Vegetable Crop Insect Scouting

Cucurbits
Spider mites have been observed in a few fields at low numbers. Most mites have been observed near field edges immediately adjacent to other crops or woodlines. With the warm weather, I am beginning to find spider mites on edge-weeds such as pokeweed. Last year, every pokeweed plant I looked at by mid-July had large spider mite populations on it, and quite a few predators too. Spider mites can also ‘balloon’ into fields, meaning that a population can start in the field interior.

Our lab examined rye strips from several fields at the beginning of May looking for spider mites. We collected 20 row feet of the windbreak foliage, washed it in soapy water, and filtered the water. We did not observe spider mites in the rye samples. However, this is like looking for a tiny needle in a large haystack. One of the fields we sampled had spider mites early, likely coming in from the greenhouse. This can be reduced by keeping greenhouses weed-free when not in use, and especially in late summer through fall.

The table below lists the miticide active ingredients and their mode of action group for watermelon. There are generic formulations of some of the chemicals, this list is not meant to serve as an endorsement.

 

Miticide Active Ingredient MOA Group Life Stage Active Applications per Season
Agri-Mek Abamectin 6 Mobiles (translaminar) 3-5
Gladiator Zeta-cypermethrin + avermectin 3 + 6 Mobiles (translaminar) 3
Acramite Bifenazate 25 Eggs and mobiles (contact) 1
Kanemite Acequinocyl 20B Eggs and mobiles (translaminar) 2
Oberon Spiromesifen 23 Eggs and juveniles (contact) 3
Portal Fenpyroximate 21A Mobiles (contact) 2
Magister SC Fenazaquin 21A Eggs and mobiles (contact) 1
Zeal Etoxazole 10B Ovicidal, juveniles (translaminar) 1

 

 

Please note that avermectin is in the same mode of action class as abamectin. Do not apply one right after the other. Also, some of these products will stop mite feeding quickly, but the mite will take a few days to die. If you have sprayed a field and see mites a couple of days later, wait another few days and resample. Also, many of these products have a long residual activity, meaning that if it is not active immediately on eggs, it should still be around once the eggs hatch. This year, we have plans to test these products at our research station. As always, read the label thoroughly for further guidance. Some products have restrictions on reapplication interval, and restrictions on consecutive applications. There are also requirements on some for spray adjuvants to avoid illegal residues. Good coverage is key for miticide efficacy, even on those that are translaminar. Also, be mindful of products that are in a tank-mix. For instance, Zeal may have some reduced efficacy when mixed with Boron, and stickers or ‘sticky’ fungicides can interfere with Agri-mek. Both Agri-Mek and Magister can be very toxic to pollinators, while Portal and Kanemite are not generally considered toxic to bees. All of the others advise caution.

Cucumber beetles are still moving into new plantings.

Sweet Corn
Sweet corn pheromone and blacklight traps are checked twice weekly on Mondays and Thursdays. By Tuesday and Friday morning, data is uploaded to our website: https://agdev.anr.udel.edu/trap/trap.php. For reference, action thresholds based off of blacklight and pheromone trap can be found here: http://extension.udel.edu/ag/insect-management/insect-trapping-program/action-thresholds-for-silk-stage-sweet-corn/. Moth counts continue to be elevated, and seem to be higher and a little earlier than last year. Thursday’s trap capture is as follows:

Trap Location BLT – CEW Pheromone CEW
3 nights total catch
Dover 1 2
Harrington 0 63
Milford 1 21
Rising Sun 1 45
Wyoming 2 29
Bridgeville 0 65
Concord 1 8
Georgetown 2 38
Greenwood 0
Laurel 3 18
Seaford 0 8
Harbeson 0
Trap Pond 4 12
Lewes 3 63

 

Vegetable Crop Insect Scouting

David Owens, Extension Entomologist; owensd@udel.edu

Cucurbits
We are still in need of your cucumber beetles. If you have a population that you are about to treat or treated within the past 24 hours, please contact me, owensd@udel.edu if you don’t mind me lifting a couple hundred beetles out of the field. Thanks.

With the hot weather this week, be on the lookout for spider mites, not just in watermelon but also tomato. We may get a bit of a reprieve if the weather cools down, but once mites get started in a vegetable field, weather only slows them down but will not remove them. Tomato thresholds from North Carolina are 4 mites per upper canopy leaflet (not leaf).

Sweet Corn
Sweet corn pheromone and blacklight traps are checked twice weekly on Mondays and Thursdays. By Tuesday and Friday morning, data is uploaded to our website: https://agdev.anr.udel.edu/trap/trap.php. For reference, action thresholds based off of blacklight and pheromone trap can be found here: http://extension.udel.edu/ag/insect-management/insect-trapping-program/action-thresholds-for-silk-stage-sweet-corn/.

We observed a significant increase in moth activity in several locations throughout the state.

Thursday trap counts are as follows:

Trap Location BLT – CEW Pheromone CEW
3 nights total catch
Dover 1 7
Harrington 0 48
Milford 2 45
Rising Sun 1 27
Wyoming 1 11
Bridgeville 5
Concord 1 71
Georgetown 2 47
Greenwood 1
Laurel 2 94
Seaford 0 4
Harbeson 2
Trap Pond 3 8
Trapwoods 3 8

Vegetable Crop Insect Scouting

David Owens, Extension Entomologist; owensd@udel.edu

Cucurbits
Cucumber beetles continue to move into fields. It is important to base a treatment decision from 5 to 10 locations per field. I visited a couple of fields this week where cucumber beetle activity was heavy, but only on a couple of rows and a few plants within those rows. For watermelon, we use an action threshold of 2 beetles per plant for young transplants. Other states use a threshold of 5 beetles per plant once vines start running. Unlike watermelon, cucurbits such as summer squash, cucumber, and cantaloupes are susceptible to bacterial wilt. These crops are also more attractive to cucumber beetle than watermelon, thus you may need to treat them more often or see more aggressive cucumber beetle populations. Pumpkins are not very susceptible once they have two true leaves (not counting the cotyledons), and so a seed treatment should provide sufficient control to avoid bacterial wilt. We have been relying heavily on the Group 4A chemistry early, products like imidacloprid, acetamiprid, and thiamethoxam, followed by Group 3 pyrethroids late. There are a couple of other chemistries that may provide good cucumber beetle control: Lannate, Sevin XLR plus, and two diamides, Exirel and Harvanta. Our group is in the process of collecting cucumber beetles from across the area to test susceptibility to the commonly used insecticides. If you have a treatable population, please let me know before or within 1 day of treating and I will gladly take some cucumber beetles off of your hands. Thanks!

Spider mites can be found in some fields, most likely coming in with the transplants. At this stage, you will see the light yellow stippling on the leaves. This stippling is not as apparent on older melons once the leaves thicken up until there are very high populations underneath the leaf. Agrimek or other Abamectin containing Group 6 products can provide excellent control and are systemic miticides. They are hard on bees, so if you are using them during the season, the best window for using them is prior to bee arrival and to apply in the evening when pollinators are not as active.

Sweet Corn
Sweet corn pheromone and blacklight traps are checked twice weekly on Mondays and Thursdays. By Tuesday and Friday morning, data is uploaded to our website: https://agdev.anr.udel.edu/trap/trap.php. For reference, action thresholds based off of blacklight and pheromone trap can be found here: http://extension.udel.edu/ag/insect-management/insect-trapping-program/action-thresholds-for-silk-stage-sweet-corn/. Silking sweet corn is highly attractive to moths, a trap that is nearby but not adjacent to sweet corn may not be entirely representative of the population in your block. Thursday trap counts are as follows:

Trap Location BLT – CEW Pheromone CEW
3 nights total catch
Dover 0
Harrington 1 0
Milford 0 4
Rising Sun 0 1
Wyoming 0 1
Bridgeville 0 0
Concord 2 1
Georgetown 0 0
Greenwood 2
Laurel 2 10
Seaford 2 2
Harbeson 0
Trap Pond 0 0

Flea Beetle Feeding and Tomato Early Blight

Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu

I visited a few tomato fields this week and found 2 to 4-week-old tomato plants with some early blight (Alternaria solani) and in some cases bad early blight lesions. This is very early in the season to be seeing this level of early blight. Many of the plants had a few flea beetle adults on the plant (Fig. 1) and in the areas where the early blight was found also had moderate to high flea beetle feeding (Fig. 2). In some cases I could not find any flea beetles after the rains we have had and in other cases I could find a few of them. Normally the amount of flea beetle feeding I saw would not have been of much concern, but flea beetles can cause increased infections of Alternaria leaf blight in tomatoes and potatoes and possibly other early blight susceptible crops. I found that there was a strong relationship between the amount of flea beetle feeding and the amount of early blight on tomato plants in different fields of a few farms. If you have moderate flea beetle feeding damage to your Solanaceae plants and you see any early blight starting you’ll need to control both the beetle and the disease. Pyrethroids should work well in controlling flea beetles. There is not much organically that will control flea beetles once they are causing economic damage (there are some things that can be done though, to reduce flea beetle problems before flea beetles cause damage, more at: https://attra.ncat.org/attra-pub/download.php?id=135). Using kaolin clay (Surround) before beetles begin to feed on plants is one organic possibility as is using spinosad on beetles after they start to feed.

Flea beetle adults are generally small and range in size from 0.05 to 0.15 inch. They overwinter as adults on weed hosts surrounding the field, on residues of a previous tomato crop, or in the soil if the previous crop was a flea beetle host. Some flea beetles (Systena blanda – the pale striped flea beetle being one) can feed on amaranths or pigweeds (Fig. 3) and will readily move from them over to your crops. Other flea beetles are more host specific (the eggplant, potato and tobacco flea beetles feed on Solanaceous plants while others prefer broccoli, cabbage and other cole crops). However all adult flea beetles have similar damage patterns, they chew small round holes in leaves, which make them look as if they have been damaged by fine buckshot, called “shot-holing”. The white larvae feed on underground parts of the plant, but this damage is usually not economically significant. There is normally a second generation during the summer and at times even a third depending on species. Normally foliar damage to larger plants is not considered to be economically important but feeding damage to small plants or seedlings can reduce stand or vigor of the plant. The other exception about flea beetles not being economic pests is when Alternaria is associated with their feeding on smaller tomato plants.

Figure 1. Underside of tomato leaflet with two flea beetles (Epitrix sp)

Figure 2. Tomato leaf with old flea beetle feeding and early blight

Figure 3. Pale striped flea beetle feeding on amaranthus weed

Allium Leafminer Moving South in Maryland

Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu

The new pest of onion, leek and garlic, the Allium leafminer, is moving south in Maryland. It was first observed in Maryland in Cecil Co. in 2017, but now the fly’s tell-tale marks (Figs. 1 and 2) have been found in a Baltimore City chives planting. This new pest was first found in Lancaster County, Pennsylvania in December 2015. Unfortunately, it is my guess that the pest is now probably in many northern/central areas of Maryland. New transplants or seedings of onions or leeks should be watched closely for the tell-tale signs of the fly’s damage which are several very small white dots in a row along the leaf of an allium plant (Figs. 1 and 2).

Figures 1 and 2. Tell-tale marks on allium leaf made by Allium leafminer females

Penn State has a great deal of good information about the new pest which can be found at: Penn State Allium Leafminer Pest Alert page. Growers should look for these tell-tale signs on any newly planted allium species, but especially on leeks. You can cover any Allium planting with row cover to keep the flies off or if needed treat with insecticides as found in the 2019 Mid-Atlantic Commercial Vegetable Recommendations guide.

Vegetable Crop Insect Scouting

David Owens, Extension Entomologist; owensd@udel.edu

Potatoes
Colorado potato beetle adults are active and laying eggs in potato fields. Most of the insects observed this week were confined to the edge of the field, in part because beetles do not fly when temperatures are below 80 degrees. Sample a field from 10 locations. At each location, count beetle adults and larvae per stem from 1 stem on each of 5 adjacent plants. Thresholds are 50 adults, 75 large larvae, and 200 small larvae per 50 stems. There are many non-neonicotinoid options available that can be used in a rotation strategy to ease selection pressure off of neonicotinoids. They can be found here: https://cdn.extension.udel.edu/wp-content/uploads/2012/03/23152414/Potato.pdf.

Sweet Corn
Scout for cutworm injury. Thresholds are similar to field corn. Trapping data can be found here for European corn borer and corn earworm; trap data is updated by Tuesday and Friday mornings: https://agdev.anr.udel.edu/trap/trap.php.

Watermelons
Continue scouting for cucumber beetles, especially on transplant trays that are hardening off on wagons. Recent cool, wet weather has slowed beetles down, but the weather is warming back up. This year, the Extension entomology team is looking to collect several hundred beetles from individual farm sites throughout Delaware and Maryland to conduct insecticide bioassays. If you have a cucumber beetle infestation, feel free to contact me at owensd@udel.edu. We’d love to take some beetles off your hands!

Vegetable Crop Insect Scouting

David Owens, Extension Entomologist; owensd@udel.edu

Watermelon
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: https://agdev.anr.udel.edu/trap/trap.php. 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).

Vegetable Crop Insect Scouting

David Owens, Extension Entomologist, owensd@udel.edu

Asparagus
Asparagus is emerging from the soil and air temperatures have been favorable for insect activity. Be on the lookout for asparagus beetle. If 5-10% of spears are infested with adults, or 2% of spears with eggs, treatment may be advised. Please refer to the Mid-Atlantic Vegetable Production Recommendations for treatment options if necessary, which can be found here: http://extension.udel.edu/ag/vegetable-fruit-resources/commercial-vegetable-production-recommendations/.

Brassicas
Imported Cabbageworm adults are active (see the Guess the Pest answer in this edition from last week’s challenge). Begin scouting for worm activity.

Reflect on Insect Challenges in 2018

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

Now that harvest season is starting (for corn), in sight (for soybeans) or we look like we might have some time to catch our breath after another hopefully fruitful season, it is a good time to reflect back on insect challenges or issues that came up in 2018. Were they worse or better than 2017? Did you have to deal with anything unusual? Were you pleased with the control strategy you used when you had to make an application? Did an insecticide go out that, looking back, might not have been necessary? Are there problems for which we don’t have good tools available? Reflection like this can help craft next year’s strategy. I would love to hear from you as you look back on the season and reflect. It may help you craft next year’s strategy, and it helps us understand what you dealt with and how we can target our 2019 insect game plan accordingly to help answer questions. Thank you and good luck bringing the rest of the crop in!