• Abundance of moths captured this spring has led to localized outbreaks.
• Moths lay eggs on grassy crops, covers, and weeds.
• Corn can be quickly consumed when grass cover crop is burned down.
• Wheat defoliation and head clipping can result, grass pastures can be denuded in days,

As reported in previous issues, impressive armyworm moth numbers captured in pheromone traps (see “Armyworm Pheromone Trap Report”) have led to hungry caterpillars. Moths prefer to lay their eggs on dense grassy vegetation (e.g., wheat, grass hay, and grass cover crops). Initially, tiny larvae and their damage are hard to find. Larval development, except in extreme northern counties, should now have advanced to the point that high-risk fields should be assessed for feeding damage. As of May 24, multiple reports of armyworm outbreaks have been received from central and southwestern counties. All have been at levels requiring treatment. Currently, armyworms are about ½” long in West Central Indiana. This is the time to treat them, when larger they are more difficult to kill.

Corn - Corn that has been no-tilled into, or growing adjacent to, a grass cover crop (especially rye) should be inspected immediately for armyworm feeding. Hatched larvae will move from the dying grasses to emerging/emerged corn. Armyworm feeding gives corn a ragged appearance, with feeding extending from the leaf margin toward the midrib. When larvae are numerous and/or large, damage may be so extensive that most of the plant, with the exception of the midrib and stalk, is consumed. A highly damaged plant may recover if the growing point has not been destroyed. If more than 50% of the plants show armyworm feeding and live larvae less than 1-1/4 inches long are numerous in the field, control may be necessary. Larvae greater than 1-1/4 inches consume a large amount of leaf tissue and are more difficult to control. If armyworm are detected migrating from border areas or waterways within fields, spot treatments in these areas are possible if the problem is identified early enough. Don’t rely on Bt-corn for protection, as all are vulnerable to armyworm damage.

Wheat & Grass Pasture - Examine plants in different areas of a field, especially where plant growth is dense. Look for flag leaf feeding, clipped heads, and armyworm droppings on the ground. Shake the plants and count the number of armyworm larvae on the ground and under plant debris. On sunny days, the armyworm will take shelter under crop residue or soil clods. If counts average approximately 5 or more per linear foot of row, the worms are less than 1-1/4 inches long, and leaf feeding is evident, control may be justified. If larvae are present and they are destroying the flag leaves or the heads, treat immediately.

Wk 1 = 3/16/17 - 3/22/17; Wk 2 = 3/23/17 - 3/29/17; Wk 3 - 3/30/17 - 4/5/17; Wk 4 - 4/7/18 - 4/12/17; Wk 5 - 4/13/17 - 4/19/17; Wk 6 - 4/ 20/17 - 4/26/17; Wk 7 = 4/27/17 - 5/3/17; Wk 8 = 5/4/17 - 5/10/17; Wk 9 = 5/11/17 - 5/17/17; Wk 10 = 5/18/17 - 5/24/17

Every spring we receive several calls and e-mails about a certain 3-foot tall weed with yellow flowers. Cressleaf groundsel is once again in full bloom across the entire state of Indiana in many no-till fields and pastures. This article is meant to provide information on the biology and life cycle of cressleaf groundsel, as well as how to control it in fields and pastures.

Biology and Identification

Cressleaf Groundsel is a winter annual weed that has been becoming more prevalent in Indiana pastures and agronomic crop ground over the past couple of years. The small seeds produced by this weed allow it to thrive in reduced and no-till systems as well as poorly established pastures. Cool and wet springs of the past couple of years have also favored cressleaf groundsel, as it is a weed that prefers moist soils and typically struggles in hot and dry weather.

Much like most winter annual weeds, cressleaf groundsel emerges as a rosette in the fall then bolts, flowers, and produces seed in the spring. Basal rosette leaves are deep pinnate serrations with roundly lobed leaf margins. Leaves are typically 2 to 10 inches in length (Britton and Brown 1970). Bolting stems are hollow and can reach up to three feet in height with inflorescences that contain six to twelve yellow ray flowers that are often compared to the flowers of common dandelion. When looking for cressleaf groundsel in older weed id or taxonomic guides be aware that it has traditionally been placed in the Senecio genus and only recently was placed into the Packera genus.

Toxic Properties

The competitiveness of cressleaf groundsel with agronomic crops has not been researched, though its presence as a winter annual in no-till fields will have the same implications of slowing soil warming and drying as other winter annual weeds. The presence of this weed in pastures and hay fields should be of more concern as it does contain toxic properties when ingested by livestock. Leaves, flowers, and seeds of cressleaf groundsel contain alkaloids that will cause liver damage in livestock that is termed seneciosis and typically occurs on a chronic level (Kingsbury 1964). Symptoms of seneciosis are loss of appetite, sluggish depressed behavioral patterns, and in extreme cases aimless walking without regard to fences or structures. Although cressleaf groundsel is not as toxic as many of its relatives in the Packera genus, livestock producers encountering this weed in pastures or hay should take steps to avoid prolonged ingestion by animals.

Control

Herbicide applications to control of cressleaf groundsel are most effective when applied to plants in the rosette stage, bolting plants are very difficult to control with herbicides. Infestations in pastures can be controlled with 2,4-D or a combination of 2,4-D and dicamba applied to rosettes in the fall or early spring prior to bolting (Nice 2008). Producers should be aware that applications of these herbicides will also kill favorable broadleaves that are present in pastures.

Control recommendations for cressleaf groundsel in no-till agronomic crop fields has typically been to apply 2,4-D @ 1 qt/A to actively growing rosettes in the fall. Research at University of Illinois (Lake and Hager 2009) has shown that fall or spring applications to 2-8 inch diameter rosettes with the following herbicides and rates can achieve 94% or greater control of cressleaf groundsel:

1 oz/A Canopy EX

1-2 qt/A glyphosate (4lb ai formulation)

1-2 qt/A glyphosate + 1-2 pt 2,4-D (4 lb ai formulation)

3 pt Extreme

In general the treatments applied in the fall resulted in greater biomass reduction of cress leaf groundsel, although all treatments and timings prevented plants from producing seed.

Reference:

Britton, N. and A. Brown. 1970. An Illustrated Flora of the Northern United States and Canada. Volume 3. Dover Publications, Inc., New York. Pp 540-544.

Kingsbury K.M. 1964. Poisonous Plants of the United States and Canada. Pentice-Hall, Inc., Englewood Cliffs, N.J. pp 425-435.

Lake, J.T. and A.G. Hager. 2009. Herbicide Selection and Application Timing for Control of Cressleaf Groundsel (Packera glabella). Weed Technol. 23:221-22.

Nice, G. 2008. Guide to Toxic Plants and Forages. Purdue Extension Pulbication WS-37.

Recent wet, rainy weather has created some weed management challenges for Indiana growers. In this article we will hit on a few key points to consider in corn based on current challenges.

Delayed weed control in corn

Indiana corn growers rely heavily on atrazine premixes in corn. Rain will not have completely washed all of the herbicide away, but may have compromised overall activity. Scout fields as soon as possible to determine if weeds are escaping. Obviously giant ragweed is a big concern, but wet conditions and dilution of atrazine can result in failures to control cocklebur, sunflower, velvetleaf, burcucumber, morningglories, and waterhemp. If corn is less than 12 inches tall and you haven’t used all of the atrazine allowed by the label, it would be wise to add atrazine to the other postemergence herbicides being applied to corn to control the above mention weeds and provide some soil residual activity. If corn is more than 12 inches tall, you cannot use any additional atrazine.

Weed escapes in large corn in all of Indiana

Whenever the warm weather finally hits us, we can expect emerged corn will grow rapidly. Postemergence corn herbicide options become limited when corn is 12 inches tall, and really limited on corn at the V6 or later growth stage. Also keep in mind that large weeds are much more difficult to control. To avoid crop injury on corn under other stresses, try to keep spray out of whorls, especially with ALS inhibitors and contact products. See table 8 in the weed control guide for the height restrictions of postemergence corn herbicides.

See Table 8. Rainfast Intervals, Spray Additives, and Maximum Crop Size for Postemergence Corn Herbicides from the Weed Control Guide For Ohio, Indiana, and Illinois .

The recent spate of rainy weather and chilly temperatures does not bode well for some corn fields planted prior to the onset of the nasty weather. Problems with germination, emergence, or survival of emerged seedlings are likely to occur in fields that received truly excessive rainfall and / or are poorly drained and susceptible to ponding or soil saturation for days on end. Significant surface soil crusting often develops in conventionally-tilled fields and restricts emergence of the corn plants. There can be some imbibitional chilling injury to seed in fields planted just ahead of the cold, wet spell. Other fields planted a bit earlier may exhibit corkscrewed elongation of mesocotyls and underground leafing out in response to cold temperature shock during emergence.

Please refer to “Corn Replant Considerations 2017, Pest&Crop Issue 7, May 12, 2017.

Time is running out for some Indiana fields not yet planted to their intended corn crop or those fields already planted to corn that now require replanting. Many fields are currently too wet to allow for planting. Forecast rains the remainder of the week and over the coming weekend threaten to keep corn planters out of some fields until early June.

There are two challenges with regard to choosing hybrid maturities to plant in early June in Indiana. One relates to whether the chosen hybrid maturity will mature safely (i.e., kernel black layer) before a killing fall freeze. The other is whether the chosen hybrid maturity will mature early enough to allow enough time for the grain to dry to acceptable harvest moistures.

In another, lengthier, article I describe the process for estimating “safe” hybrid maturities suitable for late planting (Nielsen, 2017). The purpose of this brief article is to simply offer a little more insight to the thought process.

As indicated above, the choice of the desired date to reach kernel black layer influences not only the estimate of available GDD from planting, but also the likely grain moisture loss (drydown) per day after maturity. If your primary objective is to simply mature the crop before a killing fall freeze in early to mid-October, then you can use a later maturity hybrid and take advantage of another couple weeks of GDDs. If you want the crop to mature in late September to take advantage of relatively better field drydown conditions, that will by necessity require planting an earlier relative maturity hybrid because of the fewer available GDDs. The difference in estimated "safe" relative hybrid maturities between the two decisions can be dramatic.

The accompanying table provides estimates of "safe" relative hybrid maturities for two planting dates (June 5 and 10) for six select counties across the state (different geographic locations) and three targeted crop maturity dates in the fall (Sept 20, Sep 30, and Oct 10). These estimates are based on the procedure described in my lengthier article (Nielsen, 2017).

Bottom line is that the time is approaching when the "safe" relative hybrid maturities for delayed corn planting will simply be too unadapted for most growers' liking, both from the lower yield potential perspective and typically unsatisfactory genetic disease resistance. Factor in the economics and crop insurance considerations (June 5 cutoff for full coverage, same for prevented planting with some policies), then the window for corn planting is beginning to close.

• Corn grain yields have steadily increased in the U.S. since the late 1930's.
• Only two major shifts in corn yield trends have occurred since records were first published in 1866.
• Year-to-year departures from trend yield are influenced primarily by year-to-year variability in growing conditions.

Historical grain yields provide us with a glimpse of yields yet to come, although like the stock markets, past performance is no guarantee of the future. The historical yield data for corn in the U.S. illustrate the positive impact of improved crop genetics and crop production technologies.

From 1866, the first year USDA began to publish corn yield estimates, through about 1936, yields of open-pollinated corn varieties in the U.S. remained fairly stagnant and averaged about 26 bu/ac (1.6 MT/ha) throughout that 70-year period. Amazingly, the historical data indicate there was no appreciable change in productivity during that entire time period (Fig. 1), even though farmers' seed-saving practices represented a form of plant breeding.

Rapid adoption of double-cross hybrid corn by American growers began in the late 1930's, in the waning years of the Dust Bowl and Great Depression. Within a very few years, the yield data indicated that a significant improvement in corn productivity had occurred, that resulted in an annual rate of yield improvement of about 0.8 bu/ac/year from about 1937 through about 1955 (Fig. 1).

A second significant improvement in the annual rate of yield gain began in the mid-1950's in response to continued improvement in crop genetics, increasing adoption of N fertilizer and chemical pesticides, and agricultural mechanization (Fig. 1). Since 1955, corn grain yields in the U.S. have increased at a fairly constant 1.9 bushels per acre per year, sustained primarily by continued improvements in genetics and crop production technologies (Fig. 1).

Some speculate that a third significant improvement in the annual rate of yield gain is "on the horizon", in part due to the advent and adoption of transgenic hybrid traits beginning in the mid-1990's. However, the USDA-NASS yield data show little evidence that the yield trend has deviated since the last big shift beginning in the mid-1950's (Fig. 1).

Annual yield estimates fluctuate above and below the yield trend line over the years (Fig. 2). The annual departure from yield is primarily in response to variability in growing conditions year to year (weather, pests). The Great Drought of 2012 certainly resulted in dramatic and historic reductions in corn grain yield relative to trend lines, but the greatest negative departure from trend yield actually occurred more than 100 years earlier during the Great Drought of 1901. The annual departures from trend yield since the mid-1950's reinforce the evidence from Fig. 1 that the advent and adoption of transgenic hybrid traits beginning in the mid-1990's has not resulted in noticeably greater departures from trend yield.

So, the good news is that corn grain yields in the U.S. have steadily increased since the 1950's. The sobering news is that, in order to support the ever-burgeoning world population in the years to come, a third and MAJOR shift in the annual rate of yield gain will be required.