Insect observations

A few Japanese beetles were sighted today on a peach tree in Columbus. Late June is the usual time that this pest begins to emerge. Beware that large congregations might be seen on their preferred crops over the next few weeks. Japanese beetle is a pest of sweet corn, snap beans, raspberries, grapes, plum, peaches, blueberries, and hops as well as ornamental plants such as roses and linden trees and sassafras, and weeds such as smartweed. This pest can be more readily controlled by insecticides if the spray is made when the congregations are just beginning to form. Insecticides that are very effective for control of Japanese beetle are old ones: carbaryl (Sevin) and pyrethrins plus PBO (EverGreen Pro).

True armyworm is active in corn fields and grassy areas. We previously reported a large surge in the number of armyworm moths caught in our blacklight trap in Columbus between 5/14 and 5/18, with a record of 210 moths in one night on 5/14. We have been seeing increased numbers of moths during the past week, including today when there were 96 armyworm moths in the trap. There have been reports of armyworm larvae being found in field corn fields around Ohio. Daily counts of armyworm and several other common moths in blacklight traps are posted here:  https://docs.google.com/spreadsheets/d/10gh3rHahdxLKkXQapGyEPxWsjHYRmgsezOoFHnwtyEo/edit#gid=1114468121

Squash vine borer is now active, and abundant at our research farm in Columbus. Its adult is a day-flying moth that will be laying eggs on zucchini and other summer squash, winter squash (except butternut), pumpkins, and gourds over the next few weeks. It generally is a severe problem in home gardens and in small plantings, but less severe in large fields. Insecticide can be effective if directed to the base of the main stem before eggs have hatched, usually at least 2 or 3 sprays at 10-day intervals. Insecticides used for its control are pyrethroids such as Asana (esfenvalerate), Pounce (permethrin), Warrior (lambda-cyhalothrin), MustangMaxx (zeta-cypermethrin), or Brigade (bifenthrin); it is usually not well controlled by Sevin (carbaryl). We have found that EverGreen Pro (pyrethrins plus PBO) is effective although squash vine borer is not listed as a target pest on its label. This year we have a field trial in progress to evaluate the non-chemical tactic of a border trap crop of unharvested zucchini.

Corn earworm has been active for the past few weeks but at low numbers, which is typical of this pest in Ohio in early summer in most years. We have not seen the surge in moth activity like we did last year in late May and early June. A pheromone trap is highly effective at detecting the presence of the moth. Farms with early planted sweet corn should have their trap out as soon as tassels are emerging. Information on using traps is available here: https://cpb-us-w2.wpmucdn.com/u.osu.edu/dist/1/8311/files/2014/12/CornTrapInstructions2009-u47rp3.pdf   Information on buying traps to monitor corn earworm is here:  https://cpb-us-w2.wpmucdn.com/u.osu.edu/dist/1/8311/files/2019/07/TrapSpecsAndSources2019.pdf . Trap counts from several Ohio locations are posted here: https://docs.google.com/spreadsheets/d/10gh3rHahdxLKkXQapGyEPxWsjHYRmgsezOoFHnwtyEo/edit#gid=0

Potato leafhopper is active and being reported from beans, potatoes, apples, and hops. The adults and nymphs of this pest are found on leaf undersides where they suck sap. Their feeding results in yellowing then browning along the edge of leaves, a symptom known as ‘hopperburn’. Leafhoppers can be controlled by sprays of a neonicotinoid such as Admire (imidacloprid) or Assail (acetamiprid), or a pyrethroid such as Pounce (permethrin), Warrior (lambda-cyhalothrin), MustangMaxx (zeta-cypermethrin), Brigade (bifenthrin), or by dimethoate.

Brown marmorated stink bug is active now. Our traps are catching only adult stink bugs so far, but a few young nymphs have been seen on host plants. This year we are continuing our investigations of the samurai wasp, which is a tiny parasitoid that specializes in killing the eggs of this stink bug. We have a colony of the samurai wasp at OSU, and we have made releases of it at ten Ohio fruit farms, in comparison with 10 Ohio fruit farms where we did not make a release. We are currently sampling those 20 farms to see if the samurai wasp has become established.

Spotted lanternfly: This invasive exotic pest has NOT yet been found in Ohio, but many people are on the lookout for it, especially in eastern Ohio, because it has been spreading from its initial infestation in eastern Pennsylvania. Its favorite host plant is the tree of heaven but it can cause damage to grapes, hops, blueberries, and other fruit crops, mostly in late summer.

-Celeste Welty, Extension Entomologist

Beware of armyworm on early sweet corn and other crops!

We have detected an extremely large population of armyworm moths in Columbus during the past week. This pest prefers to feed on grasses, including corn, wheat, rye, and grassy weeds, but if those plants are in shortage and if populations of armyworm are large, it can infest other crops including alfalfa, beans, cabbage, cucumbers, lettuces, onions, peppers, and radishes. Infestation can be worse in no-till fields than in tilled fields. Any early-planted fields of these crops should be scouted for presence of armyworm. Scouting is best done near dawn or dusk because armyworm larvae are nocturnal and hide in the soil during the day. The name armyworm is given because of the ability of older larvae to form large aggregations that move together from field to field. Infestations can appear quite suddenly in a field, and much damage can occur in a short period of time.

The proper common name of this pest is just ‘armyworm’ but it is often called the true armyworm or the common armyworm, to differentiate it from other species such as fall armyworm, beet armyworm, and yellow-striped armyworm. Its scientific name is Mythimna unipuncta, formerly Pseudaletia unipuncta. It is a member of Order Lepidoptera, Family Noctuidae.

Armyworm larvae are striped, as shown below in Figures 1 and 2. The body is greyish-green or greyish brown with broad dark stripes down its back and along each side, and with a light stripe below the dark stripe on each side. The head is yellow or yellow-brown, marked with net-like brown lines. The body is about 35 mm (1.4 inches) long when fully grown. The larval period lasts about 3 weeks. There are about 2 or 3 generations per year in Ohio. The adult is light brown with a white dot near the center of each forewing, as shown below in Figure 3.

Figure 1. Armyworm larva. Photo credit: James Kalisch, University of Nebraska, Bugwood.org.

 

Figure 2. Armyworm larva. Photo credit: Frank Peairs, Colorado State University, Bugwood.org.

 

Figure 3. Armyworm adult. Photo credit: Pest and Diseases Image Library , Bugwood.org.

The adult is a moth that can be detected in blacklight traps and pheromone traps. We have had a blacklight trap operating in Columbus since the first week of April. We detected quite a few armyworm moths (0-32 moths per night) throughout April, but there was a large surge on 5/14 when there were 210 armyworm moths in the trap after a single night. Dr Dave Shetlar has been tracking various species of moths in blacklight traps at several locations for several decades, and he thinks that 210 armyworm moths in one night is a new record high number.

The link to our pheromone trap reports is here: https://docs.google.com/spreadsheets/d/10gh3rHahdxLKkXQapGyEPxWsjHYRmgsezOoFHnwtyEo/edit#gid=1122468773

The link to our blacklight trap reports is here: https://docs.google.com/spreadsheets/d/10gh3rHahdxLKkXQapGyEPxWsjHYRmgsezOoFHnwtyEo/edit#gid=1114468121

Sweet corn and field corn that is transgenic due to presence of B.t. should have protection from armyworm feeding. Seed treatments on corn by clothianidin, thiamethoxam, or imidacloprid can offer some suppression from caterpillars such as armyworm, but they are primarily for control of beetles. For sweet corn that is not transgenic, insecticide treatment is suggested if more than 35% of plants show infestation by armyworm during the seedling or early-whorl stages. Insecticides that can be used for armyworm control on sweet corn are pyrethroids (Asana, Baythroid, Brigade, Mustang, Permethrin, Proaxis, Warrior), or Blackhawk, Coragen, Intrepid, Lannate, Lorsban, Radiant, or B.t. products such as Dipel and Javelin.

-by Celeste Welty, Extension Entomologist, 16 May 2020

Beware of late worms on peppers and tomatoes!

Fall armyworm and beet armyworm are two pests that we monitor with pheromone traps throughout the summer at several sites in Ohio. These two pests are sporadic in occurrence; they are sometimes absent in Ohio and sometimes present at damaging levels, especially in September and October. These were absent for most of this summer at Ohio sites, but are present now at some sites.

Fall armyworm attacks sweet corn, peppers, and tomatoes. This year, the fall armyworm was detected in Huron County, Medina County, and Franklin County starting in late August, and it is still being detected at those locations.

The beet armyworm has been absent at most sites but has been detected during the past week in Franklin County. It attacks peppers and tomatoes.

These two pests are challenging to manage because their appearance is so sporadic and because the larvae are generally tolerant of pyrethroids; they are better controlled by non-pyrethroids such as Avaunt, Proclaim, Radiant, or Intrepid.

Corn earworm is a third pest that is best known as a significant pest on sweet corn in late August and into September, but once the sweet corn is gone, the corn earworm can cause significant damage to bell peppers. It also attacks tomatoes where it prefers green fruit over red fruit. Corn earworm moths were detected at very high levels in late August at some sites, and they are still being detected at high density in Clark, Franklin, and Huron Counties.

-Celeste Welty, Extension Entomologist

Corn earworm remains abundant!

As detailed in VegNet on 24 August, we have seen very high numbers of corn earworm moths caught in pheromone traps since mid-August. Trap catch remained very high last week at most Ohio sites where we have traps. This pest prefers to lay its eggs on fresh-silking sweet corn but also can cause significant damage to tomatoes and bell peppers.

Our Ohio trap reports for corn earworm and several other vegetable pests are posted online, at this link: https://docs.google.com/spreadsheets/d/10gh3rHahdxLKkXQapGyEPxWsjHYRmgsezOoFHnwtyEo/edit?usp=sharing

One of the details shown on our trap report page is the type of trap. At most of our sites, we are using the type of trap called a Scentry Heliothis trap, which is a large cone-shaped trap made of white nylon mesh. At two of our sites, South Charleston and Columbus, we have the type of trap called a Hartstack or Texas Cone trap, which is the same shape but larger and made of metal hardware cloth. The Hartstack trap tends to catch much higher numbers of corn earworm moths, and tends to detect low density populations of corn earworm more effectively than the Scentry Heliothis trap. The Hartstack trap is not readily available from trap supply companies, thus we recommend the Scentry Heliothis trap to our cooperators. However for anyone who is interested in Hartstack traps, here are two tips. The plans for making your own Hartstack trap are shown in a fact sheet from Kentucky: https://entomology.ca.uky.edu/ef010 . We purchased our Hartstacks several years ago from a source in Illinois (see http://www.agrinews-pubs.com/news/building-a-better-bug-trap/article_c69e27e7-fa1e-58b5-b5f7-442112bfb2a0.html )

-Celeste Welty, Extension Entomologist

Increasing activity in corn earworm (tomato fruitworm)

Mid- to late-August is the time of year when we usually see a large increase in the populations of corn earworm, the pest that is also called the tomato fruitworm. As of last week, this trend has been seen in some parts of Ohio but not in others, which is unusual; we usually see an increase at all sites at this time of year. Our pheromone trap in Clark County jumped to 555 moths last week, up from 36 moths the previous week. Our pheromone trap in Franklin County showed an increase to 43 moths last week, up from 12 moths the previous week. The current moth population is likely composed of some recently immigrating moths from the southern USA as well as moths that emerged locally as the later generation of moths that migrated into Ohio back in early June.

Trap reports for corn earworm at several Ohio locations can be viewed using this link:  https://docs.google.com/spreadsheets/d/10gh3rHahdxLKkXQapGyEPxWsjHYRmgsezOoFHnwtyEo/edit?usp=sharing

Fresh-silking corn is the preferred host of the corn earworm, but tomato is another common host. It can also attack a variety of other crops, including bell peppers, lettuce, beans, potatoes, cole crops, cucurbit crops, as well as many weed species.

Infestation of the tomato fruitworm on tomatoes in Ohio is most likely in late August and September, but can sometimes occur much earlier, as has been seen this year. It prefers green tomatoes over ripening red tomatoes. Larvae often feed on one tomato fruit for a short time then move to another fruit. Damage in fruit appears as deep wet cavities. Eggs are usually laid on a leaf below the highest flower cluster.

Each female moth of corn earworm can lay 500 to 3000 eggs. Eggs usually hatch in 3-4 days but can be faster when weather is very hot. As the larvae feed, they progress through six instars or sub-stages, with each instar lasting 2-3 days. The larval stage lasts about 15 days at 86 degrees F. Once larvae are fully grown, they drop to the ground, where they tunnel 2-4 inches deep to pupate. The pupal stage lasts about 13 days. New moths start to lay eggs about 3 days after emerging from the pupal stage. The moths are active mostly at night, and hide in vegetation during the day. The moths feed on nectar in flowers of various trees and shrubs and weeds. The moths usually have a 5-15 day lifespan, but can live up to 30 days.

When corn is in the fresh-silk stage, it is attractive to corn earworm. During the time that Ohio’s large acreage of field corn is silking, our relatively small acreage of sweet corn and tomatoes is usually not attacked much by this pest. Once the field corn in any area begins to mature and dry, it is no longer as attractive to the earworms as late sweet corn and tomatoes. This year, much of Ohio’s field corn was planted later than normal due to frequent rains, so this protective effect of nearby silking corn has been happening later than usual this year but is now likely ending in most locations.

One of the most effective ways to monitor this pest is to use a pheromone trap to catch adult moths. As soon as the target moth is found in traps, fields of sweet corn and tomatoes and bell peppers should be scouted for signs of larval damage so that control measures can be taken in a timely and preventive manner.

In addition to the challenge of knowing when the corn earworm arrives, another challenge is its susceptibility to insecticides and transgenic crops. Observations over the past 12 years in the Midwest have shown that pyrethroid insecticides (Warrior, Brigade, and others) are not as effective at controlling corn earworm on sweet corn as they were previously. In years when the corn earworm population density is low, we have seen that pyrethroids can provide very good control, but in years when their density is high, pyrethroids are not very effective. Alternatives to pyrethroids for sweet corn are Coragen, Radiant, Blackhawk, Lannate, and Sevin. Alternatives to pyrethroids for tomato are Avaunt, Coragen, Exirel, Intrepid, Lannate, Radiant, Rimon, and Sevin. Among the transgenic sweet corn hybrids, we are seeing that the old Attribute hybrids are no longer very effective for caterpillar control, but the Attribute-II hybrids are very effective. Some growers are reporting that some of the Performance Series hybrids are not providing adequate control. We have a field trial in progress to determine how well the transgenic hybrids are currently working under Ohio conditions.

-by Celeste Welty, Extension Entomologist

Spider mite management

With hot and dry weather persisting over much of Ohio, there are reports of spider mite outbreaks on specialty crops. Because mites are tiny, they are often overlooked or misdiagnosed as a disease. Infested leaves have fine webbing on the leaf undersides. Tomato leaves damaged by spider mites usually have yellow blotches, while bean leaves show white stipples or pin-prick markings from mite feeding. Pumpkins can tolerate moderate levels of mites, but watermelons are more sensitive to injury from mite feeding. A simple method of diagnosing spider mites is to shake leaves over a piece of paper and look for moving specks that are visible to the naked eye. A closer look with a magnifier can show the tiny mites that are white, marked with two large dark spots on the middle of the body.

Mites have many natural enemies that kill them, such as specialized predatory mites or generalist lacewings, ladybugs, and pirate bugs, but these helpful predators are often killed by pesticides. Mites can be suppressed by periodic overhead irrigation.

Chemical intervention can be needed to keep the crop alive if spider mites are abundant. In some fields, the mite infestation is worst on a field edge by a dusty road. When a mite infestation is limited to field edges, infested fields should be scouted, and a miticide applied as a spot treatment to isolated infestations. Mite control is better when higher volumes of water are used; 25 to 50 gallons of water per acre is better than 10 gal/A.

Several pesticides are registered for spider mite control; some are restricted use, and some are for general use, as shown for vegetable crops in Table 1, and for hops and fruit crops in Table 2. At some locations, organophosphates are still effective for mite control, with Dimethoate being the best bet and MSR (Metasystox-R) as another choice. Dimethoate is an option for melons but is not allowed on squash or cucumbers; it has been a preferred product for mite control on soybeans. Dimethoate is prohibited from use on ornamental crops in high tunnels and greenhouses but is not prohibited from vegetable crops in high tunnels and greenhouses. Where organophosphates are not effective, Agri-Mek (abamectin) is generally the most effective product for mite control but it is a restricted-use product, while Acramite (bifenazate) and Oberon (spiromesifen) are nearly as good but are not restricted-use products. Other options for some crops are Portal, Envidor, Zeal, Nealta, Onager, Savey, Apollo, and Kanemite. Although Brigade (bifenthrin) and Danitol (fenpropathrin) are labeled for spider mite control when used at the high end of the rate range, they are generally not as effective as the true miticides. Dicofol is an old miticide that is still effective at some sites, but does not perform well at sites where resistant populations have developed. Vydate (oxamyl) is a Restricted Use product that is registered for use on eggplant for mite control. On organic farms, insecticidal soap (such as M-Pede or Des-X) can be used for mite control, but thorough coverage of the undersides of leaves is needed for good control. Soap can cause phytotoxicity if applied under sunny hot conditions. Soap is a good alternative in conventional fields that are too close to harvest to use a true miticide; insecticidal soap has a 12-hour re-entry interval and a 0-day pre-harvest interval.

-Celeste Welty, Extension Entomologist

Mid-summer insect observations

Corn earworm (CEW) showed a moderate surge of activity during this past week, from 19-22 July when our pheromone trap in Columbus caught 49 moths in a 4-day period. This follows a few weeks of low CEW moth catch, after high CEW moth catch in late June. A pheromone trap near Fremont caught 74 CEW moths this past week. The corn earworm moths will be laying their eggs on silks of sweet corn. Sweet corn can be protected from corn earworm infestation by insecticide sprays during silking. When the number of CEW moths caught in traps is moderate  (1 to 13 moths per day, or 7 to 90 moths per week), then sprays should be applied every 4 days if the daily maximum temperatures is below 80 degrees F, or every 3 days if the daily maximum temperatures is above 80 degrees F. More information about CEW, traps, and trap-based spray schedules is available using this link: http://u.osu.edu/pestmanagement/crops/swcorn/ .

The typical insect pests of mid-summer are currently being found on Ohio farms. Squash bug eggs and young nymphs are being found in squash and pumpkin fields. Cucumber beetles, both striped and spotted, are feeding in flowers of squash and melons. Squash vine borer is past its peak in terms of the number of adult moths caught in pheromone traps, which peaked in early July. The tobacco hornworm is feeding on tomatoes in the field and in high tunnels. Imported cabbageworm is feeding on cabbage and other Brassica crops. Colorado potato beetle adults are on eggplant and potato. Blister beetles are reported on potato. Sap beetles and western corn rootworm beetles are being seen on sweet corn. Japanese beetles are found on sweet corn, asparagus ferns, and various fruit crops, but they seem to be less numerous now than several weeks ago when huge numbers were seen.

The second generation of the European corn borer has not yet been detected, but it should start within the next week or two, and will be important in peppers and sweet corn.

An encouraging note is that many beneficial insects are also active in vegetable crops. Recent sightings include many Orius predatory bugs and the pink lady beetle in sweet corn, lady beetle larvae, lacewing larvae, the spined soldier bug, and damsel bugs in a variety of crops.

-Celeste Welty, Extension Entomologist

Corn earworm arrived early in sweet corn

Corn earworm has showed up unusually early this year and has been infesting early sweet corn that was not adequately protected. The earworm population as detected by moths caught in pheromone traps was very high in early June (161 moths in one trap in one week in Columbus), and again in late June at some sites (125 moths in one trap in one week). However, this past week, the number of moths caught dropped greatly (7 in one trap at Columbus). Similar trends have been reported from other parts of Ohio. As long as corn earworm moths are active, sweet corn fields that are in the early silk stage will become infested by corn earworm unless preventive measures are taken. The infestation will be less intense in sweet corn fields if the local fields of grain corn are in the silking stage, but due to the early summer rains causing delay in planting, grain corn in much of Ohio is not yet at the silking stage, thus sweet corn will be extra vulnerable to earworm attack. Once corn earworm is detected, silking sweet corn should be sprayed with insecticide every 2-6 days. The choice of an appropriate spray interval is as important as the choice of product to use. Details about the most appropriate spray interval based on pheromone traps are shown in the chart below.

Growers who do not yet have a trap can find information about buying a trap with this link: https://cpb-us-w2.wpmucdn.com/u.osu.edu/dist/1/8311/files/2019/07/TrapSpecsAndSources2019.pdf

and information about using the trap with this link:

https://cpb-us-w2.wpmucdn.com/u.osu.edu/dist/1/8311/files/2014/12/CornTrapInstructions2009-u47rp3.pdf

Our testing of insecticides for corn earworm control over the past 13 years has shown that pyrethroids (Warrior, Asana, Pounce, Mustang Maxx, Brigade, Baythroid, Hero) are generally effective for earworm control when the earworm population is low to moderate but generally not effective when the population is high. If pyrethroids are used, they should be used at the maximum labeled rate. Among pyrethroids, Hero is generally the most effective; it is a pre-mix of two different pyrethroids (Mustang Maxx and Brigade). Alternatives to pyrethroids are Coragen, Radiant, and Blackhawk, and the pre-mix Besiege, which was formerly called Voliam Xpress. Organic growers can use Entrust or a B.t. such as Javelin or Dipel.

For plantings of B.t. transgenic hybrids (the Attribute II series and the Seminis Performance series), we have found that the B.t. provides adequate control of corn earworm when populations are low, but not when earworm populations reach high density. These hybrids provide the best control when silks are fresh but less control when silks begin to dry. Thus insecticide sprays during the later part of the silking period are helpful to prevent earworm infestation in transgenic sweet corn.

-Celeste Welty & Jim Jasinski

Insecticide update for vegetable and fruit crops

There have been a few insecticide registrations that have come through since previous updates this past winter (summaries from January are available with these links: https://cpb-us-w2.wpmucdn.com/u.osu.edu/dist/1/8311/files/2019/02/PAT_Jan2019_1-page-1hvqfhg.pdf and https://cpb-us-w2.wpmucdn.com/u.osu.edu/dist/1/8311/files/2019/02/Summary_Jan2019_1-page-22nf965.pdf ).

Torac and Apta from Nichino America both contain tolfenpyrad as the active ingredient; both are in IRAC’s mode-of-action group 21A. Since March 2019, new crops on the new Torac label are onions and other bulb vegetables, lettuce and other leafy vegetables, and celery and other leaf petiole vegetables. Torac controls thrips, aphids, leafhoppers, flea beetles, and some caterpillars. Since February 2019, new crops on supplemental labels for Apta are strawberry and other low growing berries, raspberries and other caneberries, and blueberries and other bushberries. Apta controls thrips, plum curculio, fruitworms, Lygus (tarnished plant bug), and suppresses spotted-wing Drosophila.

Versys is a new insecticide from BASF that contains afidopyropen as the active ingredient, which puts it in IRAC group 9D. On the initial label in October 2018, the target pests were only aphids, as controlled at a low rate of product. A newer label now includes control of whiteflies at a higher rate of product.

Exirel is now allowed on raspberries and other caneberries, as shown on a supplemental label from November 2018. Use on caneberries is with a 1-day pre-harvest interval, for control of spotted-wing Drosophila and adult root weevils. Exirel is from FMC, and contains cyantraniliprole as the active ingredient, in IRAC group 28.

PQZ is a new insecticide product from Nichino America that has been registered since November 2018 but was missed in our earlier updates. PQZ contains pyrifluquinazon as the active ingredient. It is in IRAC group 9B. It controls aphids, whiteflies, and leafhoppers, and is allowed for use on Brassica head and stem vegetables, cucurbits, fruiting vegetables, leaf petiole vegetables, leafy vegetables, tuber and corm vegetables, as well as on pome fruit, stone fruit, and grapes.

Ethos-3D is a new insecticide/fungicide product from FMC that has been registered since 2018 but was missed in our earlier updates. It is for use on sweet corn. It contains bifenthrin (the same AI as in Brigade; IRAC group 3A) as the insecticidal component, and Bacillus amyloliquefaciens as the fungicidal component. It is for application at-planting for control of corn rootworm larvae, Asiatic garden beetle, wireworms, grubs, seedcorn maggot, cutworms, and armyworms.

-Celeste Welty, Extension Entomologist

Beware of thrips on strawberries

Although strawberries are not considered to be a vegetable crop, using VegNet is a good way to get information out to growers who have both vegetables and berry crops.

Strawberry fruit that have been injured by thrips are a dull or bronzed color, and are often small, hard, seedy, and fail to ripen. They can cause uneven maturity of fruit. When severe, their injury can make the strawberry crop completely unmarketable.

Thrips are an occasional serious pest of strawberries. This means that in most years, they are not a problem, but in some years, they can be a big problem. One such year was 2018 for some growers in Ohio. As far as we understand the problem, the reason for variability from year to year has to do with weather systems. In some years, conditions are right that large numbers of small insects such as thrips and leafhoppers are carried on strong weather fronts moving from the southern USA into Ohio during the time that strawberries are in bloom. In other years, this long-distance movement does not happen at all, or happens later, at a time when strawberries are no longer in bloom.

Thrips are small, slender, elongate, cigar-shaped insects, about 1 mm (1/25 inch) long. They differ from other insects by having narrow strap-like wings that are fringed with hairs (Figure 1). The wings are usually folded lengthwise over the back when they are resting or feeding (Figure 2). They have asymmetrical mouthparts (Figure 3) that have a well-developed left mandible and an underdeveloped right mandible. They feed by piercing plant cells by the mandible then sucking sap that oozes out of the punctured cells. Thrips generally have flowers as their preferred plant part. They are found in flowers of many species of plants. Thrips are often overlooked due to their small size and their tendency to hide in protected places. When present at low density, thrips are often not harmful to plants.

The thrips species that infests outdoor strawberries is Frankliniella tritici, which has the official common name of ‘flower thrips’, but which is widely known as the eastern flower thrips. It does not tolerate cold weather well so does not survive winter well in places like Ohio. The adults are yellowish brown, and the larvae are whitish-yellow. The larvae are similar to the adults in shape but smaller and without wings. On strawberries, the infestation starts by adult thrips during bloom but then can continue during fruit set by adults and their offspring larvae. Thrips hide under the cap of the berry or in grooves around the seeds on the berry.

A key to thrips management is frequent monitoring, at least once per week. Growers should examine early flower clusters on early cultivars. In each of five to 10 areas of the field, five to 10 blossoms should be tapped into a white cup, or into a zip-top sandwich bag, which should then be examined for the dislodged thrips running around on the surface. Count the number of thrips found, then calculate the average number of thrips per blossom. A rough action threshold for treatment with insecticide is the presence of 2 or more thrips per blossom. Once fruit are ¼ inch in diameter, an action threshold is 0.5 thrips per fruit. If thrips are above threshold, the trickiest part of management is to avoid spraying insecticide that will harm pollinators. Insecticide should be applied pre-bloom or before 10% of the plants have open blossoms. If thrips are found above threshold on early cultivars, then a preventive spray can be made on the later cultivars before their flowers open, to avoid harming pollinators.

Insecticides used to control thrips on conventional strawberries are Radiant, Assail, and Sivanto, all of which have thrips listed as a target pest on their labels. Thrips are well controlled by Lorsban, Brigade, and Danitol, which are allowed for use on strawberries, but thrips are not listed as a target pest of the label of these three products. Note that Lorsban has a 21-day pre-harvest interval. Products for thrips control on organic strawberries are Entrust and azadirachtin products such as Neemix and Aza-Direct.

If a biological control approach is preferred, several kinds of natural enemies are available for purchase from commercial insectaries for thrips control: Orius (predatory flower bugs), and two species of predatory mites: Amblyseius cucumeris and Ambylseius swirskii. Biocontrol is not feasible to begin once the thrips population is large but can be planned in advance at locations that have a consistent problem with thrips.

Figure 1. Typical appearance of a thrips.

Figure 2. A thrips with wings folded over its back.

Figure 3. Close-up of thrips head and mouthparts.

by Celeste Welty, Extension Entomologist