In the winter (February) of 2013, a field of raspberries in Watsonville was discovered to be infected with Pseudomonas syringae, the causal agent of Pseudomonas blight disease. This was the first documentation of this disease on raspberry in our region.

As pictured below, the infection of raspberry plants is manifested by brown, angular-shaped, water-soaked spots on the developing leaves, petioles and emerging plants. The grower reported a sort of “sweating” of the infected plants early in the morning, which could be due to leakage from tissues broken by bacterial activities. Many of the smaller, emerging plants had died back, but thanks to the carbohydrate reserves in the crowns and roots, they grew back and recovered once the weather warmed up. Outside of the great delay in growth, the field bore fruit normally.

As is the case for most bacterial problems, once the weather becomes warm and dry, this bacterium becomes less active in raspberry and disease normally subsides. This field indeed improved with the warming and drying weather over subsequent weeks. However, it would be interesting to see if the disease again would develop in the fall with the return of cooler and wetter conditions and the presence of wounds created in the foliage from insects, wind, or cultural practices. Pseudomonas syringae survives the winter in the plant buds and also lives as an epiphyte (growing on the surface of the plant but not invading it).

Chemical control should be used with caution, since many of the chemicals recommended for treatment could also damage the plants, especially the delicate, early season foliage. However, if this disease is a significant problem, it is strongly recommended that the grower apply either a fixed copper or Bordeaux mixture to canes after harvest but before the fall rains. Such applications can reduce the bacterial inoculum on the canes and buds. We will be monitoring caneberry plantings for Pseudomonas blight so as to determine whether this will be an on-going disease concern for the industry.

As of the date of this blog (spring 2014), Pseudomonas blight has not yet been observed and reported for this current season on caneberry in our coastal region. If you see suspect symptoms, submit samples to our Cooperative Extension office for laboratory testing and confirmation.

While raspberry crown borer, Pennisetia marginata, is not an unusual pest in local blackberries, this is the first time we've found it in raspberry on the Central Coast for a while.

As one can see from the the first photo below, the wilt of the affected raspberry plant is quite sudden.  Unlike what we find in blackberry however, the borehole in these raspberries is well below the soil line, more than a half an inch easily. Pointing to a diversity of population, some channels leading into the cane from the borehole were empty, while others had larvae and yet others had soon to eclose pupae nestled within.

There are several approaches to management of raspberry crown borer.  The commonly practiced shortened production period of two years or less of raspberries on the Central Coast goes a long way to limiting the establishment and in my mind has made greatly minimized the presence of this pest in its namesake host.   In short, removal of infested cane will do a lot in limiting infestations, especially if one is removing canes with late stage raspberry crown borer within.

There are also pesticides labeled for use against raspberry crown borer, and these can be effective, especially over a two year term of treatment in bringing infestations under control.  Please note the restrictions and special conditions of these two:

Diazinon is registered for a drench application for raspberry crown borer, but the label restricts this application to “spring, before bud break.  Potential users of Diazinon should be aware that there are water quality issues associated with this pesticide. 

Admire has a label for caneberries, the only caveat would be the 7 day PHI and caution to not use it when bees are actively foraging.  This is a material that is going to be traveling around actively in the plant, but one should bear in mind that applications should be made with plenty of water as the active ingredient in Admire of imidacloprid has a real affinity for soil particles and can get hung up there if there isn’t enough water behind it.

8/29/13 addition:  If making the decision to use Admire, please do take note that this material should not be applied during bloom and when bees are foraging. 

Thanks to the grower for having me out, I always appreciated getting these calls to come out and have a look at something new and interesting.

The above article discusses the use of several pesticides for management of raspberry crown borer in caneberries.  As always, 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.

A cover crop can be a useful way to prevent weeds in anchor rows.

Cover crops in anchor rows can suppress weed growth and additionally help to minimize soil erosion and nutrient and sediment loss when it rains. Densely planted cover crops can outcompete weed seedlings germinating from the soil and prevent wind-dispersed seeds from reaching the wet soil surface. Have a look at the newly revised weed section in the Caneberries Pest Management Guidelines on the UC IPM web site. 

As readers know, tunnels used for caneberry cultivation have the advantage that even when it rains caneberries remain dry which helps with fruit quality and yield. However, during rains, the water drains from the plastic cover of the tunnel and down into rows that contain the anchoring posts of the tunnel structure. The accelerated runoff in these post rows can cause soil erosion, sediment and nutrient loss. As such, the persistent soil moisture in post rows also promotes weed growth.  These weeds, while maybe not competing directly with canes, can reproduce and quickly spread into neighboring cane rows.

Cover crops in the anchor rows are especially helpful when managing weeds that are difficult to control with fumigation because of their hard impermeable seed coats (mallows and filaree), or that have developed resistance to herbicides such as glyphosate and paraquat (hairy fleabane and horseweed).

Cover crops can be managed with mowing or herbicides to avoid seed production.

Two weeks I was called out to investigate the situation in organically farmed red raspberry that the reader can see below.  The plants are pushing forth an impressive crop of fruit and overall the plant stand is strong yet numerous laterals are showing a yellowing of the leaves, especially towards the tips. 

The Problem: The youngest leaves on the ends of fruiting laterals were showing a distinctive yellowing.   Looking closely at affected leaves, one can see that the veins of the affected leaves remain green to some extent.

Field Evaluation:  The farm manager and I initially looked around for arthropods (insects and mites) or damage as well as extirpating a few plants to examine the roots and generate samples for submission to the UCCE diagnostic laboratory in Salinas.

We then took 4 replicated samples of yellow leaves and then four replicated samples of green leaves from the same stage (between the 5^th and 7^th leaf from the tip) of apparently healthy laterals.  We also took soil samples down to about six inches deep from four distinct areas of the field.  All samples were submitted to the Soil Control Laboratory in Watsonville for analysis.

Results:

No arthropods of any consequence were found during our visit, nor did the UCCE diagnostic laboratory come up with any plant pathogens.  The mycelial threads we found on the crown and roots (last photo below) of the cane are those of a saprophytic fungus and present no threat to the plant.

The means of the replicated tissue samples were compared through a Student’s t-test and the results are presented below in Table One.

Table One.  Average Mineral Concentration of Green and Yellow Leaves

As one can see, there are several minerals, being magnesium, manganese, calcium and iron, which are significantly lower (p<0.05) in concentration in the yellow leaves than in the green.  Conversely, potassium is much higher in the yellow than in the green.

The unfortunate thing is that since we don’t have published guidelines for these sorts of raspberry varieties  (for example like the recently published DRIS study in strawberry), we have to refer to out of state raspberry fertility guidelines for other varieties to get a handle on the meaning of all these numbers.  Using these guidelines, we find that the concentration of manganese in the yellow leaves falls below the consensus of a lower threshold of sufficiency of about 30 ppm.  In contrast, concentrations of iron, calcium, and magnesium, even though they are significantly lower in the yellow leaves than the green, are still within the generally accepted ranges of sufficiency.

We do get a glimpse also of the tolerances of these raspberry plants to chloride and sodium, which can be useful for future reference.  The green leaves contain about 5000 ppm chloride and around 170 ppm sodium.  These concentrations in my experience would be cause for some plant distress in strawberry, but apparently these levels are fine here.

The averages of the soil samples are below. As there was no area in the field showing more yellow than others, simply four composites of six individual samples were taken to get an understanding of the background mineral concentration of the soil.

Table Two.  Average Mineral Concentrations of Soil

Nothing jumps out here from this table of soil concentrations.  Nitrates might be a tad lean at 10 ppm, phosphorous is typically high, pH is normal, ECe is a comfortable 0.91 and the micronutrients are available in some quantity.

The question is then what is the conclusion?  We have no arthropod or pathogen compromising the plants ability to take up nutrients or anything else.  Lacking any other explanation, my take would be twofold.  One is that the pH of 7.6 in the soil is limiting the manganese, and that the big fruit load could be also drawing off this nutrient from the leaves and moving them to the fruit.  My choice of corrective action would be to add manganese, along with iron and magnesium, just to be sure, to this planting.

Thanks to Patrick Kingston and his boss for having me out on this call.  It’s always great to collaborate on issues with such enthusiastic and smart up and comers in our industry.