Late October in the vineyard regions of California is a beautiful time- in between the summer heat and the winter rains, we have lovely, sunny days with temperatures hovering around 70 degrees. Especially beautiful is our version of the East Coast autumn, the vineyards aflame in a wide variety of colors- purple, red, rust, brown, orange, yellow or a variegated combination of those colors. While the vibrant autumn colors are a treat for our eyes, they are somewhat of a trick on the vines themselves.
So, a question that we are frequently asked is “do those beautiful colors mean anything- perhaps represent different varietals?” The answer is, with the exception of the varietal Alicante, in a healthy vine, the leaves go from deep green, to pale yellow, then light brown before falling to the ground.
Notice I said “healthy”- which means the vines with all of those different variations in color are stressed to some degree. Red, purple, rust, black, orange, etc. are usually the result of either nutrient deficiency, viral infection, or a pest species (hmm, sounds like the same things that stress me out during the fall) that has influenced the vine during the growing season.
Nutrient deficiency occurs when certain macro and micro-nutrients, such as potassium, nitrogen, phosphorous, magnesium, and calcium aren’t in ample supply in the vine- and each will have their own “colorful” symptom. Viruses are another culprit, one of the most notorious being the leaf roll virus, which causes a deep, dark red color with yellow veining (yeah, I know, beautiful) in the leaves, with the distinctive curling under-from which the virus gets its name. Esca, a type of root rot, produces multi-hued variegated leaves- horribly beautiful- or beautifully horrible. On the pest front, mites can cause late season damage, causing a bronzing effect on the leaves. Determining what exactly is going on in the vine is a bigger trick still as it can be hard to determine what is nutrient deficiency and what is viral or fungal infection since many of the symptoms of both overlap. For example, color-wise, the leaf roll virus in a vine presents the same way as if it had a magnesium or iron deficiency- so is the color the beginning of leaf-roll or a more easily treated nutrient deficiency? Add in the fact that red varietals may present symptoms of the same issue differently than a white varietal and you have a very tricky situation.
Have I put the fear of fall into you yet? For all the doom and gloom, it’s not the end of the world- many of the viruses and pests can be lived with and nutrient issues can be reversed if the correct diagnosis and actions are taken. The key is to have a highly knowledgeable and experienced viticulturist staying on top of things in the vineyard. Just so happens, we have one at Naggiar, and he’s a pretty darn good winemaker as well-sounds like a treat to me.