Studies on short hole Xylosandrus crassiusculus on grapes cv. Bangalore Blue

Abstract

The investigations on different aspects of grape shot hole borer, Xylosandrus crassiusculus (Motshulsky) (Coleoptera: Scolytidae) were carried out during 2002-03. The studies included distribution of the beetle infestation on grapes in and around Bangalore, potential of ethanol in trapping scolytid beetles, effect on growth parameters of grape vide with relation to infestation, spatial distribution of beetle damage on main trunk and management of X. crassiusculus. During the survey, two species of scolytid beetles viz., Xylosandrus crassiusculus and compactus (Eichooff) were recorded on grapes vines. Of these, the latter is new record, which has been sighted only on cuttings of Vitis vinifera. The present study revealed that Xylosandrus crassiusculus mainly preferred cv. Bangalore Blue grapes and its infestation was more in Bangalore North (Urban) area than other areas like in Bangalore rural and Kolar districts. Significant relationship was not observed between beetle infestation and number of vines in a garden or type of irrigation. However, infestation was more as the age of the vines increased. Traps with 20% ethanol were found most effective in trapping scolytid beetles. The trap catches of scolytids showed significant negative relationship with minimum temperature and wind speed. However, there was no significant correlation with other abiotic factors viz., maximum temperature, relative humidity and rainfall. The number of scolytid damaged holes on the main trunk was significantly and negatively correlated with total number of sprouts. This implied that as the infestation levels of scolytids increased on the vine trunk, the number of sprouts produced by the vines after pruning reduced. Due to the stress caused by the beetle attack on the main trunk of the vines, the flow of water and nutrients to the growing tips and leaves, after bud sprouting may have been affected. Similarly as the number of sprouts decreased with the severity of the shot hole borer infestation, the number of bunches per vine also decreased. However, within a bunch, the number of berries, which directly contributed to the weight of the bunch, was not affected. But overall productivity was affected. From the study carried out at the IIHR vineyard, it was found that if control measures are taken immediately after noticing the shot hole borer attack on the trunks by regular and close monitoring for pest attack, the growth and development of the vines and yield (No. of bunches) are not affected. Distribution of Xylosandrus crassiusculus damage holes was found to be clumped or aggregated at all height intervals on the main trunk as variance-mean ratio was more than unity. This was further confirmed by indices like negative binomial of ‘ k’ and David and Moore Index. The correlation coefficients were worked out to know whether the infestation(bored holes) at different height intervals, was related to the overall density of holes on a trunk. It was found that scolytid holes density at all height intervals was significantly and positively correlated with total number of holes on the trunk. However, the number of holes present at 0-30 cm and 60-90 cm height intervals showed highly significant ‘r’ values with total number of bored holes on the trunk. Based on these ‘r’ valued, different models were developed. The models which had higher ‘R2 values were used for predicting the total number of holes on a vine. At 0-30 cm height, power model, y=6.28 x 0.95 and 60-90 cm height power model, y= 18.780.66 would explain the reliability of variation of total number of scolytid holes of a vine up to 81% and 94%, respectively. So these models can be recommended for further sampling and prediction. Further, the predicted estimates using the above said models were not significantly different from observed values(based on ‘t’ test). Management studies showed that the efficacy of chemicals viz., dichlorvos 76 EC @ 0.228%, acephate 7SSP @ 0.225%, dichlorvos + acephate, dichlorvos+ acephate + carbendazim 50% WP @ 0.30%, Neem oil @ 1% and cypermethrin 25EC @ 0.225% were evaluated against Xylosandrus crassiusculus on grape vine trunk in the form of two swabbing at 30 days interval. Of these, dichlorvos + acephate + carbendazim , dichlorvos+ acephate and dichlorvos emerged as the most promising treatments from two trials. Accephate, neem oil and cypermethrin had moderate effect in controlling Xylosandrus crassiusculus. For low levels of infestation, especially if detected early, dichlorvos is sufficient. The swab with combination of chemicals was more efficacious, cost-effective and less hazardous, in terms of drift to non-target areas compared to sprays taken by farmers.