Early Season Grape Disease Management Reminders

Phomopsis cane and leaf spot

One of the diseases you need to consider soon after bud break is Phomopsis cane and leaf spot. It causes minor leaf spots, which are more evident to our eyes, but necrotic lesions cause more critical damage on shoots and rachis. It also causes berry rot; however, it is not common with wine grapes because of our spray programs. 

The Phomopsis pathogen requires water for infection, and Phomopsis spores can germinate in a relatively cool environment (the upper 40s). This pathogen produces spores in spring from previously infected canes and cordons. Thus, springtime rain events are ideal for the development of Phomopsis. It is vital to protect young tissues when they come out from the older canes and trunks because we do not have any curative fungicides against Phomopsis. This disease typically takes a while to establish in the vineyard. It may take 4-5 years for Phomopsis to become noticeable after you start a new vineyard. However, once established in a vineyard, getting rid of this disease is difficult. The fungus survives in canes and trunks that were infected in previous years, and it can cause damage to cordons and trunks. In other words, this disease can cause long-term damage to cordons and trunks. Some cultivars, such as Viognier, Cabernet Sauvignon, and Seyval Blanc, are more susceptible to Phomopsis than others.

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. Since shoots will proliferate quickly, you may need to spray several times against Phomopsis, depending on how much rain we receive. One or two applications, starting from 1-2 inch shoot length and repeated seven to ten days apart, are sufficient in a typical year. After that period, your downy mildew or black rot applications, which happen in the late spring, will cover Phomopsis. 

QoI (FRAC = 11), such as Abound and Pristine, and SDHI (FRAC = 7), such as Luna Experience, Miravis, and Aprovia, are effective too. However, you probably will need these materials for the latter part of the season to control other diseases (e.g., ripe rot and bitter rot). 


The other disease you may need to consider around this time of the year is anthracnose, which is more common with certain hybrid species. Typical symptoms are black necrotic lesions on leaves, shoots, and fruits, and often, 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. 

Downy mildew

Downy mildew has become one of the most problematic diseases for us in the past several years. Especially if you had an outbreak in 2022, you might wish to tighten up your spray schedule so that you can protect your vines better. Some people refer to the three-tens rule, 10 cm shoots, 10 mm rain, and 10 C in temperature (4 in, 0.4 in, and 50F) for the initial spray timing, which means that we need to spray soon after bud break for us. (This rule may make more sense in arid regions.) This will give us another reason to spray for Phomopsis so that the same spray covers for downy mildew.

Protective materials for downy mildew are Mancozeb (FRAC M3) [Gavel has mancozeb + zoxamid (FRAC 22)], Captan (FRAC M4), Fixed copper (FRAC M1), Revus or Forum (FRAC 40), or Zampro (FRAC 40 + 45), or Ranman (FRAC 21)). NOTE: there are increasing cases of Revus-resistant downy mildew isolates in VA. Plus, resistance to Ranman is known among downy mildew pathogens of other crops. Kick pack materials are phosphonate (Phostrol, Prophyt, etc. FRAC P07) and Ridomil products (FRAC 4).

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