Dead Arm Disease

Have you ever slept on your arm wrong, and it went numb? Or had a nerve block?
 
Dead arm disease is not about that experience.
 
Gardeners used to think dead arm was a single disease with two sets of symptoms. Now we know better.
 
Grape dead arm describes what happens when your vines are infected with Eutypa dieback and Phomopsis cane and leaf spot at the same time.

​Phomopsis cane and leaf spot
 
Phomopsis cane and leaf spot provides the first symptoms of grape dead arm. Caused by the fungus Phomopsis viticola, dead arm starts out as tiny red spots on new shoots. These spots merge and turn black, causing the stem to die. Then brown and yellow spots appear on the leaves, and fruit rot begins. And Eutypa dieback

Phomopsis cane and leaf spot (Bobysolo)

Phomopsis lesions on grapes (UGA, Bugwood.org) CC BY 3.0 US DEED

Eutypa dieback
 
Eutypa dieback is caused by the fungus Eutypa lata. Fungi stay hidden under the bark for up to three years before symptoms become obvious. Areas of bark may look flattened. If you peel the bark back, there’s no mistaking the dark, V-shaped lesions hidden inside. These lesions often cause stunted shoots and cupped, yellow leaves that stay attached to the tree in a behavior known as flagging. You may also see a gummy ooze.

Symptoms of Eutypa dieback in grape leaves (A. Andolfi, et al) CC BY 3.0

Characteristic V-shaped necrosis of grape vine trunk infected with Eutypa dieback (A. Andolfi, et al) CC BY 3.0

Dead arm management
 
Once these fungal diseases appear, careful pruning is needed to prevent them from spreading. Infected limbs should be cut at least 12 inches below any noticeable infection, and cutters should be dipped in a household cleaner between each cut to prevent the spread of disease. Infected plant material should be thrown in the trash and not composted. Fixed copper sprays or fungicides may also be needed.
 
How to prevent dead arm
 
Moisture is nearly always a contributing factor to fungal diseases. Make sure your sprinklers are not hitting vines or tree trunks.
 
Pruning for good air flow will help prevent these and many other diseases. Plants susceptible to Eutypa dieback should be pruned in summer, rather than during dormancy. This allows wounds to dry and heal before fungi can enter.
 
Contrary to popular opinion, do not use sealants on your vines or trees after pruning. Sealants seal moisture in, creating a protected environment for fungi to grow unseen until it’s too late. Let a callus form naturally instead.