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.

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.

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.

Guess the Pest! Week 6

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. This week is another potentially tricky scenario of “What’s going on?”, this time in peas. Herbicides were not involved in this one.

To submit your answer, please go to:

Guess the Pest! Week 4 & 5 Answer: Blowing Sand Burial

David Owens, Extension Entomologist,

Congratulations to Richard Wilkins for correctly guessing this week’s GTP as wind driven sand burial. Richard will be sent a sweep net, which I suppose might be semi-useful for brushing sand off of plants, and his name and other correct participants will be entered in the end of season raffle. Wind-blown sand is another reason early season vegetable growers are fond of putting in rye strips to help shield tender transplants. I am convinced we live on some of the windiest ground in the East.

The wheat in last week’s photo could be described as sandblasted, where damage occurs from windblown sand to plant tissues. However, this type of damage is more associated with corn in the Mid-West, while this wheat was suffering from sand burial. From the aerial image it is more obvious that the road and field with no cover were a source of wind erosion, allowing an accumulation of sand that didn’t kill the wheat, but simply buried most of the tillers, giving the
appearance of poor plant growth. When the wheat was uncovered the plant was still (at the time) healthy.


Guess the Pest! Week 4 & 5

David Owens, Extension Entomologist,

Last week’s Guess the Pest is a bit tricky. The second photo below is another picture of the field. As you can see, the injury happened earlier in the year. It is a physical type injury, one that many vegetable growers are especially concerned with. You may enter a new guess if you would like by clicking on the link below or stick with the one you have entered. Remember, you can’t win bragging rights if you don’t play!