Our Chardonnay is about to break buds. It is about 2 weeks ahead of “normal” year, whatever it means at this point…
One of the diseases you need to consider soon after bud break is Phomopsis cane and leaf spot. It causes minor leaf spots, which is more evident to our eyes, but the more critical damage is caused by necrotic lesions on shoots and rachis. It also causes berry rot; however, it is not common with wine grapes because of our spray programs.
(Typical shoot symptoms)
Phomopsis spores can cause infection under the relatively cooler environment (the upper 40s). Thus, springtime rain events are ideal for Phomopsis to produce spores and cause infection. Unfortunately, we do not have curative fungicides for Phomopsis management. Therefore, it is vital to protect young tissues when they come out from the older canes and trunks. Since shoots will proliferate quickly, you may need to spray 1-2 times against Phomopsis, depending on how much rains we receive.
If rain events are coming into the picture after bud break, mancozeb (FRAC = M3, Penncozeb, Dithane, Manzate, etc.), Ziram (FRAC = M3), and captan (FRAC = M4) are useful protective materials against Phomopsis. In a typical year, one or two applications, starting from 1-2 inch shoot length, will be sufficient. After that period, your downy mildew or black rot applications, which happens in the late spring, will cover Phomopsis.
(I would spray at this point, or even a bit earlier, especially if you have an on-going issue with Phomopsis.)
QoI (FRAC = 11), such as Abound and Pristine, as well as SDHI (FRAC = 7), such as Luna Experience, Miravis, and Aprovia, work too. However, you probably don’t want to use them this early in the season because you will need these materials for the latter part of the season to control other diseases. Once again, protection is the only mean of chemical management because no materials are effective after the infection.
Phomopsis typically takes a while to establish in the vineyard. It may take 4-5 years for Phomopsis to become noticeable if you start a new vineyard. However, once established in a vineyard, it is difficult to get rid of this disease. The fungus survives in canes and trunks that were infected in previous years, and it can cause damages to cordons and trunks.
Materials for black rot and downy mildew are often effective against Phomopsis. Thus, the fungicide coverage for these diseases is also working as management of Phomopsis, especially later in the spring and early summer. Some cultivars, such as Viognier, Cabernet Sauvignon, and Seyval Blanc, are more susceptible to Phomopsis than the others.
The other disease that you may need to consider around this time of the year is anthracnose, which is more common with a certain hybrid species. Typical symptoms are black necrotic lesions on leaves, shoots, and fruits, and often time, the black lesion has an ash-colored center, as if you burnt the leaf or shoot tissue with a cigarette. The management strategies will be similar to that of Phomopsis, and in addition to the list above, Topsin-M (FRAC = 1) is also known to be effective. For more information on anthracnose, please refer to this link (Michigan State’s Extension Website on grape anthracnose management).
Beyond diseases, climbing cutworms sneak in around this time of the year. I thought it has been cold enough, but I was wrong… Please check our Pest Management Guide (will open a PDF document) or Doug’s page for the recommendations.