Guess the Pest! Week 9 Answer: Sulfur Deficiency

David Owens, Extension Entomologist, owensd@udel.edu and Jarrod O. Miller, Extension Agronomist, jarrod@udel.edu

Congratulations to Ben Coverdale for correctly answering sulfur deficiency on corn. Ben is going to be the proud new owner of a sweep net, to which all sorts of useful equipment could be attached on the handle, like a soil probe or a knife to take nutrient samples. Now if a sweep net could be included with a swiss army knife… All other correct guessers will be entered for an end-of-season raffle.

From Jarrod Miller
Sulfur deficiencies have been observed in the last couple of weeks across the state. Sulfur deficiency starts on the new growth because S is not mobile in the plant. In fact, S deficiency can cause the whole plant to be lighter in color. Another symptom of S deficiency is the appearance of stripes (interveinal chlorosis), as seen in this photo. While these stripes may also indicate a micronutrient or magnesium deficiency (and those who guessed magnesium are also entered for the end of season raffle), the most likely cause of this striping is a lack of S. We feel confident that S is likely the cause of this symptom, as we have observed it in similar conditions; corn grown on sandy, low organic matter soils. Plus, we have confirmed S deficiency with tissue testing in past seasons. Crops used to get more than enough S from the atmosphere. However, S deposition has been greatly reduced as technologies have reduced S release to the atmosphere when we burn fossil fuels. Now, the primary source of S to growing crops is soil organic matter. Unfortunately, Delaware soils are typically low in natural organic matter. In addition, the sulfate form of S is easily leached below the root zone; S leaching is also more likely in sandy soils. We recommend tissue testing to confirm S deficiency for sandy soils, especially if the field has not recently received manures or S containing fertilizers. Sample the whole plant up to 45 days after emergence or the 3rd leaf between 45-80 after emergence. If S in tissue is below 0.18% or if the N:S ratio in tissue is greater than 15:1, the corn is S deficient. If caught early in the season, apply 30 to 40 lb/acre of S. Apply a lower rate if you have evidence of S deeper in the soil profile (deep soil sample), or if you already added S with your starter fertilizer. However, remember that excessive application of ammonium sulfate (or a reduced form of S) can have an acidifying effect, resulting in lower soil pH. Soils receiving regular applications of acidifying fertilizer will require more frequent application of limestone to manage soil acidity in the long-term.

Time to Scout for Weeds

Kurt M. Vollmer, Postdoctoral Researcher – Weed Science, University of Delaware; kvollmer@udel.edu

With most of the corn and soybeans planted, now is the time to start scouting for weeds. Doing so will prevent major headaches later in the growing season. While scouting, be sure to note the weed species present, height, life-cycle, and severity of the weed infestation. When looking at fields this year, pay attention to those areas that were drowned out last summer. The weeds in many of those spots produced seed and now have very high seed banks. So while weed pressure in the rest of the field may not be too heavy, weeds present in these spots may be at unacceptable levels.

In particular, Palmer amaranth can quickly become unmanageable if not spotted early. Many herbicide labels suggest spraying this weed when it is less than 4 inches tall, but the UD Weed Science program recommends applying postemergence herbicides before its 3 inches tall. Our research with soybean shows that the best time for this second application is no later 28 days after applying a residual herbicide. Furthermore, Palmer amaranth can quickly exceed 4 inches, and research at the University of Maryland has shown that delaying the postemergence application to 32 days or longer can result in reduced levels of control. Remember, the earlier Palmer amaranth is spotted the better. Furthermore, keep in mind there could be several days between scouting and actually getting the sprayer into the field, allowing Palmer amaranth to reach heights that prevent complete control.

2019 Weed Science Field Day

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

The 2019 Weed Science Field Day will be held Wednesday, June 19, 2019 at the University of Delaware’s Carvel Research and Education Center, Route 9 (16483 County Seat Highway), Georgetown, DE.

Dr. Alyssa Koehler (plant pathology), Dr. David Owens (entomology), and Dr. Jarrod Miller (agronomy) will also be on hand to discuss their summer research projects as well.

The weather delayed getting some of the plots planted, but the past three weeks have been very productive and we will have lots to view. All of our corn studies will be part of the tour, which includes most of the commercially available herbicides. Some of corn trials include different approaches and timings for herbicide application. We will view trials for full-season no-till and conventional tillage soybean production; including a number of soybean trials with postemergence treatments.

The day will begin with registration beginning at 8:30 at the Grove near the farm buildings and new office building on the north side of the road. We will start to view the plots at 8:45 a.m. Coffee, juices, and donuts will be provided. We will also provide sandwiches for lunch. Pesticide credits and Certified Crop Advisor continuation credits will also be available.

Growing Degree Days through June 2

Jarrod O. Miller, Extension Agronomist, jarrod@udel.edu

Steady warm weather and periodic rainfalls have moved corn along pretty well. Most corn planted here in Georgetown in late April is at V6-7 and has been sidedressed. Fields planted through mid-May are at V5/V6, matching the predicted GDD pretty well.

The next milestone to watch for would be tasseling (VT), which occurs at 1135 GDD. At this stage just consider how weather may determine pollination and later grain fill as another determinant of final yield.

Table 1: Accumulated growing degree-days based on planting dates through May 20th.

If you planted

Sussex Kent New Castle
Apr 14 805 760 723
Apr 21 713 669 636
Apr 28 632 593 556
May 5 532 512 484
May 12 431 414 393
May 19 361 350 333

V6 = 475 GDD, V12 = 870 GDD, VT = 1135 GDD, R1 = 1400 GDD

Statewide Temperatures Since April 1st

Statewide Rainfall Accumulation Since April 1st

Glyphosate and Liberty Tank Mixtures

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Glyphosate plus Liberty has been a pretty good treatment to burndown weeds prior to planting double-cropped soybeans in the past few years. With some of the newly released soybean traits, tankmixing glyphosate with Liberty is also an option for postemergence applications. We have found this combination to work very well in many situations but just a few things to keep in mind.

  • Neither of these herbicides will provide residual control, so if weeds with long germination periods are present (i.e. Palmer amaranth) consider including a residual herbicide such as Dual, Zidua, Anthem, or Warrant when spraying postemergence.
  • Liberty needs good spray coverage to maximize effectiveness, including when its tankmixed with glyphosate. A minimum of 20 gallons per acre should be used with medium to coarse spray droplets.
  • I will occasionally see poor control of fall panicum with this combination. I am assuming the Liberty is interfering with glyphosate providing complete control. This is more likely to occur when spraying for burndown with large fall panicum plants, but I have seen it when spraying postemergence to fall panicum that is 3 to 4 inches tall. I have not seen this reduction of control with other annual weed species, but giant foxtail and large crabgrass are the only other grasses in most of my trials. I suspect an increase in glyphosate rate would help reduce the likelihood of this happening, but I have not tested this.

Agronomic Crop Insect Scouting

David Owens, Extension Entomologist; owensd@udel.edu

Field Crops
Field corn and soybean insecticide recommendations have been updated and posted to the Extension webpage. Field corn: http://extension.udel.edu/ag/insect-management/field-corn/, soybeans: http://extension.udel.edu/ag/insect-management/soybeans/. Click on the link that says ‘Insecticide Recommendations.’

This update will not affect the QR-code functionality. The QR codes that you may have picked up at AgWeek will take you to the crop landing pages. From there, you can open the recommendation pdf. If you did not pick up a QR code card, we still have some left, just let me know which crops and how many you want.

The biggest changes in this year’s addition are the listing of soybean insecticidal seed treatments and the listing of ‘other labeled formulations’. In addition, the insecticide mode of action groups are listed as well as the signal word on the label that indicate the level of hazard with each product. The mode of action groups are general classifications, all of the insecticides in that group work in the same general way.

Field Corn
Wheat serves as an early season host for brown stink bugs, and the stink bug’s first generation develops in wheat and other small grains. If wheat borders your field corn, scout the wheat with a sweep net or look for stink bugs on the corn plants. When the wheat is cut, stink bugs will move to corn and could affect the developing ear and kernels. Thresholds for stink bugs in corn can be found here: https://entomology.ces.ncsu.edu/2018/04/new-stink-bug-thresholds-in-corn/. When plants are at V14 to VT, 21 to 26% of plants infested with stink bugs warrant a treatment. Thresholds are even higher for silk stage corn. These bugs will be located on the edge, and they will spend some time on the edge before moving into the field interior

Sulfur Deficiency on Field Corn

Jarrod O. Miller, Extension Agronomist, jarrod@udel.edu and Amy Shober, Extension Nutrient Management and Environmental Quality Specialist; ashober@udel.edu

As corn has reached V3-V5 across the state, we have started to observe visual symptoms of sulfur (S) deficiency. Like nitrogen (N), sulfur deficiency can cause plant tissue to appear light green or yellow in color. However, one can tell the difference between N and S deficiencies by where they occur on the plant. Nitrogen deficiencies start on the lower (older) leaves because N is mobile in the plant. In contrast, S deficiencies start on the new growth because S is not mobile in the plant. In fact, S deficiency can cause the whole plant to be lighter in color. Another symptom of S deficiency is the appearance of stripes (interveinal chlorosis), as seen in this photo. While these stripes may also indicate a micronutrient or magnesium deficiency, the most likely cause of this striping is a lack of S. We feel confident that S is likely the cause of this symptom, as we have observed similar conditions that is grown on sandy, low organic matter soils. Plus, we have confirmed S deficiency with tissue testing in past seasons.

Crops used to get more than enough S from the atmosphere. However, S deposition has been greatly reduced as technologies have reduced S release to the atmosphere when we burn fossil fuels. Now, the primary source of S to growing crops is soil organic matter. Unfortunately, Delaware soils are typically low in natural organic matter. In addition, the sulfate form of S is easily leached below the root zone; S leaching is also more likely in sandy soils.

This year we have observed S deficiencies statewide, including in finer textures soils around Middletown. This may be explained by the cold temperatures observed mid-May. With nighttime temperatures in the lower 40s, release of S from organic matter was slower than normal, causing S deficiencies to appear when temperatures increased, and corn growth increased. We suspect that crops growing in soils with no history of S deficiency will grow out of the deficiency with time as warmer temperatures increase organic matter mineralization and roots begin to reach S that is held in subsoils.

However, corn growing on sandy soils with low organic matter may not grow out of their S deficiencies with warmer temperatures and increased rooting depth. We recommend tissue testing to confirm S deficiency for sandy soils, especially if the field has not recently received manures or S containing fertilizers. Sample the whole plant up to 45 days after emergence or the 3rd leaf between 45-80 after emergence. If S in tissue is below 0.18% or if the N:S ratio in tissue is greater than 15:1, the corn is S deficient. If caught early in the season, apply 30 to 40 lb/acre of S. Apply a lower rate if you have evidence of S deeper in the soil profile (deep soil sample), or if you already added S with your starter fertilizer. However, remember that excessive application of ammonium sulfate (or a reduced form of S) can have an acidifying effect, resulting in lower soil pH. Soils receiving regular applications of acidifying fertilizer will require more frequent application of limestone to manage soil acidity in the long-term.

Final Fusarium Head Blight Considerations

Alyssa Koehler, Extension Field Crops Pathologist; akoehler@udel.edu

We are now about 3 weeks past flowering in wheat and symptoms of Fusarium Head Blight (FHB) are becoming visible (Figure 1). Fields with high incidence of FHB may be at risk for elevated levels of deoxynivalenol (DON). Steps for scouting fields for FHB were introduced in the May 17 WCU. When assessing FHB incidence, remember to select heads randomly to not bias your sample. If you have high levels of FHB in your field, or in part of a field, you want to consider harvesting as early as possible. Increasing the fan speed at harvest can help to remove lightweight, diseased grain with chaff. This technique is feasible when the rest of the grain is of good quality; the goal is to blow the lightweight, diseased kernels with high DON without blowing out heavier high-quality kernels. It is also best to dry grain to at least 15%, and store grain with FHB issues separate from cleaner grain.

Figure 1. Bleaching of wheat heads due to Fusarium Head Blight

Orchardgrass Decline in the Mid-Atlantic

Jarrod O. Miller, Extension Agronomist, jarrod@udel.edu

Orchardgrass decline is an important topic amongst Mid-Atlantic growers, and the overall cause has been elusive. A study from Virginia Tech surveyed farmers and fields in Virginia, Maryland, and Pennsylvania for reduced stand persistence. Surprisingly, neither overall soil fertility nor disease were strong indicators of lower stand persistence. However, higher soil organic matter and manure application were both related to increased stand persistence. Both of these factors could be tied to soil fertility, which may indicate that soil test levels are not great indicators of orchardgrass decline. Another interesting point in the study was that as soil test P increased, stand persistence decreased. Perhaps soils with higher P levels in the Mid-Atlantic were restricted from receiving additional manure applications, which may explain the importance of manure in these fields. This is supported by the orchardgrass biomass results, where biomass increased with soil test P levels. It should be noted that persistence was based on the grower’s perspective of their current stands, while biomass was a direct measurement. The final factor that influenced a decline in orchardgrass stands was the historic maximum temperatures. Further declines in orchardgrass may be observed with future increases in temperature due to climate change.

The study can be found here, but may be behind a paywall: https://dl.sciencesocieties.org/publications/cftm/abstracts/5/1/180003

 

Agronomic Crop Insect Scouting

David Owens, Extension Entomologist; owensd@udel.edu

 

Early Season Moth Activity
This is the last week of early season moth trapping, a big thank you to all the host farmers for letting us put up and service traps. Please let me know if you observed either pest in your fields causing damage, when, and what the field conditions were. Overtime with your feedback we can figure out just what pheromone traps for armyworm and cutworm mean.

Early Season Moth Activity

Trap Location True Armyworm per night Black Cutworm per night
Willards, MD 0 0.6
Salisbury, MD 0 2.3
Laurel, DE 0 7.7
Seaford, DE 0 2.3
Bridgeville, DE 0 0.1
Harrington, DE 0 2.6
Smyrna, DE 0.7 2.3
Kenton, DE 0 0.4
Pearson’s Corner, DE 0 0.4
Sudlersville, MD 0 0.9

 

Soybean
It can be tempting to put in a cheap insecticide with a post emergence herbicide spray, but is it worth it? Vegetative, full season soybeans with good plant stands can withstand a beating without losing yield. Some studies from southern states indicated that non yield-limiting defoliation can be greater than 66%. Current thresholds are very conservatively set at 30%. Bean leaf beetles are active, in most cases they are not at threshold levels of 2 beetles per plant + stand reduction. Other insects that may be present in soybean fields early include thrips (cause a cosmetic injury) and thrips predators such as Orius and minute pirate bug. Later in the season, both will feed on Lep eggs and early instar worms. Predators are slow to build up their populations and are very sensitive to insecticides. Bottom line, if in doubt, take a quick look in a few spots in the field. Doing so could very easily save a spray, save some predators, and save insecticide money.