The 2017 growing season has officially started as vines are budding out. As we go through the next couple of weeks, it is important to realize that some potential pest and disease problems require early season sprays. The first is Phomopsis, a major problem on many grape varieties in the Midwest. Mancozeb should be applied starting at 1-3 inch shoots and repeated each 7-10 days, especially prior to a predicted rain event. I recommend spraying at a dilute rate of 1 to 1-1/2 lb per 25 gallons of water. This is equivalent to the labeled rate of 1-1/2 to 4 lb per acre (100 gallons). But since there is so little foliage now (small target) thorough coverage is possible with lower volumes. Shut off nozzles except those pointed directly at the cordon. This will also help growers avoid using more than the season maximum amount allowed of 24 lb.
Macozeb sprays are very effective at controlling Phomopsis. Liquid lime sulfur, Sulforix, and fixed copper (copper hydroxide) is also effective. A single application at bud swell can provide a significant degree of Phomopsis control (a 50 to 60 percent decrease in disease severity on the grape leaves as well as clusters), but will not reduce the need for mancozeb sprays for Phomopsis control during the early part of the growing season. However, it might provide additional control where the disease has been severe. And if anthracnose is a problem (see below) then this is a good spray. It is important to recognize that sanitation is part of a Phomopsis management plan. Prune out dead canes and stubs as much as possible since they are the main sources of Phomopsis spores.
Anthracnose is a less common disease, but one that we are seeing more frequently. This may be due to warmer weather or susceptibility of new varieties. We have seen that Frontenac and Marquette are very susceptible to anthracnose, as is Vidal. A delayed-dormant lime sulfur or Sulforix spray is very effective against anthracnose. This application goes on as buds are swelling, but before leaves are exposed. While sulfur and copper can be toxic to certain varieties, there is minimal chance of phytotoxicity if the products are applied at bud swell, just prior to bud break.
Grape Flea beetle and climbing cutworm can be problems in some vineyards. Grape flea beetle is more common in Indiana. Scout vineyards for this pest and its damage, (holes eaten into swelling buds) or look for adult beetles. If more than 4% of the buds show damage, apply an insecticide to prevent further damage. Carbaryl (Sevin) is generally recommended, but other options are available.
Each of these problems needs to be controlled during the first few weeks of the season. Don’t wait until you see Phomopsis and anthracnose show up to start spraying. These diseases must be controlled preventatively.
See the 2017 Midwest Fruit Pest Management Guide (https://ag.purdue.edu/hla/Hort/Pages/sfg_sprayguide.aspx ) and Midwest Small Fruit Pest Management Handbook for a complete discussion of grape pest management.