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.

It was perhaps only inevitable that some laboratory work with a private industry researcher has discovered a high level of tolerance, maybe even resistance, to the popular organically registered pesticide Pyganic  (active ingredient pyrethrin) in spotted wing drosophila.  Using the system of Petri plates photographed below, groups numbering from 15 to 22 flies were subjected to the label rate (18 fl oz) and twice the label rate (36 fl oz) of Pyganic 5.0 II with the result that spraying them had very little effect and most survived.  This has been repeated several times, so we know it is not by chance that this is happening.

The population subjected to this laboratory testing has been exposed in the source field to many applications of Pyganic- there's not a lot of choices in organic culture- over the past two years, so it comes as no surprise.  Admittedly it seems rather fast.  Do note also that pyrethrin is a weaker version of the synthetic pyrethroids such as zeta cyper-methrin (Mustang Max) and bifenthrin (Brigrade) so we do have a flashing yellow with these materials also. 

It is so important that we continue to rotate the pesticides we are using against spotted wing drosophila.

It is at times perhaps tempting to take an uncomplicated view of nutrient deficiency in strawberry.  The mantra goes a little bit like yellow leaves are nitrogen deficient, phosphorous deficiency is given by purple leaves, potassium shortages easily marked by scorched leaves and so on.

I don’t believe any of this is so simple and so attempt to challenge this facile thinking when I have the opportunity to do so.

The following situation was a good one.  A smallish field of ‘Albion’ variety strawberry was not given supplemental fertilizer beyond a standard dose of preplant slow release 18-8-13 in the area of 500 lbs per acre.  The result in late June was as seen below- severely chlorotic plants with a strong tendency towards purpling of the middle age to older leaves.  Additionally, flower production had nearly ceased and fruit was sizing down substantially.

I tested the soil to 6 “down at six different points throughout the field, amalgamated them and got the following results:

Soil pH was a perfectly normal 6.4.  As one can see from the numbers above, plant available nitrogen sources nitrate and ammonium were sort of low (usually want to be 10 ppm for either one), while phosphorous was a quite sufficient 58 ppm.

Tissue samples consisted of leaf blades.  Four separate samples were taken from different sections of the field and each sample consisted of a dozen leaflets of middle age- meaning not the very old ones at the bottom of the plant nor the young tender leaves emerging from the center of the crown. 

Comparing the nitrogen results from the leaf blade with the 2.6-2.8% concentrations described as sufficient as from UC Publication 4098 and Dr. Tim Hartz’s work last year, we see that this vital nutrient is a full percentage point below what is deemed necessary for normal production.  Phosphorous, while below the 0.36% field average taken by Dr. Hartz’s study last year, is still understood to be well above the 0.10 % baseline given by UC Publication 4098.  All other nutrients, with the exception of zinc (15 ppm compared to a recommended 18-20 ppm), in this sample are well within sufficiency ranges.

Why then the pronounced purpling of the leaves if the phosphorous is not dramatically, if at all, insufficient in the tissue?  There are in fact other possibilities.  A lack of nitrogen, which is a component of some amino acids and other compounds, can result in a similar build up of excess carbohydrates as in phosphorous deficiency.   Essentially, both deficiencies have the same result then that these carbohydrates can end up being used in anthocyanin synthesis resulting in accumulation of these flavonoid pigments.  Some are red, others pink and some purple.  This may be an explanation why strawberry leaves lacking in nitrogen but not ostensibly lacking in phosphorous are actually turning red to purple. 

So, while undoubtedly light green to yellow leaves are still a good indication of nitrogen deficiency in strawberry, don't be fooled that the purple that often accompanies it is actually caused by something else like a lack of phosphorous.

Thank you to Soil Control Lab in Watsonville for processing and evaluating these samples.

There have been a few reports as of late concerning a rather abrupt wilting of blackberry plants in certain fields.  Some of these wilts have been found to be caused by raspberry crown borer, which merits a discussion of this pest in this space.

Crown borer is actually simple to diagnose in the field.  One will notice a rather pronounced wilt of the plant, and a subsequent evaluation of the crown of the plant will find a hole there, usually with some sawdust like material deposited outside.  Excavation and opening this section of the plant will find significant tunneling and usually a rather large larva of a half an inch or longer in length, which of course explains the wilt, since most of the water conducting elements are ruined by all this activity and no longer functioning in bringing water higher up to the plant.

As the reader can see from the picture below, crown borer adults look a lot like a wasp, but they are not.  They are a clearwing moth that looks like a wasp to protect it from predation.  Note the long antenna and extensive scales on the individual that distinguish it from a regular wasp in the picture below. 

Briefly, the life cycle of crown borer is two years long.  It appears that the adults are active here in Watsonville in late June and so they would be laying their red-brown eggs on the undersides of leaves around this time as well.  Larvae, after emerging from the eggs somewhere in the area of a month later, work their way down the cane, where they either find a place in the bark to hide or begin excavating a tunnel in the crown.  In either case, the larva is not embedded in the cane yet and rather shallowly situated.  The larva continues to tunnel into the crown through the following year, by the time which the damage can be quite extensive.  Late in the summer, the larva must go into pupation, a state which it apparently remains in until the following spring.   There is unfortunately no degree day model available for raspberry crown borer yet- this would be an exceedingly useful tool, since we are able to use pheromone traps to detect emerging adults and would be able to count with fair accuracy when the susceptible larvae are emerging and working their way down the cane.

A test using drenches at the base of the cane (Johnson and Kim, 2011. The Bramble pp 8-9) found that Brigade, Assail and Entrust all reduced the amount of crown borer in infested caneberries.  Altacor, also registered in caneberries, has also been recommended for crown borer but it is not clear how well this worked in controlling them.  These applications are a function of how closely one is to getting the small, superficially hidden larvae of the first year after they hatch.  The deeply embedded larvae of the second year would be near impossible to get to and kill, by my estimation.

It is still my recommendation that crown borer infested plants be removed immediately from the field and destroyed.  I have yet to see an infestation that is extensive in a field, so plant removal is essentially rouging and keeping the populations of this still rather infrequent pest in check rather than reducing yield by large scale plant removal.  This is important, since blackberry plantations tend to be long lived, and maintaining them as clear as possible of crown borer is a good step in the direction of maintaining long term field viability.

There are pesticides mentioned for management of raspberry crown borers 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.

Thank you to Chris Matthews and Doyle Goins for their assistance with the information for this article.