Efficacy of Insecticides for the Management of Cashew Stem and Root Borer, Plocaederus ferrugineus L (Coleoptera: Cerambycidae) in Bapatla Andhra Pradesh

Cashew (Anacardium occidentale L.) an important foreign exchange earning horticultural crops in India, with an annual production of 7.73 lakh tonnes of raw nuts (Anonymous, 2021-22, Erasadappa and Mohana, 2016 and Jena et al., 2024). India is the largest exporter of cashew kernel (48574 MT) with a value of 2840.39 crores (Anonymous, 2020-21). The productivity of the crop is threatened by several insect pests. Globally, more than 400 species of arthropods are known to infest cashew and in India there are 200 insect pests reported on cashew (Anonymous, 2015). Depending on the climate, location, tree age, geographic region distinctive pest complex are noticed and in all growing regions, majorly, stem and root borer (Plocaederus ferrugineus L.) is the deadliest insect in all the cashew growing areas of the country as well as the world (Ayyanna and Ramadevi, 1986). The intensity of infestation and extent of damage may vary widely across the regions. On an average this borer kills about 2-5 per cent productive trees every year (Rai, 1984 and Reddy et al., 2013a). The CSRB infestation went up to 40 per cent in different periods at Guntur (Arjunarao, 1978) and Prakasm (Ayyanna and Ramadevi, 1986) districts of Andhra Pradesh. The pest is very severe in nature having potential of causing even up to total yield loss, if proper management measures are not taken up timely. Severely infested trees die within a period of two years causing capital loss to the growers.

For the management of cashew stem and root borer, periodical monitoring of the crop is very essential to prevent the infestation by cashew stem and root borer. Trees with symptoms of yellowing, dried and dead trees should be removed immediately along with roots by digging pit of two feet around the base of the trunk and disposed off (Phytosanitation). Tree base must be kept clean and weed free so as to observe the frass and gum exudation as early symptom of borer attack. Currently, management of CSRB infestation is through adoption of post extraction prophylaxis (PEP), wherein the different pest stages like grubs,  pupa and adults are extracted by chiseling carefully from infested cashew trees.  Further treated by swabbing and drenching the infested trees with chlorpyriphos 20EC @ 0.2% to prevent further  oviposition,  but still effective management is very challenging due to cryptic nature of the pest. In view of the existing practices, efficacy of newer insecticides as curative control measures against Cashew Stem and Root Borer, Plocaederus ferrugineus L. is needed for effective control, hence the present study has been taken up at AICRP on Cashew, Cashew Research Station, Bapatla, Dr. YSR Horticultural University Andhra Pradesh.

The studies on efficacy of newer insecticides against Cashew Stem and Root Borer (CSRB) as curative control measures i.e. Post Extraction Prophylaxis (PEP) was conducted from 2015-16 to 2020-21 at AICRP on Cashew, Cashew Research Station, Bapatla, Dr. YSR Horticultural University Andhra Pradesh. The experiments were laid out in completely randomized block design with four replications and for each replication five infested trees were selected randomly. The infested cashew trees were identified based on the external symptoms viz., oozing of the frass and gum from the bored hole at collar, stem and exposed roots or fork region. The pest stages (grubs, pupae and adults) present in selected infested trees were traced and extracted skillfully by chiseling the infested portion of the tree. The frass and chipped materials from such trees were collected and disposed off. Later, the chiseled portion on main stem  up to 1 m height from the ground surface and on the exposed roots and fork of branches was swabbed with the insecticidal solution to be evaluated. The same solution (5.0 liter insecticidal solution) was drenched to the root zone, in case of root infestation.

The insecticides evaluated were Fipronil 5%SC @ 2 ml/l, Neem oil @ 5%, Imidacloprid 17.8 SL @ 2ml/l, Chlorpyriphos 20% EC @ 10 ml/l and the untreated check (only removal of CSRB grubs) without application of insecticide. The treatments were applied sequentially as swabbing and drenching after manual removal of CSRB grubs on infested trees as and when infested trees were available. The treatments were applied three times during October - November, January - February, April - May (Reddy et al., 2013b and Anonymous 2016).

The observations on the fresh infestation of CSRB infestation was checked based on the external symptoms of the damage at monthly intervals both on the treated and uninfested trees. The data on number of trees without re-infestation was recorded and later per cent of trees without re infestation was worked out.  The physical parameters of the infested trees such as stem girth (stem diameter), age of the tree, per cent of bark circumference damage, zone of attack and canopy yellowing was also recorded simultaneously to infer the parameter favours CSRB infestation. (Raviprasad, 2005).

The experiments on evaluation of efficacy of newer insecticides against Cashew Stem and Root Borer (CSRB) as curative control measures was initiated during 2015-16 and continued up to 2021. The results indicated that all the treatments were superior over the untreated check in reducing the cashew stem and root borer re-infestation throughout the experimental period. However, the treatments applied as Post Extraction Prophylaxis (PEP) revealed that Imidacloprid 17.8 SL @ 2ml/l was found more effective in reducing the re-infestation of CSRB throughout the experimental period with pooled average of  21.90 per cent of trees with re-infestation. Whereas fipronil 5% SC @ 2 ml/l has recorded next best treatment with 31.5 per cent trees with re infestation, followed by Chlorpyrifos 20% EC @ 10 ml/l i.e. treated check  with 34.4 per cent of trees with re-infestation and which was on par with Fipronil 5% SC @ 2 ml/l treatment. These findings were in line with the findings of (Zote et al., 2018), they reported that fipronil was found effective and reduced the re-infestation of CSRB and reported that 93.33 per cent of trees without re-infestation. Further they reported that imidacloprid swabbing and drenching was found 76.66 per cent of trees without re-infestation. According to the Ravi Prasad and Co-workers (2009) reported that Chlorpyrifos 20% EC (0.2%) was found to be the best PEP treatment with 96.43 per cent trees without re-infestation followed by Monocrotophos (0.20%)  with 78.57 per cent trees without re-infestation and both the treatments were on par each other. Further, Mohapatra et al., (2004) and Gupta (2020) reported that, 88.13 and 69.75 per cent of trees being free from re-infestation of CSRB with chlorpyrifos (0.20%) respectively. Neem oil @ 5% applied as swabbing and drenching recorded 47.7 per cent of trees with re-infestation and superior over the untreated check (only removal of cashew stem and root borer grubs without any application of insecticides) (Table 1). These findings were in agreement with the findings of Jaya Prabhavathi et al (2016), they reported that 35.0 per cent of trees free from re-infestation with neem oil 5% applied as PEP.



Another separate experiment was conducted to study the physical parameters of the infested  cashew trees to know the parameter favours CSRB infestation. Several physical parameters like stem girth (Diameter of the stem), age of the tree, zone of attack, yellowing of the tree canopy and per cent of bark circumference damaged by CSRB on infested trees were recorded on 654 infested trees during 2015-16 to 2020-21 (Table 2). 



With respect to the diameter of the stem (stem girth), cashew trees were categorized into <60 cm, 60-80 cm, 80-100 cm and >100 cm. Out of the total infested trees observed (654 trees), 8.1, 22.9, 39.5 and 29.5 per cent trees having <60 cm, 60-80 cm, 80-100 and >100 cm of the stem diameter respectively. After the post extraction prophylaxis (PEP) the recovery percentage of trees were not re infested was highest (90.6 per cent) in <60 cm of stem girth trees i.e. 48 trees were not re infested out of 53 trees followed by 60-80 cm stem diameter trees (111 trees were not re infested out of 150 trees). 58.9 and 49.2 per cent of trees were not re-infected after PEP with 80-100 cm and >100 cm diameter of the stem respectively. This indicated that as the diameter of the stem (stem girth) increases the infestation and re-infestation by the CSRB also increases.

With respect to the age of the tree, the treated cashew trees age were categorized as  <10 years, 10-15 years and >15 years age. Totally 654 infested trees were examined for recording observations. Among them, 44 trees were falls under the category <10 year age, of which 6 trees were infested with CSRB and remaining 38 trees were free from infestation, which constitutes 13.6 per cent (Table 2). Similarly, 204 trees out of 654 trees falls under the category of 10-15 years age, of which 71 trees were infested and remaining 133 trees were free from CSRB infestation, which comprises of 34.8 per cent. Further, 406 trees out of 654 trees were falls under >15 years age category, of which 171 trees were infested and remaining 235 were not infested (42.1%). This revealed that, as age of the cashew trees increases the chance of infestation and re-infestation by CSRB also increases.

The observations were also made to know the preferential zone of attack on the cashew trees by Cashew stem and root borer, generally attacks trees at root zone, stem zone or collar zone. Data revealed that, CSRB mostly prefers collar + root zone (199 trees out of 654 trees), followed by stem + collar+ root zone (119 trees out of 654 trees) (Table 2).

Similarly another parameter was yellowing of canopy i.e. advanced stage of infestation by CSRB was also recorded. The trees with full yellow canopy were beyond recovery even after post extraction prophylaxis. During the experimental period (2015-16 to 2020-21), total 105 trees were observed out of 654 infested trees with yellowing canopy, among these only 14 trees (13.3 per cent) were not re-infested remaining 86.7 per cent trees were re-infested by cashew stem and root borer (Table 2). These results are in line with the results of Jaya Prabhavathi et al., (2016), further they stated that early detection of cashew stem and root borer infestation and simultaneous PEP with insecticides on a community basis is effective in managing the attack on CSRB.

Another physical parameter studied during the period was per cent of stem bark circumference damaged by cashew stem and root borer. If the per cent of bark circumference damage is more than 50 per cent, there is more chance of re-infestation by cashew stem and root borer and also less chance for survival of the tree. During the experimental period total 189 trees showed >50 per cent of bark circumference damage out of these trees 149 trees were re-infested again with cashew stem and root borer. If the circumference damage is less, the recovery of the infested trees from  CSRB infestation after PEP (Table 2) increases. These findings are similar with the findings of Ravi Prasad et al., (2009), they confirmed that substantial reduction in the pest population in a given location and also reduction in fresh infestation of cashew trees due to Phytosanitation activity i.e. removal of pest stages from trees infested by CSRB and removal of trees having more than 50 per cent bark circumference damage by uprooting.

From the curative treatments, it is concluded that, among the treatments, imidacloprid 17.8 SL @ 2.0 ml per liter) was found superior with 21.9 per cent of trees were re-infested after post extraction prophylaxis, followed by firponil 5% SC @ 2.0 ml per liter and chlorpyrifos 20% EC @ 10 ml per liter  recorded 31.5 and 34.4 per cent of trees were re-infested after post extraction prophylaxis respectively. Among the physical parameters studied, the  trees with stem girth of less than 60 cm were less infested by CSRB, it might be due to smooth stem surface may not supports oviposition of the beetle and vice versa.  With respect to the age of the tree, very less infestation observed on below 10 years age trees and the infestation and re-infestation by CSRB increased over increasing the age of the tree. The preferential zone of attack of CSRB on cashew tree was collar + root zone, followed by stem + collar + root zone. The tree canopy was yellowing due to severe infestation of CSRB can’t be recovered from the infestation. If the per cent of bark circumference damage is more than 50 per cent, recovery per cent of such trees were very difficult and vice versa. Hence such tree should be removed along with roots to reduce further spread of the insect.

The authors are grateful to AICRP on Cashew for financial assistance to carry out the research leading to this article and to The Director, ICAR- Directorate of Cashew Research, Puttur (Karnataka) and The Director of Research, Dr. YSR Horticultural University, Venkataramanagudem Andhra Pradesh for providing research facilities.

All authors declared that there is no conflict of interest.