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

A number of corn herbicides have label precautions about use of an organo-phosphate insecticide at planting due to potential crop injury. This includes the insecticides Counter (terbufos), Lorsban (chlorpyrifos), and Fortress (chlorethoxyfos). The herbicides include both soil-applied and postemergence herbicides. Some of the common products include Callisto (Halex GT); Resolve (Steadfast, Basis); Accent; or Capreno. Many of the Group 2 (or ALS-inhibiting herbicides) have these precautions. The list of herbicides can be found at http://extension.udel.edu/ag/files/2012/08/CornWeedguide.pdf and go to Table 19. [Read more…]

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

If no-till soybean fields have not been sprayed yet, we are facing an uphill battle. Most of the horseweed (or maretail) is now well over 6” tall, and so are a lot of the other winter annual weeds. [Read more…]

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

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