Managing Winter and Spring Annual Weeds (Crop Insights)
By Tim Chicoine and Kevin Hahn, DuPont Crop Protection
- Winter and spring annual weeds are plants that germinate in late summer, fall or early spring and complete their life cycle by early summer.
- In no-till fields, winter and spring annual weed cover reduces soil warm-up and drydown in the spring, potentially delaying planting and impacting seedbed quality.
- In conventional tillage fields with winter and spring annual weed problems, several tillage passes may be needed to prepare a suitable seedbed. Extra tillage delays planting and increases production costs.
- Winter and spring annual weeds may increase nematode, insect and disease pressure on the crop.
- A fall application of a residual herbicide program is an excellent way to burn down emerged winter annuals and provide residual control of later-germinating winter and spring annuals in no-till and conventional fields.
Weed control issues often center on controlling species with a biological life cycle similar to that of the crop grown. Traditionally, spring- or summer-seeded crops must compete with weeds emerging at or shortly after the time of planting; summer annuals such as foxtails, velvetleaf and ragweeds. Weed species emerging in the fall through early spring (winter and spring annuals such as chickweed, henbit, wild garlic, marestail and field pennycress) have historically posed a problem to fall-seeded crops such as winter wheat and were of little concern to corn and soybean farmers.
Winter and spring annuals germinate and emerge in late summer through early spring. These weeds can overwinter by becoming semi-dormant. They resume growth (or emerge) in early spring, flower, and complete their life cycle before or shortly after the typical spring planting season. In the past, cultural practices such as herbicide use patterns or tillage methods have precluded these species from becoming agronomic problems. However, weed control programs centered around the use of non-residual herbicides have increased, particularly on soybean production acres. Winter annual weeds have become a more widespread issue, presenting an additional challenge for many farmers at planting time. Infestations can range from a few plants to dense mats of growth. This Crop Insights discusses the reasons for this weed problem, the challenges it presents for spring-planted crops, and control measures including fall application of residual herbicides.
Figure 1. A sprayer skip during application to a field near Rensselaer, Ind., demonstrates the effectiveness of fall application to control winter annual weeds. Application on November 14, picture taken on May 3.
Why is there a Problem Today?
In some areas of the country where cultural practices have allowed them to flourish, winter annuals have been a production problem for years. In many corn and soybean growing regions, however, these weeds are a relatively new concern beginning in the late 1990s. The 2 primary reasons for this change were the movement away from preplant or preemergence residual herbicides and the elimination of tillage in many weed management programs. This has occurred as growers have increasingly adopted non-residual glyphosate-based herbicide programs as their sole weed control strategy. Weed biology is a very dynamic process in which weed populations evolve to fill voids created by opportunity. In this case, the opportunity has been created for species that can occupy an ecological niche germinating in the fall or early spring.
Another factor that can increase growth of winter annuals is relatively mild weather during the winter. Mild winters result in shortened dormancy periods for emerged winter annuals like chickweed, deadnettle and henbit. Continued growth of these weeds throughout the winter months allows for thick, deep purple and green vegetative mats by mid to late March.
Late fall or early spring tillage can reduce winter and spring annual weeds, but it may not eliminate them completely. Tillage patterns have evolved over the years toward reduced or no-till programs, especially in soybeans. Also, planting times have been edging earlier and earlier, leaving less time for the control of winter annuals prior to planting. The earlier planting and reduction in tillage have combined to diminish tillage as a control measure.
This combination of factors has allowed weeds such as chickweed, deadnettle, henbit, dandelion, marestail and other weed populations to increase, often presenting management challenges. Some traditional winter annual weeds such as marestail are now also emerging well into the spring and appear to have adapted their life cycles to compete under a wide range of environments from late fall through mid spring.
Problems Created by Winter Annuals
The problems created by the growth of winter and spring annual weeds impact many aspects of crop production. Dense annual weed growth often affects seedbed quality and crop establishment, including timely planting. These weeds can also act as an alternative host for soybean cyst nematode, attract black cutworm moths and may facilitate seedling disease. Finally, weed competition itself may be an issue, as some species persist well into the summer.
Poor Seedbed Conditions
Maximum yield potential for a hybrid or variety is reduced by every stress it encounters from planting through harvest. Planting conditions, soil type, weather, pests and management practices all interact with the hybrid or variety to determine final yield. The crop's early growth and development success is largely determined by the seedbed, and how it fares at this juncture usually impacts how it will respond to subsequent stresses. Controlling winter annuals is the first step in preparing a suitable seedbed and ensuring the best possible start for top yields.
Heavy growth of winter and spring annuals may mean increased difficulty in the event spring tillage is needed for seedbed preparation or to help dry a field prior to planting. Spring tilling of wet soils with heavy vegetation can lead to compaction and a poor seedbed, resulting in poor furrow closure, poor seed-to-soil contact and subsequent stand issues.
When wet weather and soil conditions prevent tillage or spraying, winter and spring annuals continue to germinate and grow. These large weed masses will require even more field preparation time prior to planting, thus intensifying the springtime management challenges.
One of the biggest issues with increased winter annual weeds is their effect on timely planting in the spring. DuPont Pioneer research has consistently shown the value of timely planting for optimizing yields and reducing grain moisture at harvest. Heavy mats of winter and spring annuals such as chickweed prevent the soil from drying and warming early in the spring, thus reducing early planting opportunities. For this reason, Iowa State University researchers indicate that if winter annuals are found on more than 25% of a field, some form of control will likely be beneficial (Owen et al., 2001).
Higher Soybean Cyst Nematode Levels
The impact of winter annuals can begin shortly after harvest in the fall, long before any planting decision has been made. Several winter annual weed species, including field pennycress, shepherd's purse, henbit, small-flowered bittercress, common chickweed and purple deadnettle can serve as alternative hosts for soybean cyst nematode (SCN) (Table 1). Greenhouse studies have shown that SCN reproduction on henbit and purple deadnettle can actually exceed that on soybean (Mock et al., 2007). Controlling winter annual weeds is an important component of SCN management.
Table 1. Winter annual weed species known to serve as alternative hosts for SCN (Mock et al., 2007).
Research suggests that the most effective way to manage winter annual weeds for reduction of SCN populations is to control weeds early in the fall. SCN are active when soil temperatures are above 50 F. Weed control treatments applied after soil temperatures have fallen below this point will likely have little impact on SCN; therefore, fall herbicide applications should be made as soon as possible after harvest to reduce SCN population densities. Products with residual activity can help control winter annual weeds through the following spring.
Black Cutworm Infestations
Female black cutworm moths are attracted to winter annuals such as chickweed, deadnettle, shepherd's purse, dock and mustards in the spring for oviposition (egg-laying). Larvae then migrate out of these sites into adjacent corn or soybean fields when weeds are controlled just prior to or after planting.
A mat of winter annual weeds (alive or dying) will provide a moist and dark environment through which crop seedlings must emerge. This creates an environment conducive for damping-off of germinating seedlings.
Timing of Control – Consider Fall Application
Numerous crop production problems can result from the unchecked growth of winter and spring annual weeds. The increase in the prevalence of these weeds in major corn and soybean production areas means that affected growers should consider weed control options to prevent or reduce the occurrence of these weed-related problems.
Winter and spring annual weed control measures may be implemented any time from immediately after harvest through post-planting, and can include mechanical and/or herbicide options. The choice of timing may be influenced by the severity of the infestation, spring work schedules and planting intentions.
Herbicide applications at or shortly prior to planting must fit in with other spring activities, and require field conditions that will support sprayer traffic and weather patterns conducive for application. Postemergence contact materials are often less effective under cooler spring conditions. Weeds are also slower to die back and dry down to a point where they won't interfere mechanically with planting. The slower weed dieback also means the soils beneath them will be slower to dry out and warm up. Thus, applications ideally should be made well in advance of planting to ensure adequate drying of vegetation and the soil prior to planting.
The use of residual products in the fall or early spring tends to provide more consistent weed control than spring treatments. This may be due in part to a smaller weed size at application, more abundant moisture for activation, and a greater length of time for the herbicide to control the weeds. Fall is also the time when perennial weeds (e.g., dandelion) translocate reserves down into the root system, resulting in better control from herbicide applications.
University of Nebraska research showed that the majority of weed emergence occurred up to early November, indicating that treatments applied in late October or early November would likely provide the most effective control (Werle and Sandell, 2013). Drier field conditions, equipment availability and time management factors may also make fall application an attractive option for winter annual weed control.
Winter Annual Weed Control Options
Several herbicide and/or tillage options may be utilized for winter annual weed control in the fall. Research conducted at several universities indicates that a residual herbicide program offers the best results because it controls both emerged weeds at the time of application and later flushes of winter or spring annuals. The residual activity may also extend into the spring, reducing the competition from early emerging summer annuals such as giant ragweed, marestail, waterhemp, giant foxtail and lambsquarters.
DuPont Herbicide Options for Fall Application
DuPont™ Basis® Blend herbicide
DuPont™ Canopy® EX herbicide
DuPont™ Panoflex™ herbicide
Figure 2. Winter annual weed control 1 week after corn planting from fall herbicide applications at 2 Missouri locations in 2005 and 2006 (Monnig and Bradley, 2008).
Figure 3. Winter annual weed control at soybean planting from fall herbicide applications at 3 Missouri locations in 2005 and 2006 (Monnig and Bradley, 2007).
Sprayer skip (background) in a no-tillage field demonstrates the efficacy of fall-applied Basis® Blend herbicide (foreground) for winter annual weed control. (Note: 0.825 oz/A Basis Blend + 1.5 pt/A 2,4-D + COC applied Nov. 13, 2012 in a field near Blandensville, Ill. Photo taken April 13, 2013.)
Untreated check strip (right) demonstrates excellent efficacy of fall-applied Basis Blend herbicide (left) on dandelion and other winter annual weeds in a field near Cambridge, Ill. (Note: 0.825 oz/A Basis Blend + 2,4-D + COC applied in November 2012. Picture taken April 2013.)
Untreated check strip (left) demonstrates excellent efficacy of fall-applied Basis Blend herbicide (right) on winter annual weeds in a field near Streator, Ill. (Note: 0.5 oz/A Basis + 2,4-D + COC applied in late October 2010. Picture taken in spring, 2011)
Mock, V. A., J. E. Creech, B. Johnson, J. Faghihi, V. R. Ferris, A. Westphal, K. Bradley. 2007. Winter Annual Weeds and Soybean Cyst Nematode Management. Purdue Univ. Extension WS-36.
Monnig, N. and K. W. Bradley. 2007. Influence of fall and early spring herbicide applications on winter and summer annual weed populations in no-till soybean. Weed Technol 21:724-731.
Monnig, N. and K. W. Bradley. 2008. Influence of fall and early spring herbicide applications on winter and summer annual weed populations in no-till corn. Weed Technol 22:42-48.
Owen, M., B. Hartzler, and B. Pringnitz. 2001. Managing winter annuals in row crops. In Int. Crop Mgmt Newsletter IC-486(5), 4/16/2001. Iowa State Univ., Ames, IA.
Werle, R. and L. Sandell. 2013. Managing Winter Annual Weeds Starts this Fall. Univ. of Nebraska-Lincoln CropWatch. Oct 11, 2013.
This article is not intended as a substitute for the product label for the products referenced herein. Product labels for the above products contain important precautions, directions for use and product warranty and liability limitations that must be read before using the product. Applicators must be in possession of the product label(s) at the time of application. Always read and follow all label directions and precautions for use when using any pesticide alone or in tank mix combinations.
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