C.O.R.N. Newsletter: 2022-13
-
CFAES Ag Weather System 2022 Near-Surface Air and Soil Temperatures/Moisture (Update 6)
Figure 1: Daily average air temperature (dashed red), two-inch (green) and four-inch (blue) soil temperatures for spring 2022. Current daily average soil temperatures are noted for each location. Soil type and location of measurements (under sod or bare soil) are provided in the lower right corner of each panel. A map of all locations is in the bottom right. Data provided by the College of Food, Agricultural, and Environmental Sciences (CFAES) Agricultural Research Stations located throughout the state.
Overall, the past week was on the cool side for the first week of May, with air temperatures averaging in 60s for highs and lows in the mid-40s to low-50s. This kept soil temperatures steady, ranging from the low to mid-50s across the north, to the upper 50s across southern Ohio (Figure 1). Much warmer weather this upcoming week, with several days in the upper 70s to mid-80s, should cause a significant rise in soil temperatures.
Figure 2: (Left) Total precipitation for the week ending May 9, 2022. Figure provided by the Midwestern Regional Climate Center. (Right) Calculated soil moisture percentiles as of 05/08/2022 according to the Climate Prediction Center.
Along with the cool temperatures came plenty of rainfall across the Buckeye State (Fig. 2 -left). Locations along I-71 between Cincinnati to Columbus then east to Jefferson County picked up between 2.5-4”. Isolated amounts of 6-7” were reported in parts of Clinton and Fayette Counties. While soil moisture had improved in late April over early season surplus conditions, last week’s rainfall has many fields across Ohio saturated with widespread ponding conditions. Soil moisture percentiles are now ranked in the 80-90th percentile across the state (Fig. 2-right). Portions of the far south, northeast, and northwest avoided the heaviest rain and may take advantage of this week’s dryness. Saturated areas will take a while to dry, and with temperatures in the mid to upper 80s possible across the southern counties this week, soil crusting may be an issue for some. The Weather Prediction Center is calling for 0.25-0.50” of rain of the next 7 days, the majority of this not falling until Sunday.
The May 2nd Ohio Crop Progress Report (https://go.osu.edu/cropprogress) did show limited planting occurred for the week ending April 29th with 3% of corn and 2% of soybeans were planted. The report released on May 9th will show further progress. The April planted fields will be closely watched for emergence. Germination progress is soil temperature and moisture-related. The temperature relationship is reasonably predictable for corn, requiring 100 to 120 growing degree days (GDDs) to emerge. We refer you to a 2021 CORN for more on calendar vs. GDD for corn emergence at https://go.osu.edu/cornemergence. Table 1 below shows accumulated GDD at CFAES weather stations since April 23rd, when fieldwork broadly began across the state. 2-inch soil temperatures from the CFAES network are used to generate GDD. Based on the earliest planting dates we should be seeing corn emergence in the southern part of the state.
Table 1. GDD Accumulation at CFAES weather Stations based on 2-inch soil temperatures since April 23rd
CFAES Weather Station
GDD 2-in Soil
April 23 to May 8
Emergence (Yes or No)
Corn emergence would be expected for planting dates before
1-Ashtabula
73
No
--
2-Northwest
54
No
--
3-North Central
74
No
--
4-Wooster
71
No
--
5-Western
135
Yes
4/24/2022
6-Eastern
151
Yes
4/26/2022
7-Piketon
158
Yes
4/26/2022
For more complete weather records for CFAES research stations, including temperature, precipitation, growing degree days, and other useful weather observations, please visit https://www.oardc.ohio-state.edu/weather1/.
-
Early Season Wheat Diseases and Fungicides
The wheat crop in Ohio is now between early boot (Feekes 10, in the south) and approaching Feekes 8 (flag leaf emergence) in northern counties. Cooler-than-usual conditions over the last few weeks have slowed the crop down considerably, but as temperatures increase, the crop will advance through several growth stages over a relatively short period. Cool conditions have also kept foliar diseases in check, but Septoria, and to a lesser extent, powdery mildew are still showing up in some fields. Septoria tritici leaf spot is favored by cool, wet conditions similar to those experienced over the last several weeks. It usually shows up first on the lower leaves as yellowish flecks that later develop into irregularly-shaped, brownish-gray lesions, with easily-seen dark-brown to black spots (called pycnidia) in the center. Cool temperatures and high relative humidity are also required for the development of powdery mildew. Typical symptoms of powdery mildew are whitish fungal growth (pustules) on the surface of leaves and stems. If the variety is susceptible and conditions continue to be favorable, a fungicide application may be warranted to prevent both diseases from reaching the flag leaf before grain-fill.
Septoria tritici leaf spot on wheat – note the black dots (pycnidia) inside the lesion.
Powdery mildew on wheat leaf – as the name suggests, note the powdery, white pustules.
Most of the fungicides commonly used on wheat are rated as very good or excellent against Septoria and good or very good against powdery mildew. See the attached chart for fungicide options and efficacy. Remember, always read and follow the labels when making an application. For both diseases, a single application between Feekes 8 and Feekes 10 would be sufficient to protect the flag leaf and minimize yield loss. However, applications made at these early growth stages will not provide adequate control of late-season diseases like head scab and Stagonospora glume blotch. So, you should scout fields before making your fungicide application decisions. If powder mildew and Septoria levels are low as the crop approaches heading (Feekes 10.5), you may be better off waiting to treat fields at anthesis (Feekes), as this will help to suppress head scab, which is still the most damaging and important disease of wheat in Ohio, while at the same time provide very good control of Septoria, powdery mildew, and late-season diseases such as Stagonospora and rust.
Click on the image above to view a pdf printable version of the chart.
-
Soybean Planting Progress, Emergence, and Misconceptions
Recent wet weather across the state has slowed soybean planting progress, but should be picking up with warmer and dryer weather. As of the last week of April, 2% of the soybean acres in Ohio were planted. Last year at the same time, 17% of soybean acres were planted. However, 2018 through 2020, planting progress was similar at 1-2%.
Table 1. Percent soybean acres planted in Ohio by week for the past five years (USDA NASS).
Week
2022
2021
2020
2019
2018
2nd Week of April
0%
1%
0%
0%
0%
3rd Week of April
0%
8%
0%
0%
0%
4th Week of April
2%
17%
2%
1%
1%
1st Week of May
--*
20%
7%
1%
8%
*Not reported yet reported when this article was written.
As soybean planting continues and plants emerge, here are some things to look for as well as some common misconceptions from soybean extension specialists across the U.S.
What Matters at Planting and Emergence: At this point in the growing season, obtaining a stand of sufficient plant population is the first step in ensuring maximum soybean yield. It is important to seed at a rate that will provide an adequate and relatively uniform stand. In Ohio, for soybean planted in May, we recommend a seeding rate of approximately 140,000 seeds/acre with the goal of at least 100,000 plants/acre.
Soybean Emergence Misconceptions: There are several common misconceptions about soybean emergence:
Misconception
Reality
Soybean plants need to have uniform emergence and uniform spacing aka “the picket fence” to maximize yield.
Emergence uniformity is not critically important in soybeans. Recent research has shown planter downforce did not impact grain yield regardless of tillage, soil texture or gauge wheel type. Rate of emergence over four days was altered but did not result in yield differences. Additional research has shown no difference between random drop and precision planting until seeding rates were reduced to 40,000 seeds/acre.
Seed size of planted seed influences end of season crop yield.
Seed size can influence percent emergence (smaller seed size increased emergence 10%), but as long as an adequate stand is established, there is no influence of planted seed size on yield. Effect of seed size on emergence is dependent on soil texture, planting depth and environmental conditions from planting through emergence.
Supplemental nitrogen is essential to maximize yield in high yield environments.
Soybeans with active nodules do not require additional nitrogen, even in high yield environments. Yield responses to N are rare, unpredictable and not economically viable.
Suboptimal stands (<80,000 plants/acre) call for an automatic replant.
Visual stand assessment at VE often underestimates the total number of plants that will emerge. We often ask growers and crop consultants to wait until the VC growth stage to make the call about replanting. Even at suboptimal stands, an automatic replant is not always the best economic decision. Cost of replanting plus added planting date penalties must be considered before replanting.
For more information on soybean emergence misconceptions, this Science for Success video featuring my colleague Dr. Michael Plumblee from Clemson University: https://www.youtube.com/watch?v=MpdokEECT5M and also this Science for Success FactSheet: https://soybeanresearchinfo.com/wp-content/uploads/2022/01/Science-for-Success-Soybean-Growth-Stages-V3.pdf
-
Corn Planting Progress in Ohio is Slow but Coming Along
Better weather: more planting
April was a difficult month for farmers in Ohio; conditions were cold. Some snow and late freeze events were part of the month. This was conducive to limited water evaporation/evapotranspiration, and hence, generally, soils stayed wet.
Getting into May, the first week was still wet with some more precipitations spread around the state. As we move forward into May, warmer and drier weather would help push planting progress around the state. According to models, chances for freeze in May seem to be over on a positive note. The last Ohio weather report can be accessed here for more information.
Corn planting: USDA Crop Progress reports
For the week ending on May 1st, 2022, corn planting progress in Ohio was at 3%, while emergence rates were virtually 0%, which is understandable due to the weather conditions outlined above. For the week ending on May 8th, 2022, corn planting progress in Ohio only increased to 5%, while emergence rates remained at 0%.
Planting and emergence progress in 2022 is slower than records from past years. Progress in Ohio for the week ending on May 8th in 2021, planting was at 26% and emergence at 8%. If looking at the 2017-2021 averages for that same week, 27% of corn was planted, and 6% emerged.
On the other side of the Corn Belt (May 8th, 2022 report), states like Iowa (14% planted) and Nebraska (39% planted) have had stronger starts to the planting season. Like Ohio, closer east, Indiana (11% planted) and Pennsylvania (13% planted) are also having a slower start.
Certainly, some areas of Ohio can have more progress than others. The results presented in these reports can be variable, and they give a general understanding of the overall condition for each of these states. If you would like to see some more information on weekly Crop Progress Reports, you can access the USDA-NASS information here.
-
Soil Crusting Considerations for Corn and Soybean
Warmer temperatures combined with dryer weather will push planting progress along. For fields that have been already planted, recent precipitation and warmer days ahead can build conditions for soil crusting. When heavy rains occur after planting, soil crusting can become a concern, inducing a shallow hard layer on the soil surface that forms due to rapid drying (e.g., warm days and wind). Conditions prone to soil crusting include conventionally tilled fields (in addition to soil erosion), low cover crop residue, fine soil textures, and soils with low organic matter. Besides affecting seedling emergence, soil crusting can result in poor growing conditions, reduced stands and plant vigor, and less water infiltration to the soil profile (Figures 1 and 2).
Figure 1. Soybean seedling struggling to emerge in a surface-crusted, poorly-drained clay soil from Northwest Ohio, 2020.
Figure 2. Corn plant lacking optimum growth in a surface-crusted heavy texture soil from Eastern Nebraska, 2020.
For soybean, if you suspect poor emergence due to soil crusting (or any other factor), take a stand count from several areas within your field at the VC growth stage (unifoliate leaves unrolled sufficiently, so the leaf edges are not touching). See the AgCrops Team YouTube channel for a stand count demonstration. Although a plant population of 100,000 plants/acre is ideal, we do not suggest replanting until the plant population drops to 50,000 plants/acre. Fields with crusting problems can look extremely poor, but the plant stand is adequate, and the field does not need to be replanted. At low plant populations, soybeans can compensate by increasing the number of branches. In general terms, soybean plants tend to be more/better compensative than corn.
For corn, depending on the planting date, the potential yield loss from a reduced stand may be less than expected. To assist in this process, the relationship between planting date, plants per acre at harvest, and crop yield for corn and other adjustments/conversions can be found in the AGF-502 Factsheet. For example, a field planted on May 9th or before and with a stand of 25,000 plants/acre at harvest can still achieve 92% or more of the yield obtained at the optimum planting date and population. Replanting does not guarantee an increase in yields; if replanting happens late, the result can be lower yields (even with higher stands).
Some alternatives for mitigating the effects of soil crusting, other states have recommended: 1) if not planted yet, planting a little deeper for better seed/soil contact and access to moisture (but deep planting has associated risks due to inhibiting growth and vigor, seed running out of energy, uneven stands); 2) reduced or no-till systems that have more residues in the soil surface; 3) rotary hoe in the crusted layer (if crop is germinated and still below ground, but damage to seedlings may occur); 4) a row crop cultivator can be used if the crop is tall enough (limited to crops grown in rows spaced at 30-inch). More information on soil crusting and potential solutions can be accessed here. Although these may be some options, we have not tested these practices in Ohio.
In any case, assessing how strong the crusted lawyer is, where the crop stands (e.g., planted, germinated, emerged), weather forecasts, and timing is critical to inform the decision process better. Before decisions are made, keep in mind that about 5 to 10 percent of planted seeds can fail to establish and that plants can and often compensate for some damage/losses and still be able to produce ‘normal’ yields.
-
Alfalfa Continues to Mature
Alfalfa stands across Ohio continued to mature in the past week despite our cooler temperatures and significant rainfall totals. Alfalfa fields jumped about 2-3 NDF percentage units in the last week depending on the geographical location. As warmer temperatures are expected to persist across the state in the next week, %NDF values will likely increase 5 percentage units or more. As a quick reminder, alfalfa values ranging near 40-42% NDF are ideal for lactating dairy cows. Higher NDF values are acceptable for classes of livestock with lower nutrient demands. Below is an updated table with the most recent alfalfa % NDF Field estimations.
Date
Location (County)
Average Height
Stage
Average %NDF
5/6/22
Adams
22
Vegetative & Bud
33.5
5/9/22
Crawford
18
Vegetative
29.9
5/9/22
Geauga
11
Vegetative
NA
5/9/22
Licking
24.7
Vegetative
34.5
5/9/22
Putnam
16
Vegetative
28.6
5/9/22
Stark
19
Vegetative
30.6
5/9/22
Wayne
18.3
Vegetative & Bud
30.6
*Alfalfa fields with a max height below 16 inches cannot be calculated using the PEAQ method
There have also been some reports of alfalfa weevil feeding across the state. In addition to keeping a close watch on alfalfa development for making harvest decisions, producers should be monitoring alfalfa weevil to determine if harvesting earlier is warranted. If alfalfa weevil damage is at or over the economic threshold, growers should consider cutting earlier to eliminate the risk of losing quality due to weevil feeding. Visit HERE for a factsheet on alfalfa weevil.
-
Forage Quality Targets Based on Animal Class
The optimal time for making a first cutting of forages is fast approaching. But what is the optimal timing to take the first cutting (or any cutting for that matter)? Many will answer by saying it is when you have time and there is a good weather window to get the forage cut and put up! Yes indeed, that is a valid answer. Both of those factors are important and can’t be ignored. However, we know that forage quality declines as the crop moves into flowering stages. The first cutting is usually the highest yielding cutting, so we should try to aim for good quality for as much of it as possible!
But what is “good quality” forage? The correct answer is that it depends on what you feed it to. The concentration of neutral detergent fiber (NDF) is a measure of most of the fiber in forages. The concentration of forage fiber increases with maturity and is negatively correlated with feed intake by animals and the energy concentration of the diet. With hay crop forages, digestibility of the fiber and NDF concentrations have a strong negative correlation so one can assume forages with greater NDF concentrations have fiber that is less digestible.
Below are good forage NDF targets to aim for when feeding different classes of livestock (Table 1). These are general guidelines, but forage within these NDF ranges should provide good animal performance in properly balanced diets.
Table 1. Optimal ranges for forage neutral detergent fiber (%NDF) for different classes of livestock.
Forage type
Dairy cows:
high producing & early lactatingDairy cows: average producing (<27,000 RHA1)
Beef cows: Gestating
Beef cows: lactating
Horses
Legumes
35 – 40%
38 – 45%
50%
45%
42 – 46%
Grasses
48 – 53%
50 – 55 %
60%
55%
55 – 60%
Grass/legume mixture
42 – 46%
46 – 50%
52 – 56%
47 – 51%
48 – 52%
1 RHA = rolling herd average, calculated as the total pounds of milk produced in the last 365 days for the average cow in the herd.
So how do these targets help us with harvest timing? How do we know when the forage growing in the field is approaching these targets? Many factors affect forage quality, but we can make some educated estimates. An article published last week in this newsletter explains how to estimate alfalfa NDF in the field and we are tracking alfalfa NDF in fields across Ohio each week for the month of May (see this week’s article for updated estimates of alfalfa NDF).
The lower value of the NDF ranges in Table 1 should be the latest starting point to begin harvest, weather permitting, because the cutting, field curing, and harvesting process always results in higher NDF values than what the NDF value of the forage was at the time of cutting. Because forage quality changes so fast it is better to start too early than a little too late.
Grasses mature quickly and the optimal harvest window can be only a few days. In general, for high quality grass forage (50 – 55% NDF) suitable for lactating cows, the first harvest should be taken in late vegetative (pre-boot to very early boot stage) in the spring. The grass stem will have one to two palpable nodes (you can feel and see them on the lower stem) and no flowers have emerged. As soon as you see flowering heads emerging in the grass, the NDF is most likely just over 55%. As harvest is delayed, the NDF levels will quickly increase to 60% or higher. Maturity of the grass has a much bigger effect on forage NDF level than does grass species.
For subsequent harvests after the first, alfalfa can be harvested in the bud to early bloom stage (about every 30 days) for excellent quality. Bud stage alfalfa will usually contain 22% or higher crude protein (CP) and 40% NDF, while early bloom alfalfa will average 20% CP and 40 to 45% NDF. However, protein and NDF are not strongly correlated; often CP concentrations will be much higher or lower than these values. A good compromise to extend stand life of alfalfa in a dairy operation is to harvest at least one cutting during the summer months in the early bloom stage. The first two cuttings should be taken near 40% NDF, and later summer cuttings can be taken in the early bloom stage. The NDF content of alfalfa declines more rapidly with maturity early in the season, so the late summer harvests can be made at a later maturity stage without as great a penalty on forage quality. The PEAQ estimation procedure for alfalfa NDF works well in all cuttings and for all types of alfalfa, including reduced lignin varieties. But reduced lignin varieties will have slightly higher fiber digestibility than standard varieties across all levels of NDF concentration. So reduced lignin varieties can offer a wider harvest window to achieve acceptable fiber digestibility when compared with standard alfalfa varieties.
For high quality pure grass stands, subsequent cuttings of grasses after the first harvest should be taken every 24 to 28 days, depending on location. For example, in northeastern Ohio, cutting intervals of about 28 days have provided forage of adequate quality for lactating cows. Delayed cutting beyond these intervals greatly reduces nutritional value of grass forage. Such cutting intervals are challenging, and that is why grass-legume mixtures should be considered if higher quality forage is needed. Legume-grass mixtures provide a much wider harvest window for good to high quality forage as compared with pure grass stands.
My hope is that this article helps you be alert and prepared to cut forages in a timely manner, and that the weather cooperates for a successful harvesting season this year!
-
Lep Monitoring Network Update – Black Cutworm
Black cutworm
We are currently in our second week of monitoring for the black cutworm (BCW, Figure 1).
Traps were checked between May 2 – 8 for the presence of BCW adult moths. Over the past week, a total of 28 traps in 9 counties were monitored. Moth numbers in the majority of monitoring counties have increased over the past week (Figure 2). Both Trumbull and Van Wert recorded an average of greater than 10 moths (Figure 2). Counties with high trap numbers should plan to monitor for BCW larvae after corn is planted, especially in fields with a lot of broadleaf weeds such broadleaf weeds, such as chickweed and purple dead nettle. For more information about BCW please visit: https://aginsects.osu.edu/sites/aginsects/files/imce/ENT_35_14%20BCW.pdf
For corn varieties tolerant of BCW, please review the Handy Bt Trait Table: https://aginsects.osu.edu/bt-corn-trait-table
Figure 1. Black cutworm moth (BCW). Distinct black, dagger shaped markings on the forewing (circled in yellow). Photo credit: Curtis Young.
Black cutworm moth report - Week 2
May 2 to May 8, 2022
Figure 2. Average black cutworm (BCW) moths captured from May 2nd to May 8th. Large number indicates the average moth count for the week and the small number in parentheses is the total traps set up in the county.
-
Spring SCN Testing and a Research Opportunity for Ohio Growers
KNOW YOUR SCN NUMBERS, OHIO!
The presence of SCN in a field, but most importantly, the SCN numbers, will determine the best management strategy. It is important, therefore, to Test your Fields to Know your SCN Numbers.
Spring, before or at planting, is a good time to sample for SCN. A soil test in spring will reveal if SCN is present and if so, at what levels. If you are planning to collect samples for soil fertility or participate in an on-farm trial that requires soil sampling, a subsample can be used for SCN testing.
With funding from the Ohio Soybean Council and The SCN Coalition we will process up to TWO soil samples, per grower, to be tested for SCN, free of charge. Download and complete this Soil Sample Submission Form and mail your samples to:
OSU Soybean Pathology and Nematology Lab
Attn: Horacio Lopez-Nicora, Ph.D.
110 Kottman Hall
2021 Coffey Rd.
Columbus, Ohio 43210
A GREAT OPPORTUNITY TO UNDERSTAND SCN REPRODUCTION IN OHIO
Additionally, with funding from the Ohio Soybean Council, we invite growers, researchers, and extension educators to help us better understand the relationship between SCN reproduction, soil texture, and soil health measurements. It doesn’t matter if you will plant soybean or corn, if you are a grower in Ohio, you can still participate in this research.
Sampling a soybean or corn field in spring (before or at planting) will reveal the initial population (Pi) of SCN. Sampling that same area at harvest will reveal the final population (Pf) of SCN. From these soil samples, edaphic parameters including nutrient analysis (pH, organic matter, CEC, extractable nutrients), soil texture, and biological indicators (POXC, respiration, protein) will be obtained.
For each field, SCN reproduction factor (RF = Pf/Pi) will be calculated. If SCN population increased during a growing season, a RF > 1 will be observed; on the other hand, no increase or decrease in SCN population will take place if RF ≤ 1. At the end of the season, we will be able to relate SCN population dynamics to soil health parameters, soil texture, and crop planted.
For more information on how to collect and handle soil samples for SCN, visit our article here.
-
Spray Drift: A Serious Problem You Can Manage
Spray drift not only result in wasting expensive pesticides and pollution of the environment, it may damage non-target crops nearby, and poses a serious health risk to people living in areas where drift is occurring. Drift happens! It accounts for about half of all non-compliance cases investigated by the Ohio Department of Agriculture. As you know, we are experiencing an unusual weather situation in Ohio and several other corn-belt states this year. Wet fields have made planting of corn and soybeans delayed or in many cases forced farmers to abandon it altogether looking for alternatives such as planting cover crops. Either situation presents added caution when applying herbicides in terms of spray drift which is defined as movement of pesticides by wind from the application site to an off-target site during or soon after application is done. When the same types of crops, such as Genetically Modified GM) beans, or non-GM beans are planted in neighboring fields, herbicide drifting from one field to another may not show injury symptoms. However, drift must be one of your most serious concerns when spraying herbicides in fields where the adjoining fields have been planted with some other crops or with cover crops. Even a small amount of drift may create significant damage on such crops under these conditions.
Although complete elimination of spray drift is impossible, problems can be reduced significantly if you are aware of major factors which influence drift, and take precautions to minimize their influence on off-target movement of spray droplets. The factors that play a role in either the creation, or reduction of spray drift are: a) Spray characteristics, such as volatility and viscosity of pesticide formulation; b) Equipment and application techniques used for spraying pesticides; c) Weather conditions at the time of application (wind speed and direction, temperature, relative humidity and stability of air around the application site); and most importantly, d) Operator care, attitude, and skill. Extensive information related to factors influencing spray drift, is in OSU Extension publication FABE-525. “Effect of Major Variables on Drift Distances of Spray Droplets.” (http://ohioline.osu.edu/factsheet/fabe-525). Here are some cost-effective things you can do to minimize spray drift.
- Pay attention to wind speed. The risk of spray drift will increase with increases in wind speed. There is no magic wind speed number below which drift will not be a concern. There are many other factors some of which I already mentioned and some others mentioned below will influence the wind speed that may be considered dangerously high from the drift point of view. Generally, wind speeds below 5 mph, coupled with other good management practices, will significantly reduce the injury caused by drift. The best investment you can make is to buy a wind meter that tells you how high the wind velocity is at any given time. Having a wind meter handy will help you avoid a costly problem associated with spray drift.
- Pay attention to wind direction. If the wind is blowing in the direction of some sensitive crops downwind, stop spraying. Don’t take the risk. Come back later in the day or the next day when the direction of the wind has shifted away from the sensitive crops.
- Keep nozzles as close to the target as possible while still producing a uniform distribution of spray on the target. This doesn’t cost any money as long as it is practical to make it happen.
- When you’re ready to change nozzles, consider selecting nozzles that produce much fewer of the extremely small droplets that are most likely to drift away. Low-drift nozzles are in the market and do a tremendous job of eliminating extremely small, drift-prone droplets from the droplet spectrum. This is especially important when spraying systemic chemicals like Glyphosate. Since the active ingredients in these types of chemicals are translocated, not requiring a thorough coverage on the target weeds, there is no need to use small droplets that increases the risk of drift.
- There are chemicals that are designed to increase the droplet size, and reduce the number of very small droplets when added into the spray mixture. They are usually referred to as “drift retardants”. Most of them are some sort of polymer that tends to increase the viscosity and density of the spray mixture which leads to larger droplets. This, however, should be the last defense against drift. First consider the other options such as better targeting of the spray and switching to low-drift nozzles.
- If you are using nozzles that produce relatively smaller droplets, avoid spraying under extremely hot and dry weather conditions. Under these conditions, evaporation of liquid from a droplet decreases its mass rapidly, which increases the drift distance of droplets.
- Pay attention to conditions that may be conducive to formation of a phenomenon called thermal inversion. Normally, warm air rises up. So, during late morning to early evening, the surface temperature is usually warmer than the air temperature near the ground. So, the small droplets discharged from a nozzle may follow this normal air movement from ground up, and eventually evaporate during this process. However, during very early morning (before sunrise) or sometime after the sunset, the air temperature at some distance above the ground may be warmer than the ground temperature. Under these conditions, the cold air above the ground is trapped between the ground and the inversion layer. Under these conditions, as shown in the picture below, the small droplets suspended in the air simply follow the horizontal air movement miles away from the application site. So, avoid spraying during very early in the morning or very late in the evening, if the weather is extremely calm.
Practicing the recommendations I mentioned in this article will help you reduce the risk of spray drift significantly. At the end, you will be the one making spraying decisions. If there is any doubts about a spraying job that might result in drift, wait until there is no longer that element of doubt. Review the forecast and schedule spraying accordingly. Use APPs that provide current, local wind conditions and estimate periods of time to spray or not to spray
More detailed discussion on these tips and other drift reduction strategies are outlined in following OSUE Extension Fact Sheets available online:
FABE-525 (http://ohioline.osu.edu/factsheet/fabe-525),
FABE- 523 (http://ohioline.osu.edu/factsheet/fabe-523), and
FABE 524 (http://ohioline.osu.edu/factsheet/fabe-524)
Erdal Ozkan, Professor and Extension agricultural engineer, can be reached at ozkan.2@osu.edu.
Crop Observation and Recommendation Network
C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.
Contributors
Disclaimer
The information presented here, along with any trade names used, is supplied with the understanding that no discrimination is intended and no endorsement is made by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.
CFAES provides research and related educational programs to clientele on a nondiscriminatory basis. For an accessible format of this publication, visit cfaes.osu.edu/accessibility.