MSU Extension Grapes

By Mark Longstroth, MSU Extension educator

Editor’s note: This article was published in 2002 in response to extreme frost conditions of the season.

As a result of last week's frost, many grape growers are looking at vineyards that will not produce an economic crop this year. Following on the heels of last year's poor crop, growers will not want to spend much money on their vineyards. It is tempting to just ignore your vineyards this season and cut your losses. An important thing to remember is that many of the buds that push now may be fruitful. It is important to get a handle how much crop you may actually end up with. Areas that look like a disaster now may have a marketable crop at harvest. The vines will also be growing wood for next year. With little fruit on these vines, their energy will go into shoot growth. Like last year we will end up with lots of shaded wood that makes for poor fruiting canes. Shaded buds have reduced fruitfulness. In frost-damaged vineyards you need to keep costs down and develop good wood for next year.

I think one of the most important things growers can do is shoot positioning or combing this summer. Positioning shoots outward decreases shading and eliminates running brush. Positioning the shoots downward slows their growth, preventing excess wood development. Lots of growers will be doing mechanical pruning next year to save money and this is very effective on vines that are set up for it rather than a mess you walked away from last year. Combing will also increase the effectiveness of the pesticides that you apply.

Do not eliminate your pesticide program (see also Pest Management in Frost-Damaged Vineyards). The pre-bloom and post-bloom sprays are still vital, especially if you think you might have a crop. Determine your spray needs by scouting in your vineyards for pests and diseases. Certainly in some vineyards with little or no crop we can let foliar pests and diseases take their toll and thereby reduce the vigor of the plants but I think that all of you will need to spot spray some areas in your vineyards where pest and disease pressure explode.

The same goes for herbicides. Stick to your scheduled herbicide applications to keep weeds in the trellis row down. You still want to maintain a clean vineyard. Suckering is expensive and many growers will just burn them off, but this frost does give you a good opportunity for trunk renewal in your vineyards. Many growers will reject this out of hand as too expensive in the middle of two bad crop years. Many of our vineyards would benefit from this and you might choose one or two vineyards to improve this year. You might make back your losses later with increased yields.

Many growers will cut back on their fertilizer program. Most growers have already put on part of their nitrogen and all of their potash. I do not see a reason to put on more nitrogen after last year's growth and what looks like two years of light crop. I would recommend applying nitrogen only and only to vineyards where shoot growth is poor. I do not see a need for other nutrients.