Pierce’s disease

The first sign of Pierces disease infection is drying or “scorching” of leaves.  This usually develops by mid or late summer. Initially, scorching of leaves may be observed as yellow or red color along the leaf margins.  Leaves continue to dry from the edges in concentric zones.  Different varieties show slight variation in the development of the leaf symptoms. Infected leaves fall off leaving the petiole attached to the cane.  Fruit clusters may also wilt and dry up. The bark on affected canes often matures unevenly. From summer through harvest, look for the above symptoms in the vineyard and mark vines showing these symptoms. Laboratory testing will confirm the diagnosis. 

Red leaves – leafroll disease or something else?

Red leaf symptoms are alarming and may serve as a warning sign of something being wrong with the vine since normal fall color of red skin varieties is yellow, not red.  Red leaf symptoms can be caused by several different reasons- Leafroll disease is one candidate but nutrient deficiencies such as potassium, magnesium or phosphorus may also cause reddening of leaves which, similar to leafroll, starts on older leaves. Some root diseases or gopher damage may also lead to appearance of red leaves. Feeding of mites may also turn leaves red as well as physical girdling of trunk or cordon.

Laboratory testing helps out to identify the cause of red leaf symptoms. Proper sampling is necessary to ensure that the virus was distributed into the sample being tested. Pick from symptomatic leaves and from multiple sites.

Grapevine Red Blotch Disease

A new DNA virus, Grapevine Red Blotch associated Virus, or GRBaV, was discovered in grapes in 2012. The virus is named after the symptoms it was found to be associated with: irregular blotches of red color appearing in leaves and leaf blades of red varieties in late August. Characteristic of the disease is that leaf veins also turn red. Brix values on the grapes infected with the Red Blotch virus appear to be 4-5 units below normal.

Although red blotch disease symptoms may sometimes resemble those of the leafroll diseases, distinguishing characteristic of this disease is that leaf blades do not roll down as they do in leafroll-infected vines. Also, in GRBaV-infected vines secondary and tertiary veins are clearly red, while in leafroll-infected vines, veins always stay green.

A laboratory assay for qPCR detection of GRBaV is available at AL&L Crop Solutions.

The post Seasonal Grapevine Symptoms first appeared on AL&L Crop Solutions.

Fungal diseases caused by vine decline fungi (Phaeoacremonium and Phaeomoniella species) are often the culprits of delayed growth in spring. Infections caused by these fungi can remain silent for many years until vines become stressed due drought, overcropping, etc., which makes the symptoms to appear. In such stress conditions these fungi produce toxins that interfere with the vine’s normal growth. Vines infected by these fungi just don’t have the stamina to push the way the healthy vines do. 

Cylindrocarpon-infected vines also show growth delay in spring.  After closer examination and removal of the bark in the soil line, these vines can show brown/black cankers at the crown area. After so much of the vine’s water conducting tissues being compromised by the disease, there is not enough surface area to support the new growth. Depending on the amount of the injuries, these vines often collapse in the heat of the summer.

Canker diseases of grapevines caused by Eutypa and Botryosphaeria become easily detectable after the vines come out from the dormancy. Dead spurs or arms are often the first indication of the presence of these diseases. Eutypa can also cause curling or cupping of leaves, or shriveling of the berries. These symptoms are caused by the Eutypa-toxins that travel from the cankers into the sites of new growth.

A newly described pathogen of grapes, a Botryosphaeria-related fungus, called Neoscytalidium diminatum has been detected this year by AL&L Crop Solutions. The fungus was detected from young vines grown in Sonoma county. Affected vines had shown poor growth, and in some cases the vines had suddenly collapsed. Large cankers were detectable in the trunks of these vines. Neoscytalidium, which also causes disease on walnuts, was found first time on table grapes in Coachella Valley, in 2013.

Pierce’s disease can also be detected by an observant eye during spring. Keeping in mind that the symptoms are not the same as they are in the late season. In spring, vines that had been infected by this bacterium in the previous season, start showing delayed growth and chlorotic leaves. 

Some of the viral diseases of grapes can also cause growth delays and the infected vines can be spotted in spring. Leafroll viruses and vitiviruses have been often detected in underperforming vines in spring. Some clients also claim that Red Blotch infected vines had were developing shorter shoots. 

Early summer will also bring out symptoms of fan leaf and other nepoviruses. Vines infected with these viruses commonly grow leaves with yellow mosaic, or yellow veins, and sometimes leaves may be of abnormal shape. Since many viruses can cause these types of symptoms, spring testing can rule out whether any of these viruses are present. 

The post Spring Time Symptoms at the Vineyard first appeared on AL&L Crop Solutions.