by Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

I have seen a number of corn fields with pokeweed emerging along field edges or in patches. These areas should be sprayed before the plants are 10 to 12 inches tall and as result may require some spot applications before the whole fields need to be treated for summer annual weeds. In addition to glyphosate, other effective postemergence treatments include Callisto, NorthStar, Yukon, dicamba (1 pint/A), or Status (5 oz/A). Also note that NorthStar, Yukon and Status all contain dicamba (Banvel) and take precautions so that sensitive plants will not be affected.

Source: Read More from Weekly Crop Update

By Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Preemergence herbicides will provide a period of residual weed control, based on rate and incorporation. Typically we can expect 3 to 5 weeks of residual control in most situations. So if our preemergence herbicide application is made 3 to 4 weeks before planting, we can expect weeds starting to emerge shortly after planting and a need for a postemergence herbicide application 2 to 3 weeks after planting. On the other hand, if preemergence herbicides are made at planting, they will provide enough residual control to allow postemergence application closer to canopy closure.

Source: Read More from Weekly Crop Update

By Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Due to the seriousness of glyphosate-resistance, and the tendency of Palmer amaranth to develop resistance to glyphosate, UD Weed Science recommends:

1. The field should be clean at planting, using effective burndown herbicides or tillage;

2. Use a residual herbicide, applied as close to planting as possible (within 7 to 10 days);

3. Never apply glyphosate alone; an additional herbicide should be used as a tank mix partner;
a. additional mode of action must be highly effective on Palmer amaranth as well;
b. applications should be made to plants less than 3 inches tall;

4. Be sure to rotate herbicide mode of action
a. use a Group 27 herbicide in corn (Callisto, Impact, or Laudis products), avoid use of Group 14 (Valor, Sharpen, etc) herbicides in corn, except in cases of continuous corn;
b. use a Group 14 herbicide in soybeans (i.e. Valor, Reflex, or Cobra); and

5. Fields with soybeans planted two years in a row need extra precautions to avoid resistance (particularly in regards to Group 2 or ALS herbicides).

Source: Read Full Article from Weekly Crop Update

By Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

The label for Sharpen and other Kixor-containing herbicides says not to apply with any other Group 14 (PPO herbicides) or within 30 days of other Group 14 herbicides. Other Group 14 herbicides include flumioxazin (Valor, Valor XLT, Envive, Fierce, etc), Anthem, fomesafen (Reflex, Prefix, Flexstar numerous generic products).

Source: Read More from Weekly Crop Update

By Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Working with Bill Bamka, County Extension Educator from Burlington County NJ, UD Weed Science Program confirmed that a population of common ragweed in New Jersey is resistant to glyphosate. The long-term history of the field is not known, but the past couple of years it was planted with soybeans. Last year, the preemergence herbicides did not provide adequate control and multiple applications of glyphosate were used postemergence. This is not the first confirmation of glyphosate-resistant common ragweed in the region; but the first in New Jersey. We have no reports of common ragweed resistant to glyphosate in Delaware.

In this situation, rotating to corn and use of atrazine is the best option. When rotating back to soybeans, use no-till because germination will be less than if tillage is done. The field will need to be treated with a preemergence application of cloransulam (i.e. Sonic or Gangster) or metribuzin (Tri-Cor, Boundary, or Canopy, generics). But there will definitely be a need for a postemergence herbicide and the best options would include Blazer Ultra, Cobra, Reflex, and Liberty (with Liberty Link soybeans). If cloransulam was not used at planting, FirstRate or Permit Plus (with STS soybeans) would also be options.

Source: Read More from Weekly Crop Update

By Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

This is an article written by Dwight Lingenfelter and Bill Curran from Penn State and modified for Delaware.

As more farmers use vertical tillage to manage crop residues or to mellow the seedbed prior to planting (especially soybeans), questions have arisen about possible impacts of using these types of tillage operations in combination with certain soybean herbicides. The PPO herbicides (Group 14) in particular are drawing attention in these discussions. The soil applied PPOs include flumioxazin (Valor SX, Valor XLT, and Envive); sulfentrazone (the Authority family lineup and Sonic), fomesafen (Prefix, Reflex); and saflufenacil (Sharpen, Verdict, Optill). In general, if a vertical tillage operation is done before the PPO herbicide application, residual weed control will typically not be negatively affected. However, if the PPO herbicide was applied before the tillage operation then weed control could be compromised. In particular, flumioxazin and saflufenacil-containing herbicides can be affected the most. In this case, any tillage after herbicide application disrupts the uniform layer of herbicide potentially causing weed escapes or patchy weed control.

Source: Read More from Weekly Crop Update