- Posted By: Mark Bolda
- Written by: Mark Bolda
I was taken to several raspberry fields today to investigate an unusual and rather concerning plant disorder. As one can see from the pictures below, leaves were significantly yellowed, with an abrupt change without regard to leaf venation from yellow to green in many cases. Some leaves had fallen off, and severely yellowed leaves fell off at the touch. Within the field of yellow, there were many spots of green. The undersides of the leaf were showing the same, but with the addition of fluffy orange spots throughout. The symptoms were widespread and affected the lower quarter to third of nearly every plant in the visited fields. Clearly, this was fungal but the question was what fungus?
The literature does admit that downy mildew can occur on raspberries and even result in yellow discoloration. However, this disease is always marked by purple blotches on the upper side of the leaf, and fluffy mycelial growths on the underside of these very spots. Microscopic evaluation of several infected leaves today gave no sign of the telltale bunches of mildew mycelia and sporangia masses. This disease is definitely not downy mildew, since few of the symptoms are consistent with this pathogen.
Rather, and this can be seen from the photos below, the masses of orange to yellow spores on the undersides of infested leaves had were typical of the rusts, and in many more advanced cases one could find the diagnostic teliospores of Phragmidium rubi-idaei, the causal organism of yellow rust.
The extent of leaf yellowing in the pattern depicted below is unusual. Especially the sharp demarcation of green to yellow. Short of the defoliation, the literature does not refer to yellowing of the leaf in association with yellow rust infestation. This bears watching.
Growers report that these symptoms have appeared very rapidly, and have advanced significantly over the past few days. Rust spore germination is contingent on water, so that we have had a significant rainstorm followed by mostly cool weather since has a lot to do with the severity of this current epidemic, in my opinion.
The rusts are controlled by a reduction of moisture. One way is of course to increase air circulation in the hedgerow, but even better is the use of tunnels which sharply reduce the humidity on and around the plants. The fungicides Rally and Pristine are registered and very effective against rust. Organic growers have access to fixed coppers and oils. All of these materials can reduce fruit yield if used excessively and too early on sensitive developing plant tissue, so growers should not strive to eliminate rust from the hedgerow with repeated fungicide applications, but rather just limit it's spread to the upper foliage where flowering and fruiting is going on.
There are several fungicides mentioned for management of rusts in this article. Before using any fungicides, 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.
There have been now two field closures over the past week in the Watsonville-Salinas berry production district, and the following is meant to make some sense to growers for what to do to minimize losses in the event of a leafroller larva detection.
USDA inspectors are not agriculturalists, nor pest managers for that matter. We in the industry should be aware that they are bound by a set of rules that at times may seem at odds with sound pest management, but it yet is incumbent upon us as professionals to work with them and come out with the best solution for both parties which is the elimination of leafrollers and re-opening of the field with as little impact to the normal management of the field as possible.
Growers should be aware that outside of the USDA inspections taking place monthly at each cooler, fruit sent for export out of the USA is being sampled and inspected by county personnel. They have long done this to look for pathogens and other insects and recently this repetoire has been including leafroller larvae. On finding a suspect larva, the county inspector forwards it to USDA inspectors, who will make an identification of the larva if possible at the cooler and also forward it on to the DNA identification laboratory in Sacramento. The process from find to absolute positive identification at the DNA lab is about a week, but can take longer in the case of very small larvae or pupae.
It appears that growers are advised of a possible LBAM find on the same day, and a hold is put on the source field. Inspectors will pay a visit to the hold field to find larvae, which they inevitably do. Now, the grower has the option of re-routing fruit from the field under the hold order to clients within the quarantine area or destroying it. Both have happened this last week. It is truly tragic when another market cannot be found for fruit, but such is the nature of this quarantine.
Once advised of the hold, arrangements are made to have inspectors observe a pesticide application of the infested field with the purported goal of controlling LBAM. In the interest of time, the process of arranging a pesticide application and field re-inspection is allowed to move forward even in the absence of a full positive identification for LBAM. Time of initial suspect LBAM find to time of observed spray seems to depend on a number of factors, but generally happens within a week.
In berries, the list of allowed pesticides for inspector observed, mandated sprays is unfortunately rather short. For strawberry growers, fortunately Intrepid, Entrust and several Bt formulations are included, but notably Coragen, Success and Radiant, which are highly effective and actually have light brown apple moth on their labels along with being pretty soft on beneficials and the surrounding environment, are not allowed. Instead, we are additionally allowed crude materials such carbaryl (7 day pre-harvest interval, pollinator caution, devastating to beneficials), and chlorpyrifos (21 day pre-harvest interval, seriously harmful to beneficials). A superior type horticultural oil is allowed, but only at a minimum rate of 1% volume to volume, which for a petroleum distillate is pretty risky in sensitive crops like strawberries or caneberries.
Once the approved pesticide application is done, arrangements are made to have the field re-inspected in the interests of confirming that it has been cleared of leafroller larvae and re-opening it. This is a rather important point for berry growers, because when this happens depends on what material that has been applied. Based on our experience, inspections have been taking place one day after an application of Entrust, and more than several days after Bt formulations. If you are willing to take a chance of burning your plants and fruit, the superior type oils also are supposed to give one day. Intrepid and Confirm as insect growth regulators (IGR's) are known to act more slowly so again garner a re-inspection after more than a few days.
It seems in light of all of the above, the strategy that berry growers should be taking in relation to leafroller management should be as per the following:
1- Keep fields clear of leafrollers. Period.
2- In the unfortunate event of a possible LBAM find and hold on the field, spray the field IMMEDIATELY with the very effective and labeled materials such as Coragen or Radiant in strawberries and Delegate in caneberries. By doing so, you are giving these materials time to act in full while you make arrangements for inspections and sprays with the USDA.
3- Make arrangements for mandated spray with the USDA.
4- Make application of Entrust since you should be able to get inspectors in the next day to confirm that it has cleared the field of leafrollers.
5- Undergo inspection from USDA to re-open field. Note that your spray of the better material from the day of the hold will now have taken full effect along with the effects of the Entrust, and you should by now have dramatically reduced, if not eliminated, leafroller larvae from your field.
There are pesticides mentioned for management of leafrollers and light brown apple moth 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.
The pictures below are of a sample submitted today of physical damage to raspberry cane. Apparently this problem occurs across all varieties and areas more or less to the same degree.
Closer inspection of the affected canes reveals that the brown areas are very thin and indeed when one peels it back with a razor blade it is no thicker than a millimeter or two. There is no damage any deeper, nor are there signs of fungal or bacterial infection of any sort.
The diagnosis of the problem is that this was caused by a period of unfavorable weather, perhaps wind, sun or cold. Since it is being described as being distributed so evenly across different varieties, it must be something that imposed itself from without at the same magnitude, of which unfavorable weather can really be the only one.
That said, this issue certainly bears watching, and if it becomes worse I would appreciate readers bringing in some samples or calling me out to the field.
4/26/2011 Update: It seems further visits to the field turned up a large number of snails, probably stemming from the high levels of moisture we have experienced of late. The damage seen on these laterals would be consistent of course with the scraping feeding of snails. If one is concerned about the level of damage, there are baits for snails, but the current warming trend and drier weather is going to do much to reduce their numbers as well.
The use of carfentrazone (Shark) has recently become popular for suppression of primocanes in raspberry. It is a good option for growers because it is substantially less expensive than the standard hand pruning and also a lot safer and more effective than gramoxone (Paraquat).