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Nutrient Deficiencies
Nitrogen deficiency – Deficiency symptoms appear as uniform lightening of green tissue, or yellowing of leaves when compared to vines that have received adequate nitrogen. Severe nitrogen deficiencies may result in small fruit size and poor fruit set. In the commercial setting, you may see the symptom development near veraison due to movement of nitrogen from leaves to berries. Nutrient test of plant tissue and soil followed by application of necessary nutrients is recommended.
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Magnesium deficiency –Symptoms are usually expressed in older basal leaves. Leaves become yellow on along the margin, while the tissue around the main veins of the leaf remain dark green. Red cultivars express reddening rather than yellowing. Magnesium deficiencies are common in vineyards with high potassium to magnesium ratio and/or low pH in soils (<5.5 pH). Nutrient test of vines and soils followed by application of necessary nutrients and/or soil pH adjustment is recommended.
Boron deficiency -Symptoms can appear as dramatic stunting of the vine. Shoot growth can be compromised, leaves turn yellow, and fruit set can become very poor. The initial symptoms may show up as dark knotty bulges forms on tendrils near the shoot tips at bloom. It is observed on soils with high acidity (pH 3.5-4.5). Also, since boron is a soluble nutrient, it may be leached out from the soil, especially with sandy soils. Nutrient test of vines and soils followed by application of necessary nutrients and/or soil pH adjustment is recommended.
Iron deficiency-– It is very common in vineyards with high pH soils. Symptom of iron deficiency is fading of green color (due to loss of chlorophyll) from the edge of leaves that progresses interveinally. This symptom is expressed throughout the season as yellowing of the leaves with veins remaining pale green. Iron can be applied by as a foliar application, and pH of the soil can also be adjusted. Nutrient test of vines and soils followed by application of necessary nutrients and/or soil pH adjustment is recommended.
Viruses
Tomato Ringspot Virus & Tobacco Ringspot Virus – Both viruses can cause irregular berry development; poor fruit set, and stunted shoots on infected grapevines. These viruses were vectored by a dagger nematode (Xiphinema americanum), and infected vines may result in death within 3 to 4 years. Resistant rootstocks, such as Kingfisher, Matador, and Minotaur, are available and recommended in eastern North America where ToRSV infects many fruit crops and broad leaf weeds species. (Tomato Ringspot virus, also known as yellow vein virus.)
Pinot Gris Virus – This is a newly identified virus. So far, this virus was found in Pinot Gris, Pinot Noir, and Traminer. The virus causes young leaves to be malformed, yellow and puckered, and shoots to be stunted. Fruit quality and yields can be negatively affected by the infection.
Phytoplasmas
NAGY– North American Grapevine Yellows is caused by phytoplasmas. Symptoms are fruit abortion, yellowing and curling of leaves (especially with white-fruited cultivars), purplish hue on shoots, and irregular lignification
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