The following is a description and evaluation of tip dieback in Arapaho blackberry in a field outside of Watsonville .

As the reader can see from the pictures below, the issue is a rather abrupt manifestation of wilt, followed by a blackening of the tip.  Cutting back the outer layer of the cane reveals (Photo 2 below) that the necrosis is advancing in the interior of the cane, but as with the tip blackening itself, seems to be restricted to the top 4 or 5 inches.

This problem of tip dieback was reported some weeks ago on a few tips of the Arapaho planting and none of the other varieties in the same field.  As of last week this dieback has advanced through most of the planting and most of the tips are now affected and again restricted only to Arapaho. 

There are no signs, for example oozing typical of bacteria or fruiting bodies or mycelium associated with a fungus, of disease.  Seeing that the tip dieback is similar to the blackening of young leaf tissue caused by insufficiency of calcium ( for example black heart in celery) we tested with a two replicate sample the nutritional status of cane tips just starting to wilt and compared them to others still apparently healthy.  The output of this evaluation is below.  Also please note that substantial portions of cane were included in the sample, which would be expected to have different - probably lower - levels of minerals than the normally tested leaf tissue. 

Table 1: Comparison of Mineral Concentrations of Healthy and Tip Burned Tissue on Arapahoe Blackberry.

Concentrations of nitrogen, phosphorous, potassium, sulfur, copper and zinc are higher in the healthy tips, while concentrations of manganese, calcium, sodium and chloride are higher in the wilted tips.  While the levels of chloride are nearly double in the cane which has died back, these levels of chloride are still not consistent with what we know to be damaging to plant tissue, usually ranging about 3000 or 4000 parts per million.

Considering that if the problem is not a disease, nor nutritional, what is it then?  The answer comes to us from people with experience with the variety and the problem.  We go to John Clark from the University of Arkansas, who has noted previously this very tip dieback on Arapaho blackberry in cooler climates (for which the summer Central Coast obviously qualifies) to the extent that he cautions growers in cooler regions about planting it. 

In conclusion we can be fairly certain that the tip burning we are currently observing here in Arapaho blackberry is physiological and caused by an interaction of the variety and our climate.

Zeal (etoxazole) is now registered for control of phytophagous mites in caneberries.  Zeal is a very welcome addition to our limited suite of miticides in caneberries.  Link to the label is here:

http://www.cdms.net/LDat/ld7DK007.pdf 

Had lunch at the Nickel with Tom Dewitt from Valent to get some clarification on the use of this material.  Our conversation was as follows:

Breadth of Control: Zeal controls phytophagous mites in the Tetranychid family very well, so this includes both twospotted spider mites and Lewis mites.  It does not kill eriophyid mites such as redberry mite nor tarsonemid mites such as cyclamen mite.  As a translaminar material, it doesn't matter that the residue doesn't stick around that long on the leaf surface, since plant feeding mites will still pick it up when they penetrate the leaves to feed.  It is important then also to not apply Zeal with surfactants that are stickers because they will impede the translaminar activity and instead to go with a good nonionic surfactant.

Activity on Predatory Mites: Zeal should not be applied on top of a population of predatory P. persimilis mites since it renders the males sterile and the population will cease to grow.  It is recommended to hold off on releasing predatory mites until 30 days after an application of Zeal so as not to impede with their activity.

MRL's: Growers and shippers please take note that while Zeal now has a MRL (maximum residue limit) for Canada in strawberries, it does not have an MRL yet in caneberries. 

I discuss the use of a miticide in this article.  As always, before using this of product, check with your local Agricultural Commissioner's Office and absolutely consult the product label for product registration, restrictions, and use information.

A thread I have been participating on with the North American Raspberry and Blackberry Association (NARBA) email discussion group regards the heavy fruiting of the blackberry variety 'Natchez' and the subsequent repercussions on fruit ripening and to some extent flavor.  This is a fairly common problem here on the Central Coast with growers of this variety and I have been asked on several occasions what to do about it.

As one can see from the picture below, the ability of 'Natchez' to produce fruit is tremendous, but unfortunately the leaf area to fruit ratio is rather low here, resulting in the ripening problems mentioned above.

This past week we were fortunate enough to have plant breeder John Clark, who among other blackberry varieties bred 'Natchez', weigh in on managing overcropping of this variety. 

He writes that 'Natchez' plants without any lateral shortening, ie pruning of the laterals, overcrop (load up with too much fruit), especially on plants which are fruiting in the first year after planting. He suggests that laterals be shortened to 15-25 inches long (prior to flowering obviously) to limit the crop down to what the plant can ripen with the available leaf surface area and carbohydrate reserves in the plant itself.

Simply put, the key to getting 'Natchez' to ripen and flavor up properly is maintaining an adequate ratio of leaves to fruit by pruning the laterals back to 15-25 inches.

Here is another example of orange rust, which are caused by two fungi, Arthuriomyces and Gymnoconia, the two of which are distinguished by the shape of their spores and life cycle length.  To re-iterate, growth of orange rust is strictly on blackberry and is favored by cooler temperatures and high humidity, but I have yet to see an infection of this rust explode across the landscape no matter what the conditions are.  Instead, several plants around a single locus will show infection at one time and the advance of the disease, if not addressed, is measured in years rather than days or weeks. 

Orange rust is distinguished by the intensity of its orange color and the sharp outlines of the infected area.  Usually one can see the spores by rubbing or brushing up against the leaves.

Probably the most important point about managing orange rust in the field is that it is systemic and cannot be controlled by any fungicide we have labeled in blackberries.  Leaving plants alone or trying to spray one’s way out of it will end in tears.  Orange rust MUST be removed by hand, that is to say the whole infected plant dug out with a shovel.  It is best to remove plants directly adjacent to the infected area as well, since they are quite likely infected but not yet showing the symptoms.  Take care to remove the whole plant, including the roots down to at least 12 inches.  Plants should be bagged at the point of removal and disposed of properly.  Personnel removing the plants should use clothing which can be disposed of or washed quite soon after working with the infected plants so as not to continue to spread spores across the blackberry field over the course of the remaining workday.

One last point, graphically illustrated in the last picture, is that groundsel in blackberry fields gets a type of rust also, but this is not the same rust the orange rust occurring on blackberry and is rather a species of Puccinia.  Rusts tend to pretty specific to their hosts, so removing groundsel with the goal of reducing the rust pressure on blackberries will not work.

Yet another hat tip to the PCA and grower for letting me know about this one.