Guess the Pest! Week 10

David Owens, Extension Entomologist,

Test your pest management knowledge by clicking on the GUESS THE PEST logo and submitting your best guess. For the 2019 season, we will have an “end of season” raffle for a $100.00 gift card. Each week, one lucky winner will also be selected for a prize and have their name entered not once but five times into the end of season raffle. A lucky winner will also receive a heavy duty sweep net.

You enter a field with a sweep net expecting to find bugs and instead find a few widely scattered plants with yellow leaves and hooked leaves. What is going on?

To submit your answer, please go to:

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.

Time to Scout for Weeds

Kurt M. Vollmer, Postdoctoral Researcher – Weed Science, University of Delaware;

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.

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.

EPA Announces Scientific Findings: Glyphosate is Not a Carcinogen

Kerry Richards; University of Delaware Pesticide Safety Education Coordinator;

In an important step in the ongoing process for their review of glyphosate, in a recent Office of Pesticide Program Update, the U.S. Environmental Protection Agency (EPA) stated that they continue to find that glyphosate is not a carcinogen, and there are no risks to public health when glyphosate is used in accordance with its current label. Additional information about EPA’s evaluation of the carcinogenic potential of glyphosate can be found at

According to the April 30 update, “The agency’s scientific findings on human health risk are consistent with the conclusions of science reviews by many other countries and other federal agencies. While the agency did not identify public health risks in the 2017 human health risk assessment, the 2017 ecological assessment did identify ecological risks. To address these risks, EPA is proposing management measures to help farmers target pesticide sprays on the intended pest, protect pollinators, and reduce the problem of weeds becoming resistant to glyphosate.”

The proposed management measures will be announced in the Federal Register. Once the Federal Register notice publishes, the public will be able to submit comments on EPA’s proposed decision at in docket # EPA-HQ-OPP-2009-0361. Public comments will be due 60 days after the date of publication in Federal Register. EPA’s responses to the comments received on the drafted ecological and human health risk assessments and benefits assessment will be in the docket. This docket also provides links to all previous information released during the glyphosate, including comments when they were previously requested.

The April 30 announcement can be found at and additional information regarding glyphosate can be found at

Guess the Pest! Week 7 & 8

David Owens, Extension Entomologist,

There is still time to guess what is going on with corn. Below is another image of field corn being affected by the same cause. This image actually is a two-fer, there is slug injury on the bottom leaves, but slugs do not cause the whorl wilting. This plant will not recover. Less severe injury will show up as the yellowing in last week’s images.

To submit your answer, please go to:

Guess the Pest! Week 6 Answer: Soil Compaction

David Owens, Extension Entomologist, and Gordon Johnson, Extension Vegetable & Fruit Specialist;

Congratulations to Will Carlisle for correctly answering soil compaction. Will will receive a sweep net and be entered along with all correct guessers for the end of season raffle. Unfortunately, this is one case where a sweep net is not going to do much to alleviate the problem, unless you put a shovel or soil corer on the end of the handle.

This from Gordon Johnson:

Peas do not perform well in soils that are worked when they are too wet. Compaction will lead to poor emergence and reduced growth. Wet soil conditions, compaction, and poor drainage are also associated with higher rates of infection of root rots in peas such as Aphanomyces root rot, or common root rot. Soil compaction limits root development and root function and will reduce yield potential in vegetable crops such as peas.

There are two processes at play when soils are compacted by equipment. The first is destruction of soil structure. In most Delaware soils, our surface soil structure is granular or crumb in nature and consists of small aggregates. It takes considerable time and good cropping practices to build up soil structure. When compacted by equipment, structure is destroyed, making soils denser. Excessive tillage also destroys soil structure.

A second compaction process is the compression of soil particles, pushing them closer together. This happens with equipment traffic across fields. The heavier the loads carried by equipment passing over soils, the more the compaction. With large equipment and heavy axle loads, significant soil compaction is expected; the heavier the weight on an axle, the more the compaction. Other equipment factors affecting compaction include tire size, tire pressure and operating speeds. Wider tires or dual tires will distribute weight over larger areas, reducing deep compaction but increasing the amount of area with shallow compaction. Higher tire pressures will result in more deep soil compaction and slower speeds will also result in more compaction.

In wet soil, there is less resistance to soil particle movement and soil is more “plastic”. This means that potential for compaction is greater in wet soils than dry soils. It is important to wait until soil conditions are favorable for tillage. Waiting a day or two for soils to dry will improve yield potential by reducing compaction.

Subsoiling in the fall is a short-term solution to deep compaction. The use of forage radish cover crops has shown great potential to reduce shallow and deep compaction. Research in Delaware has shown that peas can be no-tilled after a winter-killed radish cover crop successfully with equivalent or better yields than conventionally tilled peas.

Spotted Lanternfly Hatch Out as Temperatures Rise

Stacey Hofmann, Chief of Community Relations, Delaware Department of Agriculture;

The steady increase in daily temperatures has spurred spotted lanternfly nymphs to hatch out of their egg masses. While the hatching will continue for the next few weeks, this causes concern for businesses, residents, and the agriculture industry because this notorious hitchhiker will be on the move.
“From the time we enacted the emergency quarantine in March, New Castle County residents and businesses had a window of time to look for and destroy spotted lanternfly egg masses,” said Jessica Inhof, Delaware Department of Agriculture Plant Industries Administrator. “We had a good response from the public on taking action against this invasive
pest, learning what the quarantine means, and from businesses engaging in the permitting process. Now that the insect will be mobile, regulated articles moving within and out of the quarantine zone need to be inspected.”

The Delaware Department of Agriculture (DDA) quarantined eleven zip codes in New Castle County to eradicate, control, and prevent the spread of spotted lanternfly in Delaware and to surrounding states. The following zip codes in New Castle County are quarantined in their entirety: 19702, 19703, 19707, 19711, 19801, 19802, 19803, 19805, 19807, 19809, and 19810. The quarantine can expand if there is reason to believe that the pest has moved to a nonquarantined area. Spotted lanternfly nymphs and adults can fly, hop, or drop onto a vehicle – meaning this pest can easily be transported to new areas where it can create another infestation.

“We know from working with this pest that as many egg masses destroyed from the ground, there are that many, if not more, up in the tree canopy, that people cannot access,” said Stephen Hauss, DDA Environmental Scientist. “As the nymphs move down to find nutrition, these are the ones we need to work to eradicate this year.”

The spotted lanternfly is a destructive invasive plant hopper that attacks many hosts including trees, shrubs, orchards, grapes, and hops. The insect is detrimental to Delaware’s agricultural industry, forests, and residential areas. Due to quarantines in other states, interstate commerce will be impacted if the pest is transported out of the Delaware quarantine area.

Examples of regulated articles include:
• Any living life stage of the spotted lanternfly
• Landscaping, remodeling, or construction materials
• Firewood of any species
• Packing materials (e.g. wood crates, boxes)
• All plants and plant parts including all live and dead trees, perennial and annual plants, and mulch
• Outdoor household articles like RVs, lawnmowers, chairs, grills, tarps, tile, stone, deckboards, and other vehicles not stored indoors.

In order to move regulated items, the general public will need to complete a residential compliance checklist indicating they inspected and know that no living life stage of the spotted lanternfly is present on the articles. The checklist is available online at

Any person conducting business for a commercial business, municipalities, or a government agency that requires movement of any regulated item within or from the quarantine area must have a permit, available through the DDA spotted lanternfly website. To obtain a permit, a designated individual from an organization must receive training and pass an online test to demonstrate a working knowledge and understanding of the pest and quarantine requirements. Training of other employees, inspection of vehicle and products, and removal of living stages of spotted lanternfly must be completed. The permit demonstrates the individual understands how to identify the pest and can ensure the items transported are not carrying the insect.

For more detailed information regarding the emergency quarantine, permitting, treatment, or to report a sighting of spotted lanternfly, visit the Delaware Department of Agriculture’s dedicated spotted lanternfly webpage at or call the dedicated spotted lanternfly hotline at (302) 698-4632. When leaving a message, leave your contact information and, if reporting a sighting, please provide the location of the sighting.

Unhatched spotted lanternfly egg mass

Hatched spotted lanternfly egg mass

Spotted lanternfly nymphs