Approximately 100 vines in the vineyard are showing troubling signs: dormancy; stunted growth; dried baby shoots; discolored yellowish leaves. Managing a vineyard requires being a sleuth to discern what's going on. Four cases, with accompanying photographs, are discussed below. (Click on the photos to enlarge.)
Case #1. Two blocks of 3rd leaf Petit-Sirah vines (about 50 plants) are not putting out shoots along the cordon. To paraphrase Monty Python, are they dead or just resting? It's late in the season for them not to have budbreak. At first, I thought we had burned the vines by applying too much lime sulfur mixed with organic JMS Stylet oil during their dormant spray. (Repeat, the vines were dormant, no green showing when we sprayed in winter.) Pete Anderson, who teaches vineyard management at Mira Costa Community College, assures me that is impossible. (On the other hand, in our backback sprayer the sulfur concentrates at the bottom and I'm sure these vines received an extra fortified dosage.) Pete asked me to clip the "deadwood" of the vines back to see if they are alive, and when I cut the ends of the cordon, I find that the sap is flowing. The vines seem to be alive, and shoots are coming out from the bottom of the trunks. Pete said another possibility is Pierce's Disease (PD), but to my understanding, to test for PD you need leaves, and these vines are not putting out leaves (except some new shoots at the base). At first, I didn't think PD was likely for this block, because it wasn't an area where we had seen many glassy wing sharp shooters (GWSS), which are vectors for the disease (plus, we had administered AdmirePro in the spring to ward off the GWSS). Could a pair of gophers have wiped out the vines? I began to see PD as a real possibility, so I called the San Diego County Dept. of Agriculture and left a message. My call was promptly returned (excellent customer service!) by Ms. Pat Nolan, an expert on PD whom I had heard give an engaging, authoritative lecture on PD at Mira Costa Community College last year. Ms. Nolan suggested I dig up a whole vine with roots intact so that she could run some tests to see what's bothering it. (The picture at left shows the spot where the sacrificial vine came from -- along with its colleagues down the row with no leaves). Mateo dug up the vine in protest saying it was healthy. I drove the vine down to the county office and dropped it off for Ms. Nolan's department to conduct the autopsy.
Case #2. Similar to the above, except that the vines are not dormant. They have put out shoots. However, many of the shoots have wrinkled leaves and are not vigorous. And, the leaf color is not as deep a green as healthier cousins. A whole block (30 vines of Petit-Sirah) looks similar to this. I invited Matt Hand of Southern California Entomology, a disease expert, to come and inspect. He suspects PD, but to be sure, he suggested we test it. I took leaf samples from this vine (shown at left) and brought it to the County for evaluation.
Case #3. Case three involves a row of Tempranillo vines which is the most vigorous row in the vineyard as it is at the bottom of the hill where there is actually some top soil, and, some vines may have tapped into the nutrients and moisture of the leach field. Of 25 vines in this row about 20 are impacted. The signs are little growth (which Mr. Hand calls "witchbrooming"), uneven growth (with shoots concentrated at the center of the vine and not pushing out the ends) and discoloration (which Mr. Hand calls "chlorosis"). This was an area of heavy sharpshooter concentration at the end of last year's growing season, and Mr. Hand strongly suspects PD. I'm preparing the chain saw to cut them down and a crew to dig them out and placing an order to Novavines for replacements. I sent a sample of leaves from the vine shown at left to the County for analysis, just to be sure. (PD can be transferred from an infected vine to a healthy vine by sharpshooters; hence the need to remove infected vines from the vineyard.)
Case #4 is not as clear cut. This involves the Grenache block on the opposite side of the vineyard. Very few sharpshooters have been observed in this area. Yet, to borrow a phrase from Sesame Street, "some of these vines are not like the others." The vine at left is showing slightly off colored leaves, and some very weak shoots. Could the small dead shoots be caused by too much wind? Did compost I place around the vines in Winter rob them of nitrogen? Has a dodgy gopher been attacking the vine unknown to us? Is the vine not getting enough nutrients? Concerning nutrition, it's almost time to take a petiole sample to conduct an analysis of the vine's uptake of nutrients, which is done when the grapes are "flowering." Meantime, to find out if PD could be the cause, I took a sample of leaves from this plant and sent it to the county.
So, you want to be a farmer?