- Author: Mark Bolda
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.
- Author: Mark Bolda
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.
- Posted By: Mark Bolda
- Written by: Mark Bolda
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.
- Posted By: Mark Bolda
- Written by: Mark Bolda
Starting Friday and over the weekend, a number of area blackberry growers have reported high numbers of lygus bugs in their fields. I checked on one field this morning, and indeed the level of infestation is astonishing. Somewhere in the area of ten early stage nymphs can fall out from a few shakes at a single spot at any number of points all across the field. This is without precedent in any type of berry and merits some thought and discussion.
The field that was viewed this morning was in full harvest with a lot of fruit in the yet green to pink stage. Primocane was still growing vegetatively with no flowering. I do not think lygus presents any harm to the quality of the fruit or the vegetative plant, other than as an incidental contaminant in the baskets of harvested fruit, much along the lines of what we have recently seen with stinkbugs. Lygus bug feeding damages the flower and developing fruit, so once the druplets have made and the fruit has formed, these bugs will no longer be able to harm it. Since the field examined today has next to no flowers, the nymphs must be feeding on sap from the newly developing vegetative tissue. Whether this causes harm to the plants remains to be seen.
Beyond the contamination of harvested cited above, the possibility that this colossal lygus population shifts over to later bearing varieties which are entering into flowering would give some reason for concern.
Fortunately, blackberry growers have several options available to them to control these pests. One of the best combinations we found from our work in managing lygus in strawberries has been a pyrethroid + neonicotinoid applied when the lygus are very small as they are now. Always bear in mind that this powerful combination of pesticides will weigh heavily on beneficials. Additionally, the neonicotinoids registered in blackberries present some issues with maximum residue limits (MRL's) to fruit exported to Canada.
Organic growers have few options short of border weed removal and vacuuming available to them unfortunately.
There are pesticides mentioned for management of lygus bugs 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.
- Posted By: Mark Bolda
- Written by: Mark Bolda
As many readers know by now, raspberries destined for sale in Canada have been included in the European grapevine moth (EGVM) quarantine. Raspberries are on the host list for European grapevine moth in Canada (but not the USA) and quite likely this has something to do with the rather nebulous description of Rubus spp as being a host in one or more older papers (like early 1900's sort of old) on this pest. Raspberries are Rubus ideaus, while blackberries arise from a wide number of species within Rubus.
Currently, raspberry growers within the quarantine area, loosely described as being to the west of Green Valley Road, Dalton Rd and on out to Casserly (see attachment below), are not eligible to ship into Canada.
At any rate, the USDA Project will not be inspecting raspberries within the quarantine, they will only continue to inspect blackberries. Raspberries within the quarantine that would be eligible for export to Canada will be undergoing inspections and subsequently be issued compliance agreements next week by County Agricultural Commission personnel. I do not yet know how this inspection will be done, but we will find out that out very early next week.
7/6/11 Update: It looks like shippers who have raspberry fields within the EGVM quarantine area from which they want to export fruit to Canada would be subject to the same inspection regime as for all blackberries- ie 20 lbs of fruit from 40 acres of raspberries. These fruit would be inspected by County Agricultural personnel rather than USDA personnel.
It is of course very advisable to growers that they keep their fields clear of leafrollers to the extent possible.
So, questions about export of blackberries should be directed to the USDA Project 796-9699 and questions about the export of raspberries should go to the Santa Cruz County Agricultural Commissioner's office 763-8080.
EGVM quarantine boundary