginning flag leaf emergence (growth stage 8) in the more advanced fields in the southern part of the state to fields in just beginning to develop the first node (growth stage 5 to 6). Very cold temperatures (low 20s) could damage wheat any time after growth stage 6.

The yield potential for this years wheat crop is excellent because the mild winter provided the right conditions for winter survival and maximum tiller production. Some growers are interested in applying additional nitrogen to take advantage of the high yield potential of the crop. High tiller numbers and high nitrogen rates may lead to increased lodging. Before applying high rates of nitrogen check the standability of the variety to make sure it is one that is not prone to lodging. Secondly, check fertility records to see that adequate levels of P and K have been applied. Balanced fertility is necessary for strong stem development. Lastly, if an additional application is to be made, do it sooner than later. Applications made near growth stage 6 have a better chance of increasing yield than applications made later near boot stage of development.

Overall disease level in Ohio is still quite low. Cold night temperatures have probably limited the development of powdery mildew and Septoria throughout the state. We have reports of Septoria leaf blotch on a susceptible variety in southern part of the state, but this may be a localized problem. We have also observed powdery mildew on a susceptible variety in west central part of the state. In both cases the development of the disease has not progressed to the level where a fungicide application should be made. Fields should be scouted again just prior to flag leaf emergence to determine if the upper leaves are in danger of infection. It is important to note that the disease is present in the field so the field can be scouted at a later date.

B) Some Reminders on No-Till Burn Down - Mark Loux CORN Questions

The warm weather we have experienced over the past months has resulted in fairly rapid weed emergence and growth, compared to most years. We have already observed emergence of a number of summer annual weeds such as foxtail and lambsquarters, which normally are not evident this early. Expect the early emergers (giant ragweed, smartweed, atriplex) to be larger than normal when planning no-till BURN DOWN programs. It is always advisable to scout fields when planning a BURN DOWN program, but scouting is more critical this year than most, due to the advanced emergence and growth of weeds.

Emerged foxtail may cause a revision in BURN DOWN herbicide selection, but this may not be necessary if foxtail is very small. While broadleaf weeds are usually targeted this time of year by adding 2,4-D ester to preplant herbicides, some of the preplant herbicides will also kill small grass. In corn, atrazine and Bladex will often control grasses up to 1 1/2 inches tall, and Extrazine will kill larger grasses. Application with crop oil concentrate and/or 28% is recommended for best activity. Preplant soybeans herbicides containing metribuzin (Turbo, Sencor/Lexone, Canopy) or Pursuit (Pursuit Plus, Steel) will control small grasses. Axiom and Canopy contain low rates of metribuzin; Canopy is labeled for control of grasses up to 1 inch tall only - mixing with additional metribuzin will improve BURN DOWN of small grasses. Canopy XL/Authority Broadleaf is also labeled for control of grass up to 1 inch tall. Application of soybean herbicides with crop oil concentrate will generally ensure best activity on emerged weeds.

If herbicide application continues to be delayed by windy and wet weather, be sure to revise BURN DOWN programs accordingly. It may be necessary to add Roundup, Touchdown, or Gramoxone to control larger weeds, especially grasses. Low rates of these products are sufficient to control small annual grasses, but large annual broadleaf weeds or perennial weeds will require higher rates. Some other points on BURN DOWN applications:

- Activity of Gramoxone, a contact herbicide, will be improved when it is mixed with other contact herbicides, such as atrazine, Bladex, Extrazine, Sencor/Lexone, Turbo, Canopy, and Canopy XL/Authority Broadleaf. A tank-mix of Canopy or Canopy XL/Authority Broadleaf with Gramoxone is probably one of the better dandelion treatments when application is too close to planting to use 2,4-D.

- Roundup and Touchdown activity will be most consistent when applied alone, or with 2,4-D only, rather than tank-mixing with other preplant herbicides. Contact herbicides such as those mentioned above have some potential to reduce Roundup/Touchdown activity. This type of antagonism will be more likely when annual weeds are more than 4 to 6 inches tall or when perennials are present. Using 28% as the spray carrier can also reduce activity, but should not be a problem early in the season if small annual weeds are the target. Hard water reduces Roundup/Touchdown activity, but the addition of ammonium sulfate (8 1/2 to 17 lbs/100 gallons) will overcome this problem.

- The activity of Roundup/Touchdown is generally maximized through use of spray volumes of 10 gpa or less. Low spray volumes may not be the best option when tank mixing with other preplant herbicides (such as atrazine premixes), or when spray drift is a concern. Gramoxone will be most effective in spray volumes higher than 10 gpa. The Gramoxone label recommends increased spray volumes as weeds become larger and more numerous.

- If possible, try to avoid application under cold conditions, and especially when nightime temperatures approach freezing. Best control with most BURN DOWN herbicides will occur under warm, sunny conditions.

- Where a no-till drill is used to plant soybeans, try to apply the BURN DOWN herbicide at least one day before planting. The soil disturbance from a drill has the potential to disrupt weeds and reduce the effectiveness of herbicides applied immediately after planting.

Axiom received Federal Registration

Axiom (Baker) has received a federal label. This product is a premix of a low rate of metribuzin with a new chloroacetamide herbicide, thiafluamide. Spectrum of control is similar to other chloroacetamides (annual grasses, yellow nutsedge, nightshade, pigweeds), and the addition of metribuzin improves control of lambsquarters, common ragweed, pigweeds, and also slightly improves foxtail control. Axiom is formulated as a dry flowable, and use rates (active ingredient basis) are significantly lower than other chloroacetamide products.

C) Black Cutworm and Common Armyworm Moth Collections - Jim Jasinski CORN Questions

Black cutworm (BCW) and Common armyworm (CAW) pheromone traps were placed in Miami county locations on or about 3/30/98. Results last week were as listed below.

Miami county site #1 - Pheromone trap - BCW 7 moths / trap / week
Miami county site #1 - Pheromone trap - CAW 0 moths / trap / week
Miami county site #2 - Pheromone trap - BCW 7 moths / trap / week
Miami county site #2 - Pheromone trap - CAW 1 moth / trap / week

Not a lot of flight activity yet at either location, but the moths are present. Keep an eye on no-till fields with a healthy population of winter annuals, particularly chickweed. Additionally, recent comments in the Kentucky Pest Newsletter indicate sustained flight activity of these moths in the state.

D) European Corn Borer and BT Corn - Curtis Young CORN Questions

E) Early Planted Soybeans and Bean Leaf Beetle - Curtis Young CORN Questions

Early planted soybeans could be threatened by Bean Leaf Beetles (BLB)(Cerotoma trifurcata (Forster)). BLB is a chrysomelid leaf beetle that varies in color from golden brown to green to red, generally has 4 black spots on the wing covers, and always has a black triangle on the area centrally behind the thorax. BLB overwinters as an adult insect in protected habitats near production fields. These habitats include woodlots, clumps of grass in field margins and in leaf litter under trees. Because Ohio's winter was exceptionally mild this year, BLB winter survivorship should be high. Overwintered adults will become active during April, with many of them moving into alfalfa fields where they will feed, mate and lay some eggs. These BLB will switch over to soybeans as soon as they are available. Thus, the earliest planted, first emerged soybean fields will draw large numbers of BLB into them from the surrounding habitats. Those fields closest to alfalfa fields and woodlots have the greatest potential for being severely attacked by BLB this spring. The first emerged soybean fields should be monitored frequently to detect intense BLB activity before serious injury occurs. Early season soybean scouting is done by direct observation of numbers of adult BLB per plant and estimations of defoliation. Five to eight locations in each field should be assessed for making management decisions. Sampling should be done away from field edges. A rescue treatment to prevent severe defoliation and/or stand loss is justified when damage to emerging soybeans is resulting in stand loss or when defoliation of 50 to 60 percent occurs and numerous BLB are observed on each plant examined. An early season threshold of 6.5 BLB per plant (for soybean market value of $6/bu and control cost of $6/A) for plants in the V2 stage of development has been established in other soybean producing states. The risk of serious injury to the first emerged soybean fields declines as additional fields of soybean emerge and the overwintering BLB disperse to neighboring fields. Overwintered BLB will be present in fields from time of soybean emergence to mid-May.

The following insecticides are recommended for rescue treatments of BLB: Ambush, Asana XL, Dimethoate, Lannate, Larvin 3.2, Lorsban 4E, Orthene, Penncap-M, Pounce, Sevin and Warrior 1E.

Bean Leaf Beetle Adult on Soybean Leaf

F) Warrior Receives Label for Alfalfa - Bruce Eisley CORN Questions

We have been informed by personnel from Zeneca Ag Products that Warrior has received label for use on Alfalfa. Warrior is labeled on all of the common pests on alfalfa including alfalfa weevil and potato leafhopper. The rate for use on alfalfa weevil is 2.56 to 3.84 fluid ounces per acre. The rate for leafhopper is 1.92 to 3.20 fluid ounces per acre. The waiting time for Warrior on alfalfa is 1 day for forage and 7 days for hay.

A new formulation of Warrior has recently received label. This new Warrior is a 1CS formulation and will be marketed under the name Warrior T. The signal word on the new formulation is Caution.

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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.

Contributors to C.O.R.N. this week include: Pat Lipps (Extension Specialist, Plant Pathology), Ann Dorrance (Extension Specialist, Plant Pathology), Mark Loux (Extension Specialist, Weed Science), Curtis Young, Jim Jasinski and Bruce Eisley (Extension Associates, Integrated Pest Management), Larry Lotz (Fayette Co.), Barry Ward (Marion Co.), Ray Wells (Ross Co.), Roger Bender (Shelby Co.), Gary Wilson (Hancock Co.), Steve Bartels (Butler Co.), Howard Siegrist (Licking Co.), Clark Hutson (Seneca Co.), Tom Krill (Van Wert Co.), Mike Estadt (Pickaway Co.) and Steve Prochaska (Crawford Co.).

Information presented above and where tradenames are used, they are supplied with the understanding that nodiscrimination is intended and no endorsement by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.

All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.

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