To Control Perennial Weeds

On November 12, 2018

To Control Perennial Weeds

With the recent cold spells we have just experienced around the state, some people are wondering if it is too late to control weeds, especially perennials. In the fall, foliar applied herbicides can be effective as long as the plants are green and appear healthy. 

Extension Agronomist Dwight Ligenfelter explains for best activity, apply herbicides when daytime temperatures are above 50 F and night time temperatures are above 40 F for several days during application time (don’t apply herbicides immediately after a frost). Some research from Iowa State and Ohio State indicates the following: many perennial and biennial weeds can still be effectively killed after a few hard frosts.  Research with quackgrass and glyphosate actually found greater translocation of the herbicide after the first frost than before frost.   Plants having a prostrate growth habit such as the biennial musk or bull thistle will be more tolerant of frost since they are protected somewhat by heat released by the soil.   With most plants it is possible to determine whether the foliage has been severely affected by frosts, thus scouting the field prior to application is important to ensure that active foliage is still present. 

Regarding quackgrass and Canada thistle regrowth after harvest, if these weeds are greater than 8 inches in height, then an application of glyphosate may provide good control of the above and below ground plant parts.  If temperatures drop below 28 degrees at night for more than 4 hours then these plants may die and a herbicide application may not be effective.  Quackgrass can handle colder temperatures than Canada thistle.  If warm temperatures (greater than 65 degrees) return for several days and the plants appear to be growing, then a herbicide treatment may still be effective. Fall is the best time to control dandelions, while both fall and early spring are the good times to control winter annuals. 

In fallow fields, a combination of glyphosate plus 2,4-D ester is fairly effective for control of most winter annual weeds and dandelion. Application of 2,4-D alone controls many winter annual weeds, but 2,4-D will not control chickweed and is less effective on dandelion than when in tank mixture with other herbicides. (Also, if you have a pure stand cereal rye cover crop that has broadleaf winter annual and/or perennial weeds, 2,4-D ±dicamba can be applied to control these weeds either now or in the early spring.) 

As we move into late November, foliar herbicide effectiveness decreases and the inclusion of a residual herbicide may be desirable in corn or soybean rotations. If you include a residual herbicide, research over the last several years has shown that any chlorimuron-containing product (Canopy EX, Blend, etc.) is at the top of the list for soybeans and simazine is one of the better products for corn. Other products that have had some success include Valor for soybean and Basis Blend for corn. In general, 2,4-D should be tank-mixed with any residual product. Also, when applying systemic herbicides this late in the year, make sure to include adjuvant such as AMS and/or crop oil concentrate/methylated seed oil to insure adequate uptake of the herbicide. (However, if you are applying systemic herbicides with these spray additives in a cereal rye cover, crop injury might occur.)

To Repair Ruts In Your Fields

The summer of 2018 has certainly been one for the record books. Since about mid-July, the deluge has not let up, and that has left many of us in a bind this harvest season. In an effort to harvest quality corn silage, many of our fields have become rutted and compacted. Extension Agronomist Casey Guindon explains if we have below normal precipitation through the end of November, we have an opportunity to correct the ruts and allow the condition of our soils to continue to improve as they freeze and thaw this winter.

While the impacts of surface compaction are not as long-lasting as those from sub-soil compaction, they are much more severe in the seasons immediately following the compaction event. Ruts that remain unamended make planting at an even depth much more challenging in the following spring. An even planting depth is essential to a healthy crop stand, and surface ruts stand in the way of achieving that goal. Next year’s yields can be greatly improved by taking action this fall. However, it is important to wait until soil conditions are optimum for field activity- or you risk making the damage worse.

It may be tempting to resort to deep tillage to resolve the issue, but no-till soils remain more resilient to surface compaction over the long term. Long-term no-till soils exhibit a higher aggregate stability and are better able to support the weight of equipment. Instead, focus on flattening the areas exhibiting the worst symptoms. Skid-loader buckets and other similar implements can be effective in smoothing rutted areas. In fields with more severe compaction, light disking or chisel plowing may be necessary. After either event, it is important to utilize other soil health building practices, like planting cover crops, to protect the soil from further erosion, and to rebuild the soil aggregates that have lost their stability. Soil improvements implemented this fall can pay dividends in the spring.

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