Weeds

Palmer amaranth (Amaranthus palmeri) is a summer annual broadleaf weed species taxonomically related to other pigweed species (waterhemp, smooth, redroot) common in Illinois agronomic cropping systems.  Palmer amaranth is not indigenous to Illinois, but rather evolved as a desert-dwelling species in the southwestern United States including areas of the Sonoran Desert.  Genotypic and phenotypic adaptability have allowed Palmer amaranth to expand its distribution and colonize the vastly different agricultural landscapes across much of the eastern half of the United States,…

The past several days have experienced a noticeable increase in questions about options to control marestail after crop emergence.  Many have reported poor marestail control from herbicides applied prior to planting (primarily no-till soybean), especially when these burndown applications contained only glyphosate or glyphosate and 2,4-D.  The increasing frequency of glyphosate-resistant marestail populations, the rush to plant whenever field conditions were conducive, and the less-than-ideal environmental conditions when many burndown applications were made, have contributed to a challenging situation for which a good solution might not be available. …

Earlier this month, we discussed advantages of and techniques for controlling emerged weed vegetation prior to planting.  Several winter annual weed species have reached maturity while others, such as cressleaf groundsel (Figure 1),
began to flower within the past 10 days across areas of central Illinois.  Control of these mature plants with herbicides or single passes of tillage equipment will continue to be challenging.
Preplant control is also needed for emerged summer annual grass and broadleaf weed species. …

A potential scenario of planting delays will be corn planted in fields where no soil-residual herbicide was applied.  If the corn has not yet emerged, the soil-residual herbicide can be applied as originally planned.  But, what if the corn has emerged and the soil-residual herbicide has not been applied?  Can the application proceed as planned, or will a different product need to be selected?  The answer depends on the respective herbicide.
Most, but not all, soil residual herbicides can be applied after corn has emerged. …

We invite you to attend the 2013 University of Illinois Weed Science Field Day on Wednesday, June 26th at the University of Illinois Crop Sciences Research and Education Center, located immediately south of the main campus.  Coffee and refreshments will be available under the shade trees near the Seed House beginning at 8:00 a.m.
Similar to past years, we will car pool to the fields where participants can join in a guided (but informal) tour format. …

Wet soil conditions have caused delays in both planting and efforts to control existing weed vegetation.  Much of the existing weed growth is comprised of winter annual species, such as common chickweed, henbit, purple deadnettle, etc., but emergence of several summer annual species also has begun.  The growth of all species has accelerated with warmer temperatures and abundant soil moisture.  Several species of winter annuals are flowering and could produce viable seed before they are controlled with either tillage or herbicides. …

A recent article published in this Bulletin by Dr. Mike Gray (“Soil Insecticide Use on Bt Corn Expected to Increase this Spring Across Much of Illinois”) provides insights and data that suggest the use of at-planting soil-insecticides in corn is likely to increase this season.  Many insecticide choices are available to farmers, but several of these could restrict the option to use certain corn herbicides.  Specifically, using an organophosphate (OP) insecticide at planting or after corn emergence could restrict the use of herbicides that inhibit either the ALS or HPPD enzymes. …