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.

VA Berry Conference Online

One the highlights of my spring meetings in 2009 was the March Virginia Berry Conference, organized by Reza Rafie and Chris Mullins of Virginia State University. Over 120 attendees from across the southeast listened to presentations on small fruit production and management. Meet the Farmer, a program that documents local farming systems, was also in attendance and assembled sections of the talks for one of their programs.



My section is about 23 minutes in, but all the segments are worth taking in if you have time.

A busy day in the tunnels

My technician, Anna Chapman, and I spent the morning at the Piedmont Research Station in Salisbury visiting high tunnel biological control plots. We will release predators next Wednesday, and today, we collected pretreatment samples in our test and treated buffer plots. This is the second year of this trial, and in addition to assessing reductions in twospotted spider mite numbers, we will also be periodically testing the ability of our selected predator species to remain active in tunnels over the winter. Samples from last week and this week suggest that our releases from last year may have established populations of at least 2 of the predator species in these tunnels. This may complicate our experiments, but it's certainly an interesting development!

After collecting our samples, we visited Patterson Farms where Barclay Poling and Jeremy Pattison have a collaborative project with the growers, funded by the Golden LEAF Foundation, to study the dynamics of scaling up tunnel strawberry production.

The plants look great, but I found several interesting insects crawling around. Particularly, there were lots of Lepidopterans (caterpillars).

Cutworms, likely variegated, were scattered throughout the tunnels. Only one was observed feeding on flowers (top image), which is more problematic than their typical feeding behavior (small holes on leaves and cutting of leaves as larvae grow).

In addition to cutworms, which can be fairly common in fall strawberries, there were several fuzzy (Arctiidae) caterpillars, including wooly bears (not shown). These larvae are probably moving in from weedy vegetation in surrounded woody areas. These larvae will pupate soon and not develop into crop pests.

Several stick mimicking Geometridae were also present in the tunnels--they are responsible for the small holes in the leaves on the above plant.

Although there were many caterpillars present, I do not think the density or damage justified treatment. The larvae present now will pupate soon, and the plants are large enough that they are not threatened by the small amount of feeding damage.

Also roaming around the tunnel were several southern corn rootworms (above). These may feed lightly on leaves, but will soon overwinter as adults, perhaps around the base of the plants. We're learning more about what expect in tunnel berries where we go for full out growth right away. All sorts of interesting, probably incidental, insects are moving into the same space to overwinter or grab a quick bite to eat before winter sets in. It remains to be seen what, if any, of these insects will cause damage we need to worry about it, but we're keeping eyes open.

Check out the newest Small Fruit News

The latest edition of the Small Fruit News has just been posted at the Southern Region Small Fruit Consortium's webpage. I contributed an article on the spotted wing drosophila to this quarter's edition which expands on my previous post here. The most interesting article to me was contributed by Phil Brannen, University of Georgia plant pathologist, which briefly discusses 2 viruses new to eastern blueberry production.

Blueberry scorch and blueberry shock have been detected in locations in Michigan, the nation's largest blueberry producer. Among these locations is the Trevor Nichols Research Complex, where much of the blueberry research in the state is conducted. Blueberry scorch is vectored by aphids (likely non persistently), although the potential vectors are unclear. Blueberry shock is a pollen borne virus whose spread is mediated by bees. These viruses have yet to be detected in the southeast, but their movement across the US from the Pacific northwest to Michigan raises concern.

More information on Blueberry scorch and shock is Michigan can be found here.

Southeast Strawberry Expo - Registration open

Registration is open for the Southeastern Strawberry Expo, which will be held in Durham, NC, November 8-10. I will have results from our organic trials this summer and will have a full session on insect and mite management. My main emphasis in this session will be to discuss with growers when NOT to treat insects and mites with pesticides. The decision not to spray is often the hardest, but we'll be discussing tools that can minimize the number of pesticide applications needed.

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.