Since we have had our first field closure in strawberry as of last night, it is important for us all to review how the USDA regulatory process unfolds for growers here.

Field closure is expensive and to be avoided. For readers who are not growers or familiar with commercial strawberry production, consider that the average weekly take out of a field can be 400 boxes per acre that we will conservatively price at 8 dollars a box back to the grower.  So the weekly cost of LBAM closure to a fifty acre field is 160,000 dollars.  Personally speaking, this enormous penalty is totally out of proportion with the infraction of having a quarantined pest in one’s field, but it is not my decision to make.

Cooler Inspection: USDA inspectors are to visit area coolers at regular intervals, my understanding is that because of the reduced budget for the program they will be checking in at each local facility once a month.  This may change however depending on the vagaries of Federal budgets and politics.   Once at the cooler, inspectors take a subsample from a load of fruit from each production field for that day.  The inspectors are VERY thorough, the field closure from last night came from a larva tucked under the calyx.   Unfortunately, such a larva often cannot be identified right away and so a hold is put on fruit coming out of that field.  In plain English, that means the field is closed and you can no longer harvest and send fruit out of that field.

Field Inspection: Once a field has been identified as possibly infested with light brown apple moth, the next step is for inspectors to do an inspection of the field itself.  I have seen field inspection, and it does not leave one leaf unturned.  For somebody with experience, leaf rolls are easy to see, and inspectors walk with up to six people abreast, one person per row.  Since this is their job, day in and day out, they are really good at it and if you have a leafroller, it will be found.

Treatment of Infested Fields: If no leafrollers are discovered during the field inspection, the field is opened back up.  If a leafroller is discovered and furthermore found to be positive for LBAM, the grower is mandated to make an application.  He or she chooses from a list of allowed materials, and fortunately this year, according to program director Rick McKay, surfactants and adjuvants are allowed and highly recommended.  All parts of the application are observed by inspectors from loading, mixing and the actual spray.  Nothing says that the grower can't be making applications before and after this regulated application, but they need to see the one they mandate.  Then, depending on the pesticide used, inspectors return after a specified number of days to re-inspect the field.  If no more leafrollers are found, the field is opened back up.  If a leafroller is found, the field remains closed and the application procedure is repeated.   Experience from last year says more often than not it takes more than one spray to re-open a field.  In some cases, especially in organic fields, which have a much narrower selection of effective materials, it can take more than a month to re-open.

Discussion: It is imperative that growers pay attention to leafrollers in their fields. Yes, they are around, because I have been getting phone calls about this all week long now.  Conventional growers have a wide range of materials at their disposal, organic growers less.  It is not a bad thing yet to be putting out the pheromone mating disruption twist ties, since we are probably looking at a flight of adult moths in late June, with a subsequent larval infestation in July and August again.  In light of the devastating costs of field closure, it might not be too much to have crews go through the fields regularly and be removing rolls.

This is a revision from the previous post:

A couple of samples handled by this office from strawberry over the past two weeks have turned out to be a leafroller species which might not be light brown apple moth.  Probably the reason people have been asking about these is the general concern about having leafrollers in one’s production field at all. This is understandable, considering the current regulatory environment which mandates closure of at least part of a field on discovery of one species of leafroller; the light brown apple moth.  Fields can also be temporarily shut down as regulators work on distinguishing leafrollers from one another in order to get a positive light brown apple moth identification.

The following short description will be about garden tortrix in strawberry.

This very important for those making a definitive identification in the field.  While the UC IPM guidelines refer to garden tortrix as having a "spot on the back of the head" this spot is actually a darkened prothoracic shield behind the head on not on it (see fourth picture below).  I would very much like to get a definitive sample from our area of garden tortrix for a clear picture for this blog, so will ask my readership to bring any suspect samples.  It would be very helpful.

                               by Tim Hartz and Mark Bolda

  During the 2010 production season we conducted a survey of approximately 30 commercial fields in the Watsonville-Salinas area to develop information on strawberry nutrient requirements, and to evaluate current fertilizer practices.  We did whole plant sampling in four fields, two planted with ‘Albion’ and two planted with a day-neutral proprietary variety.  In all fields the uptake of nitrogen was slow through the winter months; by the end of March total crop N uptake was less than 20 lb/acre.  From that point forward, crop N uptake was quite steady, averaging between about 1-1.2 lb N per acre per day.  By the end of August, total N uptake ranged between 140-190 lb N/acre, with the higher amounts in higher yield fields.  Total phosphorus (P) and potassium (K) uptake averaged about 40 and 230 lb/acre, respectively.

  Soil sampling showed that the majority of fields began the season with high soil test levels of P and K, in many cases high enough that P and K fertilization would not be required to produce a good berry crop.  However, it appeared that growers often follow a preplant ‘recipe’ when it comes to fertilization, and that typical ‘strawberry mix’ controlled release N/P/K fertilizers were nearly always applied, regardless of soil test nutrient levels.  The efficiency of nitrogen applied preplant is also questionable.  The N in common preplant controlled release fertilizers becomes available at a relatively steady rate over 6-8 months, meaning that if applied in late October more than half the N is likely to be released by the end of March.  Since crop N uptake by the end of March is less than 20 lb/acre, any additional fertilizer N released by that time will be subject to leaching by rain or irrigation.  A moderate amount of preplant controlled release N provides a guarantee of some N availability during the winter, but a large fall application is likely to be inefficient.

  Most of the growers we worked with provided us with their fertilization records.  On average, they applied a seasonal total of 187 lb N/acre, about evenly split between preplant and fertigated N.  However, there were large differences among growers in their N management; seasonal rates varied from less than 150 lb N/acre to nearly 300 lb N/acre, with some growers using nearly all preplant N, while others applied nearly all N through fertigation.  We found no correlation between seasonal N rate and fruit yield.

by Steven Koike, UCCE

Leaf blotch disease of strawberry is being detected in some fields in coastal California this winter. Dependent on splashing water, this disease rarely occurs unless overhead sprinklers are used or rains occur. Symptoms generally consist of tan to gray leaf lesions that commonly (though not exclusively) develop along the margin or edge of the leaflets. Leaf blotches are irregular in shape and may be surrounded by a purple border. These affected areas tend to grow fairly large; they can expand and cover from 1/4 to 1/2 of the leaflet surface.

A key diagnostic feature of leaf blotch is the presence of tiny, brown to black, fungal fruiting bodies in the gray blotches. Brown to black petiole lesions can also occur. In past seasons leaf blotch has been misdiagnosed as spray burn or phytotoxicity from applied chemicals. If uncertain about the nature of such leaf symptoms, submit samples to the UC Cooperative Extension offices in the coastal counties.

Leaf blotch disease is caused by the fungus Gnomonia comari, which also has the name Zythia fragariae. Zythia fragariae survives on strawberry crop residues. The fungus does not appear to be a true soilborne fungus, so it will not likely persist in soil unless strawberry crop debris is present. The Zythia form is especially dependent on splashing water for spore dispersal and infection. This accounts for the typical appearance of leaf blotch during winter and early spring seasons when there are rains. Leaf blotch is usually considered a minor problem and fungicide treatment programs have not been developed nor are they generally recommended. The strawberry plants usually grow out of the problem. Leaf blotch spread and development is dependent on rains and splashing water, so once the winter rains cease, leaf blotch usually becomes a non-issue for growers.