C.O.R.N. Newsletter 2006-38

Postemergence Application of Wheat Herbicides in Late Fall

Authors: Mark Loux

A number of wheat herbicides can be applied in the fall to emerged wheat. There is some potential for wheat injury from fall-applied herbicides, and many herbicide labels specify a minimum growth stage for wheat to reduce the risk of injury. Considerations for fall treatments in wheat include the following:

- herbicides labeled for application in fall to control broadleaf weeds in emerged wheat, with minimum growth stage at the time of application indicated, include: Aim and bromoxynil (Buctril, Moxy etc) – minimum wheat stage not specified on label; Harmony Extra – 2-leaf stage; dicamba and peak – after wheat emergence; metribuzin – 2-leaf stage; Weedmaster/Brash/etc (premixes of dicamba + 2,4-D) – after wheat tillers.

- although several 2,4-D-containing products are labeled for application in the fall, use of 2,4-D in the fall can cause crop injury and yield loss, and should generally be avoided if possible. Labels for these products specify that crop injury can occur and that the user assumes all risk when applied in the fall.

- be cautious about application of any herbicide too late in the fall under cold conditions. Wheat may be more susceptible to injury at that time, due to its relatively slow growth and inability to metabolize (detoxify) herbicide. Herbicide labels have some general statements about not applying to wheat under stress due to weather conditions. A general rule to follow on this might be that there should be 24 to 48 hours of good growing conditions after application, which means daytime temperatures in the 40’s and some sun. Fall is generally a good time to control winter annual weeds, but it might be wise to wait until spring if there is a risk of injury from a late-fall application.

- of the products listed above for broadleaf weed control, Harmony Extra and Peak have the most utility for control of the typical spectrum of winter weeds found in wheat fields at this time of year. When applied alone, the rates of dicamba and metribuzin that can be used on emerged wheat are not effective enough, and Aim and bromoxynil provide more limited control of winter annual weeds. Harmony Extra can be more effective than Peak on several key winter annual weeds, such as chickweed and deadnettle, and allows for more flexibility in crop rotation following wheat.

- The Harmony Extra label specifies a rate range of 0.3 to 0.6 oz/A, but indicates that rates of 0.4 oz/A or less should be used for “light infestations” of weeds. A rate of 0.5 oz/A is suggested in denser infestations. The label allows two applications per crop season, as long as the total applied does not exceed 1.0 oz/A. While we have not conducted research with this program, we know of some growers who apply 0.3 oz/A of Harmony Extra in the fall and follow with another application at a similar rate in the spring. Their experience is that the low rate applied in the fall does not generally control all of the weeds present, so that the spring application is usually necessary. Our research indicates that purple deadnettle would be one of the weeds likely to survive fall application at low rates. Where low rates of Harmony Extra are used, mixing it with low rates of dicamba, metribuzin, or bromoxynil could improve weed control. Otherwise, we suggest using a Harmony Extra rate of 0.5 oz/A where another application in spring is not planned.

- herbicides labeled for application in fall to control grass weeds in wheat, include: Axial - annual ryegrass; Maverick and Olympus - downy brome and cheat; Osprey – annual bluegrass and annual ryegrass. These herbicides can be applied anytime after wheat emergence except for Axial, which can be applied to wheat that is in at least the 2-leaf stage. Several of these herbicides have enough soil residual that double-crop soybeans cannot be planted next summer, or that STS soybeans must be planted. See labels for more information.
 

Many Opportunities to Learn the Latest at Winter Meetings

A whole host of winter meetings are scheduled and will provide an opportunity to hear the latest agronomic information from our Ohio State University Extension Specialist, Extension Educators and other industry experts. The complete listing can be found at https://agcrops.osu.edu/calendar. This link provides a flyer for each program with complete information including CCA and Pesticide Applicator Credits offered as well as registration cost and deadlines. Links on the calendar page also will lead you to dates for Private and Commercial Pesticide Applicator Programs being offered.

Upcoming Meetings in December include:

December 5th at 9:00 am, Ohio No-till Council Annual Meeting, Der Dutchman Restaurant in Plain City. Registration due 11/29 with a cost of $25. Contact mailto:reeder.1@osu.edu or 614-292-6648.

December 8th at 9:30 am, NE Ohio Regional Agronomy Day, Fischer Auditorium in Wooster. Contact mailto:kdiedrick@ag.osu.edu or 330-264-8722.

December 12th at 9:00 am, North Central Agronomy Program, American Legion Hall in Plymouth. Registration due before 12/8 with a cost of $25 or $30 at the door. Contact mailto:prochaska.1@osu.edu or 419-562-8731.

December 13th at 7:30 am, Ohio Corn/Soy Associations Annual Meeting, All Occasions Catering in Waldo. Cost is $25. Registration information coming soon. Call Ohio Soybean Association at 888-SOYOHIO or Ohio Corn Growers at 740-382-0483.

December 19th at 8:30 am, Central Ohio Agronomy Day, OSU Newark in Newark. Cost is $20 to $50 depending on credits needed. Contact mailto:siegrist.1@osu.edu or 740-670-5315.

This website will continue to be updated with details for all programs as they become available.

Stalk vs. Root Lodging in Corn

Authors: Peter Thomison

As of November 5, corn for grain harvested was at 47 percent, compared to 70 and 69 percent for last year and the five-year average, respectively. The later than normal corn harvest has contributed to some significant lodging problems across the state. When using the term ‘lodging’, it’s important to know what’s being referred to, especially with regard to hybrid selection decisions.

University and seed company agronomists characterize plants with stalks broken below the ear as ‘stalk lodged’ plants (broken stalks above the ear are not a consideration). In the Ohio Corn Performance Test (and in other state corn tests and seed company trials), the number of broken stalks in each test plot is determined just prior to harvest and only those plants with a stalk broken below the ear are considered stalk lodged. Stalk lodging is recorded at harvest because it’s usually not evident prior to maturity. Stalk lodging is reported as a percentage of final plant stand. Stalk lodging in some of our research plots this year has exceeded 50%. Affected corn includes late planted non-Bt corn exhibiting moderate 2nd generation European corn borer injury.

In contrast to stalk lodging, agronomists describe corn stalks leaning 30 degrees or more from the center, as ‘root lodged’ plants; stalk breakage below the ear is not involved. Root lodging can occur as early as the late vegetative stages and as late as harvest maturity. Both stalk and root lodging can be affected by hybrid susceptibility, environmental stress (drought), insect and disease injury. Root lodging is frequently attributed to corn rootworm injury. However, much root lodging in Ohio occurs as the result of other factors, i.e. when a hybrid susceptible to root lodging is hit by a severe windstorm. Recent tornado activity near Columbus flattened some corn fields.

A hybrid may be particularly sensitive to root lodging yet very resistant to stalk lodging. A corn field may exhibit extensive root lodging in July but show little or no evidence of root lodging at harvest maturity in September (except for a slight “goose necking” at the base of the plant). As a result, while stalk lodging data is regularly included in corn hybrid test results, root lodging is reported less often. This year may be an exception. I’m seeing and hearing about a number of fields where much of the corn is nearly flat on the ground. While stalk lodging may be significant in some of these situations, it’s going to be difficult to separate the root and stalk lodging because of the severe root lodging.