For no-till fields, a non-selective herbicide needs to be used prior to planting. If grasses or perennial weeds are present, glyphosate is a better choice than paraquat. Fields worked with a vertical tillage implement for residue management, still need a non-selective herbicide. These implements are not weed control tools.

There are few effective herbicides labeled for preemergence applications. Sharpen is labeled for wheat and barley but we have limited data in the region. Valor can be used at 1 to 2 oz with the burndown application, but there must be a 7-day period between application and planting wheat. Valor is not labeled for barley.
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Fall is the best time to treat most perennial weeds because it is the time that plants are best able to move the herbicide to the roots where it will do the most good.

When considering fall weed control the emphasis should be on what the patch of weeds will look like next spring or summer not the amount of dead stems this fall. Also, it is important to consider that a fall application will not eradicate a stand of perennial weeds; the fall application will reduce the stand size or the stand vigor. Fall application of glyphosate is the most flexible treatment for most perennial weeds such as bermudagrass, Canada thistle, common milkweed, common pokeweed, dock, hemp dogbane, horsenettle and johnsongrass. Rates of 1 to 1.25 lb acid per acre are consistently the most economical (or about 1.5X the normal use rate for annual weeds). Dicamba (Banvel) at 2 to 4 pints is also labeled for artichoke, bindweeds, dock, hemp dogbane, horsenettle, milkweeds, pokeweed or Canada thistle. Planting small grains must be delayed after dicamba application 20 days per pint of dicamba applied.

Fall herbicide applications should be made to actively growing plants. It is best to spray prior to mowing the corn stalks and allow plants to recover after harvest. Allow 10 to 14 days after treatment before disturbing the treated plants. If fall applications are delayed, remember weed species differ in their sensitivity to frost; some are easily killed by frost (i.e. horsenettle) others can withstand relatively heavy frosts. Check the weeds prior to application to be sure they are actively growing.

A number of calls have come in about options to control large Palmer in full-season soybeans. The beans are 30 to 36 inches tall and the Palmer amaranth plants are poking through the canopy. In most cases the field has been sprayed with glyphosate. There are no good options. Late-season Palmer amaranth management needs to focus on stopping seed production, and chemical choices are likely to be ineffective.
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This week in U Del Weekly Crop Update:

• Remove Weeds Before the Seeds Mature
• Livid Amaranth

Remove Weeds Before the Seeds Mature

Many weeds have started to flower in the past week or two. Weeds, depending on the species, will continue to flower from now until frost. I am often asked how soon after flowering are the seeds mature. We have some ongoing trials looking at this issue, but we have a few preliminary results to share.

First and foremost, seeds are mature shortly after flowering. By this I mean that within two weeks of flowering, the seeds on some plants are capable of germinating and contributing to the weed seedbank. So if you are pulling weeds (or mowing them or spraying them) to stop them from producing seeds, you should physically remove the weeds from the field because they may already have mature seeds.
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With small grain harvest underway, there are some questions about preplant weed control with double cropped soybeans. This has always been a challenging situation, and with the presence of herbicide-resistant weeds, it has become even more complicated and results are often less than satisfactory. Larger plants that have been cut off or damaged by the combine are going to be less susceptible to herbicides and achieving 100% control will require a lot of environmental factors falling in your favor — the recent dry spell does not work in your favor. [Read more…]

• Postemergence Management of Glyphosate-Resistant Horseweed in Soybeans
• Palmer Amaranth Control in Soybeans
• Harvest Aids for Small Grain

Postemergence Management of Glyphosate-Resistant Horseweed in Soybeans

Options for controlling horseweed (marestail) resistant to glyphosate after the soybeans have emerged are very limited. Liberty Link soybeans are an exception, because Liberty 280 is fairly effective on horseweed (be sure to keep your rates up and keep spray volume up to ensure good coverage).  [Read more…]