John Marshall: Spring Pruning and Frost Protection
As I write, it is easily the warmest March in my lifetime. In fact, it is seems like the warmest winter in history. I was watching the weather the other night and the weatherman was reciting data that suggested this was the eleventh warmest winter on record. I recall thinking the other 10 must have been before 1945 because it has been easily the warmest winter in my recollection.
It has been great pruning weather but is both gratifying to enjoy and terrifying to consider, what a spring as warm as this one holds for us. Two years ago we began getting 60s and 70s early in April which culminated in the Mother’s Day frost that reduced the grape crop in Minnesota and pretty much all across the Midwest. This year we are seeing those conditions early in March, fully a month earlier. It is clearly unprecedented conditions that we are seeing and how to handle them is an open question for all of us.
The MGGA list serve has been full of reports of dripping pruning cuts and, down south, emerging buds. There has been extremely interesting commentary within the list serve on crop oils and Sodium Alginate and some other formulations to delay bud break. However, most of these giveus a bud delay of 5-7 days. One even suggests a delay of 20 days or so. With buds coming in mid-March, or soon thereafter, a delay of even 20 days may hold buds back until the first week of April or so.
Truck farmers around my boyhood home on the outskirts of St. Paul, growing vegetables for the St. Paul Farmers Market, held back planting their tomatoes and other frost vulnerable crops until May 15th, even in a warm spring. This was the traditional time when the danger of frost was mostly past, but this is still two months away. A budding delay of 5-7 days or even 20 days seems like too little, too early.
On a practical level and given that the applications are “very messy” and some have to be reapplied after every rainfall, these solutions do not seem feasible. Moreover, some crop oils are seen to cause bud mortality when applied in too strong a mixture or at the wrong time. If we were at mid-April or so, instead of mid-March, these practices would offer important protection. Although I am thankful to have these techniques brought to attention, they do not seem to offer growers what they need in this particular season.
My recommendation is to delay pruning until the buds are actually beginning to emerge. This practice has been seen to delay bud emergence of the buds near the cordons and trunks. These are the buds that will be kept to develop the crop, the “count buds”. Some growers prune long, thus leaving extra buds so that once the end buds begin to emerge they can go back and make their final pruning cuts. While this does involve some extra pruning expense this second pruning goes quickly. It is widely practiced where spring frost damage is more common. When the end buds begin to swell, it is time to begin or finish your pruning.
If it looks like there will be frost once the buds are emerged, the Agro-K Corporation sells a foliar fertilizer called KDL (Potassium, Dextrose and Lactose). It is widely used to help correct a mid-season Potassium deficiency and to improve low sugar levels on grapes that are beginning to ripen. In regard to spring (and fall) frost protection it offers dramatic protection to foliage during such an event. It is not “messy” to apply and does not have any danger of bud mortality. Moreover it does not have to be reapplied unless there are repeated frost events some days or weeks apart.
Agro-K recommends applying it at about 1 gallon/acre about 24 hours before the frost event is likely to occur. However, it has been seen to offer excellent protection on both strawberries and grapes, even when applied a few hours before the frost event occurs. Given this amazing feature, one grower who spent his life as a chemist, theorizes that it is possible that the Dextrose and Lactose serve as anti-freeze and that the Potassium element may not be the active ingredient in frost protection. Be that as it may or may not be, KDL has been seen to be highly effective and it is what we will be using this spring if the need arises.
Even with the danger of spring frost hanging over our heads, it is still going to be necessary to complete your spring vineyard chores. If you use herbicides and did not get your Glyphosate (Roundup) down last fall better get it down before the buds and suckers begin to emerge and this is likely to be soon. Glyphosate is very hard on vines if there is green foliage particularly suckers growing. Spraying them with Glyphosate will damage the vine as a whole. Once growth begins it is too late to use Glyphosate but you can use a “burnback chemical” like Rely that will burn off young weeds and suckers, but unlike Glyphoste has no systemic effect and thus leaves the vine as a whole undamaged. Rely can be applied at intervals, as needed, all summer long.
It is also time to go around the vineyard and replace broken or rotted posts, replace missing staples and tighten the wires that may be slack now that the weight of the vines are much reduced from pruning. Pruned vines need to be retied to the trellis and canes, trunks and cordons need to be checked and retied. As long as you’re going around the vineyard checking each vine, it is a good time to be sure that the ties holding trunks and cordons in place have not grown too tight and are beginning to girdle the vine. Young vines should be tied to trellis wires loosely so the trunk has room to grow. Even so, as time goes by, some will begin to grow into and even become tight around the trunk and cordon. If you see a trunk beginning to bulge just at the tie, this vine is in danger of being girdled with the top dying or even breaking off on a windy day. Tight ties need to be cut loose and another tie made that is much looser. This is an important job that is easy to overlook. When the vines are young it does not need to be done but as your vines mature and trunks thicken, it is a valuable chore that does not take much time but is well worth doing. You may be surprised at how many ties need to be cut off and retied.
In addition, it is a good time to settle upon a spray program. Buy the chemicals you will need to carry it on well before you may need them. I am often so busy in spring I tend to forget to make these arrangements until it is almost time to make my first spray. A delay in your first spray can be costly, for as they say, “An ounce of prevention is worth many pounds of cure”.
If you had a serious disease problem last year a dormant spray of lime/sulfur is worth doing. However, with so much early warmth this year, growth will begin soon and if you feel you need a lime sulfur spray it is likely you will need to do it soon. Lime/sulfur also burns back and damages buds and leaves and so is best applied at full dormancy which is likely to be over very soon. You can still do a dormant spray even after growth begins but the lime/sulfur needs to be mixed at lower concentrations then and thus has lower effectiveness. Read the label carefully with lime/sulfur. It is hard on eyes and needs to be handled carefully and is very corrosive, so clean your sprayer thoroughly when finished.
In general, start your spray program early and look upon it as a preventive program. Regular early sprays will keep the vines clean for the first few weeks of summer and this will pay dividends all season long. Purchase and use a sticker/spreader additive. It is a surfactant that will break up the surface tension of water in your mix and allows the drops that form to be much smaller and thus coverage much more thorough. Fully as important it will make your chemicals, once applied and dried on the foliage, insoluble in rain and thus effective even if there is a good rainstorm. In fact, the sales people used to say the force of the falling raindrops actually tends to rearrange the dried spray and so “respray” the vines each time it rains until the effectiveness period of the spray material ends.
I can definitely use a good crop of grapes this year so it is with anticipation that I wait the outcome of this unique and actually bizarre spring weather. I pray for the effectiveness of KDL, the rain in due season and the sun to shine upon the rich and poor alike.
Watch your vines and take care! – John
This story was reprinted by permission of the Minnesota Grape Growers Association (MGGA) and first appeared in the Spring issue of MGGA’s “Notes from the North.” Midwest Wine Press is proud to be a member of the MGGA. Please visit their website at mngrapegrowers.com