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.

Misshapen strawberry fruit due to poor pollination (above) and a normal appearing fruit (below). Photo: HJB

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.

Strawberries damaged by lygus bugs. Photo: UC IPM Program

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.

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.

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

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.

Two adult flea beetles on strawberry foliage. The "lacy" feeding damage is characteristic of many foliar feeding beetles. Photo: John McIntyre, Duplin County NCCE.

Adult flea beetle with John's figure for size reference. Photo: John McIntyre, Duplin County NCCE.

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!

Spotted wing drosophila captures have begun

The spotted wing drosophila volunteer monitoring network (SWD*VMN) began our 2012 trapping season two weeks ago, and this week brought reports of our first SWD captures in Surry and Randolph Counties.  You can see all of our trapping data, from the beginning of the SWD*VMN in 2010 through present, here.  The 2012 map is below. Click on a county to view data for all the sites in that county.  For counties with multiple sites, you can click on each site's name to data just for that location.  Trapping data are listed in reverse chronological order (most recent first). 

Spotted wing drosophila captures by month, 2012

Alternative content

Legend

January

February

March

April

May

June

July

August

September

October

November

December

Not Found

Because trapping recently began, a number of sites have yet to report their trap captures.  Many locations will be added in the next few days.  If you are interested in participating the SWD*VMN, please contact Hannah Burrack.  Sites are only identified to the county level to protect participant privacy.

The SWD*VMN is supported by the North Carolina Tobacco Trust Fund Commission and the North Carolina Specialty Crop Block Grant Program.