Mario Viveros

UCCE Farm Advisor, Kern County

Deciduous Tree Fruits and Nuts

April 20, 2001

Noninfectious Bud Failure, or "Crazy Top" in Almonds

The noninfectious bud failure, or "crazy top," is a genetic and bud perpetuated disorder in almonds. This disorder has been an economic problem since the 1940s. Much research has been done to minimize the propagation of bud failure in trees; however, there is no sure way to avoid it. This year we have severe cases of bud failure in both Carmel and Nonpareil varieties. The disturbing fact is that second and third leaf orchards are showing severe bud-failure symptoms. This may mean that the bud source that was used to propagate these trees may be severely affected by the bud-failure disorder.
The main symptom is bud failure or the failure of vegetative buds to grow out in the spring. Such buds are dead or severely inhibited. Usually, not all buds on a particular shoot are affected and some may develop normally. They grow vigorously and often at a right angle to the shoot. Buds that fail drop off six to eight weeks after spring growth begins in the plant. Often, only buds on the center part of the shoot are affected, while buds originating both early and late in the season are normal. This produces the "muletail" look. When buds on the end of the shoot fail, dieback results. Sometimes the buds on mildly affected trees are merely delayed in their time of growth. Flower buds are not affected as much as vegetative buds, but bloom time may be delayed up to two weeks. In mildly affected trees, fewer flowers are produced, but fruit set will be equal to a normal tree. However, in severely affected trees, few or no flowers will be formed leading to a poor fruit set.

Bud-failure symptoms are easily recognized in young trees. Their bud development will be later than a normal tree. Also, buds on the lower and mid-part of the shoot fail to develop, but buds at the end of the shoots will grow in the spring. Furthermore, on some affected trees, rough bark will appear in distinct bands on some shoots.

Bud failure affected trees should be replaced when they are in their second, third, fourth and fifth leaf. By eliminating affected trees during the first four years of the orchard, the most severe bud-failure cases in the orchard are eliminated. These trees should be replaced with replants that were produced using low bud-failure potential bud wood. Also, if the trees are to be replaced by budding or grafting, the bud and scion wood must come from low bud-failure potential trees. You must resist the temptation to select bud wood from your own orchards to do any grafting or budding.
Replants means replacing bud-failure affected trees with new trees. It can be done successfully in the early years of an orchard (second to fifth leaf). Replants require frequent irrigation due to a small root system. Usually, the frequencies of irrigation of a mature orchard are too far apart to supply the water needs of a newly planted tree.

Replacing trees by budding and grafting requires planning and finding an individual with budding and/or grafting skills. If the grower decides to do budding, then he must decide on the timing (spring, June or fall). Grafting also has two timings. It can be done in the fall or the spring. For more details on budding and grafting, read the chapter on "Propagation" in the Almond Production Manual, Publication 3364, available at the Cooperative Extension office.?