ISSUE 5 June 11, 2009
CORN RATES LISTED IN WEED GUIDE
Question: I have a question regarding the rate listed for Lumax on page 29 in the 2009 North Dakota Weed Control Guide. In the guide it is said that the recommended rate is 2 to 3 pts per acre, while on the label they have 2 to 3 quarts per acre. Please clarify.
Answer: I have been getting this question from other folks. The heading at the top of the page (pg 29) shows the herbicides listed to be applied with glyphosate in RR corn. I intentionally show reduced herbicide rates of all herbicides listed on that page because: 1. full rates may not be needed since these herbicides are applied with glyphosate and 2. growers are unlikely to pay money for the full label rate.
For example, the use rate of Lumax used alone is 3 to 4 qt/A which is $33.33 to $50.00/A. Lumax at 3 pt/A is $25.00/A which will be added to glyphosate is and maybe at the top end of what a grower will pay.
If you are not planting RR corn and need full spectrum, season long weed control, then use 3 to 4 qt/A.
HIGH SURFACTANT OIL CONCENTRATE ADJUVANTS
Question: Destiny HC from Winfield Solutions is listed as both an MSO and HSOC on page 132 in the 2009 ND Weed Control Guide. Does this product fit into both classes or is this a mistake? Please clarify as it is creating confusion in the market place regarding adjuvant system with glyphosate + Laudis.
Answer: Destiny is no longer produced and is replaced by Destiny HC and used at half the normal COC rate. Under the HSOC section I list those products whose manufacturer claim them to be HSOC. I do not know for sure if they all meet the ASTM definition of HSOC but I list them in that section anyway.
In parenthesis I list the oil source of each one. For Destiny HC I list (MSO) to differentiate it from the those that contain petroleum oil (PO).
The defintion of COC / PO adjuvants and HSOC according to the ASTM definition is as follows:
COC/PO = adjuvants are emulsifiable petroleum oil-based products containing 15 to 20% surfactant and the remainder of a phytobland oil.
HSOC adjuvants are oil based (PO or MSO) and contains 25 to 50% surfactant and a minimum of 50% oil (PO or MSO).
According to this definition Destiny HC is a HSOC not a COC/PO.
POTENTIAL FOR CROP INJURY FROM SOIL-APPLIED HERBICIDES IN COOL, WET SOILS
The cool and wet soil conditions throughout the region may increase risk of crop injury from
soil-applied residual herbicides. Crop plants can absorb herbicides at a rapid rate but are not able to metabolize or break down these herbicides at a similar pace. Some injury may also be attributable to the herbicide coming into direct contact with the seed as a result of wet soil conditions and/or failure to close the seed row.
Corn can exhibit injury symptoms at or soon after emergence as a result of preemergence herbicide applications. Herbicide injury as a result of cool and wet soil conditions is common with the soil-applied acetanilide grass herbicides like metolachlor and dimethanamid, including various atrazine pre-mixes with these herbicides. In rare cases, corn seedlings may fail to emerge from the soil and "leaf out" underground as a result of injury from these herbicides. Corn that has emerged and has been injured as a result of one of these herbicides will appear malformed and have twisted leaves that do not unroll properly. This is often referred to as "buggy-whipping". Fortunately, this injury is usually short-lived and rarely causes yield reductions. Most plants that have been injured as a result of these herbicides will grow out of this injury once soil drying occurs.
Flumetsulam is another herbicide that has the potential to cause injury to corn as a result of cool, wet soil conditions. Flumetsulam is the active ingredient in Python and one of the ingredients in Hornet. Corn that has been injured as a result of Python or Hornet applications may be slightly yellowish (chlorotic) in color and will have both stunted roots and shoots. The short lateral roots are a key symptom of flumetsulam injury, which is often referred to as "bottlebrushed roots". As with the soil-applied grass herbicides, injury from flumetsulam is usually short-lived and plants typically grow out of this injury once soil drying occurs.
Dinitroaniline herbicides such as pendimethalin (Prowl) can also cause injury to emerging corn plants if cool, wet soil conditions persist after planting. Injury from this herbicide is also common when corn seed has been planted too shallow and/or comes into direct contact with the herbicide solution. Perhaps one of the most characteristic symptoms of corn plants that have been injured as a result of pendimethalin is the inhibition of main, and to a greater extent, lateral, root formation. This typically results in short and thick, or "clubbed", lateral roots. Affected corn plants may also have leaves with a red or purplish color around the margins although certain corn hybrids, compaction, or carryover of imidazolinone herbicides may exhibit similar symptoms on young corn plants.
Isoxaflutole and mesotrione are some other preemergence herbicides that may cause injury to corn as a result of cool and wet soil conditions. Isoxaflutole is the active ingredient in Balance Pro and Balance Flexx. Mesotrione is the active ingredient in Callisto and is one of the ingredients in Lumax, Lexar, Camix, and Halex. Corn that has been injured as a result of these herbicide applications will have leaves with anywhere from a chlorotic to a completely bleached-white appearance. Injury will usually appear on the older leaves while new leaves often appear normal and unaffected. Although symptoms of these herbicides are perhaps more noticeable than any other type of herbicidal injury, this injury is usually short-lived and often confined to low areas or wet spots within a field. In severe cases where a high percentage of the foliage has a chlorotic or bleached-white appearance, the plants may eventually turn brown (necrotic) and die.
Extension Weed Specialist
NORTH DAKOTA WEED CONTROL GUIDE PAGE 134 AND MORE
Due to the desire to perform shallow tillage this spring to assist in drying the soil and rapid planting, weeds were not completely controlled with tillage prior to planting. These types of fields are similar to no-tillage without a preplant herbicide application. Therefore winter annual weeds have continued to grow and reproduce. Reproduction of winter annuals will add seeds to the seedbank and potentially increase winter annual weed populations as reduced tillage increases. The lack of deep tillage this spring has allowed continued growth of dandelions and more importantly increased seed production. This will certainly increase dandelion populations over time. Dandelions can be extremely competitive with all crops. Just a few established dandelions per square foot will quickly reduce crop yields if not controlled quickly. Summer annual weeds surviving shallow spring tillage are severely stressed and tend to be more difficult to control with herbicide applications. Adding the stress of the cold and wet conditions, summer annual weeds not killed by tillage or herbicides prior to planting will be difficult to control with all herbicides.
Those fields with surviving weeds after tillage should be sprayed earlier than normal so the surviving weeds do not get any larger and older. Applying a postemergence herbicide application early will likely require a second postemergence application. This is especially true for those herbicides having little or no residual activity. Applying postemergence herbicide(s) with residual activity when crops are small may control all subsequent weed flushes and reduce the need for a second postemergence application. However, residual herbicide activity will only occur if enough rainfall is received shortly after application. Consult the 2009 North Dakota Weed Control Guide for herbicides providing residual activity.
The maximum single application rate of all herbicides should be applied to fields having weeds that survived tillage, especially if dandelions are present. Consult page 134 of the 2009 North Dakota Weed Control Guide for postemergence control options for dandelion. For herbicides applied to conventional crops be aware of the risk of crop injury when using maximum herbicide rates, especially in tank-mixtures. Include adjuvants that will maximize herbicide activity, but be aware of potential crop injury with certain combinations.
For Roundup Ready sugarbeet fields with weeds surviving tillage, apply glyphosate at 1.125 pounds acid equivalent per acre (lb ae/A). This equates to 32 fluid ounces/acre (fl oz/A) of Roundup branded products and 48 fl oz/A of 3.0 lb ae/gallon glyphosate formulations. Consult page 89 of the 2009 North Dakota Weed Control Guide for more information about product rates of glyphosate formulations. For Roundup Ready corn, apply glyphosate at 0.75 lb ae/A plus an additional herbicide that provides control of dandelion and other weeds that are present. For Roundup Ready corn 2, apply glyphosate at 1.125 lb ae/A. The addition of an herbicide that controls dandelions with this rate of glyphosate may still be warranted. The denser the dandelion population the more likely an additional herbicide is necessary. For Roundup Ready soybean, apply glyphosate at 1.5 lb ae/A. This rate of glyphosate should be effective for all weeds. The addition of FirstRate at 0.3 to 0.4 ounces per acre may improve control of dandelion and provide some residual control of dandelions, but it is limited.
For Liberty Link corn and soybeans, apply Ignite 280 at 22 fl oz/A. The addition of atrazine at 0.38 to 0.5 pounds active ingredient per acre to Ignite in Liberty Link corn should improve the control of several weed species.
Agronomist - Weed Science
Extension Weed Specialist