Pg. 24-27 Integrated management of litchi pests

In many years litchi trees often fail to mature a good crop. Possible reasons for this have been ascribed to a range of factors, such as nutrient deficiencies, high temperatures, moisture stress, etc. During 2008 up to 67% of the early drop of litchi fruit was caused by the coconut bug in a commercial Nelspruit orchard. The coconut bug prefers to feed on younger fruit and on another orchard where the relative seasonal abundance of this pest was monitored, early damage as high as 80% was recorded. Litchi moths begin to oviposit when the fruit begins to color visibly. This is the only time when control with a contact chemical will be effective, but unfortunately this occurs so close to harvest that unacceptably high residue levels could be expected. With this in mind, alternative control options were investigated. Isomate mating disruption dispensers of the oriental fruit moth were available and since the chemical composition of the pheromones of both species of moths were nearly identical, it was decided to evaluate this product in the field on a commercial basis. On both trial sites populations of the litchi moth were adequately suppressed. If these levels of control can be maintained during the 2009 season, this product will probably be registered. The advantage of using Isomate is that no pesticide comes in contact with the skin of the fruit, therefore no problems with pesticide residues are anticipated.

Summary:

• South African litchi production often suffers from poor fruit maturation due to various factors including nutrient deficiencies, temperature stress, moisture stress, and pest damage.
• Coconut bug (Pseudotheraptus wayi) was identified as a major pest causing significant immature fruit drop in litchis, with up to 67% fruit abortion recorded in some commercial orchards.
• The coconut bug prefers younger fruit and is highly polyphagous, affecting multiple crops. Its damage was more severe in the Nelspruit area compared to other regions like Onderberg.
• Litchi moth (Cryptophlebia peltastica) oviposition peaks closely follow fruit color change, which signals the most effective timing for control measures.
• Chemical control of litchi moths with contact insecticides is challenging due to timing close to harvest leading to potential pesticide residue concerns.
• Alternative control using Isomate mating disruption dispensers, originally developed for oriental fruit moth, showed successful suppression of litchi moth populations in field trials.
• Isomate offers an environmentally friendly pest control method with no pesticide residues on the fruit, increasing export marketability.
• Integrated management strategies recommend careful chemical use due to risk of secondary pests and lack of registered chemicals for coconut bug yet.
• Litchi trees may compensate for some early stink bug damage in high flowering years, but significant crop loss occurs in lower yield years when coconut bug damage is high.
• The study emphasizes sustainable pest management options, including pheromone-based mating disruption for litchi moth and monitoring of coconut bug infestation levels to inform control decisions.
• The overall message is that integrated, environmentally friendly approaches will enhance yield and fruit quality while reducing chemical residue issues for South African litchi growers.