- Posted By: Mark Bolda
- Written by: Mark Bolda
In a conversation with a Pest Control Advisor colleague the other day, we discussed the merits of lime sulfur applications in the fall on blackberries grown in the Pajaro Valley. This is something I have spent considerable time thinking about and have come around to believe, that while not completely supported by empirical evidence, fall application of lime sulfur might not be necessary in our blackberries and is to some extent an artifact of past varieties and practices.
Here is why I maintain fall applications of lime sulfur might not be necessary in blackberries:
1- Redberry mite is not controlled by fall lime sulfur. It is rather controlled by post - bloom applications of horticultural oil or sulfur. This is a fact and has been tested.
2- Lime sulfur used to be critical to control cane and stem rust, Keuhneola uredinis, on the trailing Ollalieberry and continues to be very effective when applied for this disease on that variety in the fall. However, none of our current Arkansas varieties (Apache, Navajo, Choctaw and so on), nor are the proprietary suite of varieties known to be susceptible to this rust. I have yet to see it on the primocane bearing PrimeArk either. I did see a touch of orange rust on a proprietary variety last year, but this rust is not controlled by lime sulfur.
3- Do a mental exercise to test the thesis that fall lime sulfur "cleans up" the remaining blackberry cane in the fall. Mites? Not a great material for these, ditto on whitefly and aphids if they are even around. Quite effective of course on powdery mildew (NOT downy mildew), but again this pathogen is better addressed in my mind a little later in the season when the leaves emerge and fungus more active.
I would enjoy very much for someone to prove me wrong and leave replicated strips untreated with lime sulfur and see what happens next year. I believe this would be useful demonstration and quite possibly a beneficial exercise for the industry as a whole.
The use of lime sulfur is discussed extensively in this article. Before using lime sulfur or any of other pesticide, check with your local Agricultural Commissioner's Office and consult product labels for current status of product registration, restrictions, and use information.
- Author: Mark Bolda
This article is to share some information regarding orange rust in blackberries on the Central Coast. Apparently, this fungus was detected last year and it continues to spread. Previously only seen in some local plantings of Chester blackberries it has now been found on several occasions in proprietary blackberry plantings. Orange rust is a tough disease to deal with, so it is worth being able to identify and knowing what steps one needs to take to mitigate its spread.
Orange rust is caused by two fungi, Arthuriomyces and Gymnoconia which are distinguished by the shape of their spores and life cycle length. Their growth is favored by cooler temperatures and high humidity. While it is not common that orange rust infected plants die outright, their ability to produce fruit is severely compromised.
As readers can clearly see in the photos below, orange rust is hard to miss in the field. From further away, infected canes have a spindly appearance and on approaching one will see the upper leaf margins of both primocane and floricane framed with the distinctive orange of the fungal infection on the underside of the leaves.
Of all the rust fungi that we deal with in caneberries on the Central Coast, orange rust is unique in that it grows systemically in the plant, meaning that the most important management tool for growers dealing with an infestation of orange is a shovel. There is no effective fungicide for orange rust. Infected plants should be removed entirely, meaning all canes, leaves and the roots. This is best done before the pathogen spores are ready to be spread by rain and wind in mid-April through May.