A reminder: SWD treatments may flare spider mites

Remember when treating for spotted wing drosophila (SWD), some recommended materials may also flare spider mites.  Information on how to scout and what do here.

More information
What to watch for: Broad spectrum insecticide can flare mites - Strawberry Growers Information Portal

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!

What to watch for: A preemptive question about mites and hops

Hop yard in western NC, July 2010 Hop Tour. Photo: HJB

With the news that Sierra Nevada Brewing Company is opening a facility in Mills River, NC, interest in North Carolina hop production has again surged.  I think we still have a lot to learn about the feasibility of growing hops in North Carolina, but several, mostly small scale producers are already active.  One of these growers emailed me today asking about their main arthropod pest, spider mites, and what action she might take to prevent large populations developing this year.  Last year, she released two predatory mite species, Neoseiulus fallacis and Phytoseiulus persimilis, and she was wondering if those populations could overwinter and be relied to provide control this year. 

Hops leaves respond to relatively low mite densities.  The yellow stippled area on this leaf had a population of spider mites feeding on the opposite side. Photo: HJB

 My reply: "We have native populations of N. fallacis in the western NC mountains, so it is reasonable to assume that they should be able to overwinter (although lab reared mites may be less adapted to winter conditions).  We have had success overwintering P. persimilis under high tunnels on strawberries, but I can't say how well it will do out in the open.

The only way to know if your mites from last year have stuck around is to look for them. Sample 10 leaves per variety weekly and observe with a minimum 10x hand lens.  It will take some practice, but you can see and count mites with a hand lens.  You can distinguish predatory mites from pest mites by size (they are smaller), shape (most are tear drop shaped or oval), and color (P. persilimis) is orange.  Predatory mites also move much faster than pest mites. See here for images of some of the predatory mites commonly used for biological control. Start sampling when you have new leaves and continue weekly.  When and if you release additional predatory mites will depend on when spider mite pests appear in your planting."

What to watch for: strawberry update

This morning, I visited our strawberry research plots at the Central Crops Research Station, Clayton, NC.  We will be using these plots for sap beetle, caterpillar, and spotted wing drosophila research this spring, and, like most of the southeast, our plants are pushing early.  It looks as though we will have berries in about 3 weeks, which is a month ahead of our normal schedule.

Along with this potentially early strawberry crop comes early questions about pest management.  I have fielded lots of questions about strawberry clippers and two spotted spider mites in the last few weeks.  I posted several times last spring about strawberry clippers, and you can find those posts here.  You can also find my posts on spider mites from the last several years here.  For grower with spider mite populations at threshold (5 mites/leaflet in a sample of 10 leaflets per acre) and plants that have not yet started fruiting, now is a good time to get those populations under control.  You can prevent mite issues later in the season by treating now with a miticide and avoiding the use of broad spectrum insecticides (pyrethroids and carbamates) unless absolutely necessary for other insect pests. If a broad spectrum material is needed, for example against sap beetle or SWD infestations, scout for spider mites before and watch populations carefully follow a treatment.  For growers who do not have mites about threshold (or no mites at all), you can breathe a little easier--barring a major slow down in plant growth, you may avoid the need to treat at all for mites.  Once plants are actively fruiting and rapidly growing, mite populations must be very high to cause damage--and very high mite populations typically only develop if you start off with mites earlier in year (around now). 

More information
Strawberry clipper posts - NC Small Fruit and Specialty Crop IPM
Two spotted spider mite posts - NC Small Fruit and Specialty Crop IPM

What to watch for: When treating for SWD

Female SWD on raspberry at the Upper Mountain Research Station, Summer 2010. Photo: HJB

As spotted wing drosophila (SWD) is detected in more and more locations throughout the southeast (Georgia, Florida, 4 locations in South Carolina, 13 locations in NC), many small fruit growers are treating their crops. See here for lists of registered pesticides in blueberries, grapes, strawberries, and caneberries. For several reasons (efficacy, cost, and preharvest interval), organophosphate and pyrtheroid insecticides are among the most commonly used materials against SWD. The current management recommendations for SWD are weekly pesticide applications, rotating modes of action, beginning when fruit are ripening and stopping at the end of harvest and increased sanitation (frequent & thorough harvest, cull removal & destruction). These management recommendations represents a potentially large increase in pesticide use, at least in the short term, in these small fruit crops.

While these classes of insecticides are effective against SWD, they come with risks as well. The key risk, from a pest management stand point, is non target impacts on other pests and beneficial insects. While we we cannot anticipate all of the non target impacts, some are clearly likely.

The most likely non target effect of SWD treatments is the possibility to flare spider mites.

Twospotted spider mite female and eggs. Photo: HJB

Spider mites are economically significant pests of strawberries, grapes, and caneberries (raspberries moreso than blackberries). Both organophosphate and pyrethroid insecticides have been documented as flaring spider mites.

Strawberry, grape, and caneberry growers should scout their plantings for spider mites prior to beginning SWD treatments. A good rule of thumb is to observe at least 10 leaves or leaflets per acre or per variety block, if they are smaller than an acre. Spider mites can be observed and counted with a 10x hand lens. If spider mites are present, planting should be treated with a miticide before beginning organophosphate or pyrethroid treatments. North Carolina blueberry growers more commonly use these insecticides are rarely, if ever, have issues with spider mites, and I do not anticipate a need to manage mites in blueberries.

Spider mites may not be the only non target (unintentional) pest made worse by SWD treatments. Organophosphates and pyrethroids are broad spectrum materials, meaning they kill many different types of insects, including beneficial predators. The insects these predators may control could increase in their absence, but we cannot necessarily predict which insects these may be. Growers treating for SWD should be vigilant and scout their fields at least weekly to assess whether any new or unexpected insect or damage is present.

Strawberry high tunnel production workshop - November 17

NCSU specialists Jeremy Pattison, Barclay Poling, and myself will be at the Piedmont Research Station near Salisbury, NC on Wednesday, November 17th for a workshop on high tunnel strawberry production. I will be covering twospotted spider mite biology and management in tunnels (a project we have conducted for 2 years) as well spotted wing drosophila monitoring and management implications in tunnels.

You can find information on the workshop here.

More information

Strawberry high tunnel workshop - NCSU and NCDA & CS

First strawberry preplant meeting - July 28th

The first strawberry preplant meeting of the season (is it that time already?!) will be next Thursday, July 28th at the Mountain Horticultural Research Station in Mills River, NC.  Area horticulture agent, Sue Colucci has organized this meeting, and interested growers can find more details here.  I will be sharing results from our 2010 twospotted spider mite trials, discussing new insecticide options and IPM strategies for sap beetles in strawberries, and sharing information on unusual caterpillar issues from this year's harvest season.
Hope to see the mountain strawberry growers there!


Update
Sue Colucci has just posted an announcement for the meeting on her blog, Western NC Vegetable and Small Fruits News.

Hops in the southeast - a learning experience

Before there are cones, there are flowers. A hops bine as it begins its climb. Photo: HJB

I've recently connected with a group of NC State researchers working on hops production in NC and have begun arthropod surveys in the NC State research planting at the Lake Wheeler Research Farm and several grower locations in western NC. This Monday, I took a trip out to Lake Wheeler to see what might be moving around.

Developing hops cones, the harvested portion of the bine. Photo: HJB.

The most obvious pests currently present are Japanese beetles. This polyphagous, invasive insect is a voracious feeder on many commonly grown ornamental and food crops and appears to have developed a taste for hops.

Japanese beetle injury on hops foliage at Lake Wheeler. Photo: HJB

Beetle feeding along hops bine. Photo: HJB

Several of the bines had Japanese beetle injury on their foliage, and Rob Austin, NC State Soil Science, had treated with carbaryl (Sevin) dust, the white powder visible in the image above. Carbaryl and other conventional broad spectrum insecticides can be very effective against Japanese beetles (a note about pesticide recommendations), but organic pesticide options are limited. Many hops growers are interested in organic production. We do not know how severe of a pest Japanese beetles will be in hops, nor how much summer defoliation is "too much". So at this point, we do not have treatment recommendations for this pest.

As effective as carbaryl is for Japanese beetle, this material has the potential to flare spider mites, which can be an important and difficult to manage pest of hops. If Japanese beetles are present, scout carefully for mites before choosing which material to treat with. We have been monitoring spider mites at 2 western NC hops farms and have found very low populations to date. The populations at Lake Wheeler are higher, and Rob plans to follow up with a mite treatment this week.

Browning on developing hops cones. Photo: HJB

On Monday, we also noticed browning on the tips of developing cones, which several growers have also commented on. In western NC, this injury appears to be thrips related, although there were very few thrips at Lake Wheeler this week. I have also seen some online resources which have suggested that browning can be a sign of approaching harvest.

Arctiid moth caterpiller feeding on hops. Photo: HJB

Caterpillars of several generalist moth species have been observed in hops plantings this spring and early summer. Eastern coma caterpillars were found at several mountain farms, and were subsequently treated with Bt. I found the arctiid (tiger moth) caterpillar in the above photo on Monday. I do not think these generalists are of pest concern at this time, but may be locally problematic.

Young bines at Lake Wheeler. Photo: HJB

A hops field tour, which I will be participating in, is scheduled for July 31 in western NC. As this date approaches, I will be sharing more information.

More information

NC Hops Blog

News & Observer Profile

WNC Vegetable and Small Fruit News - Hops Information Page

What does the short strawberry season mean for pest management?

There has been a lot of news lately about the fast, furious, and fantastic North Carolina strawberry crop this spring.  I have posted about the almost overwhelming harvest at the Central Crops Research Station, which looks to be slowing a bit in the next few weeks.  In fact, most of the heavy strawberry picking in NC should be tailing off by the end of May.  This is good for my research program, since we're moving on to blueberries, blackberries, and tobacco this time of year, but is not necessarily music to the ears of growers or consumers.  We are not seeing lower yields in 2010, just a more concentrated crop.

This short season has some direct pest management implications that growers should be aware of.  First for our key arthropod pest of strawberries, twospotted spider mites.  I have only gotten phone calls from one grower with spider mite issues this spring!  Either you are all comfortable with your management programs, or this was a mild mite year.  My money is on the later, as we did not have a single spider mite in our research plots at Central Crops until mid April, and even then, we had to manually infest to generate the number that were needed for our threshold and efficacy trials.  The low spider mite numbers are due to several factors:  Cold winter weather decreased mite populations and produced very hardy, healthy plants.  Healthy plants do not harbor as high mite populations as stressed plants, and they can better tolerate the populations they do have.  The fast fruiting season also reduced the importance of TSSM.  Fruiting strawberry plants can tolerate higher numbers of mites than young plants.  Finally, the rapid harvest season has likely rendered the use of miticides unnecessary.  Even the most effective conventional miticides take 2-3 week for full efficacy because they act on all mite life stages.   When it appears our season will be winding down in that same amount of time, a miticide treatment is probably not advised.  Of course, there are always exceptions to this rule, and I encourage growers and agents to contact me with questions.

Next, thrips: 2010 has been, as expected, a late thrips year with relatively low populations.  Thrips treatments are likely not justified.  I address other thrips related issues in posts here and here.

Lygus bugs are of the same ilk as thrips this season.  We will be out of strawberry harvest before they are likely to be an issue.

Finally, sap beetles.  These late season pests may rear their ugly heads in 2010 not because we have a long field season which will stretch into to heat of summer but instead because the sheer volume of fruit in a short period of time may result in less thorough picking by both employees and customers.  Sanitation is crucial for sap beetle control and is often sufficient by itself.  Chemical controls should be our last option, but they are available.

Just some of the news stories from throughout the state:
WBTV Charlotte at Hall Berry Farm
WRAL's Go Ask Mom blog on organic strawberries near the triangle 
WRAL and Dr. Barclay Poling at our research plots at the Central Crops Research Station, Clayton, NC
WECT's Strawberry Festival Coverage
WWAY on Columbus County strawberries
Sampson Independent on the large crop
In the Field on strawberries in NCDA's Food to School Program

Strawberry season - fast and furious

We harvested our strawberry research plots at the Central Crops Research Station in Clayton, NC for the first time on April 24th and were amazed at how quickly the season is progressing. As the photo above illustrates, our plants are loaded with fruit, but don't have a lot of new blossoms. This means we will likely have high yields but a short picking season. This doesn't necessary bode well for our mite threshold trials, since populations just reached treatable levels last week. We will continue, however, to maintain our plants even as harvest wanes to allow for additional miticide efficacy data regardless of the length of the picking season.

We will be picking again this week, since all the white fruit above on Saturday are now ripe! You might also notice the runners appearing on the plants above. I was concerned about this over the weekend, but an update sent by Dr. Barclay Poling on Sunday helped address this concern. Dr. Poling suggested that just because plants are runnering (vegetatively growing) does not mean they are necessarily going to stop fruiting (reproductively growing). I hope this is true and we can stretch harvest out for a bit longer.

UPDATE:  We harvested again this past Thursday and Friday, and at about 4 lb on average per plot, we harvested about 272 lb of fruit.  We are collecting yield and quality (brix) data on these fruit  to correlate to mite densities and mite management regimens. Next picking: Late this week.

Strawberry update and chilly weekend weather

Mite trial plots at the Central Crops Research Station. Plants were sourced from Aarons Creek Farms, Buffalo Junction, VA and made it through the cold winter with flying colors.

Today, we sampled our plots at the Central Crops Research Station in Clayton, NC for the 3rd time this season. Spider mite populations remain low, but we will begin calendar treatments for our threshold validation trial next week. This trial is comparing treating at threshold levels versus treating on a calendar basis. Specifically, we are comparing the following treatment regimes:

1. Untreated control

2. Frequent treatment (every 14 days)

3. Infrequent treatment (every 45 days)

4. Treatment at recommended threshold (5 TSSM/leaflet)

5. Treatment at reduced threshold (2 TSSM/leaflet)

Most plants have 2-5 blooms open, which means we plan to begin harvest in about 45 days, mid May. Strawberry plantings throughout NC are about 2 weeks later than normal.

We are assessing mite densities weekly and will also collect data on brix in the different treatments. Growers have been curious as to whether TSSM densities below yield reducing levels (our working threshold of 5 motile mites/mid tier leaflet) also reduce fruit quality, and the quality measure of greatest concern is brix. Last year, we conducted a similar trial with an organic cooperator and saw no correlation between brix and mite densities or mite days (a measure of mite density over time). This year's trial will be conducted with conventional miticides.

In addition to the threshold validation trial, we will also be conducting efficacy trials with conventional miticides, some of which are newly registered for strawberries.

Frost is called for this weekend throughout NC, and our plots were covered with floating row cover this afternoon. Dr. Barclay Poling, NCSU Horticulture, regularly posts updates on weather conditions and other production considerations at the NC Market Ready Strawberry Grower Information Portal. The latest update shares information on the upcoming cool weather as well and some pest management points from me regarding bloom and insecticide use.

UPDATE
Temperature maps from Envirsion, a weather modeling group based in Raleigh, illustrate the frost potential throughout NC for this weekend.

As the covers come off...

Those strawberry growers who have had row covers on their plants all winter are now removing them and performing sanitation on the plants (removing dead leaves and stray weeds). As these covers come off, I am getting reports of lots of arthropods appearing.

Spider mite management begins in earnest now, and growers should begin their weekly sampling of 10 leaflets/acre. The undersides of these leaflets should be examined for spider mites with a 10x hand lens (or microscope if you're well equipped). If the average number of mites/leaflet is 5 or great, miticide treatments should be applied. Scouting should continue post treatment to ensure they are effective and to determine if and when re treatment is needed.

Twospotted spider mite female and eggs on the underside of a strawberry leaf. Photo: HJB

Threshold based treatments are helpful because not only do they often reduce the number of applications, but they also allow us to select the best material for the job by providing a weekly pattern of information. This means we have a better idea if populations are small and newly established (best treated with an ovicide/larvicide) or are already large (best treated with an adulticide plus ovicide/larvicide).

Cast aphid skins (white) and dead aphids (brown) on tunnel strawberries at the Piedmont Research Station, Salisbury, NC. Photo: HJB
Click to enlarge this image for a much better view.

Aphids are also showing up as covers are removed, but I have yet to hear about damaging numbers in NC. It takes a lot of aphids to reduce yield in strawberries, and we have excellent native biological control agents. In fact, also found under the covers have been lady beetle larvae, feeding on the captive aphid buffet. Most of the aphids that were present under the covers morphed to winged (alate) forms, and have dispersed off the plants leaving only their cast skins. These cast skins appear white against the plastic or leaves.

Lady beetle larvae found on newly uncovered strawberries in the Sandhills. Photo: David Dycus.

As the weather warms and spring is finally here, the real fun begins!

A note about pesticide recommendations.

Spring Strawberry Arthropod Management Reminders

No matter what the forecast says, spring is coming. Along with it, come greater management needs. Strawberries have been in the ground since last fall and are the first fruit crop harvested in spring. The cold winter has meant most of our plants have been under row cover for at least part of the winter and our arthropod (insect and mite) issues have been out of sight and out of mind.

Row covered strawberries at Vollmer Farms, Bunn, NC. Spring, 2009.

When these cover come off, the real arthropod management begins. Here are a few key steps to start the 2010 season out right (A note about pesticide recommendations):

Green peach aphid (Myzus persicae) on strawberry. Image from UC IPM.

1. Scout for aphids, but only treat if populations are high. Aphids can rapidly proliferate under row covers, but unless early spring populations are causing sooty mold build up, treatment is likely not needed. Later spring and summer populations are often kept under good biological control in NC. If aphid populations under the covers are producing sooty mold and exceed 10 aphids/newly expanded leaf on average, treatment may be justified. If systemic insecticides are your aphid management tool of choice, the time to use these is now (before covers come off). Once blooms are exposed to bees, the labeled systemic materials for aphids in strawberries can no longer be used.

Female twospotted spider mite, our most common spider mite pest in strawberries. Image from UC IPM.

2. Begin spider mite sampling. Spider mites are the key arthropod pest in southeastern strawberries. Mite activity is typically lower in winter months, but as temperatures warm, spider mites will become more active and reproduce faster. We are currently studying the impact of long term row cover on overwintering mite populations, but our working assumption is that row covers potentially increase mite populations over the winter. This winter, of course, all bets are off. It is important to track mite populations closely and be prepared to treat when they reach our recommended treatment threshold (5 mites/leaflet). This threshold is based on a random sample of 10 leaflets/acre. It is in grower's best interest to treat at threshold levels and not on a schedule basis, because virtually all of the labeled miticides have restrictions on the number of applications and/or amount of active ingredient that can be applied to strawberries per season. We want to keep as many good options in our tool box for as long as possible.

Phytoseiulus persimilis, one of the commercially available biological control agents for spider mites. Image from UC IPM.

Biological control is also an option for spider mites, but we are in the process of optimizing methods for NC and do not have concrete recommendations at this time.

I have heard a lot of rumblings about different materials being applied systemically for mites, and I want to be perfectly clear: There are no systemic miticides. None of the materials currently labeled for soil or drip applications in strawberries are either registered for or effective against spider mites. Our best chemical control for mites is over the top treatments of miticides. I also do not recommend the use of pyrethriod insecticides against mites. The pyrethriods registered in strawberries have either shown no effect in our trials or have actually increased mite populations because they are equally toxic to beneficial insects.

Strawberry clipper damage in Lee County, NC, 2009. Photo from Stephanie Romelczyk, Lee County Horticulture Agent.

3. Do not assume you will have clippers in 2010 just because you had them in 2009. I had several reports of clipper injury in 2009. We do not have a sense of what 2010 will look like with respect to clippers, but I am not recommended a preventative treatment just because damage was observed in 2009. Most strawberry varieties compensate to a certain extent for clipper damage, and rescue materials are available for clipper management. Pre bloom preventative applications may be too early to really protect plants. When scouting for clipper damage, remember, clippers only affect flower buds (as in the above photo), not leaves.

You can find more specific information about pesticides in the NC Ag Chem Manual and the Southeastern Strawberry IPM Guide.

I will post a mid season arthropod reminder for strawberries in May which will cover late season mite management, sap beetles, thrips, and the unusual occasionals we see as the weather gets warmer.

The down side of tunnels

Tunnel 4 at the Piedmont Research Station, Salisbury, NC on Friday, February 5th.

We have been assessing the overwintering ability of predatory mites in high tunnel strawberry plots for the last 2 winters with the goal of optimizing organic management recommendations. There is a local and wholesale market for high quality winter strawberries, and several growers have begun to take advantage of this. Among theses grower is Sonny Cottle, in Faison, NC, who has produced organic strawberries in high tunnels for several years and has experimented with predatory mites and other organic twospotted spider mite management methods.

There are a lot of benefits to working in tunnels. We never have to worry about getting rained out from a miticide treatment (or a harvest), it's usually a balmy 50 degrees in the winter, and, not the least, the Piedmont Research Station personnel are top notch. However, this year has provided a primer in the challenges of tunnel production.

The differences between seasons were apparent immediately. TSSM reached threshold in the 2009 season in mid November (2008), and predators were released soon after. Our 2010 tunnel was adjacent to caneberry plots, and the spider mites migrated into our strawberries right after transplant. Our first predator release in 2010 season was in mid October (2009), and was less successful in suppressing an already large TSSM population. A second release was conducted in November (2009) which provided greater suppression.

The winter of 2009 was excellent for tunnel production--cool, but moderate temperatures, and only one snow storm to content with. We had one significant cold event in January which required irrigated frost protection, but row cover was sufficient for the remainder of the season. In 2010, we have experienced one the coldest winters in recent memory. Row covers have been in place almost every day for the last 2 months, which, unfortunately, has lead to extensive predatory mite movement between plots. We can still gather data on our primary objective, determining the ability of predatory mites to overwinter and reproduce in tunnels, but our release plots are no longer contained.

Our latest challenge has been snow. Although it was nothing compared to the recent storms in Washington, D.C., North Carolina had its share of snow the last weekend in January 2010. The 5 inch accumulation was enough to warrant the removal of our tunnel's (Tunnel 4) plastic skin to prevent collapse. As of today, our plants are covered with black plastic and row cover, and the tunnel is uncovered. Plans are to get the plastic back up today (Tuesday, February 9th), and we intend to sample Thursday to see what the impacts on TSSM and our predators are.

There's never a dull moment in agriculture--even in the "off" season!

Southeastern Strawberry Expo - A busy 3 days

The 2009 Southeastern Strawberry Expo wrapped up Tuesday. The meeting fostered lots of great conversation and research ideas. I always enjoy seeing growers who I have not encountered over the summer, including John Vollmer, who's farm we visited Sunday afternoon.

John and his family have been growing strawberries and other crops organically for 7 years, and come March 2010, his entire farm will be certified organic. John chose organic production to address a market need and has actively sought information on how optimize this system for his farm. This has lead John to cooperate with several extension specialists, including me. On Sunday, I shared some of the results for work we conducted on organic mite management in 2009 as well as some of the system-wide approaches to minimizing spider mites in organic strawberries.

John also detailed some of his other production practices and showed off a thriving winter cover crop of oats and red clover. Finding organically certified strawberry plugs has been a major challenge in recent years. This year, weather added another layer of difficultly. The California nurseries that John works with were flooded in late summer, resulting in a total loss of his intended plants. After much scrambling, John made the switch to cut off plants for his entire farm. Their first field leaves are just coming in, and they are smaller than John would like for this time of year, but they appear otherwise healthy.

On Monday, the NC Strawberry Association recognized its outstanding grower of 2009, Lee Berry (could you pick a better name?) of the Berry Patch. Lee shared his marketing strategy, which relies in no small part on his store, which he has dubbed the "world's largest strawberry". According to Lee, his only competition has been from "some folks in Iowa". Well, being that much of my extended family is from Strawberry Point, I am pretty sure I know where he's talking about! Lee's strawberry wins, hands down, despite the mid Western fondness for all things fiberglass.

Honored for their service to the industry were the NC Plant Disease & Insect Clinic at NCSU and a truly unsung hero of the NCSU strawberry horticulture program, technician Rocco Schiavone. I know I would have been lost without his advice many, many times.

My session on when not to treat strawberries is available in pdf form by request as are additional handouts. The 2010 Southern Region Stawberry IPM Guide will be online in January.

NC Strawberry Expo: 6 Days and Counting!

The NC Strawberry Expo is just 1 week away! I have several sessions at the Expo. Sunday, I will be participating in Barclay Poling's "Months of Money" workshop. We'll be breaking down the choices that strawberry farmers make each month of the year and how these choices add up to make or cost growers money. Sunday afternoon, we will visit John Vollmer's strawberry farm where I'll discuss work on organic mite management (both miticides and biological control) we conducted with John last spring. John is a fantastic cooperator and a wealth of information. This tour will include discussions of the entire process of organic strawberry growing, which has its own unique challenges.

On Monday afternoon, I will spend an hour discussing insect management in strawberries. This session, called "When NOT to spray", will focus on the use of sampling and thresholds in strawberries as well as address insects that growers are concerned about but do not typically injure NC strawberries (Lygus bugs are a prime example). Because the decision NOT to treat is usually much more fraught than the decision to spray, I will try to give growers tools to let them sleep better at night after not firing up the tractor. Look for an Expo wrap up early next week.

Meet the predators

Last Wednesday (10/21/09), we released our predatory mites into our twospotted spider mite biological control plots at Piedmont Research Station. Two weeks ago, we treated all our buffer plots with miticide and we treated again about 1 hour before releasing the mites. This strategy worked will last year; we were able to maintain populations in our untreated control plots while suppressing populations in our predator release plots without noticeable movement between them. This year our spider mites showed up about a month earlier than last year, so we'll see if this same methodology works for smaller, younger plants that have a lot of growing left to do. The spider mite populations were so high, however, that waiting to release predators would have jeopardized the trial.

We released 20 predators/plot (that's 1/sq ft). This is higher than field rates, but for the sanity of the mite counter (me) 20 is as low as I wanted to go. Each species was released alone in a plot. Last year, we combined some predators (like in this trial) but our main goal this winter is to see which, if any, of the species released remain active in the protected environment of the tunnels over the winter. We know the spider mites do--less than 10% of the twospotted spider mites observed last winter were diapausing at any given time, and eggs were present all winter long in the tunnels.

The three predator species we released are the same as last year, and 2 have been used commercially in field grown strawberries for a while. (All the photos are from UC IPM, I need to get a camera for my microscope...)

Phytoseiulus persimilis (next to a female twospotted spider mite and her eggs) has been used in strawberries pretty extensively. We don't appear to have an established population in NC, but in parts of California, they move into strawberry fields on their own.

Neoseiulus (Amblyseius) californicus has gained in popularity in the last 10 years for use in strawberries. This is likely thanks to work done in Florida and the Pacific Northwest that has demonstrated its ability to reduce spider mite populations alone and in combination with P. persimilis.

Finally, Neoseiulus fallcis were released. These mites occur in North Carolina, and according to Jim Walgenbach (On Wisconsin!) in our department, they are also found in apple orchards feeding on European red mite. The fact that these guys like cool, humid weather best was the basis for including them in this trial, although they are not widely used in strawberries.

All of our mites were from Rincon-Vitova Insectaries. There are several other suppliers as well, but we could get all 3 of the mites used from them, which will hopefully minimize variability. We do our first post release count next week.

A new field season

Strawberry plots from 2008-2009 biological control trials at Salisbury (Piedmont Research Station). These trials are being repeated in 2009-2010, with our first treatments being applied next week!

A few colleagues and grad students have been asking me lately "Is your field season winding down?", and the answer is, it's time for a whole new field season! August and September are typically my slowest months, unless there are tobacco trials that need yield assessment. There's still some tobacco out in the field, but most of the insect issues are routine this time of year. Blueberries are long gone and only leafhoppers are left to treat. Blackberry primocanes are still going strong but until we ramp up our virus vector studies, fall is quiet for Rubus. I don't have any current grape projects, but their harvest is also winding down.

So what new season is starting? Strawberries, of course! Three trials that I am collaborating on are in the ground and spider mite assessment will start next week. My own strawberry trials at Clayton, NC will be planted on Tuesday, October 6th.

What are we looking at in this trials? At Salisbury at Laurel Springs, I am piggy backing on 2 of Barclay Poling's row cover trials. We are trying to determine the impact of different row cover durations on overwintering twospotted spider mite populations. Barclay has shown a significant advantage to row covers under certain conditions, but I want to be sure that mite issues are not exacerbated under these row cover regimes. If they are, we'll then need to develop management strategies that take this into account.

We are conducting the 2nd year of winter biological control assessment for twospotted spider mite in one the high tunnels at Salisbury. At Clayton, we will be conducting threshold validation studies for twospotted spider mites and playing around with a few other row cover strategies.

Why so many mite trials?

All of these trials are focussed on twospotted spider mites for a reason; they are the key arthropod pest of strawberries in North Carolina. Their feeding activity can significantly impact plant health and yield. Spider mites can also be challenging to control--if miticides are used, good coverage is essential. If biological control is used, timing is important.

Why are you starting now?

Although it feels counterintuitive, twospotted spider mite damage results in the greatest yield reduction when it occurs early in the season, pre fruiting, when the plant is setting up the number of fruit it will produce the following spring. So, mite management following planting through the beginning of harvest is key.

Where will the information from these trials be available?

Here, for one. I will post regular updates on mite densities and any other interesting information that results from these trials. I will also present data from these trials in next summer's strawberry preplant meetings, and next spring's strawberry field day.