Guess the Pest! Week #20

Bill Cissel, Extension Agent – Integrated Pest Management; bcissel@udel.edu

Test your pest management knowledge by clicking on the GUESS THE PEST logo and submitting your best guess. For the 2018 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.

This week, one lucky participant will also win A Farmer’s Guide To Corn Diseases ($29.95 value).

You can’t win if you don’t play!

What is this insect?

Guess the Pest! Week #19 Answer: Hole Puncher

Bill Cissel, Extension Agent – Integrated Pest Management; bcissel@udel.edu

Congratulations Bob Leiby for correctly identifying the damage as mechanical 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 #19 Answer: Hole Puncher
By David Owens, Extension Entomologist

Photo by Joe Deidesheimer, defoliator is Kevin Troyer

This week’s guess the pest was a bit of a trick question, the answer is hole puncher operated by a hard-working student. Soybean canopy defoliation can be a little tricky to estimate, defoliation often appears more severe than it really is because our eyes focus on differences. We are simulating bean leaf beetle feeding injury to R-2 stage soybean by removing approximately 25% of the foliage canopy-wide.

Although this looks really severe, soybeans can compensate for this level of defoliation. Our threshold for defoliation at this soybean stage is 20% CANOPY and FIELD wide. Our most common defoliators right now feed primarily in the upper canopy. So if 25% of the upper canopy of R-stage soybean is defoliated, but only 5% of the lower canopy, total defoliation could be lower than 15% and the plants will not suffer a yield impact. If there is little to no defoliation in the lower canopy, the upper canopy can take a severe beating before canopy-wide defoliation hits 20%. We may start seeing soybean looper later in the season, this species often defoliates from the bottom up.

Vegetative stage soybean can compensate even greater defoliation. Recent work out of Mississippi indicates that 66% of the canopy of VEGETATIVE beans can be lost without a significant yield loss. In the Mississippi study they also defoliated beans during vegetative growth, at R3, and constantly during the season to simulate the impact of multiple sub-threshold ‘dingers’, and found that a constant 17% defoliation did not significantly reduce yields.

Two other important factors that reduce soybean’s compensatory ability are drought and planting date. Late planted beans have less time to recover from severe defoliation and may (but not always) loose yield. Drought stress may also reduce this compensatory ability. The Mississippi defoliation experiments involved a small army of students around the clock picking leaves off of over 100 10-ft plots.

Soybean Vein Necrosis

Nancy Gregory, Plant Diagnostician; ngregory@udel.edu

Soybean vein necrosis is beginning to show up in some soybean fields in the region. Soybean vein necrosis, caused by a thrips vectored virus, begins as diffuse yellow blotchy leaf spots, often around the veins. As lesions develop, an amber/brown color shows up. Veins and tissue around the veins turn dark over time as lesions spread. Little is known regarding yield loss from this disease.

Growing Degree Days (GDD) and Rainfall Through August 7th

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

Later planted fields (mid-June) should be undergoing pollination, but temperatures this week are in the low 90s, possibly affecting pollination. Most fields planted in late May were pollinating during ideal conditions, although weather and soil moisture could certainly vary across the state. If you have good records of when you have planted, take a look in a week or two and check for tip-back or aborted kernels along the ear. Fields planted in early April may be in blacklayer within the next week to ten days, if we keep getting about 30 growing degrees per day. Let us know if you see anything sooner. In the last week we have actually seen lighter rainfall every few days, instead of intense storms or extended drought. It is still a good idea to check soil moisture levels and irrigate if necessary.

VT: 1135 GDD – Pollination can begin
R1: 1400 GDD – Silking, pollination
R6: 2700 – Blacklayer

Table 1: Accumulated growing degree days based on planting dates through August 7th.

If you planted

Sussex Kent New Castle
22-Apr 2374 2329 2250
29-Apr 2322 2282 2216
6-May 2214 2172 2118
13-May 2110 2067 2021
20-May 1998 1960 1927
27-May 1841 1801 1779
3-Jun 1688 1649 1628
10-Jun 1565 1532 1514
17-Jun 1429 1405 1386

Soybean Insect Scouting Update

David Owens, Extension Entomologist, owensd@udel.edu and Bill Cissel, Extension Agent – Integrated Pest Management; bcissel@udel.edu

Continue scouting for defoliators and for pod feeding insects. Primary defoliators are green cloverworm, bean leaf beetle, and Japanese beetles. A few more aphids have been found in fields throughout the state, but only isolated colonies. As a reminder, defoliation the threshold in reproductive stage soybean is 15%, and for aphids the threshold is 250 aphids per plant. Stink bugs are generally present in low numbers in R-stage beans, thresholds are 5 bugs per 25 sweep sample. Take multiple samples throughout the field because stink bugs aggregate. A small number of brown marmorated stink bugs have been found so far, this is an edge species that usually does not move into field interiors; check near woodlines, especially those that have tree of heaven. The high humidity has favored pathogens of spider mites. A few hotspots we have visited in the last week have had alarming visual symptoms of mite defoliation, but close inspection revealed that all the mites were dead. Recent humid weather favors fungal pathogens and in some fields, predatory mites have moved in. Dead spider mites will look brown and fuzzy. Predatory mites will be a creamy white to pale orange color, pear shaped, and with no spots or markings. As a heads-up, soybean looper is active in South Carolina. It usually appears in our area near the end of August.

When to Plant Plasticulture Strawberries

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

Chandler has been our main plasticulture strawberry and has shown consistently high yields. For most of Delaware, the recommendation has been to plant Chandler the second week in September. However, Chandler is more sensitive to fall and winter temperatures than other varieties and in warmer conditions Chandler will put on too much growth, leading to small berries the following spring; therefore, knowing when to plant is difficult. If you could accurately predict fall and winter temperatures, you could adjust planting dates, but, of course, this is not possible.

One strategy has been to make multiple plantings of Chandler one week apart starting the second week in September. This will insure that a part of the crop will come out of winter with the proper number of crowns (not too many, not too little). Unfortunately, this means that part of the crop will be low yield and part will have small berries.

Another strategy is to switch to varieties that are less susceptible to putting on too much growth. This is where the variety Camarosa may have a fit; it is less temperature sensitive than Chandler in the fall and is not prone to putting on excessive growth. Camarosa has not performed as well on Delmarva compared to North Carolina.

Sweet Charlie, the early berry that also can put on a second late crop, is normally planted 7-10 days ahead of Chandler. It is not an option to replace Chandler. For other varieties being tried, we still do not have enough research in our region to know if they can be replacements for Chandler. Flavorfest has performed well but does not produce over as long of a season as Chandler.

Another strawberry that should be considered by growers is Albion, a day-neutral variety. It too is not sensitive to when it is planted in the fall. While much less productive in the main Chandler season, it has some unique properties that make it valuable to growers. First, it will give some early production, ahead of Chandler. Second, even though production is lower, it produces evenly over an extended period from April through early July. In general, it will give 5-6 weeks more production than Chandler. It is a large, firm berry, that, while not as sweet early in the season, has good quality in May and June. Research at Cornell and Penn State has shown that Albion needs much higher levels of nitrogen than the other common varieties and when fertilized properly will give higher yields over an extended period.

Sweet Corn Insect Update

Bill Cissel, Extension Agent – Integrated Pest Management; bcissel@udel.edu and David Owens, Extension Entomologist, owensd@udel.edu and

A whorl-stage sweet corn field on station had an economic infestation of fall armyworms, whorl thresholds are 15%. Be wary of fall armyworm in tassel-push corn, worms dislodged by the emerging tassel may go to the developing ear. Pyrethroids will not give complete worm control, scout fields soon after treatment. Other alternative mode of actions that are softer on beneficials include diamides (Coragen) methoxyfenozide (Intrepid), indoxacarb (Avaunt) and spinetoram (Radiant). Be sure to read the labels for use restrictions (indoxacarb cannot be used after tassel-push) and restrictions on the number of applications. A commonly used earworm product is Besiege which has chlorantraniliprole (Coragen) in it; earlier use of chlorantraniliprole may limit later use.

Corn earworm populations are higher than last week. Drier evening weather favors moth flight, and worms that developed in field corn are starting to emerge as adults. I expect moth flight activity to continue increasing state-wide until early-September. You may notice some trap locations that had been catching a lot of moths are now catching fewer; in some locations traps were adjacent to sweet corn that has since been harvested. However, other traps have been catching many more moths than they had been, especially in the Monday Laurel data. Blacklight trap captures are also increasing. Focus more on the state-wide trends. Monday trap capture can be found at (http://agdev.anr.udel.edu/trap/trap.php), and Monday trap captures were much higher from nearly all sites. As a reminder, what is reported on the website is on a per night basis, the table below is cumulative over Monday, Tuesday, and Wednesday night.

Trap Location BLT – CEW Pheromone CEW
3 nights total catch
Dover 0 7
Harrington 1 4
Milford 5 11
Rising Sun 7 5
Wyoming 7 25
Bridgeville 2 23
Concord 4 20
Georgetown 2 14
Greenwood 6
Laurel 0 78
Seaford 1 21