As many Central Coast caneberry growers know, this summer season has seen an astonishing number of lygus bugs in blackberries.  Counts of 10 to 20 lygus bugs per shake easily rival the heaviest infestations in strawberry.

However, contrary to the “catfacing” or misshapen fruit left by lygus activity in strawberry, there does not seem to be a documented type of damage from lygus in blackberry.  All the same, customers have been getting tetchy about having bugs in their baskets of fruit, so it is indeed important for us as an industry to take this on.

Unfortunately, management of lygus in blackberry has proven to be just as difficult in blackberry as strawberry, perhaps even more so since there are fewer insecticides registered for use in blackberries.

Thrips incidentally occur in blackberry flowers as well and did in great numbers in this trial.  Again it is not certain whether or not they cause a lot of damage.  Nevertheless, thrips were also evaluated in this trial since they are a known pest in other crops and situations.

The organically registered insecticides MPede and Aza-Direct have shown promise in controlling stink bugs (same insect order as lygus bugs), so the study described below is a screen these two materials compared against a grower applied standard of Diazinon along with an untreated control. 

Trial was composed of 4 24 ft x 26 ft replicated treatments in a blackberry field with significant lygus and thrips activity.  MPede and Aza-Direct were applied with a motorized backpack sprayer by Brian Deeter from Gowan Company.  Diazinon was applied at the label rate by the grower in an adjacent block, so while not part of the experimental design, it did provide reasonably strong information in comparison to the three other treatments. 

My research assistant and I did the evaluations which consisted of shaking 3 feet of flowering blackberry hedgerow into a five gallon bucket for the lygus and agitating three mature flowers individually onto a white sheet of paper and counting the expulsed thrips there.  Dates of evaluation were August 11 (pre-application), August 15 and August 19 (one week post application).

As the reader can see from the chart below, beyond Diazinon there is little effect on field populations of lygus or thrips from either MPede or Aza-Direct.  Furthermore, the lack of thorough control of lygus and thrips by Diazinon, long regarded as one of the most powerful pesticides available to blackberry growers, is unsettling.

Means followed by same letter do not significantly differ (P=.05, Student-Newman-Keuls)

Mean comparisons performed only when AOV Treatment P(F) is significant at mean comparison OSL.

Finally, it will be worth my while to return to this field to evaluate the effect, if any, this pest load is having on fruit development.  As already mentioned above, beyond the contamination of harvested fruit, thrips and lygus damage to blackberry has not yet been well defined.   

There are a number of pesticides mentioned for management of lygus and thrips in this article.  Before using any of these products, check with your local Agricultural Commissioner's Office and consult product labels for current status of product registration, restrictions, and use information.

We have had the misfortune of discovering Armillaria root rot on blackberry on the Central Coast.  This is significant in that root rots such as those from species of Phythophthora or Verticillium are extremely rare in blackberries cultivated in this area.

Generally known as a pathogen of forest trees and orchard crops such as apples and avocados, this root rot is known by the common name “oak root fungus” and is caused by several different species of Armillaria fungus.  The above ground symptoms of Armillaria root rot are those common to other root rots, that is to say wilt and stunting of canes and leaves (Photo 1 below).  Below ground, roots in blackberry show obvious signs of rot frequently accompanied with whitish mycelial growth (Photo 2 below).   While the literature also says this mycelium forms sheets and fans that was not the case in this particular situation.   Importantly, the symptomatic plants are found in patches which slowly advance outward over time.  In more advanced infections, one would also find black rootlike strands of 3-4 mm in diameter known as rhizomorphs.  In the situation addressed here on the Central Coast, the infected areas were limited to rows and tended not to cross over into the next, so the paucity of root growth and moisture in the area between rows may be limiting to disease spread from row to row.

Armillaria infections of blackberry are a result of previously infected orchard plantings.  Since this pathogen can persist for decades in infected stumps and other woody material, the history of a field should be of serious consideration for blackberry growers when looking at new ground to plant.

While it is undoubtedly a good idea to fumigate a piece of ground known to have been infected with Armillaria fungus, fumigation itself might not be enough because even the best fumigant may be hard put to penetrate infested stumps and other woody debris.  With this in mind, to the extent possible, remove woody debris from a cleared orchard or forest prior to fumigation. 

Once an infection is underway, the only way to address the problem is to limit the spread of the disease. This means removing symptomatic plants and as much of the roots as possible along with those plants immediately adjacent.   No, this will not eradicate the fungus from the plantation but will serve to at least limit its spread through the field to other plants.

The recent implementation of an eradication program and proposed quarantine of grapes of a small area in south Santa Cruz County due to multiple finds of European grapevine moth, Lobesia botrana, puts us in the position of having to discuss in detail the possibility that this pest could occur in blackberry.    

While blackberries are described in the literature as having been a host of European grapevine moth and thus will fall within compliance actions, I have reason to doubt that European grapevine moth will be found in our cultivated blackberry varieties here on the Central Coast because of the following:

1- The clustered inflorescences of grapes are quite distinct from those of blackberries, yet have been described as a major part of the attraction of grapes to European grapevine moth.  Blackberries occur in loosely formed inflorescences of less than 10 fruit, and are not in compare to the numerous, closely grouped fruit of wine and table grapes.   Simply put, the morphology of the inflorescences of cultivated blackberries in our area is not amenable to European grapevine moth.

2- The species of blackberries on which European grapevine moth was reported in UC and CDFA literature is given as Rubus fruticosus, which is the wild blackberry commonly known as Himalayan blackberry found alongside roads and in the woods.  Cultivated American blackberry cultivars do not come from this R. fruticosus, and rather come from R. allegheniensis, R. argutus, R. frondosus, R. ursinus, R. macropetalus and R. loganobaccus. 

3- The current campaign outside of species specific pheromone based mating disruption underway by area blackberry growers in eradicating the other invasive leafroller species, the light brown apple moth, from their fields will go a long, long way in keeping fields clear of European grapevine moth should it ever find its way there.

The link for the full provisional guidelines is here:

http://www.ipm.ucdavis.edu/EXOTIC/eurograpevinemoth.html

In spite of of the factors predicting very low odds of European grapevine moth infesting Central Coast blackberries, growers are nonetheless cautioned to be vigilant and are encouraged to contact this office should they have questions concerning this matter.

There have been now two field closures over the past week in the Watsonville-Salinas berry production district, and the following is meant to make some sense to growers for what to do to minimize losses in the event of a leafroller larva detection.

USDA inspectors are not agriculturalists, nor pest managers for that matter.   We in the industry should be aware that they are bound by a set of rules that at times may seem at odds with sound pest management, but it yet is incumbent upon us as professionals to work with them and come out with the best solution for both parties which is the elimination of leafrollers and re-opening of the field with as little impact to the normal management of the field as possible.  

Growers should be aware that outside of the USDA inspections taking place monthly at each cooler, fruit sent for export out of the USA is being sampled and inspected by county personnel. They have long done this to look for pathogens and other insects and recently this repetoire has been including leafroller larvae.  On finding a suspect larva, the county inspector forwards it to USDA inspectors, who will make an identification of the larva if possible at the cooler and also forward it on to the DNA identification laboratory in Sacramento.  The process from find to absolute positive identification at the DNA lab is about a week, but can take longer in the case of very small larvae or pupae.
It appears that growers are advised of a possible LBAM find on the same day, and a hold is put on the source field.   Inspectors will pay a visit to the hold field to find larvae, which they inevitably do.  Now, the grower has the option of re-routing fruit from the field under the hold order to clients within the quarantine area or destroying it. Both have happened this last week.  It is truly tragic when another market cannot be found for fruit, but such is the nature of this quarantine.  
Once advised of the hold, arrangements are made to have inspectors observe a pesticide application of the infested field with the purported goal of controlling LBAM.  In the interest of time, the process of arranging a pesticide application and field re-inspection is allowed to move forward even in the absence of a full positive identification for LBAM.  Time of initial suspect LBAM find to time of observed spray seems to depend on a number of factors, but generally happens within a week.

In berries, the list of allowed pesticides for inspector observed, mandated sprays is unfortunately rather short.  For strawberry growers, fortunately Intrepid, Entrust and several Bt formulations are included, but notably Coragen, Success and Radiant, which are highly effective and actually have light brown apple moth on their labels along with being pretty soft on beneficials and the surrounding environment, are not allowed.  Instead, we are additionally allowed crude materials such carbaryl (7 day pre-harvest interval, pollinator caution, devastating to beneficials), and chlorpyrifos (21 day pre-harvest interval, seriously harmful to beneficials). A superior type horticultural oil is allowed, but only at a minimum rate of 1% volume to volume, which for a petroleum distillate is pretty risky in sensitive crops like strawberries or caneberries.
Once the approved pesticide application is done, arrangements are made to have the field re-inspected in the interests of confirming that it has been cleared of leafroller larvae and re-opening it.  This is a rather important point for berry growers, because when this happens depends on what material that has been applied.  Based on our experience, inspections have been taking place one day after an application of Entrust, and more than several days after Bt formulations.  If you are willing to take a chance of burning your plants and fruit, the superior type oils also are supposed to give one day. Intrepid and Confirm as insect growth regulators (IGR's) are known to act more slowly so again garner a re-inspection after more than a few days.
It seems in light of all of the above, the strategy that berry growers should be taking in relation to leafroller management should be as per the following:

1- Keep fields clear of leafrollers. Period.
2- In the unfortunate event of a possible LBAM find and hold on the field, spray the field IMMEDIATELY with the very effective and labeled materials such as Coragen or Radiant in strawberries and Delegate in caneberries. By doing so, you are giving these materials time to act in full while you make arrangements for inspections and sprays with the USDA.
3- Make arrangements for mandated spray with the USDA.  
4- Make application of Entrust since you should be able to get inspectors in the next day to confirm that it has cleared the field of leafrollers.  
5- Undergo inspection from USDA to re-open field. Note that your spray of the better material from the day of the hold will now have taken full effect along with the effects of the Entrust, and you should by now have dramatically reduced, if not eliminated, leafroller larvae from your field.

There are pesticides mentioned for management of leafrollers and light brown apple moth in this article. Before using any of these products, check with your local Agricultural Commissioner's Office and consult product labels for current status of product registration, restrictions, and use information.