The following is an announcement for the California Farm Conference coming next year March 10-12 in Fresno.  Some berry growers might be interested, and fortunately there are scholarships available too:

Growers know that success in agriculture does not depend solely on a farmer’s ability to raise crops. Today’s successful agriculturists must also be expert business managers, marketers and stewards of the land.  The California Small Farm Conference offers diverse learning topics for small scale farmers and ranchers. The 2013 conference theme, Harvesting Knowledge: Growing Small Farms, reflects the goal of the California Small Farm Conference.

The California Small Farm Conference provides the small scale farming community with the opportunity to address industry issues, engage in educational sessions, attend local farm operations for additional insight, and participate in networking opportunities.

People should know there are scholarships available to attend this event.  Scholarships are awarded based on financial need. Depending on this need, scholarships may include conference registration, conference-hosted meals, a ticket to attend the Tasting Reception, travel and lodging costs, and a reduced Field Course rate.

“This organization exists to provide small scale farmers and those in the industry with access to relevant farming education,” said California Small Farm Conference President Casey Walsh Cady. “Our scholarship program ensures that access to farmers in California."

Please visit www.californiafarmconference.com/index.php/attend/scholarship to download the 2013 conference scholarship application. Applications will be accepted until December 3, 2012; bi-lingual scholarship advisors are available statewide to assist in the application process. Please visit the website for a list of advisors and their contact information.

University of California Cooperative Extension proudly presents the Fresh Market Caneberry Manual.  Written for California and West coast fresh market caneberry growers by UCCE caneberry experts Mark Bolda and Mark Gaskell, along with extremely valuable contributions from Michael Cahn on irrigation and Elizabeth Mitcham on post harvest fruit management, readers will find up-to-date information on all aspects of raspberry and blackberry production.

This manual is chock-full of accurate and detailed information on raspberry and blackberry production—no California grower should be without it.

Chapters include:

• Plant description
• Flowering and fruit production
• Plant varieties
• Macro-tunnel and field management
• Pest management
• Irrigation, water quality, and fertility
• Training and pollination
• Harvest methods
• Post-harvest handling

With more than 90 color photos (including some gorgeous cover and chapter lead photography by Ed Show), tables and illustrations, this manual is the perfect field reference for growing blackberries and raspberries in California and the western United States.    

It is available at the Santa Cruz County UC Cooperative Extension office at 1432 Freedom Blvd in Watsonville for $25 plus tax or you can go to the publication web site and order a copy.  Use promotion code PRCRU44 when ordering on-line and you will receive 10% off. 

Two pathogens that strawberry growers face all year long but especially now during the fall are Rhizopus and Mucor, which both cause a fruit rot that is distinctive and very different from the more common gray mold fruit rot caused by Botrytis cinerea. 

The fruit rot symptoms caused by Rhizopus and Mucor look very similar. Fruit infected with either of these pathogens become very soft and start to leak sticky red juices from the fruit tissues. In later stages of infection fruit softens to the point that it is no longer solid and cannot be picked up without falling apart. Affected fruit are usually covered with the wispy, fuzzy black and white growth of the pathogen. Both Rhizopus and Mucor fungi are fairly easy to distinguish from Botrytis gray mold. The Botrytis fruit infection does not substantially soften the fruit, extensive leaking of fruit juices does not occur, and Botrytis growth on strawberry fruit will be gray to tan in color.

While the fruit softening symptoms of Rhizopus and Mucor are similar, the two fungi can be distinguished from one another by examining the fungal growth with a hand lens. Look for the tiny, dark brown to black, spherical structures on the ends of the white fungal strands. These black spheres are the spore bearing structures, or sporangia. For Rhizopus the sporangia appear dry while the Mucor sporangia are wet or sticky looking due to a viscous liquid film. In addition, examine the general orientation or arrangement of the sporangia within the fungal growth. For Mucor the sporangia are usually lined up in parallel rows or stands. Sporangia of Rhizopus, however, appear randomly and are not found in any particular order or arrangement.

There are several ways to minimize the infection of fruit by Mucor and Rhizopus.  Use plastic mulch and drip tape, like most strawberry growers are already doing, since they minimize contact of the fruit with soil and water.  Practice good field sanitation by getting rotten fruit away from plant. Handle fruit in a way to minimize wounding, which opens an avenue for these fruit rots.  Cooling fruit quickly after harvest is helpful to minimize spread and development of Rhizopus, since this pathogen is not very active below 40^oF; conversely Mucor is less affected by cold temperatures and could slowly develop in storage.

As for fungicides, Captan and Switch are already known to be effective. Our annual fungicide evaluation experiments include a post-harvest component and provided additional information on fungicide efficacy against Rhizopus/Mucor. Ripe fruit were harvested from each treatment replicate, placed in a dry, open air box at room temperature, and evaluated for disease for several days. We found Pristine to be consistently good at suppressing both fruit rots.

Before using any fungicide product, check with your local Agricultural Commissioner's Office and consult product labels for current status of product registration, restrictions, and use information.

Since June of this year there has been a spate of yellowing and senescing (dying) of leaves of certain raspberries.  This problem is widespread in the Watsonville and Salinas production district and first appears as a yellowing of the older leaves toward the bottom of the plant.  The symptoms appear evenly distributed through the field with very little patchiness in incidence.  The yellowing tends to follow a mottled pattern (Photo 2 below) and surprisingly can be pretty bounded on the leaf, for example on one half and not the other.  Affected leaves end up separating from the main plant quite easily.  The yellowing and dieback most often occurs on the lower half of the plant, and rarely advances higher nor does it result in total plant death.  From growers and personal observations this yellowing and senescing usually does not appear to result in any reduction in plant vigor or yield, but there are occasions of total plant loss.  There are reports of occasional loss of fruit integrity and crumbliness in affected fields, but this is strictly anecdotal.

The lengthy report below is a summary of the multifold approach we took to studying this issue followed by a discussion at the end regarding what is the most likely cause.

Arthropods:  Arthropods are not the cause of this problem.  One grower reported a correlation with a certain type of mite and while there were patches of twospotted spider mites in some locations, in others there were none nor had there ever been.  Beyond the mites, no other arthropods capable of causing leaf discoloration or necrosis were found.

Diseases:   The leaf yellowing is not caused by a pathogen.  A total of five whole plant samples (plant tops and roots) from several fields experiencing leaf yellowing were submitted to the UCCE diagnostic laboratory in Salinas, and in only one case did the test come up positive for a species of Phytophthora.  As leaf yellowing can be caused by virus infection, for example Raspberry Bushy Dwarf Virus on the Autumn series of red raspberry, a set of leaf samples was tested at the UCCE diagnostic lab in Salinas and another distinct set totaling five samples was submitted to the CDFA disease diagnostic laboratory in Sacramento.  All tests for virus came back completely negative.

Nutritional:  Levels of nitrogen and phosphorous are below sufficiency and substantially lower in yellow leaves than in green leaves, and levels of calcium are above sufficiency (and well above sufficiency in a field of healthy green plants) and higher in yellow leaves than in green leaves.  Soil concentrations of nitrates are below recommended levels of at least 10 ppm in three of four fields experiencing yellow leaves.  Concentrations of the salts sodium and chloride are substantially lower in all fields experiencing leaf yellowing than a field of symptomless, apparently healthy plants.

Table 1.  Leaf Samples. ‘Healthy Green’ refers to leaf samples taken from a field experiencing no yellowing anywhere; other Green and Yellow are paired sets coming from the same field and leaves collected from floricane at the same approximate height of about 18" above the soil.  Samples consisted of at least 15 leaves coming from various parts of the field taken between July 16 and July 27.

^*Healthy sample excluded from these calculations.

Table 2. Soil Samples. Soil samples are a total of 10 6” deep cores taken from areas experiencing yellow leaves.  The surface crust of the soil was brushed away before sampling.   All soil samples were taken July 27.

^*The designations “Healthy Green, Yellow 1, Yellow 2 and so on correspond with the same designations for the leaves above, meaning they come from the same fields.

Discussion:  This issue of yellowing leaves in raspberry is not being caused by insects, mites or disease but we do find a striking difference in the concentration of some nutrients in affected leaves and the soils from from which they come.  Since all the fields in question here are being managed by extremely competent and experienced growers we can be certain this nutritional deficiency is not being caused by a simple lack of fertilizer application, so we must explore this a little further.

All of the plants experiencing leaf yellowing and senescence are being grown in macro-tunnels.  The PCA attending each of these fields reports that they have been very warm on the inside compared to outside and interestingly found a high level of humidity as well.   This adds something to our investigation, since high temperatures can be a factor affecting the growth of plants, especially plants such as raspberry adapted to temperate climates. Heat injury in plants often results leaf yellowing and senescence.

Leaf nitrogen and phosphorous are lower in yellow leaves than green leaves.  Leaf senescence is often preceded by the degradation and subsequent loss of chlorophyll, the lack of which of course means the leaf stops being green.  A quick perusal of a book concerned with the mineral nutrition of plants (the excellent “Mineral Nutrition of Plants” by Horst Marschner I recommend highly) tells us that leaf senescence results in a net mobilization or export of nutrients from the dying tissue to still living and growing tissue.   And we are seeing exactly this in the fields, since the plant tops continue to flourish and produce flowers and fruit all the while the bottoms are yellowing and dying.

But what of the higher concentrations of calcium in yellow leaves compared to green?  They are quite high, near or above what are normally considered levels of sufficiency.  Calcium, in contrast with other plant essential minerals is moved from the roots to the rest of the plant via evapotranspiration through the water conducting elements (also known as the xylem).  This is meaningful since this means we tend to see higher levels of calcium deposition in plants moving lots of water.

Soil concentrations of nitrate, sodium and chloride are all low in fields experiencing leaf yellowing and necrosis.  Knowing however that all three are leachable by water is again helpful.

The Bottom Line: What we are getting is that the tunnels are hot and killing some of the leaves towards the bottom of the plant.  The plants continue to grow though, reallocating nutrients from the dying leaves to the younger ones and pulling up plenty of water because the rate of evapotranspiration is high in the heat of the tunnel.  The grower response of adding more water to keep up is of course the correct one, but this is resulting in a lot of leaching.  For salts like sodium and chloride this good, for a plant essential ion like nitrate it is not.  So not only is nitrogen being transported away from the dying leaves, it is also being leached away in the soil before the plant can get it.

Probably the best response to this situation would be the one which has already been taken, and that is to open the tunnels to enhance air circulation and lower the internal temperatures. 

I would like to thank PCA Eryn Gray for sharing his data and insight along with the growers involved in this work without whose participation none of this would have possible.