Guess the Pest! Week 9 Answer: Sulfur Deficiency

David Owens, Extension Entomologist, and Jarrod O. Miller, Extension Agronomist,

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.

Guess the Pest! Weeks 7 & 8 Answer: Wireworm!

David Owens, Extension Entomologist,


The last Guess the Pest was a bit of a headscratcher in a picture that, if seen in a field, probably would’ve been easier to figure out. Especially if a knife is fixed to the end of a sweep net handle to dig up suspect looking plants.

In several grass and grain crops, wireworm damage is called ‘dead heart’ where the whorl or emerging leaf dies because the wireworm has destroyed the growing point under ground. Larger plants might not be fed on entirely or the wireworm does not hit the growing point. These plants are more likely to show the blotchy yellowing of the leaves. Wireworms are susceptible to seed treatments and to pyrethroids in the furrow. Our northern neighbors in Canada are required to scout fields before a seed treatment can be legally applied. This past spring, I sampled a few fields with bait traps to assess wireworm presence. Bait traps can be time consuming, and the field shouldn’t be disturbed for the 2 weeks the bait is out, a tall order when soil temperatures warm. Cover crops may also interfere with bait attractiveness. Another scouting technique is the compact soil sample method, performed in either fall or spring. This consists of digging an 8 inch x 8 inch x 6 inch deep hole and relating numbers to action thresholds. The other reason I like this method is that a hole has to be dug if the field is being baited, so if there is an economic threshold, odds are you are going to identify it in the process of digging bait holes in addition to when the bait is checked about 2 weeks later.

Vegetable Crop Insect Scouting

David Owens, Extension Entomologist;

I found a couple of aphids on my greenhouse transplants and didn’t think too much of them. I set my transplant trays outside to harden off last week and came back to them this week only to find aphids had infested several trays, causing leaf cupping. In most cases, significant parasitoid pressure was present and most aphids were already transformed into parasitoid mummies. Pyrethroids will not affect green peach aphid or melon aphids, there are numerous other products that will do the job, including neonicotinoid insecticides that also pick up cucumber beetle. Cucumber beetles were observed feeding in a field that was transplanted last week. Transplants were treated prior to setting, and beetles were affected and dying. Residual activity generally lasts between 2 and 4 weeks. If chemigating insecticide through the drip tape, figure your rate based on field footprint, not plastic footprint. For example, if a product goes out at 10 ounces/acre and a field is 10 acres, then 100 ounces of product need to be delivered. If you base the rate on the amount of actual plastic (roughly 20-30% of the field area), you could be significantly undertreating! As plants are coming out of the greenhouse, be sure to also check for the presence of two spotted spider mites. On transplants, leaf stippling will be more evident than on older plants.

Sweet Corn
The 2019 insect trapping network has largely been deployed. Trap capture data will be uploaded to the webpage as in previous years, and most recent trapping data presented here when sweet corn is closer to tasseling. You can find trap catch data here: We are picking up low numbers of corn earworm, most likely from overwintering pupae and at this point are more of a curiosity. Scout for black cutworm damaging seedlings (3% cut plants or 10% leaf feeding).

Insecticide Trial Results for Vegetable and Agronomic Crops

David Owens, Extension Entomologist, and Bill Cissel, Extension Agent – Integrated Pest Management;

Summaries of last season’s insecticide trials in peas, sweet corn, watermelon, field corn, soybean, and wheat can be viewed at

Entomology Updates

The 2019 Mid-Atlantic Commercial Vegetable Recommendations guide is now available! A couple of corrections have come to my attention that you should be aware of. The first is that Vydate L is incorrectly listed in the Potato chapter. The correct formulation is Vydate CLV; Vydate L was introduced in 2018 and does not have potato on its label. It has a much lower % active ingredient than Vydate CLV. If accidentally applying Vydate CLV with the Vydate L use rate, you will apply more than a 2x rate of active ingredient! As always, pay attention to formulations and labels on products!

Several lambda-cyhalothrin containing products in the Sweet Corn chapter have an incorrect PHI listed. The PHI for Warrior, Besiege, and Lambda-Cy is 1 d PHI; the product Cobalt Advanced is a 21 d PHI as listed in the guide.

I’ve also shared the Handy Bt trait table for field corn with you before, you can find a link to it here: At some of the recent winter meetings, I have mentioned a couple of soil insect pest sampling techniques. There’s a great 50 second video for baiting wireworms by Purdue that can be found here:

For those of you wanting to know more about spotted lanternfly, the NE IPM Center will have a series of webinars focused for the hops, berry, and vegetable grower, the grape and tree fruit grower, Christmas tree growers, and the ornamental industry. See the announcement in this WCU for more information.

Guess the Pest! Week #24 Answer: European Corn Borer

Bill Cissel, Extension Agent – Integrated Pest Management;

Congratulations to Grier Stayton for correctly identifying the insect as a European corn borer and for being selected to be entered into the end of season raffle for $100 not once but five times. Everyone else who guessed correctly will also have their name entered into the raffle. Click on the Guess the Pest logo to participate in this week’s Guess the Pest challenge!

Guess the Pest Week #24 Answer: European Corn Borer

It’s hard to believe that a pest that once caused an estimated annual economic loss of $1 billion dollars in the United States is now a rare occurrence. The European corn borer (ECB), as the name implies, is actually native to Europe and was introduced into North American in the early 1900s. In addition to being a pest of corn (field corn and sweet corn), it is also considered a pest of many vegetable and field crops. Since the adoption of transgenic corn hybrids in the mid-1990s, losses due to ECB have been virtually eliminated in Bt crops and significantly reduced in other vegetable and non-Bt field crops. This is one of the pests that the UD Insect Trapping Program monitors with black light traps. The reason we continue to monitor ECB populations throughout the state is because even though generally speaking, populations have been low, there are still local pockets where ECB is causing damage. The photo above of the ECB larva was taken on the Eastern Shore of VA by Helene Doughty from a non-BT sweet corn plot that was 100% infested with ECB.

For information on the benefits of Bt adoption, read this article: Regional pest suppression associated with widespread Bt maize adoption benefits vegetable growers

Guess the Pest! Week #22 Answer: Helicoverpa zea, Corn Earworm

Bill Cissel, Extension Agent – Integrated Pest Management;

Congratulations to Amanda Heilman for correctly identifying the insect as an adult corn earworm and for being selected to be entered into the end of season raffle for $100 not once but five times. Everyone else who guessed correctly will also have their name entered into the raffle. Click on the Guess the Pest logo to participate in this week’s Guess the Pest challenge!

Guess the Pest Week #22 Answer: Helicoverpa zea, commonly known as corn earworm

The moth in the photograph is an adult Helicoverpa zea, commonly referred to as a corn earworm. The adult moth is a nectar feeder and not considered a pest. However, corn earworm larvae are considered by some to be the most economically important crop pest in North America. They are highly polyphagous meaning they feed on many different species of plants. Corn, especially sweet corn, is a preferred host plant. However, they also attack soybean, sorghum, snap bean, tomato, and cotton to name a few. Larvae prefer to feed on reproductive plant structures including blossoms, buds, and fruits. It is because of this large host range, and the fact that Helicoverpa zea larvae are so destructive that they are known by several other common names including tomato fruitworm, cotton bollworm, and podworm.

Vegetable Insect Updates

Bill Cissel, Extension Agent – Integrated Pest Management; and David Owens, Extension Entomologist,

Fields that started silking at the beginning of the major 2018 moth flight are being harvested right now. Please let us know how well your spray program worked. Your feedback is important to us to evaluate if any recommendations need to be adjusted for 2019. Moth capture has declined slightly at several locations, and Monday captures ( were slightly lower than last week’s. Earworm flight may have peaked for the season.

Trap Location BLT – CEW Pheromone CEW
3 nights total catch
Dover 4 8
Harrington 3 44
Milford 63 127
Rising Sun 6 17
Wyoming 4 30
Bridgeville 6 19
Concord 8 27
Georgetown 2 19
Greenwood 10
Laurel 2 84
Seaford 3 12


This will be the last trap capture for 2018. Many thanks to all of our cooperators who graciously host blacklight and/or pheromone traps at their locations. We are also grateful to Jon Baker with Trap Woods Inc., Harry Thompson with Thompson’s Roadside Stand, and Donna Hamilton for sharing their trap capture data with us; their data is posted twice a week on the website. You can view season catches and graphs of previous year trapping results at the above link.

Sulfur Deficiency in Sweet Corn

Jerry Brust, IPM Vegetable Specialist, University of Maryland;

For the last couple of years, I have talked about and conducted research on sulfur (S) deficiencies in watermelon. At several meetings I was asked if the deficiency also appears in (field) corn. I could only relate the comments I have heard from several corn growers that they have often found their corn crop to be low or deficient in sulfur. I bring all this up again because I have seen several sweet corn fields lately that have sulfur deficiencies (Fig. 1). One of the possible reasons we are seeing more S deficiency is because less sulfur is being deposited into the soil from the atmosphere due to reductions in acid rain (Fig. 2). In 1986 about 24 lbs/a of sulfate were deposited in Maryland soils per year, however in 2011 it was closer to just 8 lbs/a each year. Organic matter supplies most of the sulfur to the crop, but sulfur must be mineralized to sulfate-S to be taken up by crop plants.

Because mineralization is carried out by soil microorganisms, soil temperature and moisture primarily determine when and how much sulfur is made available to the crop. Excessively wet (like we have had most of this summer) or dry conditions reduce microbial activity and reduce S availability from soil organic matter. Sulfate is relatively mobile in most soils and easily can be leached from soils, especially sandy soils. Soils low in organic matter are much more likely to be deficient in S.

In the field sulfur deficiency can be highly variable since soil sulfur availability varies considerably with soil organic matter and texture. Sulfur deficiency is often seen in sandier, lower organic matter, hillier areas of a field while low lying, greater organic matter areas usually have sufficient levels of S. Sulfur can be added to the crop in combination with several other nutrients such as ammonium or potassium and spray-grade ammonium sulfate is a good choice for foliar applications.

There are other deficiencies (and problems such as root diseases) that can cause striping (although the one pictured here was S) and only by conducting a tissue test can you be sure. Magnesium deficiency may cause striping and/or reddening of corn leaves. The yellow areas between the veins often appear as ‘beaded’ lines rather than solid stripes. Zinc deficiency may cause striping that begins at the base of the leaf and progresses to the tip. These stripes often coalesce to form a white band along the edge of the leaf or the midrib. Manganese deficiency causes striping that is olive green or dark yellow in color with veins remaining green. High pH, high organic matter, and dry soil conditions can cause Mn deficiency.

Figure 1. Striping in sweet corn leaf caused by S deficiency


Figure 2. Amount of sulfate deposited in soil from rainwater in 1986 vs. 2011.

Vegetable Insect Updates

David Owens, Extension Entomologist, and Bill Cissel, Extension Agent – Integrated Pest Management;

Sweet Corn
Bill Cissel and David Owens
Corn earworm populations are higher than last week, and yesterday’s trap capture was higher in all but one location from Monday’s trap capture. At the research station, our trap captures increased significantly in the last two nights. Blacklight trap captures are also increasing. Focus more on the state-wide trends. Monday trap capture can be found at ( As a reminder, what is reported on the web is on a per night basis, the table below is cumulative over Monday, Tuesday, and Wednesday night. These trap captures correspond to a 3-day spray schedule, though some states recommend a 2-day schedule.

Joe Ingerson-Mahar at Rutgers in New Jersey recently wrote about the need for product rotation, citing pyrethroid resistance monitoring Virginia has been doing ( We have been using Virginia’s vial testing method and have seen similar results, near 30% of tested moths can fly after 24 hour exposure. Does this mean pyrethroids are ineffective? No, but it does highlight the need for chemistry rotation. We also do not know how vial tests translate to sweet corn efficacy where we apply products several times in a narrow time frame.

Trap Location BLT – CEW Pheromone CEW
3 nights total catch
Dover 2 17
Harrington 1 28
Milford 2 41
Rising Sun 0 6
Wyoming 4 65
Bridgeville 3 63
Concord 3 56
Georgetown 4 32
Greenwood 2
Laurel 2 132
Seaford 5 52

David Owens
Spider mite populations have generally been decreasing, but can still be an issue with the warm weather. High humidity favors fungal pathogens of spider mites, but fungicide sprays can suppress them. Infected mites are going to look crumpled and may even be brown in color and a slightly fuzzy appearance as mite-killing fungi sporulate. Cucumber beetles are very active, as are various members of the rindworm complex. Yellow striped armyworms are present in fields.