Zebra chip field trials
Peter Wright, who is site manager at the Plant & Food Research centre at Pukekohe, led a field day for growers at Patumahoe in mid-january reporting on the results of field trials. His work looked at the effect of JMS Stylet Oil foliar applications combined with insecticides on the tomato-potato psyllid (TPP), crop yields, tuber dry matter content and ZC in potatoes.
Although growers generally rely on regular applications of mainly broad spectrum insecticides to control TPP, they may not be killing TPP feeding on foliage fast enough to prevent Candidatus Liberibacter solanacearum (Lso) transmission, he said. So the search had begun for a TPP repellent which could be used in integrated pest management programmes (IPM) to reduce insecticide applications. “Mineral oils have a repellent effect to insect pests that discourage egglaying and feeding, and can kill insect eggs through contact toxicity and suffocation,” he explained. The field trials were carried out over three seasons from 2012, testing JMS Stylet Oil foliar applications both on their own and in combination with insecticides for efficacy against TPP, effect on ZC incidence and severity, and crop yields and phytotoxicity to potato plants.
The trials were planted in November in a randomised Latin square design in six rows which were 10 metres long and three metres wide. There were five treatments of five replications each. The five treatments were: 1. Seven-day insecticides and regular
2. Seven-day insecticides and JMS
3. 14-day insecticides and JMS Stylet Oil alternating with just JMS Stylet Oil.
4. 14-day insecticides ticides plus JMS Stylet
Oil and Du-wett u-wett alternatingaltern with the same treatment so there was reduced water volume. 5. Seven-day JMS Stylet Oil. In the first season results on February 2, 2014: Treatment 1 had the higher numbers of TPP eggs and aphids than treatments 2 and 3. Treatment 4 had the lowest numbers of TPP nymphs, eggs but slightly higher numbers of aphids. Treatment 5 had the highest numbers of TPP nymphs and eggs, and the highest aphid numbers.
_____________________________________________________________ A three-year trial by Plant and Food Research scientists has shown that using insecticides every 14 days alternating with JMS Stylet Oil and Du-wett (which reduced water volume) lowered levels of zebra chip (ZC).
The trial also looked at the effect on TPP predators, including brown lacewing and hoverfly adults, larvae and eggs: Treatment 1 had low numbers of both insects’ eggs, while treatment 2 showed no evidence of either. Treatment 3 had low levels of brown lacewing eggs. Brown lacewing adults, larvae and eggs were all found in treatment 4. Treatment 5 had the highest numbers of brown lacewing larvae and eggs as well as hoverfly eggs.
Marketable tuber yield was highest from treatment 1. Dry matter content of marketable tubers was slightly higher for those grown under treatment2. Marketable tuber yield and dry matter content of marketable tubers were lowest in treatment 5.
“Mineral oils have a repellent effect to insect pests that discourage egg-laying and feeding, and can kill insect eggs through contact toxicity and suffocation”
But Wright said “where the rubber hit the road was the ZC score of potatoes in the different treatments and the percentages with severe ZC”. Treatment 5 had the highest percentage of severe ZC at 18%, while