By Dr. Thomas T. Yamashita
Pierce’s disease—sometimes referred to as Anaheim disease as it was first identified in Anaheim in the mid-1880s—is a disease which wilts and ultimately kills grapevines by damaging and obstructing the xylem, which plants use to transmit water.
The bacteria that causes Pierce’s disease is extremely flexible when it comes to suitable hosts.
The disease is caused by the bacteria Xylella fastidiosa, and is transmitted by sharpshooter leafhoppers and spittlebugs, both of which feed on the xylem of grapevines. X. fastidiosa is responsible for many other plant diseases, including leaf scorch, alfalfa dwarf, citrus variegated chlorosis (CVC), phony peach disease, and olive quick decline syndrome (OQDS).
The bacteria responsible for Pierce’s disease is incredibly difficult to eradicate because, as hinted at by the number of diseases it causes in other plants, it can survive in a number of host species. At last count, there are more than 90 known species of reservoir hosts, in more than 28 distinct plant families. These host species are largely constituted of grasses (Bermuda grass, perennial ryegrass, Johnson grass) and broadleaf species (willow, acacia, almond, blackberry, clover, ivy, cayote bush, stinging nettle).
Detecting X. fastidiosa in reservoir hosts is complicated by the fact that almost all such hosts are asymptomatic. The consequences of this organism are not felt until it finds its way to its desired host.
Pierce’s disease wreaks havoc on grapevines, producing wilting and scorching that progresses into dieback, and ultimately, death.
Transmission of the disease occurs when a leafhopper or spittlebug feeds on the xylem tissues of a plant infected with X. fastidiosa. An insect that picks up the organism will harbor it in the lining of its gut for the rest of its life. There, the organism reproduces, and is transmitted via the insect’s saliva to any future plant that it feeds on.
When a grapevine is infected with X. fastidiosa, it attempts to wall off affected tissues by creating tyloses, growths which serve to dam the vascular tissue to prevent disease-causing organisms from passing through. However, this reaction also blocks off the flow of water and minerals.
The early symptoms of this immune response are wilting and stunted growth. This progresses into leaf scorching, typically from the margins of the leaf, moving inward. As plant health worsens, green islands of immature cane wood become visible, and leaves are aborted, leaving the leaf stems attached to the cane. Subsequently, cane tips dieback is seen, with this being followed by the death of the vine in its entirety.
Pierce’s disease is incurable. Thus, treatment strategies revolve around preventing disease transmission and boosting vines’ natural immune response.
As much as humanly possible, growers should seek to minimize the populations and proximity of likely reservoir hosts. The EU maintains an occasionally updated list of plants known to harbor Xylella fastidiosa, which can be found here.
In addition, attempt to reduce populations of vector species, primarily the aforementioned sharpshooter leafhoppers and spittlebugs. Unfortunately, this is complicated by the extensive flight ranges of these insects, as well as the frequent inadvertent importation of new populations.
This is why it’s also critical to ensure that your grapevines are unattractive, inhospitable hosts by implementing balanced nutritional programs that maximize the plants’ physiological efficiency. When operating at peak physiological efficiency, plants have the carbon and energy reserves necessary to mount defense reactions, known as ‘secondary metabolism,’ in a timely manner, destroying the microorganisms before they can reproduce, or forcing them into dormancy.
Growers can further improve the immune response of their vines by maintaining cooler plant tissue temperatures, reducing the emission of attractive volatiles, and minimizing yellow shading, all of which are attractive to X. fastidiosa vector species.
For further assistance with implementing a nutritional program designed to prevent and mitigate the spread of Pierce’s Disease in grapevines, contact Fusion 360 today by calling (888) 634-3360, or by sending us a message using our contact form.
