http://www.ag.ohio-state.edu/~corn/

CORN
Crop Observation and Recommendation Network

April 22-29, 2002
C.O.R.N. 2002-10

In This Issue:

A) Time To Check For Alfalfa Weevil
B) Seedcorn Maggot In Field Crops
C) Rapid Wheat Growth Over Past Week
D) Applying Wheat Herbicides In Nitrogen Fertilizer Solution
E) Some Observations On Early Weed Growth

A)Time To Check For Alfalfa Weevil - Bruce Eisley and Ron Hammond CORN Questions

Close inspection of 6 inch alfalfa last Wednesday at the Western Branch, OARDC, found an average of at least 2 larvae per stem. Some of the stems had 6 to 8 larvae per stem. The larvae were small, approx. an 1/8 of an inch long, an damage was slight. By the end of the week, larvae had almost doubled in size and additional damage had been done to the alfalfa. The cool weather we are experiencing at this time will slow the weevil down but damage will continue. Damage seems to be worse in southern Ohio with lesser damage in northern Ohio at this time.

Alfalfa weevil scouting is accomplished by collecting a series of three 10-stem samples randomly selected from various locations in a field. Place the stem tip down in a bucket. After 10 stems have been collected, the stems should be vigorously shaken in the bucket and the number of larvae in the bucket counted. The shaking will dislodge the late 3rd and 4th instar larvae which cause most of the foliar injury. Close inspection of the stem tips may be needed to detect the early 1st and 2nd instar larvae. The height of the alfalfa should also be recorded at this time. Economic threshold is based on the number of larvae per stem, the size of the larvae and the height of the alfalfa. The detection of one or more large larvae per stem on alfalfa that is 12 inches or less in height indicates a need for rescue treatment.
Where alfalfa is between 12 and 16 inches in height, the action threshold
should be increased to 2 to 4
larvae per stem depending on the vigor of alfalfa growth.

Action thresholds relevant to stand height, tip feeding, and density of larvae per stem. ____________________________________________________________________
Stand Ht Recommended
Inches Tip Feeding Larvae per Stem Action
----------------------------------------------------------------------------
6 25 1 Recheck in 7 days
9 50 > 1 Spray
12 75 > 2 Spray or harvest
16 100 > 4 Harvest early
_____________________________________________________________________

Chemicals currently labeled for use on alfalfa for alfalfa weevil include:

Ambush* @ 6.4 to 12.8 fl oz/A
Baythroid* 2 @ 1.6 to 2.8 fl oz/A
Furadan* 4F @ ½ to 1 pint/A
Guthion* Solupak 50WP @ ¾ to 1 lb/A
Imidan 70-W @ 1 to 1.33 lb/A
Lannate* LV @ 3 pint/A
Lannate* SP @ 1 lb/A
Lorsban* 4E @ 1 to 2 pint/A
Malathion @ (check label for rate)
Mustang* @ 2.4 to 4.3 fl oz/A
Pounce* 3.2EC @ 4 to 8 fl oz/A
Sevin 80S @ 1-7/8 lb/A
Warrior* 1CS @ 2.56 to 3.84 fl oz/A

* Use is restricted to certified applicators.

See the OSU Alfalfa Weevil FactSheet
(http://ohioline.osu.edu/ent-fact/0032.html) for more on alfalfa weevil scouting and thresholds.

B) Seedcorn Maggot In Field Crops - Ron Hammond and Bruce Eisley CORN Questions

Seedcorn maggots are larvae of small flies, and are capable of causing significant stand reductions in both corn and soybeans under the appropriate conditions. Research over the past 20 years has shown that seedcorn maggot populations are greatly enhanced when a green, living cover crop is plowed or otherwise tilled into the soil. These covers might be old alfalfa stands, stands of wheat or rye, or even an extremely heavy growth of weeds. There is a possibility that a heavily manured field that is tilled might also result in the problem. Stand losses might occur under these conditions. Although seedcorn maggots are often found feeding on seeds in no-till situations, economic problems are rarely seen. In our research, we have not seen increases in maggot populations when no-tilling. In fields where a green cover is tilled into the soil in the spring, growers should consider an insecticide seed treatment. If the seed is not already treated when purchased, growers should check with their dealers for available seed treatments.

C) Rapid Wheat Growth Over Past Week - Pat Lipps CORN Questions

Temperatures in the upper 70s and 80s and plenty of moisture has promoted very rapid development of the wheat crop. Wheat south of Interstate 70 will be entering the flag leaf emergence growth stage (Feekes growth stage 8) soon, if not already at this growth stage. At Wooster, plants are in stem elongation growth stages (Feekes growth stage 6 to 7) and in northwest Ohio most fields are entering the stem elongation growth stages. The stem elongation growth stage marks the time when no new tillers will develop on these plants. This is important to note because the total number of head bearing tillers produced for this year will have been made by this time. Since a major component of yield is the number of heads produced in a field, the only factors yet to be determined are the number of seed per head and seed size. Adequate nutrition and good weather during heading will influence pollination and the number of seed per head and cool weather during grain fill affects seed size. Cooler weather predicted for the next week will slow growth of wheat somewhat, but this slower growth will have little impact on the crop because the wheat is a bit ahead of schedule anyway. Most growers have been able to get their spring nitrogen top dress on, but in some areas of the state it has been too wet to enter fields. It is not too late for nitrogen application! It is better to get it on a little late than not at all.

We are seeing some wheat diseases appear in the state. We have a few reports of wheat soil borne mosaic in some fields. Plants affected by this virus remain stunted and yellow in comparison to the healthy wheat surrounding the affected areas. Additionally the affected wheat tends to be in areas of the field with poorer drainage. Severely affected plants appear not to grow and remain in the "rosette" over winter stage. Nothing can be done at this time to alleviate the problem. Warm weather will reduce the virus replication in the plants, which will help plants recover somewhat. Varieties vary in their susceptibility to this virus disease so if you have problems with wheat soil borne mosaic, select resistant varieties when this field is planted back to wheat in some future year. There are reports of other virus diseases in the state (Barley Yellow Dwarf and Wheat Spindle Streak Mosaic), but so far reports have been few. Evidence of these diseases will be easier to see as the plants produce flag leaves.

As fields enter the flag leaf emergence growth stage (when you can count four leaves on the stem above the first node) wheat producers should scout fields for diseases. We have already detected powdery mildew and Stagonospora leaf blotch on the lower-most leaves in some fields. In particular, visit fields planted to varieties known to be susceptible to these varieties. The list of varieties that are planted in the state is too long to list here. Information on varietal resistance and pictures of what the diseases look like can be found on the Ohio Field Crop Disease web site at where we maintain disease management recommendations.

D) Applying Wheat Herbicides In Nitrogen Fertilizer Solution - Mark Loux CORN Questions

As wet weather continues and wheat advances in growth stage, herbicide options will become more limited. Many wheat fields appear to be infested with weeds to the point that herbicide is needed. Use of wheat herbicides relative to wheat stage was covered in recent C.O.R.N. articles. A question we did not address was the application of wheat herbicide using 28% as the carrier. Most labels allow use of 28% as the carrier. Some labels have specific recommendations regarding surfactant use or nozzle type when 28% is used as the carrier, but many provide almost no guidance other than to state that it is legal to do so. We have no data to really address this question, but our assumption is that it is safe to use 28% as the carrier if the herbicide choice is appropriate based on wheat growth stage. For example, many 2,4-D products are labeled for application before early boot, so we assume that applying the 2,4-D in 28% would be safe when the wheat is not yet in early boot stage. Some other relevant points:

Be aware that the wheat in southern Ohio may be advanced enough that many herbicides can no longer be used.
The growth stage of wheat within fields is more variable this year than is typically observed, so scout fields closely before making an herbicide decision.
The herbicide with the widest window of application, Buctril, can legally be applied using 28% as the carrier but this can result in unacceptable leaf burn.
When wheat is stressed from wet, cold conditions and not actively growing, it can be more susceptible to injury from Harmony Extra or Express applied in 28%.
The risk of injury may be reduced when using a mixture of water and 28% as the carrier rather than 28% alone.
See the figure on page 108 of the current OSU Weed Control Guide for more information.

E) Some Observations On Early Weed Growth -Mark Loux CORN Questions

Weeds are ahead of schedule this spring. A number of species that do not typically emerge until later in spring are already up and growing. Giant foxtail in the 3-leaf stage has been reported, and many early emergers are even larger. Be sure to adjust burndown treatments based on field scouting. While scouting, it is especially important to note the size of any emerged grasses. A number of preplant herbicide programs, including Canopy XL + 2,4-D or Sencor + 2,4-D, will control small (1-2 inch) grasses. Some other programs, including Python + 2,4-D or Scepter + 2,4-D, do not control emerged grasses. Be sure to add glyphosate or Gramoxone to these programs as necessary to control grasses or larger broadleaf weeds.

Readers can subscribe electronically to this newsletter by sending an e-mail message to: corn-out-on@postoffice.ag.ohio-state.edu. A successful subscription message will receive by an automatic reply from the listserv. Contact your local Ohio State University Extension Office or e-mail labarge.1@osu.edu if you have problems subscribing.

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.

Pat Lipps , Anne Dorrance , & Dennis
Mills (Plant Pathology), , Mark Loux & Jeff Stachler (Weed Science), Ron Hammond (Entomology) and Bruce Eisley (IPM), Ed Lentz (District Agronomy) Extension Agents and Associates: Woody Joslin (Shelby), Clark Hutson (Seneca), Greg La Barge (Fulton), Howard Siegrist (Licking), Glen Arnold (Putnam) Gary Wilson (Hancock), Mark Koenig (Sandusky, Alan Sundermeier (Henry), and Steve Prochaska (Crawford).

Editor: Steve Prochaska Web Editor: Tom Rosati

Information presented above and where trade names are used, they are supplied with the understanding that no discrimination 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.