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.

A recent case of wilting blackberries around Watsonville has been confirmed from multiple samples submitted to several plant pathologists (the UCCE plant pathology diagnostic lab in Salinas obviously being one of them) to be caused by Verticillium dahliae.  The pattern is one of wilted plants scattered over the breadth of the field, with very few groups of more than three dead or dying plants. Verticillium on blackberry is actually pretty rare to find; in my career of more than 10 years I have only found 4 other blackberry samples to be positive for this disease.

As one can see from the pictures below, the affected plants stand out from the rest of the field by having few to no leaves (Photo 1).  Additionally, there are some leaves on affected plants which are a stark yellow color (Photo 2) and according to the literature this yellow leaf color can be diagnostic for Verticillium wilt.  Note also the darkened color of the epidermis (Photo 3) and the obvious discoloration of the vascular tissue (Photo 4) found when cutting deeper into the cane.

Generally, it is not at all uncommon in this field to will find Verticillium infected branches and others which are apparently healthy on the same plant.  This is consistent with an infestation of Verticillium which has not invaded all the roots and consequently has left some vascular tissue healthy and functioning.

The solution to this problem is to continue cropping if the disease does not manifest itself in many other plants with an eye to maintaining good watering practices so as to make up for the Verticillium compromised vascular system.  However, when planting a new blackberry crop, it would is strongly suggested to fumigate or use a variety which is less susceptible to Verticillium disease.

Researchers have found that V. dahliae exists as a series of different strains that have different host preferences. Characteristics of the blackberry V. dahliae pathogen have not been studied. Until further research information is available, growers should therefore assume that V. dahliae from blackberry, raspberry, and strawberry all can cross infect these three crops. This assumption would be important to remember when considering crop rotations.

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.