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| Honey bees and native pollinators active in early summer blooms. Raleigh, NC. Photo: HJB |
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| Carpenter bee foraging on salvia. Photo: HJB |
Sunday, May 27, 2012
Upcoming pollinator presentation at NC State
Wednesday, May 23, 2012
Do it yourself: An update on distinguishing SWD larvae from other insects in strawberries
Early this spring, I wrote a post discussing how to distinguish spotted wing drosophila (SWD) larvae from other internally feed insects. That post was focused primarily on blueberries. This spring and early summer, however, I received several calls about SWD in strawberries, and they appeared in our research plots for the first time.
Fortunately, the majority of grower calls I received about larvae in strawberries ended up being sap beetle larvae rather than SWD larvae. Sap beetles or picnic beetles are actually a complex of beetle pests which include at least three species in North Carolina (Carpophilus lugubris, Stelidota geminata, Glischrochilus quadrisignatus, and others) and are attracted to rotting, not sound fruit. If rotting fruit are present near sound fruit, as can commonly happen when you-pickers aren't thorough or rain prevents picking, sap beetle adults and larvae can also attack sound, otherwise marketable fruit.
While sap beetle larvae are also not desirable in strawberries, they are more easily controlled than SWD. Good sanitation, meaning removal of overripe or rotting fruit, is usually enough to keep sap beetle populations in check.
How, then, can you distinguish between sap beetle larvae and SWD?
Host fruit
Sap beetles will first attack overripe, rotting, or otherwise damaged fruit. SWD will be found in fruit that appears otherwise marketable until cut open. As SWD grow older, fruit condition may deteriorate, but fly larvae found in sound fruit are more likely to be SWD than those found in rotting fruit.
Size
Young sap beetle larvae may be similar in size to large SWD larvae, but in general they will be larger than SWD larvae. Size on its own is not a good determinant, but it can be a good initial indicator.
Appearance
SWD larvae lack legs, have no distinct head, lack hairs or bristles, and are tapered on both ends (see here for more images). Sap beetle larvae have distinctive head capsules, three pairs of legs, and bristles along their bodies. Adult sap beetles may also be present along with larvae.
What other insects might be present inside strawberries?
Corn earworm (Helicoverpa zea) are occasional pests of strawberries, and the larvae can tunnel into berries. Corn earworms are caterpillars, which means they have a distinctive head capsule and three pairs of front legs like sap beetle larvae, but they also have short, grippy prolegs along their abdomen and have a pattern of stripes along their body (although their appearance can be highly variable as larvae age).
Fortunately, the majority of grower calls I received about larvae in strawberries ended up being sap beetle larvae rather than SWD larvae. Sap beetles or picnic beetles are actually a complex of beetle pests which include at least three species in North Carolina (Carpophilus lugubris, Stelidota geminata, Glischrochilus quadrisignatus, and others) and are attracted to rotting, not sound fruit. If rotting fruit are present near sound fruit, as can commonly happen when you-pickers aren't thorough or rain prevents picking, sap beetle adults and larvae can also attack sound, otherwise marketable fruit.
While sap beetle larvae are also not desirable in strawberries, they are more easily controlled than SWD. Good sanitation, meaning removal of overripe or rotting fruit, is usually enough to keep sap beetle populations in check.
How, then, can you distinguish between sap beetle larvae and SWD?
Host fruit
Sap beetles will first attack overripe, rotting, or otherwise damaged fruit. SWD will be found in fruit that appears otherwise marketable until cut open. As SWD grow older, fruit condition may deteriorate, but fly larvae found in sound fruit are more likely to be SWD than those found in rotting fruit.
Size
Young sap beetle larvae may be similar in size to large SWD larvae, but in general they will be larger than SWD larvae. Size on its own is not a good determinant, but it can be a good initial indicator.
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| Sap beetle larva on knife blade. Photo from a commerical strawberry farm in eastern NC, 2012. |
SWD larvae lack legs, have no distinct head, lack hairs or bristles, and are tapered on both ends (see here for more images). Sap beetle larvae have distinctive head capsules, three pairs of legs, and bristles along their bodies. Adult sap beetles may also be present along with larvae.
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| Sap beetle larva. Note the three pairs of legs, the distinctive brown to black head capsule and the bristles along the body. Sap beetle larvae will be mostly white or cream colored and lack patterns on their body. Photo from a commerical strawberry farm in eastern NC, 2012. |
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| Two spotted wing drosophils larvae (center) inside a day neutral strawberry, Upper Mountain Research Station, October 2011. Photo: HJB |
Corn earworm (Helicoverpa zea) are occasional pests of strawberries, and the larvae can tunnel into berries. Corn earworms are caterpillars, which means they have a distinctive head capsule and three pairs of front legs like sap beetle larvae, but they also have short, grippy prolegs along their abdomen and have a pattern of stripes along their body (although their appearance can be highly variable as larvae age).
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| Corn earworm larvae feeding on strawberries. Photo via UC IPM. |
Friday, May 4, 2012
What should growers and homeowners who find SWD do?
I am getting reports of spotted wing drosophila SWD larval activity in some southeastern locations over the past two weeks, and we have observed SWD infestation in some of our research station plots in North Carolina. Infestations in my plots are a good thing, because it allows us to study SWD here and provide you with up to date information, but infestations in grower fields are another matter. We have been catching adult SWD since January in North Carolina, but these are the earliest larval infestations we have recorded in the state. This early activity has prompted several questions about what growers or homeowners should do if they find SWD infested fruit. Here's a quick summary of the four key steps you should take in the event of SWD infestation:
1. Remove all ripe and ripening fruit and destroy it (by freezing, "baking" in the sun inside a clear plastic bag for a few days, or removing from the site). Eggs or larvae may be present in otherwise sound appearing fruit. Leaving this fruit means that potentially infested fruit is present and could be harvested.
2. Begin an aggressive (once per week if it does not rain, reapplication in the event of rain) spray program. Rotating between at least two modes of action will reduce the likelihood of resistance development. See here for information about the probably efficacy of registered insecticides in southeastern small fruit crops. Because these efficacy ratings are based on work done largely in the western US, where environmental conditions differ, they are not set in stone. We are running several efficacy trials as I type and hope to have NC specific data by mid summer.
3. Practice excellent sanitation. Remove all ripe fruit and sell or destroy it. Do not discard culls in the field, and clean up after rain and u-pickers. Unpicked fruit is a reservoir for SWD larvae.
4. Sample fruit regularly and consider trapping flies. Traps tell you SWD presence or absence and are not perfect, but they are helpful. Place traps in strawberry rows, near fruit for the best chance of catching flies. Sample fruit each harvest by either cutting them open and looking for larvae, crushing them in salt water (1/4 cup salt per gallon), or freezing them. Salt water and freezing will cause larvae to exit fruit. Sample at least 30 berries per field. See here and here for trapping information and here for larval sampling information.
All growers are strongly encouraged to monitor for SWD adults before larvae are found. If adults are present and fruit are ripe, pesticide treatments are recommended through the end of harvest. We hope that this strategy will prevent larvae from showing in fruit and triggering the actions listed here.
Update, June 22, 2012
I am aware that homeowners may be not be able or may prefer not to use insecticides on fruit in the gardens are yard. Unfortunately, sanitation alone will not eliminate and SWD population. However, if you can pick your fruit a bit earlier or a bit less ripe, it will be exposed to SWD for less time and will perhaps be at a lower risk of infestation. It's also important to note that while SWD larvae cause fruit to decay quicker and are unpalatable if present in fruit, they are not poisonous or parasitic. If you have inadvertently consumed fruit from your home garden that SWD larvae have been present in, they do not pose a heath risk.
Update, August 7, 2012
I have been reading LOTS of scientific papers about SWD in the last week. A couple of Japanese references suggest that mesh cages or bags (specifically 0.98mm mesh) prevented SWD infestation in blueberries without impacting plant growth. We use mesh bags a lot to either keep insects we are studying in or to keep insects we don't want out.
This strategy is worth a shot for homeowners who can tolerate the sight of bags on their plants. In order to exclude SWD, cages should be placed before fruit begins to change color and tightly sealed at the bottom. We'll often place a piece of quilting foam between the cage and the stem of the plant to allow us to tightly tie the cage shut (with a zip tie or twine) but protect the stem from damage. Cages should stay in place until you harvest your fruit. We use organdy mesh from fabric store and sew our cages to size, but paint strainers also work in a pinch. I plan to try this method with my backyard blueberries, blackberries, and figs next year and will be interested to hear if others also give it a shot.
1. Remove all ripe and ripening fruit and destroy it (by freezing, "baking" in the sun inside a clear plastic bag for a few days, or removing from the site). Eggs or larvae may be present in otherwise sound appearing fruit. Leaving this fruit means that potentially infested fruit is present and could be harvested.
2. Begin an aggressive (once per week if it does not rain, reapplication in the event of rain) spray program. Rotating between at least two modes of action will reduce the likelihood of resistance development. See here for information about the probably efficacy of registered insecticides in southeastern small fruit crops. Because these efficacy ratings are based on work done largely in the western US, where environmental conditions differ, they are not set in stone. We are running several efficacy trials as I type and hope to have NC specific data by mid summer.
3. Practice excellent sanitation. Remove all ripe fruit and sell or destroy it. Do not discard culls in the field, and clean up after rain and u-pickers. Unpicked fruit is a reservoir for SWD larvae.
4. Sample fruit regularly and consider trapping flies. Traps tell you SWD presence or absence and are not perfect, but they are helpful. Place traps in strawberry rows, near fruit for the best chance of catching flies. Sample fruit each harvest by either cutting them open and looking for larvae, crushing them in salt water (1/4 cup salt per gallon), or freezing them. Salt water and freezing will cause larvae to exit fruit. Sample at least 30 berries per field. See here and here for trapping information and here for larval sampling information.
All growers are strongly encouraged to monitor for SWD adults before larvae are found. If adults are present and fruit are ripe, pesticide treatments are recommended through the end of harvest. We hope that this strategy will prevent larvae from showing in fruit and triggering the actions listed here.
Update, June 22, 2012
I am aware that homeowners may be not be able or may prefer not to use insecticides on fruit in the gardens are yard. Unfortunately, sanitation alone will not eliminate and SWD population. However, if you can pick your fruit a bit earlier or a bit less ripe, it will be exposed to SWD for less time and will perhaps be at a lower risk of infestation. It's also important to note that while SWD larvae cause fruit to decay quicker and are unpalatable if present in fruit, they are not poisonous or parasitic. If you have inadvertently consumed fruit from your home garden that SWD larvae have been present in, they do not pose a heath risk.
Update, August 7, 2012
I have been reading LOTS of scientific papers about SWD in the last week. A couple of Japanese references suggest that mesh cages or bags (specifically 0.98mm mesh) prevented SWD infestation in blueberries without impacting plant growth. We use mesh bags a lot to either keep insects we are studying in or to keep insects we don't want out.
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| We have used mesh bags in blackberries to exclude thrips from developing fruit in order to determine if they impact fruit development. They don't appear to. |
Thursday, April 26, 2012
What causes misshapen strawberries?
Recently, I've gotten a few questions about misshapen strawberries. Misshapen or "wonky" strawberries can be caused by several things, but the two most common causes likely to occur in North Carolina are poor pollination and lygus bug injury. It's actually fairly straightforward to distinguish between these two types of injury.
Poor pollination
Strawberries do not require, but benefit from, insect pollination, so weather conditions that limit insect activity and pollen movement typically precede when this type of misshapen fruit appears.
Poor pollination causes misshapen fruit because unfertilized seeds remain small and the fruit around them does not grow at the same rate as the fruit around fertilized seeds. On the image above, the top fruit has seeds of different sizes next to each other while the seeds on the bottom fruit are uniform.
Lygus bug injury
North Carolina Department of Agricultural (NCDA) regional agronomist David Dycus mentioned via email today that growers in Mississippi had recently expressed concern about misshapen fruit due to lygus bug feeding. Lygus bugs (also known as tarnished plant bugs) feed on strawberry seeds and fruit and can also cause misshapen fruit. Lygus feeding does not result in variable seed size and can, therefore, be distinguished from poor pollination in strawberries. Typically, North Carolina growers do not experience extensive damage from lygus bugs, because they are active later in the year. This year, however, they may be active earlier (although, our warm spring has turned a little chillier), and it's worth keeping an eye for their damage. Lygus can be difficult to control, so if grower suspect they have damaging populations of lygus present, they should contact their county agent or myself for recommendations.
Other, non pest, insects can look like lygus bugs, include beneficial insects like big-eyed bugs and non strawberry pests insects like false chinch bugs, and it's important to correctly identify pests. BugGuide has a nice identification guide for Lygus lineolaris (the east coast species which feeds on strawberries).
Other causes of misshapen berries
Insects and poor pollination are not the only causes of misshapen fruit in strawberries. Pathogens can damage fruit, mechanical injury can scar it, and abiotic factors can change fruit shape.
Update, 27 April 2013
An update to this post has been added to the NCSU Strawberry Growers Information Portal.
Poor pollination
Strawberries do not require, but benefit from, insect pollination, so weather conditions that limit insect activity and pollen movement typically precede when this type of misshapen fruit appears.
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| Misshapen strawberry fruit due to poor pollination (above) and a normal appearing fruit (below). Photo: HJB |
Lygus bug injury
North Carolina Department of Agricultural (NCDA) regional agronomist David Dycus mentioned via email today that growers in Mississippi had recently expressed concern about misshapen fruit due to lygus bug feeding. Lygus bugs (also known as tarnished plant bugs) feed on strawberry seeds and fruit and can also cause misshapen fruit. Lygus feeding does not result in variable seed size and can, therefore, be distinguished from poor pollination in strawberries. Typically, North Carolina growers do not experience extensive damage from lygus bugs, because they are active later in the year. This year, however, they may be active earlier (although, our warm spring has turned a little chillier), and it's worth keeping an eye for their damage. Lygus can be difficult to control, so if grower suspect they have damaging populations of lygus present, they should contact their county agent or myself for recommendations.
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| Strawberries damaged by lygus bugs. Photo: UC IPM Program |
Other causes of misshapen berries
Insects and poor pollination are not the only causes of misshapen fruit in strawberries. Pathogens can damage fruit, mechanical injury can scar it, and abiotic factors can change fruit shape.
Update, 27 April 2013
An update to this post has been added to the NCSU Strawberry Growers Information Portal.
Saturday, April 14, 2012
Why are monitoring sites only listed by county?
You may have noticed that site names for the SWD*VMN are coded by county followed by a generic number. I have also shared monitoring data online for the Grape Root Borer*Volunteer Monitoring Network (GRB*VMN) and for blueberry insect monitoring programs run by my laboratory, again with sites identified to the county level. I had a request via the comments on this blog for more detailed location information for one of our SWD*VMN monitoring sites. Because of this request, I wanted to clarify that it is my policy not to provide any geographic information about trapping locations below county. The reason for this policy is two fold:
1. County is a established level for displaying insect (or other invasive organism) detection information. See the National Agricultural Pest Information System for an example, and
2. All of our monitoring networks represent a patchwork of public & private and commerical & non commerical land. Because some commerical fruit growers have generously to allowed us, county extension agents, or others to trap on their land or have contributed their trapping data to our networks, we do not want to risk any potential harm to their business by sharing more information than necessary with the public.
The purpose of sharing insect monitoring data online is to provide information growers, homeowners, and other stakeholders can use in making management decisions. It is not intended to replace site specific monitoring by growers or homeowners. Just because an insect is being trapping in your county does not mean that it is present on your farm. Knowing exact trapping sites within a county would not change this. Insect activity in your county does suggest, however, that it would be wise for you to go out and check your plants. Insect trapping data is also not intended for use by regulators or consumers. Just because adult insects are active at sites does not necessarily mean that damage to crops is occurring.
Eagle eyed readers may have noticed that I will occasionally name a site when posting about trapping data. I only do this for sites at state and/or university run research stations, like New Hanover 1, which is located at the Horticultural Crops Research Station near Castle Hayne, NC. Because research stations are non commerical operations, identifying these sites does not compromise grower cooperator privacy.
1. County is a established level for displaying insect (or other invasive organism) detection information. See the National Agricultural Pest Information System for an example, and
2. All of our monitoring networks represent a patchwork of public & private and commerical & non commerical land. Because some commerical fruit growers have generously to allowed us, county extension agents, or others to trap on their land or have contributed their trapping data to our networks, we do not want to risk any potential harm to their business by sharing more information than necessary with the public.
The purpose of sharing insect monitoring data online is to provide information growers, homeowners, and other stakeholders can use in making management decisions. It is not intended to replace site specific monitoring by growers or homeowners. Just because an insect is being trapping in your county does not mean that it is present on your farm. Knowing exact trapping sites within a county would not change this. Insect activity in your county does suggest, however, that it would be wise for you to go out and check your plants. Insect trapping data is also not intended for use by regulators or consumers. Just because adult insects are active at sites does not necessarily mean that damage to crops is occurring.
Eagle eyed readers may have noticed that I will occasionally name a site when posting about trapping data. I only do this for sites at state and/or university run research stations, like New Hanover 1, which is located at the Horticultural Crops Research Station near Castle Hayne, NC. Because research stations are non commerical operations, identifying these sites does not compromise grower cooperator privacy.
Thursday, April 12, 2012
Spotted wing drosophila adults trapped in North Carolina blueberry country
Spotted wing drosophila (SWD) detections have begun earlier this year than in the previous two years the Spotted Wing Drosophila Volunteer Monitoring Network (SWD*VMN) has been active. Now in addition to positive detections in Surry, Randolph, and Rowan Counties, SWD has been detected in southeastern North Carolina blueberries for the first time this year.
On April 5th, five male and five female SWD were captured in traps at the Horticultural Crops Research Station near Castle Hayne, NC. This site is New Hanover 1 in SWD*VMN, and you can see data from last year here. You'll notice that last year, we caught our first fly here on May 9th, a full month later than our first capture this year. You can see all the trap captures from this site, including those from last week and all future dates here.
What do these trap captures mean for growers in North Carolina?
The fact that we are catching flies at several locations throughout the state means that SWD are active. This means that growers should be vigilant for both SWD adults and larvae on their farms. Growers are strongly encouraged to monitor for SWD adults using the same traps we are using (learn how make and use SWD traps here and here). However, we don't have a good handle on how trap captures relate to fruit infestation, which means that growers should also monitor fruit carefully (learn how to sample fruit and identify Drosophila spp. larvae here). If SWD are present on your farm, we are currently recommending a fairly aggressive management strategy, because there is zero tolerance for larvae present in marketed fruit. Contact your county cooperative extension agent or Hannah for SWD management recommendations.
The SWD*VMN is supported by the North Carolina Tobacco Trust Fund Commission, Inc. and the NC Specialty Crop Block Grant Program.
More information
Insect monitoring in NC Blueberries - 2011
Spotted wing drosophila adult trapping data - New Hanover 1
SWD*VMN
On April 5th, five male and five female SWD were captured in traps at the Horticultural Crops Research Station near Castle Hayne, NC. This site is New Hanover 1 in SWD*VMN, and you can see data from last year here. You'll notice that last year, we caught our first fly here on May 9th, a full month later than our first capture this year. You can see all the trap captures from this site, including those from last week and all future dates here.
What do these trap captures mean for growers in North Carolina?
The fact that we are catching flies at several locations throughout the state means that SWD are active. This means that growers should be vigilant for both SWD adults and larvae on their farms. Growers are strongly encouraged to monitor for SWD adults using the same traps we are using (learn how make and use SWD traps here and here). However, we don't have a good handle on how trap captures relate to fruit infestation, which means that growers should also monitor fruit carefully (learn how to sample fruit and identify Drosophila spp. larvae here). If SWD are present on your farm, we are currently recommending a fairly aggressive management strategy, because there is zero tolerance for larvae present in marketed fruit. Contact your county cooperative extension agent or Hannah for SWD management recommendations.
The SWD*VMN is supported by the North Carolina Tobacco Trust Fund Commission, Inc. and the NC Specialty Crop Block Grant Program.
More information
Insect monitoring in NC Blueberries - 2011
Spotted wing drosophila adult trapping data - New Hanover 1
SWD*VMN
Thursday, April 5, 2012
What to watch for: flea beetles in strawberries?
When Duplin County extension agent John McIntyre called me asking about flea beetles in strawberries, I was skeptical. Flea beetles are common pests in tobacco & vegetables in North Carolina and one species feeds on grapes, but I had never heard of flea beetles as pests in strawberries. I figured that whatever damage was present was likely due to our bumper crop of caterpillars or other, more typical pests. However, when he sent me these pictures, it was clear that the beetles pictured were flea beetles or something very similar and that feeding damage was from them.
Also present on leaves and tunneling into at least one strawberry fruit
were what appear to be the larvae of these same beetles. After seeing these images, my first thought was that theses beetles looked an awful lot like grape flea beetle, a relatively common early season grape pest whose adults and larvae both feed on developing buds and foliage in grapes. See here for a nice set of images from Michigan State University of grape flea beetle adults and larvae. It turns out that grape flea beetle (Altica chalybea) has a close relative known as the strawberry flea beetle (Altica ignita), so it's possible that that these may be either species or a completely different critter. John brought samples of the larvae and adults by my office this evening, and I'll identify them over the weekend and post an update here.
So, now that I believe we're dealing with a flea beetle, what should the affected growers do? I do not think that the foliar injury in the images above will result in yield loss, and I suggested that the growers not treat if only foliar feeding was present. However, one larva John found had tunneled into a strawberry. If lots of larvae are present and potentially feeding on fruit, this is of much greater concern. Unfortunately, most of the pesticides effective against flea beetles are broad spectrum and may flare spider mites in strawberries, which have already become problematic in strawberries this spring throughout the southeast. There is one narrower spectrum material that might work can be organic as well, and I suggested to John that if larvae were present, this might be the best choice. See a note about pesticide recommendations.
Update, 10 April 2012
I took the adult beetle and larval samples to Dave Stephan, insect identification expert at the NC State University Plant Disease and Insect Clinic this afternoon. Dave agreed that it does indeed look like it is from the genus Altica, but he suspected that they were too small to be grape flea beetle. He is going to run them through a key to determine if they are strawberry flea beetles or something else entirely!
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| Two adult flea beetles on strawberry foliage. The "lacy" feeding damage is characteristic of many foliar feeding beetles. Photo: John McIntyre, Duplin County NCCE. |
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| Adult flea beetle with John's figure for size reference. Photo: John McIntyre, Duplin County NCCE. |
So, now that I believe we're dealing with a flea beetle, what should the affected growers do? I do not think that the foliar injury in the images above will result in yield loss, and I suggested that the growers not treat if only foliar feeding was present. However, one larva John found had tunneled into a strawberry. If lots of larvae are present and potentially feeding on fruit, this is of much greater concern. Unfortunately, most of the pesticides effective against flea beetles are broad spectrum and may flare spider mites in strawberries, which have already become problematic in strawberries this spring throughout the southeast. There is one narrower spectrum material that might work can be organic as well, and I suggested to John that if larvae were present, this might be the best choice. See a note about pesticide recommendations.
Update, 10 April 2012
I took the adult beetle and larval samples to Dave Stephan, insect identification expert at the NC State University Plant Disease and Insect Clinic this afternoon. Dave agreed that it does indeed look like it is from the genus Altica, but he suspected that they were too small to be grape flea beetle. He is going to run them through a key to determine if they are strawberry flea beetles or something else entirely!
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