NDSU Crop and Pest Report
NDSU Crop and Pest Report


ISSUE 3  May 16, 2002

 

SPARTAN BEFORE DRY PEA AND CHICKPEA EMERGENCE

Chickpeas and field peas are large seeded crops and require 3 to 5 times the water to germinate compared to other crops. They are often seeded early into cold soils of 40 degrees F or higher and seeded two to three inches deep. Emergence, in most cases, occurs within 10 to 14 days after planting. Cold weather is delaying pea development. The emerging shoot of dry pea and chickpea carries the first leaf (node) above the soil surface and the cotyledons stay with the seed. The growing point stays below the ground like wheat or corn for the first three to four weeks which makes them most frost tolerant.

A 2002 Section 18 registration allows preemergence application of Spartan no more than 3 following planting. The snow and cold weather has delayed application of Spartan after planting dry pea and chickpea and growers may wait for weeds to emerge so a burndown herbicide can be applied. Several acres of peas has been planted but Spartan has not been applied. The Spartan label indicates that Spartan must be applied no more than 3 days after planting instead of prior to pea emergence. Growers may choose to apply glyphosate without Spartan in their burndown application then apply Rezult 7 to 10 days after planting instead of the required 3 days for Spartan.

The 3 day requirement of Spartan is intended maintain a barrier between the herbicide and emerging shoot. Spartan contact with the cotyledon through soil cracking, incomplete furrow closure or substantial rainfall when the cotyledon is very close to cracking the soil surface greatly increases the risk of crop injury since Spartan can cause significant burn on any plant tissue exposed to the spray. The 3 day application requirement maintains the best crop safety recommendation. Growers should always check to make sure peas are not cracking the soil surface or very close to this stage when they apply their Spartan.

This information was supplied by Kent McKay, NDSU Area Extension Agronomist, Northcentral Research & Extension Center, Minot, ND and Sam Tutt, FMC Corp.

 

COLD TEMPERATURES AND HERBICIDE PERFORMANCE

A common question as a result of the wide temperature fluctuations is what affect does the cold/cool weather have on burndown and postemergence herbicide performance. This article addresses both situations. As with most herbicide decisions, there is not a single answer that fits all situations.

Herbicides perform best under ideal conditions when both the crop and weeds are actively growing. When the environment reduces the vigor of the crop or the weed, undesirable consequences can occur - either crop injury or poor weed control. The most noticeable effect of cool temperatures on herbicide performance is a slower kill of weeds. A herbicide kills a plant by disrupting some physiological process essential for growth. Under cool temperatures, physiological processes slow down, thus the herbicide is slower acting. In some situations the desired effect (dead weeds) will result - it just takes longer to get the job done. In other situations, the slower activity of the herbicide will allow some weeds to survive, or the crop may be injured.

The simple solution would be to wait until more favorable temperatures arrive; however, delays in application could create problems if weeds are already at the optimum size for control when the cool temperatures arrive. Factors to consider in whether to spray under these cool conditions or to wait until warmer conditions arrive include:

The likelihood of decreased weed control due to cool temperatures will vary depending upon the target weed and the herbicide and rate applied (Table 1). Weed species highly susceptible to the herbicide are less likely to show a negative response to cool temperatures than less susceptible weed species. For example, assume two soybean fields have similar weed infestations of yellow foxtail and nightshade and both fields are sprayed during a period of unseasonably cool temperatures. One field was Roundup Ready and treated with Roundup Ultra, whereas the other was treated with Pursuit or Raptor. The field treated with Pursuit or Raptor would be more likely to have foxtail escape since yellow foxtail is more tolerant of Pursuit than velvetleaf. On the other hand, nightshade would be more likely to escape in the Roundup Ready field than yellow foxtail, again due to differential tolerance of these species to Roundup. Although it is best to delay applications, the potential for a negative response to temperature can be reduced by ensuring that optimum rates (full label) are used.

Undesirable crop responses are more likely to occur when using herbicides with lower margins of crop safety. Certain herbicide labels have warnings on the label concerning increased risk of injury under cool conditions. If plans are to use one of these products, the best decision would be to delay application until more favorable conditions occur or switch to a product with a greater margin of crop safety. A partial list of products with cool temperature warnings includes Basis Gold, Accent Gold, Reflex, Lightning, Cobra, and Buctril. Read all labels to determine if restrictions or warnings are present concerning use in cool temperatures.

Crop and weed size also should be considered when determining whether or not to spray. A soybean field in the first trifoliate stage with one inch foxtail provides greater flexibility in application timing than a corn field at the V4 stage with three to four inch yellow foxtail. In the corn situation, the foxtail may exceed the height for optimum control by the time temperatures increase, even with the reduced growth rates under the cool temperatures.

In summary, the ideal solution is to wait until better weather conditions arrive to treat fields. However, if weed size or other situations dictate that fields be treated now, select the product that has the best margin of crop safety and is strong against the target species. Keep in mind that reduced rate treatments are less likely to provide acceptable control under adverse conditions than when plants are actively growing. Finally, the performance of the row-crop cultivator is not affected by temperature and would be a great choice under these conditions.

Table 1. Effect of temperature on percent reduction (%) in dry weight of green foxtail and redroot pigweed provided by postemergence Accent applications.

Temperature (F)

Green foxtail

Redroot pigweed

50

56

95

68

95

95

86

95

97

Weed Technology. 1991. Vol. 5: 92-96. Nalewaja, Woznica and Manthey.

 

ROTATION CROPS AFTER ACETOCHLOR

Acetochlor is the active ingredient in many soil applied corn herbicides, such as, DoublePlay, Harness, Surpass, TopNotch, and Degree. The label limits the crops that can be planted the year following acetochlor application to corn, soybean, sorghum, and wheat. Much effort has occurred by the basic manufacturers with EPA to allow additional crops to be planted the following year.

Dow Agrosciences has attempted to resolve this issue about rotation to sugarbeets following use of an acetochlor product. The regulatory people at Dow have been working with Jim Tompkins at EPA to secure an expedient review of the sugarbeet residue data which would support a favorable regulatory decision. Unfortunately, the EPA person in the Registration Division who was assigned the review concluded that there were "potential residues in sugarbeets." This is obviously very disappointing since it is doubtful based on lack of acetochlor residues from other crops that residues do exist.

Tompkins indicated that he will attempt to get sugarbeet tolerances on the 2003 workplan, but that will not be done until October of this year. In light of this, we need to submit letters from stakeholders (growers, processors, university, ND Dept of Ag) to EPA that will persuade EPA to prioritize this review on the 2003 plan of work. To send your requests, email Jim Tompkins at tompkins.jim@epa.gov.

Richard Zollinger
NDSU Extension Weed Specialist
rzolling@ndsuext.nodak.edu


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