Efficacy of sando 60ec and fytomax 0.1ec on the control of cotton bollworms

Introduction

Cotton (Gossypium hirsutum) is an important crop in Zimbabwe for both social and national economic improvement as it and its by-products are used in a number of industries such as textile, oil and detergent manufacturing sectors. However, the crop is attractive to a lot of pests which include sap-suckers, leaf -eaters and bollworms which is the main focus of this study. Among these pest groups, bollworms are mostly dangerous in that they affect the economic parts of the plant. G. hirsutum bollworm larvae damage bolls and squares (UC IPM, 2013) [1] . They also damage flowers. Once such parts are affected, there is a direct impact on the yield of the affected cotton plants. This will have a negative bearing on the overall yield and ultimately the farmer's income. According to Renou and Deguine, 1992 [2] , four species that make up the major cotton bollworm species in sub-Saharan Africa and these are the red bollworm (Diparopsis castanea), African bollworm (Herlicoverpa armigera), the pink bollworm (Pectinophora gossypiella) and the spiny bollworm (Earis insulana). While the D. castanea, H. armigera and E. insulana bollworm species in Zimbabwe are controlled by using different insecticides, the P. gossypiella bollworm is a quarantine pest whose presence in a certain cotton growing area or region may lead to the banning of the growing of cotton as a management measure. According to Badii and Asante (2011) [3] , however, the four bollworm species already mentioned above are among the most serious species that affect the cotton plant. The Spiny bollworm attacks cotton from leaf bud formation to maturity, damaging flower buds and acorns (Qader and Saber 2021) [4] . There are different methods used to control these cotton bollworm pests. However, this project was mostly focusing on the use of pesticides as a control method. These pesticides were being tested for their efficacy in bollworm control at different levels. Testing of the new chemicals helps to boost those that are already registered and available on the market. It also helps prevent pesticide resistance and ensures long-term effectiveness of pest control strategies (Michelle, 2024) [5] . Pesticides are generally persistent in nature (Shivkumara et al., 2019) [6] . Pests can develop resistance to pesticides they have never been exposed to when two insecticides have a similar mode of action (Stack, 2025) [7] . Development of resistance by pests leads to a significant decrease in sensitivity to a pesticide -reducing the field performance of these pesticides (EPA, 2025) [8] . Pests (populations and not individuals) change or mutate to become resistant (Buhler, 2025) [9] .Those pesticides that are already available also lose their efficacy due to the continuous use which normally leads to pests developing resistance to them. Management of the bollworm is based on scouting for eggs or small larva (Michaud, 2013) [10] .The two objectives of this research project are to determine the efficacy of Sando 60EC and Fytomax 0.1EC insecticides on cotton bollworms and also to determine the effect of Sando 60EC and Fytomax 0.1EC Insecticides on predators of cotton bollworms. Sando 60EC, a broad spectrum pyrethroid, has 30grams per litre Emamectin Benzoate, 30grams per litre Lambda Cyhalothrin and 940grams per litre inert ingredients in its composition. On the other hand, Fytomax 0.1 EC, a systemic and contact botanical insecticide is composed of 0.1% Azadiractin and 99.9% inert ingredients.

Materials and Methods

Treatments

The experiment comprised of eight treatments including the no chemical control (Table 1) and Decis Forte was the standard The bollworm eggs or their larva were determined by their natural occurrence and not by inoculations. The six plants that were scouted were randomly selected within the sampling area. These selected plants were tagged and are the ones that were used again in the second scouting for efficacy testing. Tagging together with a random selection of plants to use in data collection (scouting) was done to reduce the scout's bias towards plants with certain physiological features. Tagging was also done to identify the sampled plants in the proceeding scouting operations and use untagged ones. This would give all plants within the sampling area an equal chance of being used in data collection. The bollworm eggs and larval counts were scored after scouting using the scoring system as shown in table 2 below. Predator counting was done two days after spraying to also determine the impact of the sprayed pesticides on the predators.

Results and discussion

Effect of treatments on Heliothis Bollworm Larva

There were significant differences of p<0.001for the Heliothis Bollworm Larvae among treatments only at CRI in the 2022 -23 season. All the treatments except the no control had statistically similar performance to the standard (Decis Forte). However, Sando 60EC, a pyrethroid, had lower heliothis larval levels (0.75). Such pesticides as pyrethroids have high efficiency and low toxicity when compared to the organophosphate and carbamate groups (Yoo et al., 2016) [11] . The no-control recorded the highest larval counts of 2.08 while Sando 60EC at 750ml/ha and 500ml/ha recorded 1 each. Kuwirirana had no significant differences among treatments in 2022 -23 season. In 2023 -24 season, significant differences (p=0.071) for the Heliothis Bollworm larva were only recorded at Chitekete. The highest Heliothis larvae were recorded at the No control treatment while all other treatments recorded statistically similar Heliothis larvae.CRI and Kuwiririrana had no significant differences (Table 3) in 2023 -2024 season (p= 0.299 and 0.459 respectively). Only Fytomax 0.1EC at 750ml/ha recorded the larva at Kuwirirana while all other treatments had no Heliothis bollworm record.

Effects of treatments on Spiny Bollworm larvae 2023 -2024

Season: There were no significant differences for Spiny bollworm larvae in 2023 -24 season for all sites (Table 5). No Spiny bollworm larvae was recorded in 2022 -23 season For the ladybird adult at CRI, the highest counts of 1.25 were recorded on Sando 60EC at 500ml/ha. This was higher than the grand mean of 0.463. It was also above the check standard, Decis Forte at 50ml/ha (0.08). This highest record for Ladybird adult at CRI was followed by Sando 60EC at 300ml and Sando 60EC at 750ml/ha respectively (0.68 and 0.65). These two were similar to Fytomax 0.1EC at 750ml/ha. Fytomax 0.1EC at1000ml/ha and 500ml/ha were comparable to Fytomax 0.1EC at 750ml/ha. Both ladybird adult and larvae feed on soft bodied insects like the first instar larvae of cotton bollworms (Royer, 2022) [12] . At Kuwirirana, significant differences among treatments were recorded on the ladybird larvae at p = 0.044. But even then, records were only found at no control and Sando 60EC at 300ml/ha. All other treatments recorded zeros for the ladybird larva at Kuwirirana. There were no significant differences among treatments for Chrysopa eggs at Kuwirirana.

Effect of Treatments on predators at CRI, Kuwirirana and Chitekete in 2023 -2024 Season

For 2023 -24 season, there were no significant differences for recorded predators at CRI. There were significant differences for Chrysopa Eggs (p = 0.004), Chrysopa larvae (p = 0.025) and Spiders (p = 0.003) at Kuwirirana. The highest Chrysopa egg levels was recorded at Sando 60EC @ 500ml/ha (4.17)statistically similar to Decis Forte @ 50ml/ha with 4.08. No control treatment recorded the lowest Chrysopa eggs (0.08a) which is comparable to Sando 60EC @ 300ml and Fytomax 0.1EC at 500ml/ha respectively. The highest level of Chrysopa larvae were recorded at Fytomax 0.1EC at 750ml/ha (0.33) which was comparable to Fytomax 0.1EC at 500ml/ha (0.17) in Kuwirirana. All other treatments were statistically similar for the Chrysopa larvae. There were significant differences for spiders also at Kuwirirrana (p = 0.025). The highest number was recorded at Fytomax at 1000l/ha treatment (1.17

Bollworms Across sites

In an across site analysis, significant differences (p<0.001) were recorded on Heliothis larvae. The no control recorded the highest level (1.33) while all other treatments were statistically similar. But even then, Sando 60EC (a pyrethroid) at 300ml/ha recorded the lowest Heliothis larvae (0.73). Insecticides of the pyrethroid group are 2250 times more poisonous to insects than to higher organisms (Royer, 2022) [12] . Red and spiny bollworm larvae recorded no significant differences across sites.

Across sites -Predators

There were significant differences (p<0.001) among treatments for spiders across the sites. The highest number of spiders (0.73) was recorded on Fytomax 0.1EC at 1000ml/ha while the lowest was recorded on Sando 60EC at 300ml/ha which was statistically similar to the standard Decis Forte at 50 ml/ha (0.18). The no control recorded 0.43 which was comparable to Sando 60EC at 750ml and 500ml respectively for the spiders.

Chrysopa eggs and Ladybird adult recorded no significant differences across sites. Fytomax 0.1EC at 500 ml/ha recorded 0.47 spiders, outperforming Decis Forte at 50 ml/ha (0.18). Fytomax 0.1EC is a botanical pesticide and as in Zimbabwe, botanicals are used by 100% of farmers in some areas (Iqbal, 2021) [13] . Botanicals lower threat to beneficial insects while also reduce the risk of pests developing pesticide resistance (Hetland, 2019) [14]

Acknowledgement

AcknowledgmentThe authors would like to acknowledge the Department of Research and Specialist services directorate for the support during the study period.

References

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