Figure 1: Young almond tree killed by Phytophthora syringae. |
This year, Phytophthora syringae infections have been quite common. This is most likely due to the long, cool wet spring. Many new orchards have seen 3% or greater infection rate, especially in the variety Nonpareil. Figure 1 shows symptomatology of a tree affected by P. syringae. Leaves on these trees are lesion free, but tend to dry up, becoming crispy. Trees are not always killed, but they may be stunted in comparison to other trees within the orchard. Examination of the trunk will typically yield amber “gumballs,” which often mark the edge of the fungus canker (Figure 2). When the bark is removed, the canker becomes visible (Figure 3). This disease has been observed frequently, and is commonly referred to as “bundle rot.”
Figure 2: Amber colored “gumballs” caused by tree infection with Phytophthora syringae. |
Although common this year, infection by P. syringae does not typically cause such a large problem. When temperatures warm above 75F, the fungus within the canker dies, and the affected area heals over as the tree resumes normal growth. Weather this year has been very mild, with few days above 75F.
The fungus infects the trees through wounds that occur from digging, processing, delivering, planting, and rough weather. Upon infection, the fungus may remain latent until the tree breaks dormancy. If conditions remain favorable, the fungus continues to grow, eventually killing the tree. Most likely, we do not have a higher amount of this fungus within the orchard in comparison to any other year, but rather that the current cool and wet environmental conditions are promoting fungal growth, causing an increase in observed incidence.
Figure 3: Bark removal shows fungal canker of an almond tree affected by Phytophthora syringae. |
If tree loss or damage occurs within your block due to P. syringae. It is better to remove and replant if the the tree is dead, severely stunted, or if the trunk has been partially killed. It is advised to call your nursery as they often are willing to help with tree replacement. Some trees may be marginally affected. It is advised to keep these trees in the ground because as the temperatures warm, the fungus will die and the tree will recover. It is not advised to spray phosphanates or other anti-Phytophthora products in attempts to prevent tree infection.
jjgross
January 17, 2012How effective is Ridomil at controlling phytophthora and which is the best method of application?
The Almond Doctor
January 17, 2012Ridomil is very effective in controlling Phytophthora. Since Phytophthora, however, has continual recombination of its genetic material due to sexual reproduction, localized populations become resistant to Ridomil relatively quickly. Although, there is no hard evidence, observations suggest that the product works for 2-3 years at the most when using in perennial crop environments. It is a great tool to use when there has been a bad outbreak of Phytophthora. The product needs to have direct contact of with the fungus in the rootzone, and should be applied as a drenching spray to the soil.
The use of Phosphonates have also been shown to be effective on Phytophthora. These products are applied foliarly and have the greatest reduction of disease when applied in the fall.
Cathy
November 17, 2018Hi,
I am an almond grower in Australia and was hoping you may be able to help me?
This year i received a large number of year 1 trees from a nursery that were infected with Phytophthora syringae sp. I noticed it first in the non-pariel within 2 weeks of planting and was able to replace almost 50% of these straight away. I then started noticing it in the monterey and the carmel but it was then too late to replace these trees this year. (all trees were on nemaguard)
It has been found since that the source of the disease was the water that the roots were washed with from the nursery that was a requirement for interstate movement of trees. Two other properties also received these trees and have the same problem.
The infected trees are mostly growing well – but i have cut quite a few at the canker infection and in some cases there is only a small amount of living tissue feeding the top of the tree. I still have trees dying as the tree can not support the growth.
I have cut some trees back to underneath the infection to try to regrow the tree in the orchard – some are growing well and some are not.
I feel that the trees with the cankers are going to always be affected and not produce the same as healthy tree could?
Should i be pulling all trees out that show they have had the infection and replace them?
Could potentially all the trees i have received be infected and i may see further death in years to come?
Even the 50% of non pariel that i replanted would have been washed with the dirty water but had not been stored so had not had the same conditions for the phytophthora to infect the tree but is it now potentially in my soil and if the right conditions occur those trees could also be infected?
My orchard was virgin soil prior to planting. Could potentially every tree now have this in the soil?
Any information you could give me would be very appreciated,
Thanks and Regards,
Cathy
David Doll
December 5, 2018Cathy,
These types of infections with this species of Phytophthora tend to heat cure, meaning that they die out as the temperatures increase. This of course, is assuming that the tree survives the infection. If the tree hasnt been killed or lost a significant part of its trunk, it should be okay.
The almond scion is susceptible to P. syringae, while the rootstock tends to be relatively resistant. I wouldnt worry about it spreading from the soil to the tree – that has not been observed in California in normal conditions.
David