ISSUE 7 June 16, 2005
ERRATUM - LATE HERBICIDE APPLICATIONS IN SMALL GRAINS
In last weeks Pest Report it was reported that Silverado should be applied prior to jointing. Bayer has received labeling allowing Silverado to be applied up to 55 days before harvest or up to the boot stage of HRS and durum wheat.
APPLICATION WINDOW FOR PUMA AND SILVERADO
Application window for Puma is 60 days before harvest and Silverado is 55 days before harvest. In looking ahead, 60 days from now would be around August 15 which is the normal time for small grain harvest. The wet weather may delay harvest one or two weeks but we are nearing the end of the application window for Puma and Silverado for a mid-August harvest.
SECTION 24(c) FOR AERIAL APPLICATION OF CALLISTO
The Department has received several calls over the past few days concerning the recent heavy rains in the state and the inability to get into fields using ground pesticide application equipment. In particular, this concern was voiced by corn growers who have limited postemergence broadleaf weed herbicides that are labeled for aerial application.
To address this need, the NDDOA has issued a Section 24(c) Special Local Needs (SLN) registration allowing aerial applications of Callisto Herbicide on corn. This SLN registration is good for this season only and expires on July 15, 2005.
Supplemental labeling for this SLN registration has been posted on the Department's pesticide registration database and on the NDSU Pesticide Program page.
Have a copy of the SLN supplemental labeling in your possession during application, and to follow all directions, precautions, and restrictions on both the full Callisto label and the SLN labeling.
SECTION 18 FOR REFLEX ON DRY BEAN
The ND Section 18 application for Reflex on dry bean submitted to the EPA has not been approved. Jim Gray from the ND Dept of Ag has been encouraging EPA to review this package and approve for use. The Section 18 division of EPA has only 4 people to review all Section 18 submission for the entire country. One of the four people is dedicated to reviewing all Sect. 18 submissions for soybean rust which leaves only three people to handle the others. We hope action will be taken shortly.
NDSU Extension Weed Specialist
RAIN INTERFERENCE WITH POSTEMERGENCE HERBICIDE APPLICATION
The 2005 North Dakota Weed Control Guide, page 69, lists the minimum interval between herbicide application and rain for maximum herbicide uptake and efficacy.
Herbicide uptake by weeds and crops is most rapid immediately after application and significant herbicide uptake can occur even when the rain event begins sooner than the listed minimum interval. So, herbicides should not be automatically reapplied when rain falls sooner than the minimum recommended interval between application and rain.
If a single herbicide application was intended, assess the situation after the full effect of the herbicide can be observed but do not wait too long for a needed reapplication. Waiting may allow the target weeds to become too large for good control and the crop stage may become too advanced for safe herbicide application. Look for early indications of weed regrowth to indicate poor control. Marking weeds for reobservation may help determine if regrowth is occurring. If multiple herbicide applications were planned, the planned interval usually can be maintained, but if the rain was intense and started soon after herbicide application, the interval before the next application should be shortened.
Rain intensity and amount can influence the effect of rain on herbicide phytotoxicity. A light mist after application may sometimes even increase weed control while an immediate brief heavy rain may wash off much of the herbicide. Phytotoxicity of herbicides to weeds that are easily controlled generally will be less affected by rain after application than phytotoxicity to weeds that are difficult to control.
Rain may interfere with an on-going herbicide application resulting in a partial sprayer tank load of unused herbicide solution. Problems may occur as the spray solution sets in the tank waiting for the field to dry enough so the remainder of the spray can be applied. Some herbicides degrade slowly as they set in a water solution but most formulated herbicides will retain most of their activity over a few days. The exact amount of degradation is affected by water temperature, water pH, and the active ingredient in the tank so predicting the rate of degradation is very difficult and not precise.
Some herbicides and herbicide combinations may settle out of suspension with time so gentle agitation may be needed to prevent the herbicide from forming a layer on the bottom of the tank. The micro-rate of sugarbeet herbicides should be agitated very gently since over-agitation will increase the formation of precipitate.
Adding fresh water and herbicide to a sprayer with old spray solution is not a good idea if the herbicides in the sprayer are among those which may plug screens and nozzles after setting for a time. Dealing with a partial load of a plugging problem is much better than dealing with a full load.
Finding a way to apply an aged spray solution to a registered crop is always better than dumping the herbicide solution. Most of the benefit of the herbicide will still be realized even if some degradation has occurred so the total value of the herbicide will not be lost. Removal of the screens at the nozzles and increasing spray pressure will nearly always allow application of an aged spray solution, especially if it was kept in suspension by gentle agitation. Increased spray pressure will increase application rate, but this will be partially offset by the reduction in activity of the herbicide. Increasing spray pressure from 40 psi to 60 psi will increase spray volume by about 20% and increasing spray pressure from 40 psi to 80 psi will increase spray volume by about 40%. The amount of increase in spray pressure can be adjusted based on estimated herbicide degradation, label limits on herbicide rates and the amount of precipitate in the spray solution.
Rain during or right after herbicide application can cause problems, but management and planning can usually maintain most of the value of the herbicide treatment or remaining spray solution.
Extension Sugarbeet Weed Specialist
LEAFY SPURGE CONTROL IMPROVED WITH PICLORAM (TORDON) MIXTURES
Research at North Dakota State University has shown that herbicide mixtures can provide improved leafy spurge control compared to a single herbicide alone. The long-term standard treatment in the state has been Tordon at 1 pint plus 2,4-D at 1 quart/A. This treatment provides control similar to Tordon at 1 quart/A alone and is more cost-effective. Recently, research has shown that mixtures of some newer herbicides labeled for leafy spurge can increase long-term control compared to the Tordon plus 2,4-D treatment.
For instance, leafy spurge control is dramatically improved when diflufenzopyr is applied with picloram (Tordon). Diflufenzopyr is an anti-auxin that seems to increase translocation of auxin and auxin-like herbicides such as Tordon and Banvel (dicamba) in perennial weeds, which results in increased root kill. Diflufenzopyr is only available to land managers in a combination with dicamba in a product called Overdrive.
In general, the addition of Overdrive to Tordon has doubled leafy spurge control compared to Tordon applied alone. For instance, leafy spurge control 12 MAT (months after treatment) averaged 95% with picloram at 4 oz/A (1 pint/A Tordon) plus Overdrive at 4 oz/A compared to only 40% to 60% control with picloram at 4 oz/A applied with 2,4-D at 1 qt/A. With picloram at 6 oz/A (1.5 pints/A Tordon) plus Overdrive at 4 oz/A, leafy spurge control averaged 99% 12 MAT. In contrast, picloram at 8 oz/A (1 qt/A Tordon) alone averaged 60% control 12 MAT. Tordon plus Overdrive at 1 pint plus 4 oz/A should be applied with a methylated seed oil (MSO) or non-ionic surfactant and costs approximately $25/A, so land mangers need to consider both the increased cost and the improved control gained from this combination treatment.
A herbicide mixture, which has become popularly known in the state as the "North Dakota three-way" is an alternative to Tordon plus 2,4-D applied in spring and early summer. The treatment includes the long-term standard of Tordon at 1 pint plus 2,4-D at 1 quart/A combined with Plateau at 4 oz/A plus a MSO. This three-way mixture averaged 98% leafy spurge control 12 MAT and 73% control 24 MAT, compared to Tordon plus 2,4-D which only provided 81 and 45% control, respectively. The three-way treatment costs approximately $23/A compared to $12/A for Tordon at 1 pint plus 2,4-D at 1 quart/A.
Tordon applied either alone or with 2,4-D has been the most widely used herbicide treatment for leafy spurge control in North Dakota for many years. However, combinations of Tordon with Overdrive or Plateau have shown improved long-term leafy spurge control compared to Tordon or Tordon plus 2,4-D alone. Also, the combination treatments may reduce the number of herbicide applications required to maintain satisfactory control and should be considered in a long-term management program.
NDSU Research Weed Science
USING AERIAL APPLICATORS AFTER THE STORMS
The disagreeable weather we have had to contend with during this crucial stage of the growing season means than many folks will be turning to aerial applicators to get the job done. And they will, for the most part, get it done in a professional and workman like manner. There will be turbulence along the way so here are some things to consider:
Andrew A. Thostenson
Pesticide Program Specialist
NDSU Extension Service