The Most Important Weed Control Decision you Make! (8/25/11)

In soybean, dry bean, and other broadleaf crops (including RR) the choices and degree of control are much less. This weed will not go away for several years and until conscious and sustained control strategies are used it will keep getting worse. This is just a friendly reminder that Weed Control Rule #7 is always true.

Weed Control Rule #7 = Fields that receive a fall herbicide application will always be cleaner than those fields that don’t. In other words, dandelion infestations will be much less in fields that receive a fall herbicide application than those that don’t.

Glyphosate at 1 qt/A (generic) or 22 fl oz/A (Monsanto brands) plus 2,4-D at 1 pt/A with or without Express at 1/3 oz/A (75DF) or 0.5 oz/A (50SG) will control many annual, biennial, and perennial weeds.

The following is an article addressing general fall weed control that was written by Dr. Jeff Stachler and published in the last issue of the 2010 Crop and Pest Report:

Now is the time to begin applying herbicides for the control of winter annual weeds, simple perennials such as curly dock and dandelion, biennials such as biennial wormwood, and in some cases cool-season perennial weed species.  This is especially true for no-tillage fields, but also for those fields receiving tillage other than moldboard plowing.  For fields in which tillage is planned, apply herbicides at least 5 days prior to tillage.  Herbicides may be applied within a few days of crop harvest or until the soil is frozen.  Based upon research across the Midwest, the most consistently effective control of dandelions is obtained with fall herbicide applications.  The best way to drastically reduce or stop seed production of winter annual species is with fall herbicide applications or effective fall tillage.  It is always better to apply herbicides in the fall under less than ideal conditions, than to wait until spring to achieve marginal control of these types of weed species, especially dandelion.

The most effective fall herbicide treatment with the most cropping flexibility next spring is an application of glyphosate at 0.75 lb ae/A (22 fl oz/A of a 4.5 lb ae/gal or 1 qt/A of a 3 lb ae/gal formulation + 2,4-D ester at 1 pt/A (4 lb ae/gal).  The addition of 2,4-D is most important for dandelion control and will antagonize glyphosate's activity on Canada thistle and perennial grass species.  Another herbicide option, would be the addition of Valor at 2 to 3 oz/A to the glyphosate plus 2,4-D mixture.  Fall applications including Valor will be most beneficial west of the Red River Valley, because spring rains are not consistent enough to properly activate Valor.  Activation of Valor is almost certain with fall applications in the drier areas of the state due to more consistent rainfall throughout the state in fall.  Preliminary studies with fall-applied Valor have shown potential to control or suppress weeds such as kochia, seedling dandelion, canola, and chamomile.  However, NDSU and Valent are conducting additional research to determine proper timing of application of Valor and efficacy on spring-emerging weeds.  Valor should only be applied in no-tillage fields and any substantial soil movement next spring during planting will reduce the effectiveness of Valor on spring emerging weed species.  Read the Valor label and follow the crop rotation guidelines when applying Valor in the fall.  Only certain crops can be planted in the spring following fall-applied Valor.

Rich Zollinger - NDSU Extension Weed Specialist