This past Monday, while prepping the Aglianico block for netting, I noted an Aglianico vine in the first row with a shriveled cluster. This vine has no other signs of Pierce’s disease: it is no less vigorous than others in the block, it has no irregular cane lignification and no leaf scorch.
Last week, I noted another Aglianico vine (#5 in the same row) with scorched leaves. Yesterday, I found this vine to have irregular lignification as well as possible early shrivel of a cluster.
Pertinent Past History:
In their fourth leaf, these vines have received little Pierce’s Disease prophylaxis, despite high sharpshooter activity.
During the 2011 season, the vines were sprayed with kaolin. I planned to install a mazzi injector and start systemic imidalcloprid treatments. Unfortunately, my baby daughter Olivia, passed away just about this time last year. Grieving and caring for her surviving twin brother left little time and energy for vineyard work.
Confused if I can or cannot tank mix sulfur, kaolin and surfactant for a single application – and again strapped for time – I did not apply any kaolin this year. During this spring and early summer, Glassy-Winged Sharpshooter activity was very high in the canopies.
Sticky traps placed in previous years did not catch any sharpshooters in nearby citrus trees. Nearby Oleander bushes do not exhibit any leaf scorch.
Of possible note are the facts that I pruned late this year, the Aglianico budded much later than last year and vigor appears to be lower than last year (to counter the latter, I did not put down any fertilizers this past winter, the 2011-2012 winter was very dry and I moved irrigation emitters away from the trunks after fruit set).
First, let’s examine vine #7, row 1:
The rows slope upward slightly towards vine #8 (and vines #9 in higher rows). So vine #8 gets slightly less water. Nevertheless, the canopy of vine #7 is no smaller than that of other vines in its row.
The affected cluster was located opposite another, unaffected cluster on the same cane. There was no evidence damage to the rachis and shrivel was fairly uniform with dark berries more raisined than green ones.
The solitary shriveled cluster was the only worrisome sign observable. No patchy lignification or leaf scorch are present on vine #7.
By comparison, vine #5 exhibits prominent, concentric leaf scorch
While the clusters on that cane have a lot of shatter, there is no clear evidence of shrivel. It may be that some of the berries towards the apex of the cluster are beginning to wrinkle:
Finally, the affected cane is showing patchy, irregular lignification (maturation):
Which of the following is most likely the cause of the shrivel and scorch?
- A) Pierce’s Disease (very likely, given the irregular cane lignification).
- B) Water Stress
- C) Post-powdery mildew infection leaf damage.
- D) Chemical burn, secondary to excessive sulfur sprays
Per the UC IPM website, there are four criteria to diagnosing Pierce’s Disease:
- leaves become slightly yellow or red along margins in white and red varieties, respectively, eventually leaf margins dry or die in concentric zones;
- fruit clusters shrivel or raisin;
- dried leaves fall leaving the petiole (leaf stem) attached to the cane;
- wood on new canes matures irregularly, producing patches of green, surrounded by mature brown bark
My two vines exhibit three of the four criteria. It may just be too early in the disease process to see symptom #3.
The web paged linked above gives an overview of the pathology of Pierce’s Disease. The causative agent is Xylella fastidiosa, a bacterium spread by several species of sharpshooters in the same way mosquitoes spread malaria or a number of viruses.
The dominant species in Southern California are the Glassy-Winged Sharpshooter (GWSS) and the Smoke Tree Sharpshooter. Specimens caught in my sticky traps have been confirmed as GWSS.
As with Malaria, Pierce’s Disease is best controlled by eradicating the vector of the causative microorganism. GWSS produces two generations per year. The following is a summary of its annual cycle:
- overwinters as adult on citrus and other non decidious plants
- moves to deciduous plants in January and February
- first generation eggs as early as February, but most in late March and April
- nymphs hatch in 10 to 14 days, feed on the leaf petioles
- first generation adults begin to appear in May through July
- second generation eggs laid between mid-June through October
- second generation adults appear July through November
Needless to say, I will keep watching these and other vines for the rest of the season. These two vines will most likely be pulled and replaced this winter.
I will also have to monitor for GWSS activity starting before netting. The quandary is how to treat the vines when there is ripening fruit on the canes.
I have not mentioned my daughter’s death on this blog before. Maybe I’m struck by an irony that three days before the anniversary of her death, I discover confirmation that at least two of the vines into which I’d invested four years of hard work are going to die.
If I may have a moment of self pity and frustration, I’d like to say: