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10 Weed Control Tips for Sunflower

Friday, April 15, 2005
filed under: Weeds

The shortfall of Spartan (sulfentrazone) this year definitely throws a monkey wrench into the weed management plans for a number of sunflower growers. But that doesn’t necessarily mean forfeiting to weeds, just changing tactics. Some tips to consider:

1) Communicate with your ag supplier. There continues to be an effort in the countryside to procure the liquid formulation of Spartan 4F (FMC’s liquid formulation, used mostly in the tobacco market) and other sulfentrazone products such as Authority and Blanket that are labeled for other crops. Last-minute planting changes might also influence supply and free up previously committed purchases of Spartan.

2) Stretch sulfentrazone by reducing the application rate. The labeled rate of Spartan DF is 2-5.3 oz (lb ai/A) and 3-8 fl oz for the liquid formulation, but research and observations at both Colorado State University and Kansas State University indicate that Spartan can provide good control of kochia and other small broadleaf weeds at reduced rates (1-2 oz/ac) under some conditions. So one option to consider would be to tank mix either the dry or liquid formulation of Spartan at reduced rates, with Prowl or pendimethalin equivalent at the full labeled rate.

3) Recognize the gamble with Spartan at reduced rates. There may be a tradeoff in the chemical’s residual effectiveness, especially in lower moisture conditions. Reduced rates will especially work well in high soil pH, and light sandy soil with less than 1% organic matter. These conditions are more common in Kansas and Colorado than the Dakotas and Minnesota. If you do not have these conditions (many areas of the Dakotas and Minnesota do not) you’d be gambling with weed control using reduced rates of Spartan. Consult with a local agronomist to see what he or she would suggest for soils in your area.

4) Start with a clean slate. Plant sunflower on clean fields that don’t have problem weeds such as kochia in their recent history – this will be even more important if Spartan isn’t available as a preplant option. Weed control in the previous crop becomes a greater consideration – it might make sense to plant sunflower on the previous year’s Roundup-Ready corn or soybean ground. A number of broadleaf herbicides labeled for wheat and corn have excellent activity on kochia and other weeds that can be a problem in sunflower. But keep herbicide carryover in mind, as some broadleaf weed control products have residual activity that may not allow sunflower as a subsequent crop.

5) Timing of Preplants is Critical. Pendimax (Dow AgroSciences), Prowl and Prowl H20 (BASF) and Pendant (new from Agriliance) all have the same active ingredient (pendimethalin). Prowl H20, new in 2004, is marketed as having less odor, staining, and volatility compared to the conventional formulation. As well, observations indicate that it may be a bit more effective in high-residue situations such as no-till, because it doesn't bind as readily to stalks and other debris. Sonalan (ethalfluralin) and Trifluralin products must be incorporated. It’s generally recommended to incorporate pendimethalin herbicides as well. Without incorporation, moisture becomes the critical component to getting the herbicide into the soil and down to the root zone where weeds germinate. Thus, allowing ample time for preplant products to activate – at least three weeks before planting (some labels specify up to 30 days before planting no-till) – is extremely important.

6) Go with granules on no-till. Because a liquid product is more likely to adhere to field residue, a granular product is recommended in minimum/no-till situations. Experts say granules work better than liquid at sifting through residue to get to the soil.

7) Glyphosate burndown becomes important. That early glyphosate burndown provides the sunflower crop an equal footing with weed competition. Optimum would be a glyphosate burndown several weeks before planting to control the season’s first flush of weeds, including small wild buckwheat at the two to three-leaf stage, followed up with another glyphosate application at planting to get additional weeds. If making only one glyphosate burndown, don’t let weeds get too large. When weeds get too big, it can be difficult to get all of the axillary buds along the stem killed, and you may get regrowth or an incomplete kill.

8) Plan for cultivation, or thicken the canopy. Increasing the planting rate, or solid seeding, would thicken the plant canopy and give the crop a better chance to out-compete weeds. On the other hand, planting in rows leaves the door open for cultivation or a between-the-row application of glyphosate with a hooded sprayer.

9) Consider Taking Aim with a hooded sprayer. Before there was Spartan, some growers used hooded-sprayers to control broadleaf weeds between the rows of sunflower. FMC added sunflower to the label of Aim (carfentrazone) for 2005. Aim is labeled for use both as a preplant burndown ahead of sunflower planting, and for use in a hooded-spray application. Company representatives say Aim is a safer alternative for hooded-spraying in sunflower than glyphosate. The 2005 NDSU Pest Control Guide indicates that Aim at 1/2 oz 2EW (liquid formulation) controls kochia, lambsquarters, nightshade, pigweed, wild buckwheat, and waterhemp, with best results when applied to small weeds, less than two inches in height.

10) Recognize the strengths and limitations of Beyond in Clearfield sunflower. Beyond/Clearfield sunflower offers excellent control of marshelder, cocklebur, devil’s claw, and a number of grasses and broad leaf weeds. Performance is best at early postemergence from V2 to V8 (V2-V4 optimum). Apply before broadleaf weeds exceed a height or width of 3 inches, and before grass weeds exceed 4-5 inches. Beyond will not control ALS-resistant kochia or other ALS-resistant weeds, and the herbicide shouldn’t be viewed as a rescue treatment for large weeds that have gotten out of hand. A preplant treatment may still be needed, depending on the field. Pyrethroid insecticides (Warrior, Asana XL, Baythroid, Scout X-Tra) are safe to tank mix with Beyond. Of course, Beyond can only be used on Clearfield sunflower hybrids. – Tracy Sayler

’05 Valor Label Won’t Include Sunflower

Efforts have been underway in several sunflower-producing states to determine if a Section 18 application to EPA could be feasible for Valor (Flumioxazin) as a possible option for controlling small seeded broadleaf weeds on no-till, and to help alleviate the Spartan shortfall. The 2004 label for Valor included sunflower on the label 30 days pre-plant at 2 oz. However, the new 2005 label does not include sunflower, and there is no Section 18 for this product on sunflower at the present time.

A key concern about Valor from past research on sunflower has been the potential for crop injury. Valent, the manufacturer of Valor, plans to work with university crop scientists to gather more crop safety data in sunflower this growing season. The data will help assess consideration for labeled use of Valor in sunflower in 2006.

Weed Management Info Online

North Dakota State University Weed Science

with link to 2005 NDSU Weed Control Guide

South Dakota State University Extension

Click on ‘farm,’ then ‘crops,’ and then ‘weed control’

Kansas State University Weed Management Page

Nebraska 2005 Weed Control Guide

CDMS Ag Chem Information Services

Online ag pesticide labels

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