Pesticide usage report: Outdoor vegetable crops 2019

SUMMARY

This is the tenth survey of pesticide usage on outdoor vegetable crops in Northern Ireland, providing comparative data to that obtained in the previous surveys in 1991 (Jess et al., 1993), 1995 (Kidd et al., 1998), 1999 (Kearns et al., 2002), 2004 (Kearns et al., 2005), 2007 (Withers et al., 2009), 2011 (Withers et al., 2012), 2013 (Withers et al., 2014), 2015 (Lavery et al., 2016) and 2017 (Kirbas et al., 2018).  Information on all aspects of pesticide usage was collected from 40 holdings throughout the province, representing 45% of the total population of outdoor vegetable crop growers in Northern Ireland     (Table 1).  Quantitative data have been adjusted to provide estimates of total pesticide usage.  The area of outdoor vegetable crops grown in Northern Ireland in 2019 was an estimated 1,092 hectares; a 7% decrease compared with 2017. 

Totals of 88 products and 43 active substances were recorded in use in this survey.  By comparison with 2017, the pesticide-treated area increased by 4%, to 12,713 spray hectares, while the quantity of pesticide (active substances) increased by 51% to approximately 6,315 kilograms, primarily due to increased herbicide applications.   The fungicide-treated area increased by 35% and the quantity of fungicide active substances applied increased by 46%.  The area treated with herbicides increased by 4% but the weight applied increased by 47%.  The insecticide-treated area decreased by 8%, though the weight of insecticide active substances increased by 92%, primarily due to the high application rate of oxamyl used for nematode control on carrot and parsnip crops.  The only molluscicide active substance used in 2019 was ferric phosphate, compared with 2017 when metaldehyde was the only molluscicide used.  Treatments for slugs were more consistent with previous reporting periods in 2015 and 2013.  Maleic hydrazide was the only growth regulator used in 2019, applied exclusively to 4 hectares of parsnip crops.

The area of vegetable crops grown from treated seed (direct sown or propagated and transplanted) decreased by 6% since 2017 and the weight of active substances used decreased by 66%, from 38 kilograms to 13 kilograms, mainly due to the withdrawal from use of thiamethoxam, which was used extensively as a seed treatment in 2017.

Fungicides, applied to 24% of the pesticide-treated area, accounted for 16% of the weight of pesticides applied.  Herbicides accounted for 39% of the pesticide-treated area and 67% of the total quantity of pesticides used.  Insecticides, applied to 24% of the pesticide-treated area, accounted for 16% of the total quantity of pesticides used.  Growth regulators accounted for less than 1% of the pesticide treated area and the quantity applied.  Molluscicides accounted for less than 1% of both the total pesticide-treated area and the quantity of pesticides applied.  Seed treatments applied to outdoor vegetable crops grown in 2019 accounted for 12% of the pesticide-treated area representing less than 0.1% of the quantity of active ingredients applied. 

Carrots and parsnips collectively accounted for 62% of the quantity of fungicide active ingredients applied, representing 61% of the area treated with fungicides, with the active substance prothioconazole being most frequently used on carrots and metalaxyl-M being most frequently used on parsnips.  Brassica crops received 19% of the total weight of fungicides applied, representing 26% of the area of vegetable crops treated with fungicides.  The two most commonly used fungicide active substances applied to brassicas were the curative triazole fungicides difenoconazole and prothioconazole, primarily for general fungal control.

Glyphosate, pendimethalin and clomazone were the herbicide active ingredients most commonly applied to outdoor vegetable crops, particularly to carrot and parsnip and onion and leek crops.  Overall, 47% of all herbicide applications were applied to carrot and parsnip crops, with a further 28% applied to onions and leeks. 

Carrots and parsnips collectively accounted for 69% of the insecticide-treated area, representing 96% of the quantity of insecticide active substances applied mainly due to the pyrethroid insecticide lambda-cyhalothrin being applied extensively to carrot, parsnip and brassica crops for control of aphids.  Leafy and flowerhead brassicas accounted for 26% of the insecticide-treated area representing 4% of the weight of insecticides applied. 

With exception of the use of garlic oil in carrots for general insect control there were no records of biopesticides/biological controls in NI vegetable crops in 2019.

Crops which were propagated from seed and/or grown under glass or polythene for the duration of their life cycle are recorded in the Edible Protected Crops in Northern Ireland 2019 report (Lavery et al., 2020).  These crops have previously been included in the totals for outdoor vegetable crops.  The proportion of total treated area of vegetable crops attributed to propagation (edible protected) is estimated at <0.2%.

A number of new active substances and formulated mixtures, which were not recorded in the previous report have been used during this survey period.  The fungicides fluopicolide/propamocarb hydrochloride and metconazole, the herbicides aclonifen, chloridazon, cycloxydim, desmedipham/ethofumesate/phenmedipham and diflufenican, the insecticide oxamyl and the molluscicide ferric phosphate were all recorded as used in 2019.   

Conversely, a number of active substances and formulated mixtures which were used in 2017 have not been recorded during this survey period.  These include the fungicides chlorothalonil, chlorothalonil/cyproconazole, cyprodinil/isopyrazam and epoxiconazole/metconazole, the herbicides bentazone, clopyralid, ethametsulfuron-methyl, fluroxypyr/halauxifen-methyl, metsulfuron-methyl/tribenuron-methyl, S-metolachlor and tepraloxydim, the insecticides acetamiprid, chlorpyrifos and spinosad and the molluscicide metaldehyde.