Missouri Herbicide and Weed Update for 2006 By Kevin Bradley and Andy Kendig

New Herbicides and Systems

I. Corn
Resolve is a new herbicide from DuPont that contains rimsulfuron, which is one of the active ingredients in Steadfast. Resolve is recommended at rates ranging from 0.75 to 1 oz per acre as a preemergence herbicide that can be applied with products like atrazine for residual control of select weeds prior to planting or Resolve can also be applied as a tank-mix partner with glyphosate in RR corn to add residual activity to the postemergence glyphosate application. Resolve should not be applied to corn that is taller than 12 inches or exhibiting 6 or more leaf collars, whichever is more restrictive. A standard Resolve application rate of 0.75 oz per acre will cost approximately $6.00 per acre.

Generic Metolachlor Products. Recently, there have been several new generic metolachlor products introduced onto the marketplace. The Stalwart line of products from Sipcam Agro USA are some of the more popular of these products in Missouri, but Me-Too-Lachlor and Me-Too-Lachlor II are also generic metolachlor products from Drexler. Stalwart is registered for use in cotton and soybean while Stalwart C and Stalwart Xtra (metolachlor + atrazine) are registered for use in corn. Me-Too-Lachlor is registered for use in cotton and soybeans while Me-Too-Lachlor II is registered for use in corn. All of these products contain the active ingredient metolachlor, which technically is a mixture of equal parts of two isomer pairs of metolachlor, commonly referred to as the R and S isomers. This was also the case with the metolachlor within the older Dual and Dual II products from Syngenta, but is not the case with Dual Magnum and Dual II Magnum. Dual Magnum and Dual II Magnum are enriched, or resolved, with the S-isomer of metolachlor, which has been demonstrated to be more biologically active than the earlier “mixed isomer” formulations. For these reasons, generic metolachlor products such as those within the Stalwart line should not be considered “equivalent” to the same rates of Dual Magnum and Dual II Magnum. Although we normally consider generic products to be the same as the original trade name products (as with the isopropylamine salt of glyphosate), this may not be the case with the new generic metolachlors. For an excellent review of this topic, see a recent article written by Dr. Bob Hartzler at Iowa State University: http:www.weeds.iastate. edu/mgmt/2004/stalwart2.shtml. Another, perhaps less obvious, difference in these new products is the safener that is utilized to provide safety to corn. For example, Dual II Magnum, Dual Magnum, and Bicep II Magnum from Syngenta contain the safener benoxacor. The safener in Stalwart C is dichlormid. Some weed scientists have suggested that there may be differences in corn safety as a result of the different safeners in these products, which is a topic currently being investigated at several universities across the U.S.

II. Soybeans
Select Max is an enhanced formulation of Select with 0.97 lbs of clethodim compared to 2 lbs of clethodim in Select. Select Max may be applied at a variety of rates ranging from 6 to 24 fluid ounces per acre, depending on the height and type of grass weed species targeted. A crop oil concentrate or non-ionic surfactant in addition to ammonium sulfate is recommended for use with Select Max applications. The use rate for Select Max on volunteer Roundup Ready corn in soybeans will be 6 fluid ounces per acre on corn up to 12 inches in height, 9 fluid ounces for corn up to 18 inches in height, and 12 fluid ounces for corn up to 36 inches in height.

Generic Metolachlor Products. See information pertaining to these products above in the corn section.

III. Wheat
Olympus Flex is a new prepackaged herbicide mixture from Bayer CropScience for use in wheat. The active ingredients in Olympus Flex are propoxycarbazone-sodium (the active ingredient in Olympus) and mesosulfuron, both of which are ALS-inhibitors. Olympus Flex can be applied to winter wheat from emergence up to jointing at rates ranging from 3 to 3.5 ounces per acre. A non-ionic surfactant plus an ammonium nitrogen fertilizer is required with all Olympus Flex applications. Standard rates of Olympus Flex will cost approximately $12.00 per acre. Olympus Flex will provide wheat growers with a new option for the selective control of Bromus species like downy brome, cheat, and Japanese brome in Missouri wheat fields. In our research trials conducted in Missouri, we have seen downy brome control ranging from 70 to 75 percent with a standard fall application of Olympus Flex. This is as good or better control than other comparisons we have evaluated in these trials, and this herbicide will allow a grower to double-crop soybeans following a fall application. This has not been the case with other herbicides like Olympus and Maverick which have replant restrictions that prevent the planting of double-crop soybeans in Missouri. Olympus Flex is also registered for the control of Italian ryegrass which is becoming more of a problem in some of the southern areas of the state and also for the control of some winter annual broadleaf weeds like shepherd’s-purse, field pennycress, and certain mustards.

IV. Grass Pastures and Hay
Milestone is a new herbicide from Dow AgroSciences that will be available for use in Missouri in 2006. Milestone contains a new active ingredient, aminopyralid, which is a growth-regulator-type herbicide. Milestone contains 2 lbs of aminopyralid acid per gallon and will primarily be marketed for herbaceous weed control in pastures and rangeland. Milestone may be applied at rates ranging from 3 to 7 fluid ounces per acre. Milestone will provide control of a variety of annual broadleaf weeds and is also particularly effective on species like musk, bull, and Canada thistle. Additionally, Milestone provides good control of perennials like bull nettle or horsenettle and spotted knapweed, which has become more of a problem in some of the southwestern areas of the state. Milestone is registered as a non-restricted use pesticide, meaning that a pesticide license is not required to apply this herbicide, and does not have any grazing or haying restriction intervals that must be maintained after application. These characteristics of Milestone may help to fill a need for certain pasture and hay producers in Missouri. The 4 fluid ounce rate of Milestone is expected to cost between $11.00 and $12.00 per acre.

Milestone plus 2, 4-D is another prepackaged herbicide concept from Dow AgroSciences that is expected to be released in early 2006 but does not currently have a label in the U.S. At the time of this printing, a specific trade name is not known for this prepackaged combination. This mixture is expected to provide better control of certain perennial weeds like vervains, goldenrod, and ironweed compared to applications of Milestone alone.

V. Alfalfa
Roundup Ready Alfalfa became available for use in mid-2005 however seed supplies should reach a level where this technology will realistically be available to producers in Missouri in the spring of 2006. Priority on seed supplies has obviously been given to other states and regions that have larger acreages of commercial alfalfa production. There are many issues surrounding the release of Roundup Ready alfalfa and perhaps the biggest is price. The technology fee for a 50 lb bag of seed in Missouri will be approximately $125.00, or put another way the technology fee will run approximately $2.50 per lb of seed planted. This price does not include the cost of the seed itself, this is the technology fee only. We feel that for smaller acreage alfalfa producers, the cost of this technology is hard to justify. However, we feel that Roundup Ready alfalfa could prove useful for spring establishment of alfalfa and for the control of troublesome weeds like curly dock that are difficult to eliminate with current herbicidal options. As we continue to conduct our research trials with Roundup Ready alfalfa, the economic utility of this system versus conventional alfalfa production systems will become a more important component of our investigations.

VI. Cotton
Generic Metolachlor Products. See information pertaining to these products above in the corn section.

Roundup Ready Flex Cotton. Roundup Ready Flex cotton will be available in 2006. Flex cotton allows glyphosate to be used over-the-top through most of the growing season, as opposed to only before the 5-leaf stage. Seed is available for approximately 30 to 40% of cotton acres. It is recommended that special "Flex-Cotton" glyphosate formulations be used, as some formulations can cause a burning or speckling, surfactant-line phytotoxicity. These formulations will be available from Monsanto (a special emblem will be on Monsanto-branded glyphosate), as well as other glyphosate suppliers.

VII. Burndown/Fallow
Gramoxone Inteon is a new, safer formulation of paraquat from Syngenta. Gramoxone Inteon contains 2 lbs of paraquat per gallon compared to Gramoxone Max which contains 3 lbs of paraquat per gallon. Gramoxone Inteon will be registered in a similar manner and in similar environments as Gramoxone Max. In addition to the obvious changes in use rates, this formulation will be much safer for users than previous Gramoxone formulations.

Label Updates

I. Corn
Distinct is now registered for preplant application in corn. Distinct may be applied at 2 to 8 ounces per acre depending on the weeds present and choice of tank-mix partners. Corn can be planted 14 days after a Distinct application of 6 ounces or less, and 21 days if greater than 6 ounces is used. In corn, the Aim label will be modified for use up to the 14-collar growth stage.

II. Soybean
In soybean, the Aim label will be modified for use up to the 10th trifoliate. Additionally, Aim has received a harvest aid label with a 3 day preharvest interval for the burndown of large weeds like pigweed that may be remaining at harvest.

All remaining stocks of Authority 75DF from DuPont have been sold out and FMC expects to have Spartan 4F available as the only formulation of sulfentrazone available in 2006. Spartan 4F may be used at 4 ½ to 12 fluid ounces per acre depending on soil type, organic matter, and pH. The price of Spartan is expected to increase considerably compared to the old Spartan or Authority dry formulations.

Valor has received several special 24C labels for fall weed control in soybeans. These labels are valid for use throughout Missouri except in the boot heel counties of Butler, Dunkin, Mississippi, New Madrid, Pemiscott, Scott, and Stoddard. These labels include the following possible herbicide combinations: 1.) Valor + Scepter + Glyphosate and/or 2, 4-D ester, 2.) Valor + Express or Express XP + 2, 4-D ester, 3.) Valor + Canopy EX + 2, 4-D ester or glyphosate, 4.) Valor + Synchrony XP.

Synchrony XP (mp) is a new extruded paste formulation of Synchrony STS (Classic + Harmony GT). It has the same relative ratio of components as the older Synchrony STS, but has a lower overall percentage of active ingredients. For example, the 1/2 oz rate of Synchrony STS is equivalent to 3/4 oz of Synchrony XP.

Experimental Herbicides and Systems

I. Corn
KIH-485 is a new experimental herbicide from Kumiai America that is being investigated at a number of university research trials throughout the country as a preemergence corn herbicide, although other crop labels may also be pursued before this product comes onto the market. In our research trials, the spectrum of weeds controlled with KIH-485 appears to be similar to the preemergence acetanilide herbicides used in corn such as Dual II Magnum and Harness. In many university trials, however, KIH-485 has consistently provided better control of certain key weeds like common ragweed, velvetleaf, broadleaf signalgrass, and Texas panicum when compared to these other products.

Update on Herbicide Resistant Weeds

I. Common Ragweed
A biotype of common ragweed resistant to glyphosate was discovered in Missouri in 2004.   So far, this common ragweed population is confined to approximately 20 acres in a field with a history of glyphosate use in long-term soybean production. In greenhouse experiments, it appears that this biotype is approximately 10 times more resistant to glyphosate than a susceptible common ragweed biotype. In field trials, the addition of lactofen (Cobra or Phoenix) to a standard in-crop glyphosate treatment significantly enhanced control of this species. Resistant common ragweed plants also exhibited a shorter growth habit when compared to other wild-type biotypes. Additional studies are being conducted to further understand the mechanism of resistance in this species. We have received a few more glyphosate failure complaints on common ragweed in 2005 and glyphosate resistance is suspected (but not confirmed) in at least one other location in Missouri. In the remaining cases, however, resistance is not suspected and it appears that poor ragweed control may have been related to poor application timing, poor choice of glyphosate rate, ragweed plants that were too large at application, the presence of a ragweed borer infesting these plants, or a combination of these factors.

II. Common Waterhemp
Two biotypes of common waterhemp that are potentially resistant to glyphosate were discovered in northwest Missouri in 2005. Initial greenhouse dose-response investigations indicate that both biotypes are resistant to glyphosate at above-labeled glyphosate rates. For example, a high percentage of individuals in one of the populations survived treatment with as much as 6 lbs of glyphosate acid per acre when sprayed at a 6-inch height. The initial seed from this northwest Missouri population was collected from a 190 acre field and surveys are underway to determine the prevalence of this biotype in surrounding fields. Results from all initial experiments indicate that these biotypes are glyphosate-resistant, however additional field and heritability studies need to be conducted before this can be confirmed. Additional field experiments are planned for 2006 to determine best management programs for glyphosate-resistant common waterhemp in corn and soybean.

III. Palmer Amaranth
Glyphosate-resistant Palmer amaranth (a pigweed species) was discovered in 2005 in a Roundup-Ready cotton field in Georgia. Palmer amaranth is already a troublesome weed in Missouri cotton production, and was a major driving force in the adoption of Roundup Ready cotton. Weed scientists are concerned that glyphosate-resistant Palmer amaranth will be very difficult and expensive problem to manage, and are urging growers to include alternative chemistry wherever possible in a Roundup Ready cotton program. Growers using the flex cotton should still apply traditional, residual layby-type chemistry. Early postemergence mixtures of glyphosate and metolachlor-type products are also encouraged, along with preemergence herbicides.

Kevin Bradley and Andy Kendig
573-882-4039 and 573-379-4031