Crop & Pest Report - All
Professor of Climatological Practices
Weather Forecast: May 19 – May 25, 2016
April 2016 recorded above to well above average precipitation for almost all of North Dakota. May, on the other hand, has recorded well below normal precipitation to this point. There is potential for this to change over the course of the next seven days. In the short term, the weather is expected to remain dry and very windy at times. This weekend into early next week, the upper-level wind flow will transition to the southwest over the upper-Midwest as a trough forms over the western portion of the United States (Figure 1). Almost all significant rain events in North Dakota are associated with this type of pattern.
Temperatures are expected to be 5-10 degrees above seasonal averages through this weekend with a stiff south wind on many of these days. That wind will be in association with an area of low pressure that will be forming in the Rocky Mountains. That low pressure center will come out in two pieces, one weaker system on Sunday/Monday and another probably stronger piece next week. It will be that second system that will have potential for more significant rain across some portions of North Dakota. It will likely be an event with “winners and losers” meaning widely varying rain totals and may linger off and on through much of next week.
That storm next week will not only have rain potential, but the cloudiness associated with the storm, cooler temperatures for a few days. Yet, through Sunday above average temperatures will create some needed bonus growing degree days. Those projected Growing Degree Days (GDDs), base 34°, 44° and 50° for the period May 19 through May 25, 2016 for some select North Dakota cities are presented in Figure 2.
Assistant State Climatologist/Meteorologist
(701-231-8209) Twitter: @darylritchison
Temperatures in the region dropped below freezing towards the end of last week. According to NDAWN Hettinger reached down to 24 °F on May 14th and further north it ranged from 25-31 °F as a low. With these low temperatures it is important to scout fields for potential frost damage. The extent of frost damage depends on factors such as the growth stage of the crop, soil moisture content, and the length of time the temperature is below freezing. Where the old vegetation may look frost damaged, it is important to consider where the nodes and growing point of the plant are located. After a frost be sure to wait 4 days to a week to make a decision. If the growing point is not damaged and the new growth looks healthy there is a good chance the crop will survive.
Many growers in the region have small grains, pulses, and canola in the ground. In Hettinger County growers are close to finishing corn and flax with sunflowers next in line to be planted. In Stark County corn is about 50% planted with most not having started on sunflower yet. Alfalfa in the region is looking good, however some fields may have suffered from frost.
Area Extension Specialist/Cropping Systems
The region’s NDAWN stations indicate rainfall of 0.2 to 0.4 inches only in southern counties during the past week (May 11-17). Rain is welcome throughout the region. The NDAWN station with lowest air temperature was 21 degrees F at Pillsbury on May 14 while other sites that day had low temperatures ranging from 23 to 30 degrees. Frost damage to crops appear to be limited to superficial leaf damage, e.g. corn (see picture).
Barley and spring wheat seeded the first-half April are at the 3-leaf stage (tillering). Corn planted on April 30 has accumulated 125 to 180 growing degree day (GDD) units through May 17. April-planted corn is in the one- to two-leaf (V1-2) stages. Planting of soybean acres should be nearly completed by the end of this week. Planting of dry bean and sunflower is beginning. See the following website for a NDSU research summary on early versus normal dry bean planting dates: www.ag.ndsu.edu/publications/crops/impact-of-planting-dates-on-dry-edible-bean.
Pre-emergence herbicide application for planted row crops continues, though challenged by environmental conditions. Also, post-emergence herbicide application in small grain is in progress.
Area Extension Specialist/Cropping Systems
NDSU Carrington Research Extension Center
The northwest region did not experience as many hours of freezing temperatures as did locations farther east as a result of the cold front that moved through the area week. Daily high temperatures were in the 40s and 50s the latter half of the week but were back into the 60s by the weekend. Overnight temperatures only dipped a little below freezing in the northern most counties but otherwise stayed at or a few degrees above freezing in most of Northwest ND.
Small grains planted in early April are at the 3 or 4 leaf stage and winter wheat in many fields is jointing. Pulse crops planted in mid to late April are emerged and looking good. For those still planting and/ or looking to apply pre-emergence herbicides, we have a windy week ahead with high winds predicted for Friday and Saturday. If you need to spray, plan to spray early in the morning before the wind picks up and ahead of possible thunderstorms early next week.
Area Extension Specialist/Cropping Systems
NDSU Williston Research Extension Center
Low temperatures from 19°F to 23°F reported in area counties over the weekend. Early seeded canola is frost damaged and is expected to be re-seeded. Sugarbeets have been hurt by frost, wind or sand-blasting with re-seeding occurring. Also, a small pocket of soybeans and edibles were emerged during this frost event and did not survive.
No disease development reports for this week. Flea beetles are beginning emergence. The dry weather has been good for farm progress; however, we need rain. Dry powdery seeds continue as we move into the heart of soybean planting and the beginnings of dry edible beans and sunflowers.
Area Extension Specialist/Agronomy
Small Grain Virus Update – NDSU Plant Diagnostic Lab
Small grain samples, primarily winter wheat, have been arriving at the Plant Diagnostic Lab for virus testing. Our routine protocol is to test each sample that comes in for wheat streak mosaic virus (WSMV), high plains virus (HPV), cereal yellow dwarf virus (CYDV), and two strains of barley yellow dwarf virus (BYDV). WSMV and HPV are vectored by the wheat curl mite and become problematic when the green bridge was not broken (seeding wheat into volunteer wheat). BYDV is vectored by cereal aphids and risk can be assessed if an early arrival of cereal aphids occurs (see article in last week’s crop and pest report). Visual diagnosis of a viral disease can be difficult as they can mimic abiotic disorders. Therefore, it is important to submit samples for accurate diagnosis.
As of May 18th, WSMV has been detected in samples from Adams, Dunn, Hettinger, McHenry, and Mountrail counties. Samples positive for both WSMV and HPV have been submitted from Dunn and Hettinger counties.
Waterhemp has Emerged in the Southern Red River Valley
I received two images yesterday, one from near Sabin, MN and a second near Walcott, ND, confirming waterhemp has emerged in eastern North Dakota and Minnesota. Waterhemp is in the pigweed family but typically germinates later than redroot pigweed. Waterhemp is very similar to redroot pigweed, especially when it is young. Waterhemp cotyledons tend to be wider than and not as long as redroot pigweed (rounded). First true leaves are lanceolate shaped.
I have been working on a Growing Degree Day (GDD) model to track waterhemp germination and emergence. GDDs have been used to classify weeds to simplify scouting (Iowa State University IPM-64). By tracking GDDs, it may be possible to estimate waterhemp germination and emergence in order to time application of soil-applied herbicides applied early postemergence herbicides (lay-by) in sugarbeet.
The model did not correctly estimate waterhemp germination and emergence indicating more development work will be needed. One positive, there is much greater knowledge and awareness of waterhemp in corn, soybean and sugarbeet fields than a few years ago which is providing a stronger ‘training’ data set for adjusting the model for future use in future years.
Extension Sugarbeet Agronomist
NDSU & U of MN
How Long Soil-Applied Herbicides can Lay on the Surface before Precipitation?
Two questions are on farmers minds. First, how long will soil-applied herbicides ‘last’ on the soil surface if it doesn’t rain and second, should a farmer consider using a rotary hoe or drag harrow to incorporate herbicides?
Volatility (evaporation), adsorption, and soil moisture effect soil-applied herbicides. Volatility is the change in herbicide physical state, from a liquid to a gas. Most soil-applied herbicides used by farmers have a medium or low vapor pressure meaning they generally will not volatilize during warm and dry conditions. Adsorption is the attachment of herbicides to soils. Herbicides must be bound to soils or they would easily leach away. Most herbicides are moderately or strongly bound to soils colloids and should not be impacted by our dry conditions. Herbicides can lay on the soil surface for 7 to 10 days, perhaps even 2-weeks without loss of efficacy.
A greater concern in 2016 is blowing soil, especially soil-applied herbicides attached to blowing soils. It is very possible that herbicide will move from target field to off-target fields with blowing soils. Damage once activated might be similar to spray drift; damage greatest near the source and diminishing with distance.
Soil moisture (and rainfall) affects soil-applied herbicides in two ways. First, rainfall moves the herbicide from the soil surface and into soil. Second, rainfall contributes to the amount of herbicide available for absorption by weeds. While ‘half an inch’ is a good rule of thumb to activate herbicides, soil moisture conditions at or after the time of soil-applied herbicide application will influence herbicide activation. Rainfall must first wet the soil surface before water and the herbicide can move into the soil profile under dry conditions. Additionally, herbicides bind more tightly to soils and are less active for weed control in dry conditions. Thus, under our dry conditions, it might take more than 0.5 inch of rainfall for satisfactory levels of activation and resultant weed control. But on the other hand, your herbicide should be ‘there’ and available for activation once we get rain...provided the soil does not blow.
Can I assist Mother Nature by using light tillage such as a dray harrow or rotary hoe? It depends on your purpose. I would consider light tillage if the concern is small seeded broadleaves starting to emerge. I would not consider light tillage to incorporate the herbicides as good intentions may lead to steaks from inadequate or uneven incorporation?
Extension Sugarbeet Agronomist
NDSU & U of MN
Minimum Time Between Herbicide Application and Tillage
Question: I am aware that the time interval between when glyphosate is applied until the ground is tilled is (ideally) 5 days. There are some who say that one can till after three days, if the weather is warm, 60 degrees or warmer. My question is what would be the minimum time interval in days, after spraying, to harrow the field to scatter/break up straw and roll out rocks? Thank you for all your help.
Answer: There are two processes that must occur after spray droplets are retained on leaf surfaces:
1. Deposition of the active ingredient on the surface of the plant foliage.
2. Absorption of herbicide active ingredient across the cuticle and active translocation to sites of action.
A review of published, peer-reviewed literature on glyphosate absorption and translocation show a range of absorption between 3 and 49% of the applied amount. Generally, there is an average adsorption of 33% across most weed species. Glyphosate is a very hydrophilic (water loving) herbicide and is repulsed by lipophilic (oil loving) compounds found in oil adjuvants and the waxy cuticle on leaf surfaces. The cuticle is a strong barrier to glyphosate adsorption. Humidity plays an extremely important role in aiding glyphosate adsorption (See #6, #14 on page 71-72 in the ND Weed Control Guide for further discussion). Growers and researchers consistently see greater weed control from glyphosate when applied in humid conditions (eastern ND compared to western ND or application prior to a rain event). Most small annual weeds require less total amount of herbicide applied and less time for the adsorbed herbicide to translocate than biennial or perennial plants. Plant death from glyphosate is slow and may take from 10 to 20 days depending on temperature and environmental conditions.
Small annual weeds may require only 3 days following application for maximum glyphosate absorption and kill. However, large winter annual weeds that have bolted, biennial and perennial weeds may require the full 5 days before tillage should be performed. Plants that have bolted or have an extensive underground root system will require at least 5 days for the herbicide to translocate to stems and roots for optimal control. In summary, small weeds, warm temperature, high humidity will increase adsorption and possibly allow a shorter interval between herbicide application and tillage. Bolted winter annual weeds, biennial and perennial weeds will require the full 5 days to get maximum kill.
Extension Weed Specialist