Longan Leaf Curl Symptoms in Chiang Mai and Lam Phun

Abstract

During September 1996 to March 1997 the field survey of leaf curl symptoms in major longan plantation area within Chiang Mai and Lam Phun Provinces were conducted, the percentages of trees exhibited the leaf curl and witches’ broom symptoms were recorded. Out of 1,322 observed plants from 15 planting areas in Chiang Mai approximately 18% of the trees displayed varying degree of leaf curl symptoms, 13% of those abnormal trees were also infected by eriophyid mite, another 3% demonstrated witches’ broom like symptom, and additional 2% were damaged by herbicide. The total of 2,530 trees were observed from 28 plantation areas in Lam Phun, over 32% of the trees showed leaf curl symptoms of which 23% were herbicide damage, besides, 9% were mite damage and 0.06% showed witches’ broom like symptom.         

Herbicide leaf curl symptom apparently occurred specifically on the outermost canopy around the affected trees, of which two different type symptoms were observed. For the first type, the leaf size of the affected shoots were diminished with downward rolled edges, while the second damage type, the affected leaves appeared strait and narrow with wavy edges. Evaluation of herbicidal effect on the size of damaged leaves at Ban Soppa and Ban Hong Lam Phun, indicated that the leaf sizes of the affected trees were significantly decreased as compared with leaves from the normal ones.

The trees exhibited eriophyid mite leaf curl symptom were also demonstrated shoot and blossom deformities. The infested young leaves along the shoot were appeared stunted and twisted with the edges rolled up or down toward the midrib. The flower clusters of the mite infested trees appeared aggregated with shorten peduncles and pedicels. The mite also induced the abnormal development of the dense tiny hairs (erineum) which covered most surfaces of the shoots and blossoms of the infested trees. The length of samples of infested inflorescences at Ban Hong, Lam Phun were measured and they were significantly shorter than the normal flower clusters.         

Abnormal shoots similar to witches’ broom symptom were also found in longan cultivars: Biew Kiew, Haew, Daeng and Ma Teen Kong excepted Daw cultivar was not shown such the symptom. Witches’ broorn like symptom occurred on shoots at terminal branches on outer most and inside conopy including the shoots along branches within tree canopy. Broomlike growth or massed proliferation caused by the dense clustering of branches was seen on witches’ broom like symptom.