The vineyard fertilizer status of this element is sort of controversial. The picture to the left is from the cover of a Univ. of California publication - California Agriculture. It is labeled phosphorus deficient Cabernet Sauvignon leaf. The red flecking of the upper leaf is attributed to phosphorus deficiency. In this case the vine was growing in a soil with no detectable phosphorus and the vines responded to phosphorus fertilizer.

You will find many references that state that grapes do not respond to phosphorus application - I have had a failure to correct vines with identical leaf symptoms and very low phosphorous petiole concentration (0.08 %).

The phosphorus in the soil was not available until we raised the soil pH at which time the red flecking symptoms went away. It seems that most often a phosphorus vineyard problem will be associated with low pH or very high applications of Zinc (zinc phosphate is very insoluble).

This is Pinot noir on Long Island in a vineyard with very low soil pH and very low petiole P concentration

This is a leaf from a Riesling vine growing in a low soil pH vineyard - note that there are some dark flecks, but the white variety does not produce the red color

Grape berries and clusters contain a large amount of potassium. Because fruit potassium is taken away from the vineyard ecosystem at harvest, potassium levels tend to decline in a vineyard over time. Some soils have a very large supply of exchangeable potassium, but many vineyard soils do not. Potassium is one of the more important fertilizer elements for grape production.

Potassium deficiency produces an interveinal chlorosis which starts at the margin of leaves in the middle (not the base) of shoots. With increasing severity the number of affected leaves and the severity of infection increase. The leaves below are severely affected. At this level fruit development, fruit color, vine growth and winter hardiness would all be reduced.

Here potassium deficiency symptoms increase from right (normal) to left (severe). Note that the first symptoms are seen along the leaf margin and that the area between the veins is affected. The veins produce wide green bands in a field of yellow or brown.

The deficiency symptoms of this shoot are much worse at leaves 7-8 than at more basal positions. This is an important diagnostic symptom for potassium deficiency. Most nutrient deficiency symptoms start at the base of the shoot on the oldest leaves and progress upward. Note that these leaves are somewhat curled. This is also common with potassium deficiency.

These leaves are infected with the Grapevine Leaf roll Virus. The symptoms are very similar to those of potassium deficiency because the causation is the same - low concentrations of potassium in the leaf blade. Leaf Roll interferes with the translocation of potassium in the vine. To differentiate Leaf Roll and -K. Leaf Roll will affect the oldest leaves first, -K first shows up on mid-shoot leaves. Leaf Roll affected vines will have high petiole K concentration and low leaf blade K concentration. Both petioles and blades of deficient vines will have low K values. There are molecular tests for leaf roll virus.

Both the concentration and the balance of dibasic cations, Magnesium and Calcium, and the monobasic cation, Potassium, are important to vine health and function. A soil that is low in pH is almost by definition low in calcium and magnesium ions. Soil pH is raised by adding limestone - calcium or magnesium carbonates. If agricultural lime low in Magnesium is used to raise soil pH, an imbalance may be created. Dolomitic limestone which contains both magnesium and calcium is the preferred material to use.

Magnesium is a component of chlorophyll, and low magnesium causes an interveinal chlorosis of leaf blades. One symptom of low pH nutrient disorders is pale yellow leaves which are deficient in magnesium (see picture of low pH Riesling leaves above.)

Magnesium deficiency does not always start at the leaf margin. Many leaves may have marginal chlorosis, but if you have magnesium deficiency and look closely, you will see that early chlorosis starts between the veins away from the leaf margin.

Epsom salt foliar sprays may be used bring quick relief for vines showing symptoms of magnesium deficiency, but the long term solution is to add magnesium ions in the form of magnesium carbonate.

Magnesium and potassium ions compete for the same uptake sites in the grape root. Therefore the balance between the concentration of K and Mg is important. If K is added to a vineyard low in both K and Mg, a magnesium deficiency may be created. Similarly adding Mg may create a K deficiency. If there is any doubt about the K status, then potassium should be added along with lime to correct a magnesium deficiency. Some people advocate adding sulpomag which contains both K and Mg ions.

Boron is a micro nutrient, the vine only needs a low level (>25 ppm) and at high concentration boron is toxic to grapevines. In New York boron deficiency is found in vineyards where the topsoil has become eroded, and in very acid soils. In other areas boron deficiency is associated with very high pH soils.

These boron deficient leaves are from California. Such major deficiency symptoms are rare in New York. The primary symptom of boron deficiency noted in New York is the failure to set a normal crop of berries, the presence of a few large berries with oblate (pumpkin) shaped berries and the presence of small undeveloped, seedless shot berries.

Boron deficiency has great impact on vineyard productivity and boron levels should be monitored carefully. We were formerly concerned that adding boron as a fertilizer on a routine basis might lead to toxic build-up. We have found that this is an unlikely scenario.

Zinc, like boron is a micro nutrient. We don't really know whether there is zinc deficiency in New York, but we have seen low nutrient concentrations in vineyards where set was a problem. Like boron, zinc deficiency can cause reduced fruit set.

Zinc deficiency in California (where this picture was taken) is sometimes called little leaf. Symptoms include:

• greatly reduced leaf size
• interveinal chlorosis
• zig zag shoot growth
• misshapen leaves - the basal sinus is opened up and often the leaf is markedly asymmetrical.

These Sangiovese are Zn deficient and were found in a New York vineyard. Note the chlorosis, the reduced leaf size and the opened leaf sinus.