Water stress– One of first symptoms of water stress is the cessation of shoot elongation. Shoots on the water stressed vines tend to be short, and flowers may abort or results in smaller berries. Periderm may form earlier on shoots with the water stressed vines. Water stress occurs when the vine is unable to uptake enough water to support the canopy and crop load. Drought is the main cause of water stress; however, excess water, which can kill roots by soil oxygen deprivation, can also cause water stress-type symptoms. Check your local weather history as well as the site conditions such as soil drainage. Severe drought stress can cause leaves to yellow, brown and eventually dry and fall off.
Mechanical damage – Trunks may become damaged by mechanical means. Feeding activities by animals, girdling from wires or vegetation, or human activities such as a use of weed eater or improper removal of sucker shoots, can injure the vine. The injury itself can result in water stress-type symptoms (short internodes, yellow discoloration of leaves, etc.), but the injured trunk is often subject to be infected by plant pathogens or necrotic microorganisms, such as grapevine crown gall.
Insect damage – On trunk: In southeastern US, the larva of Grape root borer (Vitacea polistiformis (Harris)) can bore through the trunk of infested grape to cause damage. Severe damage often results in collapse of the infested vine. Use of a mating disruption is often recommended. On green tissues: Female grape cane girdler (Ampeloglypter ater (LeConte)) create cavity on a new shoot to lay egg. Also, when periodical cicada (Magicicada spp.) lay eggs on shoots, it will leave a slot up to 4 inches in length. The damaged shoots are prone to breakage, causing tissues above to drop or die off. Galls that are as twice as thick as the shoot can form after female grape cane gallmaker (Ampeloglypter sesostris (LeConte)), lay eggs. Often times the damages caused by the grape cane gallmaker is minor, but heavy infestation can hinder the normal growth of shoots and flower parts.
Crown gall -This disease can restrict the water movement by creating galls that blocks vascular tissues. The affected vine may show water-stressed-type symptoms or may collapse suddenly. Inspect vines for formation of galls. Please click this link to learn more about Crown Gall .
Apoplexy – Apoplexy refers to the complete collapse of canopy and crop load of a vine, usually associated with severe cases of grapevine measles, also called esca, black measles or Spanish measles. Please click this link to learn more about ESCA and Grapevine Measles