North Dakota State University
NDSU Extension Service
Volume 15, No. 4 -- October 1997
Weed Control
Some Thoughts on Field Problem
Investigation Related to Herbicides
Conclusions from NAPIAP Survey of
2,4-D
Progress in Perennial Weed Research
Evaluation of Plateau for Leafy Spurge
Control
Evaluation of BAS-662 and BAS-654 for
Leafy Spurge Control
Aphthona Spp. Flea Beetles Movement Along
Railroad Right-of-Ways
Integration of Herbicides with
Aphthona Nicriscutis
Velpar Labeled in North Dakota
Biological Control Agents Released for
Purple Loosestrife Control
New Purple Loosestrife Publication
Available
SLN Allowing Use of Roundup Ultra in Sunflower
In This Issue
Coordinator's Comments
Pesticide Perceptions
Law
Insect Control
Disease Control
Equipment
Safety
Training
Keep an open mind and investigate all possible causes and sources of the observed problem when making a field visit. Do not accept, without question, statements of involved persons about the cause and the source of the problem. The truth often is not obvious. Remember that crop injury can have many causes other than herbicides, and symptomology does not always provide definitive answers. Do not make concluding statements until your investigation is complete. Only make statements that can be supported by facts. Assume that any statements you make while investigating a problem may be repeated to you while you are under oath.
The Plant Diagnostic Laboratory at North Dakota State University will accept samples and provide an opinion on the cause of the problem. However, the Plant Diagnostic Laboratory does not analyze plant tissues or soil for herbicide residues. Opinions on the cause of plant injury will be based on injury symptoms.
Be aware that analysis of plant tissues or soil may not provide a definitive answer to the cause of the problem. Each herbicide must be tested individually, so testing can be very expensive if numerous herbicides are the possible cause of the problem. A positive detection of a herbicide can be useful, but the detected herbicide may not have caused the symptoms. A negative test for a herbicide does not prove that the herbicide did not cause the problem since the herbicide may cause injury at levels less than the detection limit or the herbicide may have been degraded before the samples were taken.
The pattern of crop injury in a field will help identify the source of the injury. A sprayer skip in a field will be valuable in diagnosing a herbicide problem, especially if the applicator remembers the reason and the time that the skip occurred. The history of herbicide use on the field for the past 2 to 5 years should be examined. Uniform damage over the field would suggest herbicide carryover or injury from a direct application rather than drift.
Drift is nearly always worse near the source of the drift with damage becoming less as the distance becomes greater. The lessening of injury with distance may not be evident shortly after the drift has occurred but the differences should become more visible with time, since the recovery of the damaged plants will be more rapid and more complete as the distance from the drift source increases. Crop injury that is associated with one or two sprayer tank loads would suggest sprayer contamination or a mistake in mixing where the wrong herbicide or too much of the correct herbicide was put in the spray tank. An aerial photograph often is very useful in identifying patterns of crop injury in a field.
The family of the herbicide that caused the injury often can be identified by the injury symptoms and the species which are not injured. Look in the affected field, in surrounding fields, and between fields. The approximate date of injury can sometimes be determined by observing or learning the date that the injury first became evident. The size of plants when affected by a growth regulator herbicide can sometimes be determined by the height of the stem where malformed leaves first occur. Plants that are affected as soon as they emerge usually are being damaged by a herbicide in the soil rather than drift. Dates that injury occurred can be related to dates of herbicide application on and around the damaged field.
The direction of the source of herbicide drift can sometimes be determined by finding "drift shadows" by trees, buildings or elevated roads. Anything that intercepts or deflects spray droplets can cause an area of undamaged plants on the downwind side of the object. The shape and direction of the "drift shadow" often will identify the direction of the drift source. The damage from spray drift sometimes moves at an angle across nearby fields with a rather distinct line between damaged and undamaged plants at the edge of the line. Placing tall stakes at the edge of this line through the damaged field will often form a line that points at the edge of the field that was the source of the spray drift. Spray droplets move with the wind. Spray droplets will only move down wind so the wind direction during application will often indicate which potential drift sources are possible and which are not possible. Some herbicides like 2,4-D ester, MCPA ester and Banvel are volatile, and a wind shift after application may cause vapor drift in a different direction than the drift of spray droplets. Spray droplets only move in the direction that the wind is moving.
Some sources of unintended herbicide exposure are very difficult to identify. For example, drift or an accidental and unreported spraying of a long residual herbicide on a tolerant crop would have no effect that year, but the residual in the soil the next year could damage a susceptible crop. Another example is soil movement due to wind or water erosion which causes a damaging level of herbicide to move with the soil.
The person who has the damaged field will want to know if the field should be destroyed or kept. A general rule of thumb is that damage from drift is not as bad as it looks and a decision should not be made within one week of the drift. With growth regulator herbicides, about 10 days is needed before surviving plants will begin to produce new leaves. Evaluation of the level of injury from growth regulator herbicides should not be attempted prior to 10 days after exposure. With ALS inhibitor herbicides and glyphosate, the less damaged plants begin to visibly recover and separate themselves from plants with more injury about two weeks after exposure. Rapid conclusions can lead to bad decisions with spray drift.
Everyone involved will want to know how much yield loss will be caused by the herbicide damage. Accurate visual estimation of yield loss from a non-lethal exposure to herbicide is not possible. Some means of collecting meaningful yield comparisons is essential in obtaining an accurate estimate of yield loss. When part of a field is injured and part is not injured, yield in the uninjured portion of the field can be compared to yield in the injured portion. Hand harvesting at several places, harvesters with yield monitors or harvesting and weighing yield from strips through the field all could be used. Usually, splitting the field into six or eight strips or pieces is better than comparing one half of the field to the other side of the field.
Obtaining accurate yield loss data is very difficult when the entire field is damaged. Comparisons to nearby fields can be done but variability among fields is great. Use of the average yield of several nearby fields also could be considered.
(Submitted by: Alan Dexter Extension Sugarbeet Weed Specialist)
The following are summaries of research by members of the NDSU Perennial Weed Research Project
Plateau has shown promise for leafy spurge control in North Dakota. However, grass injury has been observed, especially to cool season species. The labeled rate for optimal leafy spurge control is 2 oz ai/A applied with a methylated seed oil and nitrogen two weeks before a killing frost. The objective of this research was to evaluate leafy spurge control from Plateau applied with and without adjuvants and applied in the spring or fall to maximize leafy spurge control and minimize grass injury.
Plateau was applied to leafy spurge in the flowering stage in the spring and regrowth was treated in September but plots were only treated once.
In general, leafy spurge control was better with fall applications (100%) than spring applications (70%) at comparable rates. Grass injury ranged from 10 to 35% with fall applications and from 2% to 9% with spring applications. Grass injury increased and leafy spurge control increased when Plateau rate increased from 2 to 4 oz/A. Grass injury and leafy spurge control increased when an MSO adjuvant was added to spring applications.
Plateau at 1 oz/A plus MSO provided 96% leafy spurge control, similar to 2 oz/A alone and gave leafy spurge control and grass injury similar to Tordon + 2,4-D at 1 qt/A + 1 qt/A. Adding nitrogen Plateau with and without MSO adjuvant did not affect control.
Research is in progress to evaluate the effect of fall application timing with Plateau on leafy spurge control and grass injury. Application times range from August 15 through October 15. The effect of various adjuvants combined with Plateau on grass injury is also being evaluated.
BAS-662 is a combination of Banvel + BAS-654 in a ratio of 2.5:1 Banvel: BAS-654. BAS-654 inhibits the transport of naturally occurring plant hormones like indoleacetic acid (IAA) and synthetic auxin-like compounds in plants. In general, BAS-654 interferes with the auxin balance needed for plant growth. The purpose of this research was to evaluate BAS-654 alone and in combination with dicamba and other herbicides for leafy spurge control in a series of greenhouse studies.
BAS-662 was applied to leafy spurge plants to achieve Banvel rates of 0.5 to 4 oz/A. The plants were evaluated for top growth injury 1 and 2 weeks after treatment (WAT) Then all top growth was removed and the plants were allowed to regrow for 4 weeks (6 WAT), at which time the leafy spurge regrowth was evaluated.
There were no visible differences in injury symptoms between Banvel applied alone or with BAS-654. However, leafy spurge regrowth was much less when Banvel was applied with BAS-654 compared to dicamba applied alone at the same Banvel rate. Leafy spurge did not regrow when dicamba at 4 oz/A plus BAS-654 was applied.
Leafy spurge control also increased when BAS-662 was applied with Tordon, 2,4-D, and Tordon + 2,4-D, but not with quinclorac (experimental herbicide from BASF). In general, leafy spurge regrowth was reduced nearly 50% when Tordon or 2,4-D was applied with BAS-662 compared to either herbicide alone and by 98% when Tordon plus 2,4-D was applied with BAS-662 compared to the herbicide combination alone. It is not known what amount, if any, the Banvel portion contributed to the increase in control when BAS-662 was applied with these herbicides.
The addition of the BAS product does not alter the visible topgrowth injury but seems to increase root kill. Perennial weed control would greatly increase if the greenhouse results are reproduced in the field.
Leafy spurge is often found in long narrow corridors such as railroad right-of-ways and is difficult to treat. Two experiments were conducted to determine the establishment, population increase, and movement of Aphthona species flea beetles in confined area of leafy spurge.
A. nigriscutis was released in a dense stand of leafy spurge along a railroad corridor in June 1993 at 100, 200, 300, 400, and 500 adult insects released per treatment. A. nigriscutis flea beetles were found in all treatments each year after release and leafy spurge stem density began to decline in 1995. The greatest stem density decrease was 72% when 500 beetles/plot were released. The maximum stem density decrease and highest beetle population occurred within 10 feet of the release point regardless of treatment.
A similar experiment was established in July 1995 when a mixed population of A. czwalinae/ lacertosa near Lisbon, N.D. at 500, 1000, 1500, and 2000 adults per treatment.
A. czwalinae/lacertosa were found at all release sites in both 1996 and 1997. The average stem density in the 2000 insects/release treatment declined by 71% 2 years after release. The average stem density declined 48, 60, and 23% within 10 feet of the release point for the 1500, 1000, and 500 insect treatments, respectively. A. czwalinae/ lacertosa were found up to 70 feet from the release point. Flea beetles will establish on industrial sites such as railroad right-of-ways. The larger the release number the more rapid the site stem density declines.
Aphthona nigriscutis has reduced the density of leafy spurge at many locations. However, there are locations where A. nigriscutis has not established or is found at densities too low to be effective. Therefore, it may be necessary to integrate biological and chemical control to reduce leafy spurge densities to non-economic levels. The objective of this experiment was to integrate Tordon plus 2,4-D and A. nigriscutis for leafy spurge control.
Experiments were conducted at Chaffee and Fort Ransom, North Dakota. Approximately 450 A. nigriscutis were released into cages. Tordon plus 2,4-D at 1 qt/A + 1 qt/A were applied on August 15, September 1 and 15, and October 1. The experiment at each location was repeated the following year on leafy spurge that was not infested with flea beetles.
The effect of Tordon and 2,4-D on A. nigriscutis population was estimated by counting the number of adults emerging from soil cores harvested in the fall and spring. The number of beetles collected from soil cores was similar among herbicide application dates both across locations and years. An average of two A. nigriscutis adults were recovered from each soil core harvested in the fall of 1995 compared to only one per core from spring harvested soil cores across both locations in 1996.
Overwintering mortality decreased the number of flea beetles recovered from spring harvested soil cores. Overwintering mortality was not observed in the A. nigriscutis population from soil cores harvested in the second year of the study in 1996 and 1997. An average of two and three flea beetles were collected from each soil core harvested in the fall and spring, respectively.
Leafy spurge stem densities 12 months after treatment were lowest in the plots that were treated with Tordon plus 2,4-D on or after September 1 compared to the August 15 application, insects only, and the check in 1996. Leafy spurge stem density was lower inside the cage when Tordon plus 2,4-D was applied to established flea beetles compared to Tordon plus 2,4-D and insects alone. This integrated treatment of flea beetles and herbicide has an additive/synergistic effect with respect to leafy spurge control.
Velpar herbicide, manufactured by DuPont has received Special Local Needs (Section 24(c)) labeling for weed control in forage alfalfa in North Dakota. Velpar has been labeled in many states for several years and an important herbicide in controlling many weeds associated with older alfalfa stands.
Make a single application to dormant alfalfa before new growth begins in the spring. Apply to alfalfa used for forage only. For optimum results, 0.5 to 1 inch of rain must occur after application and before weed germination. If weeds have emerged at the time of application, use a nonionic surfactant with Velpar at 1 qt/100 gallons of water.
Treat only healthy alfalfa stands older than one year and the alfalfa has well established root system. Apply Velpar at 0.67 to 1 lb DF/acre for light soils, 1 to 1.33 lb DF for medium soils and heavy soils.
Do not apply Velpar on seedling alfalfa, alfalfa-grass mixtures, or other mixed stands.
NDSU weed research with Velpar in 1996 showed near 99% control of common mallow, common lambsquarters, seedling dandelion, field pennycress, kochia, wild mustard, cockle, biennial wormwood, Russian thistle, tansy mustard, redroot pigweed, cutleaf nightshade, sulfur cinquefoil, fairy candleabra, yellow whitlowwort, curly dock, goldenrod, fair to good control of quackgrass, and poor control of black nightshade, established dandelion, Canada thistle, and perennial sowthistle.
Earlier this year purple loosestrife was added to the North Dakota noxious weed list. Implications of this action are severe limitations where this plant can grow. In addition, strict regulation will be enforced on sale and purchase for home plantings.
On July 17, 1997, a mixed population of the biocontrol beetles Galerucella pusilla and G. calmariensis were released to control purple loosestrife along the English Coulee in Grand Forks. Approximately 5,000 adults each were released at two locations in an urban area where control with herbicides would be difficult. It is expected to take 2 to 3 years for the insects to become established in high enough numbers to reduce the purple loosestrife infestation.
These biocontrol agents have a different life-cycle than the Aphthona spp. flea beetles which are used for leafy spurge control. The purple loosestrife beetles overwinter as adults in the soil, not as larvae like Aphthona beetles do. In the spring, Galerucella adults reemerge, mate, and begin to lay eggs on the stems of purple loosestrife. The eggs incubate for approximately 12 days, and then larvae emerge and feed on the purple loosestrife plant for approximately 2 weeks. The larvae pupate into adults in July and August. The adults also feed on purple loosestrife but the majority of the damage is due to larvae feeding.
The Grand Forks release will become the insectary location in North Dakota for redistribution of these insects to purple loosestrife infestations throughout the state. Biocontrol insects are best used in large infestations of purple loosestrife and/or where spraying herbicides is impractical. However, these insects will not be effective where mosquito control programs are in progress. Insecticides used for adult mosquito control will also kill the purple loosestrife beetles. Small infestations should be controlled with herbicides to prevent spread to large areas. Consult the recently published NDSU Extension Service Circular W-1132, Identification and Control of Purple Loosestrife, for specific control recommendations.
W-1132, Identification and Control of Purple Loosestrife is available through the NDSU Extension Distribution Center or through your local county agent.
The publication provides information on the general characterization of the plant, description, and mechanical, chemical, and biological control methods available for control.
Chemical purple loosestrife control can be achieved through the use of Roundup (glyphosate) in non-aquatic sites or Rodeo (glyphosate) in aquatic sites, or through the use of Garlon (triclopyr). Garlon received an emergency use permit for postemergence and residual purple loosestrife control. Residue from Garlon may cause injury to other broadleaf plants intercepting the spray.
Consult NDSU Extension Circular W-1132 for more information.
The EPA has established a tolerance for glyphosate (Roundup Ultra) on sunflower at 0.1 ppm. As a result, Roundup Ultra can be applied as a preplant burndown prior to sunflower emergence which is similar to many other crops.
North Dakota has issued a Special Local Needs label allowing Roundup Ultra to be applied as shielded postemergence application between sunflower rows. Currently, there are no postemergence herbicides labeled for this use in sunflower. The application must be made with a shielded sprayer. The shield must consist of guards on all four sides and on the top. Other instructions include:
Spraying small sunflower plants increase the likelihood of spray contact and sunflower injury. Leaves of larger plants are higher off the ground and less likely to come in contact with spray fines that escape from under the hood.
Broadleaf weed control in sunflower is one of the greatest problems in sunflower production. NDSU and Kansas State research has shown complete control of several weed species with excellent crop safety. Roundup Ultra through shielded sprayers could provide excellent broadleaf weed control but does require sprayer modifications and does not address weed control in the sunflower row.
(Submitted by: Richard Zollinger, Extension Weed Specialist)
[ In This Issue /
Coordinator's Comments ]
[ Pesticide Perceptions ]
[ Law / Insect Control / Disease Control
]
[ Equipment / Safety / Training ]
ND Pesticide Quarterly, Vol. 15, No. 4 -- October 1997
NDSU Extension Service, North Dakota State University of
Agriculture and Applied Science, and U.S. Department of
Agriculture cooperating. Sharon D. Anderson, Director, Fargo,
North Dakota. Distributed in furtherance of the Acts of Congress
of May 8 and June 30, 1914. We offer our programs and facilities
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North Dakota State University
NDSU Extension Service